https://www.geologybites.com/mikesearle daily 0.75 2021-02-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594774197103-50ARSPVK5KJR74HQE8SX/IMG_5309.JPG Mike Searle Mike Searle in Annapurna Sanctuary, Nepal https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159349018-YEP7F38KD680UY8N13MA/300px-Continental-continental_convergence_Fig21contcont.gif Mike Searle - Collision of two continents, which creates mountains such as those stretching from the Himalaya to the Alps. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159413726-SEEY7006UNRXE436G1WT/Space+Shuttle+annotated+w+NS.jpg Mike Searle The Himalaya taken from the Space Shuttle, annotated with the main faults along which the Indian plate slides under Tibet. Courtesy of NASA and Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159465112-MDGWCJDOPXAMUTLNT4XR/Himalaya+subduction+in+Nepal+Tibet+Region.PNG Mike Searle Geological section of the subduction of the Indian plate below the Asian plate. The high Himalaya is shown as in green (GHS: Greater Himalaya Sequence). Courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159501009-MJ2TXX6PUWMOZELSVSX5/Subduction+Zone.PNG Mike Searle - Subduction of an oceanic plate below a continental plate. This produces a chain of volcanoes above the subducted plate, such as the Andes, which are being formed by the subduction of the Nazca plate below the South American plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159550999-9Y023Y8A2DQBHLXHBELQ/Mid-ocean+ridge.jpg Mike Searle - A mid-ocean ridge in which new ocean plate crust spreads out on either side of the ridge. An example is the Mid-Atlantic ridge, which is creating new ocean crust and widening the Atlantic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159610726-LXR66A3GP8G120KZOKF7/Continental+rifting.jpg Mike Searle - Rifting of a continental plate to create mountains on either side of the rift. The East African rift valley in Kenya is an example. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159657898-CT1B88X6CXVA7RTT8C2A/Hotspot.jpg Mike Searle - In the middle of a plate, volcanoes form over a “hot spot,” which is thought to be a hot plume of mantle that may extend to great depths, approaching the core-mantle boundary at 2900 km. Hot-spot volcanoes in the middle of a plate. The Hawaiian islands are above a hot spot in the Pacific ocean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596140450972-5C1DGJUSABRSCVJVCK0A/Book+Cover.PNG Mike Searle - Colliding Continents Mike Searle has a beautifully illustrated book about how mountains form when two continents collide. Along with the geology, it is packed with engaging accounts of a lifetime of exploration and adventure in places such as Nepal, Oman, and Myanmar. https://www.geologybites.com/types-of-mountains daily 0.75 2020-07-29 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594777057064-2WQS2DAMYXRFM2PJC64X/300px-Continental-continental_convergence_Fig21contcont.gif Types of mountains Collision of two continents, which creates mountains such as those stretching from the Himalaya to the Alps. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596048013738-9K5TQM6P6GHS63BYMC35/Space+Shuttle+annotated+w+NS.jpg Types of mountains The Himalaya taken from the Space Shuttle, annotated with the main faults along which the Indian plate slides under Tibet Courtesy of NASA and Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595463059433-I5L0NHL5T64HYF786ZTB/Himalaya+subduction+in+Nepal+Tibet+Region.PNG Types of mountains Geological section of the subduction of the Indian plate below the Asian plate. The high Himalaya is shown as in green (GHS: Greater Himalaya Sequence). Courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594776576292-6X17XJCMY6F24VLA5WUA/Subduction+Zone.PNG Types of mountains Subduction of an oceanic plate below a continental plate. This produces a chain of volcanoes above the subducted plate, such as the Andes which are being formed by the subduction of the Nazca plate below the South American plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594777468928-HLYVPJG5LTKKL5QOE3IK/Mid-ocean+ridge.jpg Types of mountains A mid-ocean ridge in which new ocean plate crust spreads out on either side of the ridge. An example is the Mid-Atlantic ridge, which is creating new ocean crust and widening the Atlantic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594777779497-3YQBSOUOVQ0OW2HGGYJW/Continental+rifting.jpg Types of mountains Rifting of a continental plate to create mountains on either side of the rift. The East African rift valley in Kenya is an example. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1594778256012-6EFQ0CHVW0T5EP28CIIZ/Hotspot.jpg Types of mountains In the middle of a plate, volcanoes form over a “hot spot,” which is thought to be a hot plume of mantle that may extend to great depths, approaching the core-mantle boundary at 2900 km. Hot-spot volcanoes in the middle of a plate. The Hawaiian islands are above a hot spot in the Pacific ocean. https://www.geologybites.com/james-jackson daily 0.75 2023-02-11 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595364826943-OZ5IVWUZEY5YVY7T3I2R/2011_bam_1.jpg James Jackson James Jackson at the Arg-e-Bam, an ancient citadel in southeastern Iran a few years after a 2003 earthquake that killed 30,000. Courtesy of James Jackson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596158162807-VWE3S8P8ZO660ETMSDQI/world_eqs.jpg James Jackson The world distribution of earthquakes. Each earthquake indicates an active fault. The faults occur in narrow bands in and on the edge of the oceans and are dispersed throughout the Alpine-Himalayan belt. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596158457499-MZRYW4I9PL3ZSGW5O8VU/asia_eqs.jpg James Jackson The distribution of earthquakes in Asia indicating a complex network of active faults. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596159100549-N1E6Y9N4ZLXVY5VUQQ74/Green+map+edited.jpg James Jackson Earthquakes that killed more than 10,000 people in the last 1000 years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596158783192-0A8KD493KPYLJACBLO8Y/Historical+w+trade+routes+edited.jpg James Jackson Earthquakes that killed more than 10,000 people from 1000 to 2008 AD with trade routes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596158873217-UUE69L8DKWTZNC3DHB9M/Histogram.jpg James Jackson Histogram showing the number of earthquakes for each century of the last millennium that killed more than ten thousand people. https://www.geologybites.com/home daily 1.0 2026-03-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/28b7fcb7-b04f-4d47-9b68-c528e1f07601/ES-1.jpg Home Though turbidity currents are massive and frequent underwater events, we have rarely observed them directly. Esther Sumner is one of the few researchers who has. In the podcast, she describes what it's like to instrument an active submarine canyon, what these flows have revealed about the way sediment moves across the seafloor — and the day her team accidentally flew an underwater robot into a live turbidity current. She is an Associate Professor of geology and geophysics at the University of Southampton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/66f075f9-1adf-4ad6-a5c0-23c733dbeef2/HL+from+SciTechDaily.png Home - Hal Levison on the Mission to Jupiter’s Trojan Asteroids There are many unanswered questions about the early history of the Solar System. In the podcast, Hal Levison explains why the Trojan asteroids of Jupiter offer us the best opportunity to address some of these, and, in particular, to discriminate between the various models of early Solar System evolution. And that is why a spacecraft called Lucy is now well on its way to a rendez-vous with these asteroids. Levison is the Principal Investigator of the Lucy mission and Chief Scientist in the Department of Space Sciences at the Southwest Research Institute in Boulder, Colorado. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2d11267d-e7fd-441d-ac0a-475977405242/IMG_3646.jpeg Home - Sara Pruss on the First Reef Builders The first multicellular animals to build reefs lived in the Early Cambrian around the time of the Cambrian explosion. They were sponges called archaeocyaths. In the podcast, Sara Pruss suggests that the rise of the archaeocyaths fostered an increase in animal diversity. But they were relatively short-lived, dying out in the Middle Cambrian. But over geological time, reef-building organisms appear and disappear again and again until the corals we have today appeared in the Middle Triassic, about 240 million years ago. Pruss is a Professor of Geosciences at Smith College. In the image, she is examining an outcrop with her student Emma Roth (right). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/73a5da7e-6da9-48f3-a290-6b143776984e/MM+office.png Home - Michael Manga on Wet Eruptions Water can have a dramatic effect on the style of an eruption. In the podcast, Michael Manga explains how the most powerful eruptions, such as the 2022 Hunga Tonga eruption, occur when hot magma comes into contact with water and suddenly generates vast quantities of steam. Water dissolved in magma as it rises to the surface and depressurizes can also drive destructive volcanic eruptions. Manga is a Professor in the Earth and Planetary Science department of the University of California, Berkeley. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f377988-fa67-4a00-8db9-638284909a86/CH-additional+edited-3.jpg Home - Carina Hoorn on the Evolution of the Amazon Basin The Amazon Basin is the most biodiverse region on Earth. How did this come about? In the podcast Carina Hoorn explains that to answer this question, we need to go back at least 23 million years to two key geologically-caused drivers of biodiversity — the rise of the Andes and marine incursions. Hoorn is an Associate Professor in the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam and Research Associate at the Negaunee Integrative Research Center, Earth Science Section, Field Museum of Natural History, Chicago. Photo: Daniel Winitsky https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/363b7a64-6e2d-4456-916b-6ebfb4355f82/InLab2.JPG Home - Anat Shahar on What Makes a Planet Habitable Over 6,000 exoplanets have now been found, and the number is constantly rising. This has galvanized research into whether one of them might host life. A key requirement for life is the presence of liquid water. In the podcast, Anat Shahar describes her theoretical and experimental work showing how hydrogen atmospheres observed on exoplanets react with magma oceans thought to prevail during planet formation to form water. The Earth could have produced enough water in this way to fill the oceans and also supply the mantle with another oceans’ worth of water. Shahar is a Staff Scientist and Deputy for Research Advancement at the Earth and Planets Laboratory at the Carnegie Institution for Science in Washington, DC. Photo: Extreme Conditions Lab at IPGP, Paris https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2d42f542-06a2-408c-aa93-a98c03f9d6bf/edited-2.jpg Home - Keith Klepeis on How Plutons Form Keith Klepeis describes how magma travels from the base of the crust to the upper crust forming conduits, feeder dykes, and mushroom-shaped intrusions along the way. Many of his discoveries come from a region that provides an exceptional window into the origin, evolution, and structure of plutons – the Southern Fiordland region of New Zealand’s South Island. Klepeis is a Professor in the Department of Geography and Geosciences at the University of Vermont. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/40879f5c-be23-4bbe-9400-f91e4187ca2a/TAH_near_top_of_very-tall-Building.jpeg Home - Tom Herring on High-Precision Geodesy Tom Herring describes how satellite-based geodesy systems and very long baseline interferometry are giving us new insight into plate motions, slow and fast deformation associated with faults and earthquakes, the Earth’s rotation, as well as applications in civil engineering, such as dams and tall buildings, and agriculture. Herring is a pioneer in high-precision geodetic analytical methods and applications for satellite-based navigation systems to study the Earth’s surface. He is a Professor in the Earth, Atmospheric, and Planetary Sciences department at the Massachusetts Institute of Technology. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5cb893dc-050d-4f82-ac5d-3bd653367826/DSC00944-01.jpg Home - Jiří Žák on the Orogenies that Shaped Central Europe Jiří Žák describes the two main orogenies whose remnants figure prominently in central European geology. First, the Cadomian orogeny that lasted from the late Neoproterozoic to the early Cambrian and took place on the northern margins of Gondwana, only later to rift and travel north to form what was to become Europe. And second, the Variscan orogeny that occurred in the late Paleozoic and accompanied the collision of Gondwana with Laurussia in the final stages of the assembly of the supercontinent Pangea. Žák has been studying the geology of central Europe for over 25 years using methods ranging from structural studies in the field to detrital zircon geochronology. He is a Professor in the Institute of Geology and Paleontology at Charles University in Prague. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87748bee-cf8e-44a1-9f52-131b36ea5a7a/IMG_3139.jpeg Home - Claudio Faccenna on the Dynamics of Subduction Zones The trenches of subduction zones rarely stay still. Instead, they often roll back toward the subducting plate, though sometimes they move laterally or even advance away from the subducting plate. In the podcast, Claudio Faccenna describes this behavior and explains our current theories as to what causes subduction zones to migrate. Faccenna has been studying how convergent margins evolve for over 30 years, concentrating particularly on the Mediterranean region. He is Head of the lithospheric dynamics section at the Helmholtz Center for Geosciences at GFZ in Potsdam in Germany and also a Professor at the Department of Science at Roma Tre University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cc971615-8fef-4122-b953-e454b0297153/CVS+edited.jpg Home - Cees Van Staal on the Origin of the Appalachians In his podcast episode, Rob Strachan described how a single extended orogeny, the Caledonian orogeny, formed rocks now in the northern British Isles, eastern Greenland, and western Norway. In this episode, Cees Van Staal explains how the Appalachian Mountains are also part of this same story, even though they now lie across the Atlantic ocean. These mountains stretch for over 2,000 miles, all the way from Newfoundland in Canada to central Alabama in the United States. Van Staal has been studying the Appalachians for over 35 years, focusing especially on the large-scale tectonics of their formation. He is Emeritus scientist at the Geological Survey of Canada and an Adjunct/Research Professor in the Department of Earth and Environmental Sciences at the University of Waterloo in Ontario. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1dea7a33-7834-4a82-a7aa-da18ce89fd05/AF+-+credit+Winkler.jpg Home - Andreas Fichtner on the Frontiers of Seismic Imaging In previous episodes of Geology Bites, Barbara Romanowicz gave an introduction to seismic tomography, and Ana Fereira talked about using seismic anisotropy to reveal flows within the mantle. In this episode, Andreas Fichtner explains how, despite the many fiendish obstacles that stand in our way, we are making steady improvements in our ability to image the Earth on both regional and global scales. These give us confidence that we can make three-dimensional maps of certain structures, such as the plume below Iceland, cold continental interiors, mid-ocean ridges, and the large low-shear-velocity provinces. Fichtner is a Professor in the Department of Earth and Planetary Sciences at the Federal Institute of Technology in Zurich. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c34022cc-4175-4899-a3a4-420ba955f686/RT+snip.jpg Home - Renée Tamblyn on the Origin of Continents When the Earth formed, it was covered by a hot magma ocean. So when and how did thick, silica-rich continental lithosphere form? Were the first, ancient continents similar to the present-day continents? And did the continents form in a burst of activity at a certain point, or was it a gradual build-up over Earth history? In the podcast, Renée Tamblyn addresses these questions, as well as how early geological processes created molecular hydrogen that may have powered the first forms of life. In her own research, she has focused on the critical role played by water released from hydrous minerals that formed within oceanic lithosphere on the sea floor. Tamblyn is a Postdoctoral Researcher at the University of Bern. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9335cac2-75f7-46a2-8141-d41932c897a5/P5190633_ed.jpg Home - Folarin Kolawole on Continental Rifting What happens when continents start to rift apart? In the podcast, Folarin Kolawole describes the various phases of rifting, from initial widespread normal faulting to the localization of stretching along a rift axis, followed by rapid extension and eventual breakup and formation of oceanic lithosphere. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf5a103a-04d1-48e6-a831-972d75f151ec/MH.jpg Home - Mike Hudec on Salt Tectonics Most of Earth’s salt is dissolved in the oceans. But there is also a significant amount of solid salt among continental rocks. And because of their mechanical properties, salt formations can have a dramatic effect on the structure and evolution of the rocks that surround them. This gives rise to what we call salt tectonics — at first sight, a rather surprising juxtaposition of a soft, powdery substance with a word that connotes the larger scale structure of the crust. In the podcast, Mike Hudec explains the origin of salt in the Earth’s crust and describes the structures it forms when subjected to stresses. He also discusses how salt can play an important role in the formation of oil and gas reservoirs. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2a2ad379-21be-48b8-953d-62f847dc2af3/VB+in+scablands.jpg Home - Vic Baker on Megafloods Megafloods are cataclysmic floods that are qualitatively different from weather-related floods. In the podcast, Vic Baker explains our ideas as to what causes megafloods and describes the striking evidence for such floods in the Channeled Scablands of Washington State and in the Mediterranean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4432e3f2-5bdf-4385-a7e0-816c5adf78bb/LEK+talk.jpg Home - Lindy Elkins-Tanton on the Origin of Earth’s Water Understanding how the Earth got its water gives us clues as to the conditions in the solar nebula out of which the planets formed, and also helps us learn about conditions on the early Earth. In the podcast, Lindy Elkins-Tanton explains the two main theories on the origin of Earth’s water and why she favors one of them. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9dfdb8ea-4ded-44e8-908d-f109803facf7/Joeri+pic.jpeg Home - Joeri Witteveen on Golden Spikes Golden spikes are not golden, nor are they generally spikes. So what are they, and, more importantly, what exactly do they represent? In the podcast, Joeri Witteveen explains how we arrived at our present system of defining the boundaries of stages in the rock record with a single marker. Paradoxically, it turns out that the best place for a golden spike is where “nothing happens.” Listen and find out why. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0bf3f22f-71e5-4d0d-a665-a8716b13e291/IM+UCD.jpg Home - Isabel Montañez on Using the Late Paleozoic Ice Age as an Analog for Present-Day Climate The late Paleozoic ice age began in the Late Devonian and ended in the Late Permian. It was similar to the present day in two key respects: low but rising atmospheric CO2 and recurrent major ice sheets. In the podcast, Isabel Montañez explains how we can use proxies to learn about the climate and ocean conditions that prevailed then. And with the help of a model calibrated to that period, she says that we can also learn about sensitivities and feedbacks of Earth systems to rising CO2 that apply to the present day. This leads her to some alarming conclusions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d13913e5-51d0-4a7d-a863-5aa856ae6602/RS.jpg Home - Ruth Siddall on Urban Geology At first sight, urban geology sounds like an oxymoron. How can you do geology with no rocky outcrops anywhere in sight within the built-up environments of cities? It turns out you can do a great deal of geology, and Ruth Siddall has been doing just that for the past 10 years. In the podcast, she describes some of the many aspects of geology, from petrology to paleontology, that can be seen very clearly in building stone. She also takes us on a walking tour in London from the Monument to the Great Fire of London to the Tower of London. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/24469582-e48c-4185-8ee2-ff59869a32a9/Richard+Fortey.jpeg Home - Richard Fortey on Deep Time The Earth is about 4.5 billion years old. How can we begin to grasp what this vast period of time really means, given that it is so far beyond the time scale of a human life, indeed of human civilization? In the podcast, Richard Fortey talks about how we came to a realization of deep time, how we have attempted to tame it, and how it has changed our conception of the primacy of humankind in Earth history. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/837c8ff4-d2d8-4989-a42f-d27f034e42a8/IMG_9292.jpg Home - Mike Searle on the Mountain Ranges of Central Asia The Himalaya are just one, albeit the longest and highest, of several mountain ranges between India and Central Asia. By world standards, these are massive ranges with some of the highest peaks on the planet. The Karakoram boasts four of the world’s fourteen 8,000-meter peaks, and the Hindu Kush, the Pamir, the Kunlun Shan, and the Tien Shan each have many peaks above 7,000 meters. No mountain ranges outside this region have such high mountains. Yet we seldom hear much about these ranges. In the podcast, Mike Searle sets these mountains in their tectonic context and describes some of their unique geological features. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/890c4d84-471f-437b-9311-80821c1c6872/4.+Rob+C.jpg Home - Rob Strachan on the Caledonian Orogeny The Caledonian orogeny is one of the most recent extinct mountain-building events. It took place in several phases during the three-way collision of continental blocks called Laurentia, Baltica, and Avalonia during the early stages of the assembly of the supercontinent Pangea. In the podcast, Rob Strachan describes the sequence of events that led up to and formed part of the orogeny. He also ties together the field evidence from northeast America, the British Isles, Greenland, and Norway that enables us to reconstruct what happened. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2a3ebbbb-dabc-4717-ac37-7cdf00941dbd/IMG_1106.jpg Home - Joe MacGregor on Mapping the Geology of Greenland Below the Ice With most of Greenland buried by kilometers of ice, obtaining direct information about its geology is challenging. But we can learn a lot from measurements of the island’s geophysical properties — seismic, gravity, magnetic from airborne and satellite surveys and from its topography, which we can see relatively well through the ice using radar. In the podcast, Joe MacGregor explains how he created a new map of Greenland’s geology and speculates on what we can learn from it. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a13ca8f-7839-441c-8508-4c0f05e1e8c9/Kaweh+Ijen+in+East+Java.++The+crater+lake+has+a+pH+of+0+and+is+the+most+acidic+in+the+world.++The+lake+is+filled+with+magmatic+fluid+that+is+similar+in+composition+to+fluids.jpg Home - Adam Simon on Battery Metals As we wean ourselves away from fossil fuels and ramp up our reliance on alternatives, batteries become ever more important for two main reasons. First, we need grid-scale batteries to store excess electricity from time-varying sources such as wind and solar. Second, we use them to power electric vehicles. So far, the battery of choice is the lithium-ion battery. In addition to lithium, these rely on four metals — copper, nickel, cobalt, and manganese. In the podcast, Adam Simon explains the role these metals play in a battery. He then describes the geological context and origin of the economically viable deposits from which we extract these metals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/83949dec-14ea-423b-8f07-0f87fbfde585/ebse-5_0.jpg Home - Rufus Catchings on Pinning Down California’s Faults Knowing exactly where faults are located is important both for scientific reasons and for assessing how much damage a fault could inflict if it ruptured and caused an earthquake. In the podcast, Rufus Catchings describes how we can use natural and artificial sources of seismic waves to create images of fault profiles. He also explains how faults can act as seismic waveguides, an effect that enables us to determine whether faults are connected to each other. In Napa, an area near San Francisco, he used guided waves to determine that an active fault is actually 10 times longer than previously thought. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0bd66fac-cbff-4553-b543-e39a600c6d74/sara-seager+Canada+global+news.png Home - Sara Seager on Exoplanet Geology That we can say anything meaningful at all about the surfaces and interiors of exoplanets is startling. They are so incredibly faint compared to their host stars, and their distances are measured in tens, hundreds, and thousands of light years. Yet, thanks to the work of researchers such as Sara Seager, we are beginning to tease out data from star-exoplanet systems that reveal whether or not an exoplanet has an atmosphere; what the major constituents of such an atmosphere are; whether there is a magma or water ocean; and, for a tidally-locked, rocky exoplanet, what rock type dominates its surface. Photo courtesy of Canada Global News https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c56e1901-afee-4571-9e08-a72c3ce7ae38/Evan+Smith+holding+large+rough+CLIPPIR+diamond.jpg Home - Evan Smith on Diamonds from the Deep Mantle We have only a tantalizingly small number of sources of information about the Earth’s deep mantle. One of these comes from the rare diamonds that form at depths of about 650 km and make their way up to the base of the lithosphere, and then later to the surface via rare volcanic eruptions of kimberlite magma. In the podcast, Evan Smith talks about a new class of large gem-quality deep-mantle diamonds that he and his coworkers discovered in 2016. Inclusions within these diamonds serve as messenger capsules from the deep mantle. They show an unmistakable genetic link to subducted oceanic slabs. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a1597afe-262e-4714-8cbe-e1e437fdd28b/RR+2015.jpg Home - Roberta Rudnick on the Continental Crustal Composition Paradox Continental crust is derived from magmas that come from the mantle. So, naively, one might expect it to mirror the composition of those magmas. But our measurements indicate that it does not. Continental crust contains significantly more silica and less magnesium and iron than mantle-derived magmas. How can we be sure this discrepancy is real, and what do we think explains it? In the podcast, Roberta Rudnick presents our current thinking about these questions. Surprisingly, more than 30 years after she and others first identified the so-called continental crustal composition paradox, there is still no consensus among geologists as to which of the many proposed hypotheses most convincingly solves the paradox. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a1c06072-39fb-44d7-9424-124deea18736/1.jpg Home - Alex Copley on Soft Continents We tend to think of continental tectonic plates as rigid caps that float on the asthenospheric mantle, much like oceanic plates. But while some continental regions have the most rigid rocks on the planet, wide swaths of the continents are not rigid at all. In the podcast, Alex Copley explains how this differentiation comes about and points to evidence that the responsible processes have been operating since the Archean. In the photo, Copley is standing on what is left of an ancient mountain belt in Scotland. On his hammer is a sample that is rich in garnets that were produced when the mountains formed during the Caledonian orogeny. Photo: Owen Weller https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/493fd480-0e9a-401d-92c2-378c687faf14/SP+Offices.jpg Home - Shanan Peters on Quantifying the Global Sedimentary Rock Record Stratigraphic field studies, by their very nature, cover a particular geographical region. Linking these studies into a global record is difficult because each study focuses on special features of the studied region, and there is enormous spatial variability in the rate at which sedimentary rock thicknesses accumulate, if they accumulate at all, and if they survive erosion to the present day. So one might think that with the “tattered manuscript” of the rock record, to use Darwin’s term, discerning global trends in the stratigraphic record over Earth history would be impossible. But that is what Shanan Peters is doing. In the podcast, he describes how he is assembling stratigraphic data from around the world and how this already enables us to address some fundamental questions about the long-term secular evolution of the Earth-life system in a quantitative manner. Photo: David Tenenbaum https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4f15cb61-a98e-4595-8713-1030c8f2d0ce/2012_08_29_006a.jpg Home Complex life did not start in the Cambrian — it was there in the Ediacaran, the period that preceded the Cambrian. And the physical and chemical environment that prevailed in the early to middle Cambrian may well have arisen at earlier times in Earth history. So what exactly was the Cambrian explosion? And what made it happen when it did, between 541 and 530 million years ago? Many explanations have been proposed, but, as Paul Smith says in the podcast, they tend to rely on single lines of evidence, such as geological, geochemical, or biological. He favors explanations that involve interaction and feedback among processes that stem from multiple disciplines. His own research includes extensive study of a site where Cambrian fossils are exceptionally well preserved in the far north of Greenland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b78f6ed7-002d-490e-90c8-b6f609b3b833/SB+with+model.PNG Home - Scott Bolton on the Most Volcanically Active Body in the Solar System Io, the innermost of Jupiter’s Galilean moons, is peppered with volcanos that are erupting almost all the time. In this episode, Scott Bolton, Principal Investigator of NASA’s Juno mission to Jupiter, describes what we're learning from this space probe. Juno has given us our first-ever views of Io’s polar regions — and they, too, are covered with volcanoes. Juno has also made detailed measurements of Io’s gravity field, enabling us to determine whether or not there is an ocean of magma below the surface that feeds the volcanos. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c7aa4a7a-15db-42b7-a77d-e2d0239ce26a/Bob+White+processed+2-2.jpg Home - Bob White on How Magma Moves Through the Crust As magma pushes its way up through the many kilometers of lithosphere to the surface, it pauses in one or more magma chambers or partially melted mush zones for periods of up to a few millennia before erupting. But while we have seismic evidence and models and support this picture, we have not hitherto been able to watch how magma actually moves in the upper mantle and crust. Using a dense array of seismometers, White and his team pinpointed thousands of tiny earthquakes to follow the detailed movement of melt through the thick crust of Iceland just before it erupted. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/535711ec-566f-439e-9aed-8d5c3b998da6/RE+in+China+2023+-+cropped.jpg Home - Richard Ernst on Large Igneous Provinces At 15-25-million-year intervals since the Archean, huge volumes of lava have spewed onto the Earth’s surface. These form the large igneous provinces, which are called flood basalts when they occur on continents. As Richard Ernst explains in the podcast, the eruption of a large igneous province can initiate the rifting of continents, disrupt the environment enough to cause a mass extinction, and promote mineralization that produces valuable mineral resources. In the image, Ernst is pointing out the contact between a 1.3-billion-year-old dolerite sill (above) that formed part of the plumbing of a large igneous province and the host black shale in northern China. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fb17bfdd-a296-4fc8-82f3-3819aebcde1c/DN-1.jpg Home - Damian Nance on What Drives the Supercontinent Cycle Perhaps as many as five times over the course of Earth history, most of the continents gathered together to form a supercontinent. The supercontinents lasted on the order of a hundred million years before breaking apart and dispersing the continents. For decades, we theorized that this cycle of amalgamation and breakup was caused by near-surface tectonic processes such as subduction that swallowed the oceans between the continents and upper mantle convection that triggered the rifting that split the supercontinents apart. As Damian Nance explains in the podcast, newly acquired evidence suggests a very different picture in which the supercontinent cycle is the surface manifestation of a process that involves the entire mantle all the way to the core-mantle boundary. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3bc6c1b8-a65a-4e6b-9cde-6cacbd6822ee/DK+landing+page.jpg Home - David Kohlstedt on Simulating the Mantle in the Lab The Earth’s tectonic plates float on top of the ductile portion of the Earth’s mantle called the asthenosphere. The properties of the asthenosphere, in particular its viscosity, are thought to play a key role in determining how plates move and subduct, and how melt is produced and accumulates. We would like to know what the viscosity of the asthenosphere is, and how it depends on temperature, pressure, and the proportion of melt and water it contains. Few mantle rocks ever reach the Earth’s surface, and those that do are altered by weathering. So, as he explains in the podcast, David Kohlstedt and his team have tried to replicate the rock compositions and physical conditions of the mantle in the lab. Using specially-built apparatus such as the one shown in the picture, he has been able to determine the viscosity of the asthenosphere to within an order of magnitude, which is an enormous improvement on what was known before. Photo courtesy of Sally Gregory Kohlstedt https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/16baa48b-762a-46bf-abd7-3d9f03a9bfbc/Claire+studying+glass+corrosion-7.jpg Home - Claire Corkhill on Geological Radioactive Waste Disposal In many countries, nuclear power is a significant part of the energy mix being planned as part of the drive to achieve net-zero greenhouse gas emissions. This means that we will be producing a lot more radioactive waste, some of it with half-lives that approach geological timescales, which are orders of magnitude greater than timescales associated with human civilizations. In the podcast, Claire Corkhill describes the kind of geological storage being planned to keep such waste safe. Here she is using a synchrotron beam at Brookhaven National Laboratory to measure corrosion layers at the surface of glass. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3c52d033-a3b4-45b1-a74e-0170f77fa8e1/MA+OU+w+lunar+rock.jpg Home - Mahesh Anand on What Human Return to the Moon Means for Lunar Geology Our ideas about the geological history of the Moon have changed radically over the past few years owing to new results from analysis of lunar samples returned to Earth by Apollo 17 and Chang’e 5, as well as detailed remote sensing from orbiters. As Mahesh Anand discusses in the podcast, these results have in turn thrown up new questions about the nature and timing of lunar volcanism. And as we prepare to support a long-term human habitation on the Moon, we need to learn about the presence of water and other useful resources on the lunar surface. Anand argues that the return of astronauts to the Moon will greatly accelerate research on understanding the geology and habitability of the Moon and other nearby bodies in the Solar System. Photo courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec44a662-bc34-499d-842f-b16b2c1518de/SB+with+augur-1.jpg Home - Susan Brantley on Earth’s Geological Thermostat The remarkable stability of the Earth’s surface temperature over billions of years is thought to result from a balance between the injection of greenhouse gases into the atmosphere by volcanos and the removal of such gases by the weathering of rocks in the presence of water. To help understand how this operates as a negative feedback mechanism, Susan Brantley has performed detailed studies of the weathering reactions of silicate minerals in the lab to understand what controls the rate of such reactions. As discussed in the podcast, she has recently analyzed how such reactions work in the field in different climatic and geomorphological contexts and on various spatial scales up to the global scale. In the photo, Brantley is preparing to augur a soil in Yosemite National Park to determine mineral abundance as a function of depth and relate it to the rate of weathering. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21dcd95f-2c79-4eb8-abab-3831f04dead3/Clark_DSC-0728_Field_Portrait_cropped.jpg Home - Clark Johnson on the Banded Iron Formations In the early Proterozoic, about 2.5 billion years ago, enormous thicknesses of iron-rich rocks were deposited on continental shelves. Striking cliffs of these rocks form the walls of many canyons in Western Australia and South Africa. They are called the banded iron formations (BIFs) because they show vivid banding between the reddest, most iron-rich layers and ochre-colored layers containing siliceous material such as chert. What is the origin of the BIFs? For many years, the prevailing theory was that large amounts of dissolved iron were present in the early oceans, and it was the oxygen from the first oxygen-producing life forms in the water that oxidized this iron into an insoluble form, which then precipitated out of the oceans to form the BIFs. In the podcast, Clark Johnson explains how biological processes may have been responsible for oxidation of iron in seawater under oxic or anoxic conditions, as well as later reduction as the BIF sediments compacted on the seafloor. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b0c5a59e-535e-4647-adc7-36c579756145/CM+cropped+in+lab-1.jpg Home - Catherine Mottram on Dating Rock Deformation The geological history of most regions is shaped by a whole range of processes that occur at temperatures ranging from above 800°C to as low as 100°C. The timing of events occurring over a particular temperature range can be recorded by a mineral that crystallizes over that range. The mineral calcite is suitable for recording low-temperature processes such as fossilization, sedimentation, and fluid flow, and it is especially useful as it is virtually ubiquitous. But using uranium-lead radiometric dating in calcite is very challenging as it often contains very little uranium, and the ragiogenically-produced lead isotopes can be swamped by common lead within a calcite crystal. In the podcast, Catherine Mottram explains how these challenges are being overcome and shares some of her findings based on radiometric dating of calcite. Photo: University of Portsmouth, Sam Shaw https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d10eb267-e59b-4265-9ad9-72f90c5f5776/MVK+cropped-1.jpg Home - Martin Van Kranendonk on the Earliest Life on Earth Stromatolites are the layered structures left behind by microbial communities. They are the fossil evidence for far and away the earliest life on Earth. But the interpretation of the very earliest stromatolite-like structures as being biogenic in origin is controversial. Martin Van Kranendonk tells the story of the discovery of almost pristine stromatolites in 3.48-billion-year rocks of the Pilbara of Western Australia. By meticulous study of their structure, relationship to their geological environment, and chemical and isotopic composition, he establishes a convincing case for life on Earth going back at least as far as the age of these Pilbara rocks. In the image, Martin Van Kranendonk is on one of the main stromatolite outcrops in the Pilbara , looking down on the tops of multiple cone-shaped stromatolites of the 3.4 Ga Strelley Pool Formation, only slightly younger than the 3.48 Ga Dresser Formation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cad953f8-a286-4dcf-b869-0af2cc759f52/RWHB_2.png Home - Rob Butler on the Origin of the Alps The Alps are a relatively young mountain range, having started to grow only about 25 million years ago. But, as Rob Butler explains in the podcast, for the Western Alps, this growth was preceded by 15 million years of subduction of the greatly thinned continental crust that once formed the margin of Europe. Subduction was choked off by the arrival of crust that had experienced rather little pre-alpine rifting. The diversity of structures seen on mountainsides and the styles of crustal deformation (thrust faulting and distributed strain) can be related to the variations in the structure of the European margin at that time. In this way, the Alps, and most other collision mountain belts, can be viewed as amplifications of pre-existing geological heterogeneities – and detecting these heterogeneities, recorded in the stratigraphy of rocks deposited before mountain building began, is a key to tectonic understanding. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bbbfd32c-ff61-4ab2-b730-30bc596a3ff6/From+Fresno+Bee+video.png Home - John Wakabayashi on the Franciscan Complex The Franciscan Complex is a large accretionary prism that has been accreted onto the western margin of the North American continent. Unlike most such prisms, which are submarine, it is exposed on land, making it a magnet for researchers such as John Wakabayashi. In the podcast, he describes this remarkable complex and explains the mechanisms that may have operated over its 150-million-year history. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1a3ba4a0-ea95-488a-ad27-22f475bc8cd8/HLCH9794.JPG Home - Bruce Levell on Bias in the Sedimentary Record When we look at sedimentary rocks, we are seeing the accumulation of material that has been preserved. But if we use the sedimentary record to make inferences about the past, we need to understand how what we see today is filtered by preservational bias. As Bruce Levell describes in the podcast, it can be difficult, or even impossible, to infer what is missing, or indeed whether anything is missing at all. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/865777cc-74f4-4319-8f3a-35304be3e8b6/Sujoy_MassSpecFix.JPG Home - Sujoy Mukhopadhyay on Probing the Hadean World with Noble Gases In a recent episode, Nadja Drabon spoke about newly discovered zircon crystals from the late Hadean and early Archean. The zircons revealed information about processes occurring in the Earth’s nascent crust, casting light on when and how modern-day plate tectonics may have started. In this episode, we talk about a very different source of information about the early Earth, namely the abundances of noble gases occurring within present-day basalts. It turns out that these can probe the Earth’s mantle and atmosphere even further back in time – to the first 100 million years of Earth history. Sujoy Mukhopadhyay leads a team of researchers who have developed new techniques for measuring the abundances of noble gas isotopes in a variety of Earth materials. He used his results to identify mantle reservoirs that formed during the first 100 million years of Earth history and, amazingly, survive to the present day. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/051c14cb-b66d-4ec8-b267-f5d2a37b8a44/Patrick-Fulton-220902-PSP-1536x864.jpg Home - Patrick Fulton on the 2011 Tōhoku Earthquake In 2011, a massive earthquake struck off the eastern coast of Japan. The destructive power of the earthquake was amplified by a giant tsunami that swept ashore, killing over 15,000 people. A major cause of the tsunami was the 50-m slip along the plate boundary fault between the subducting Pacific plate and the overriding North American plate. Patrick Fulton and his team set out to find out why there was so much movement along the fault by installing a temperature observatory in a borehole drilled right through the fault zone. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bd85610e-338c-47f8-9915-1727f94b0729/Joliver+Iceland.jpg Home - Romain Jolivet on the 2023 Turkey-Syria Earthquakes The devastating earthquakes that struck near Turkey’s border with Syria on February 6, 2023, killed over 50,000 people. One reason for this appalling loss of life was the occurrence of a second major earthquake just 10 hours after the first one, while rescue efforts were under way. How might an earthquake trigger delayed slip on a different fault? Romain Jolivet uses radar satellite data to pin down how plate boundaries deform between and during earthquakes. This casts light on the mechanisms that relate slow and rapid slip along the major bounding faults of tectonic plates. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/85c7db55-67e0-4d6a-a679-4ceb684f0f77/DR+blackboard_helen.jpg Home - Dan Rothman on Thresholds of Catastrophe in the Earth System The geological record shows that the Earth’s carbon cycle suffered over 30 major disruptions during the Phanerozoic. Some of the biggest ones were accompanied by mass extinctions. Dan Rothman analyzed these disruptions to find a pattern governing their magnitude and duration. As he explains in the podcast, this pattern is suggestive of a non-linear dynamical system that, once excited, undergoes a large excursion before returning to where it was. Could we be exciting such a disruption now? Courtesy of Helen Hill https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/14dafb73-4272-40c0-8022-443513b99ba4/ND+Cropped.jpg Home - Nadja Drabon on a New Lens into the Hadean Eon Vanishingly few traces of the early Earth are known, so when a new source of zircon crystals of Hadean age is discovered, it makes a big difference to what we can infer about that eon. In the podcast, Nadja Drabon describes how she analyzed the new zircons she and her colleagues discovered and what they reveal about the Earth’s crust between about 4 and 3.6 billion years ago. Nadja Drabon in the Green Sandstone Bed in South Africa https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92576563-5d93-4289-a1d6-4c68fa47b272/DSC01080-2.jpg Home - John Cottle on the Petrochronology Revolution Over the course of Earth history, many parts of the crust have undergone multiple episodes of metamorphism. Modern methods of dating and measuring trace-element abundances are now able to tease out the timing and conditions of the individual episodes. But new techniques were needed before these methods could be scaled up to unravel regional tectonic events such as the formation of mountain belts and subduction zones and continental rifting. In the podcast, John Cottle describes one such technique that he and his group developed that has radically changed the scope of metamorphic rock studies. John Cottle examining a sheared coarse-grained granitoid near the Byrd Glacier in Antarctica, courtesy of Graham Hagen-Peter https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a3c03dfa-2f25-46c1-9674-34b5bd33fea1/MG+in+Iceland.jpg Home - Martin Gibling on Rivers in the Geological Record Rivers can seem very ephemeral, often changing course or drying up entirely. Yet some rivers have persisted for tens or even hundreds of millions of years, even testifying to the breakup of Pangea, the most recent supercontinent, about 200 million years ago. In the podcast, Martin Gibling talks about rivers old and new, and how they are affected by tectonic processes over tens of millions of years, as well as by human activities over a few thousand years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7beefb9f-1606-47ce-a376-bc6eb0263f81/Dolerite+-+credit+Murdo+MacLeod.jpg Home - Anna Fleming on the Experience of Rock Climbing This episode is a bit of a departure from the objective approach to geology of past episodes in that here we address the subjective nature of various rocks as experienced by a rock climber with a literary bent. A rock climber’s very survival can depend on the properties of a rock encountered along a climbing route. This engenders a uniquely intense relationship between climber and rock. Anna Fleming has written perceptively about this intense relationship gained from climbing in Britain and the Mediterranean. In a book entitled Time on Rock, she writes about her experiences climbing gritstone in England’s Peak District, gabbro and granite on the Isle of Skye, sandstone on the northeast coast of Scotland, and limestone cliffs on the Greek island of Kalymnos, among others. Courtesy of Murdo MacLeod https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bb0ff33a-f697-4785-bdf6-0ceeb78c13f8/BU+from+Anne+Burgess+edited.jpg Home - Brian Upton on the Unique Rift Zone of South Greenland Between 1.3 and 1.1 billion years ago, magma from the Earth's mantle intruded into a continent during the assembly of the supercontinent called Nuna. Through good fortune, the dykes and central complexes that resulted have been preserved in near-pristine condition in what is now the south of Greenland. The dykes are extraordinarily thick, and the central complexes contain an order of magnitude more exotic minerals than otherwise similar complexes around the world. In the podcast, Brian Upton describes what he found during over 20 seasons of field work there and explains how extreme fractionation of the magma might be responsible for the one-of-a-kind central complexes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/acfe474b-c452-45ec-a1b9-7e852522d942/GA+Kodiak.jpg Home - Geoff Abers on Subduction Zones and the Geological Water Cycle Slabs of oceanic lithosphere dive into the mantle at subduction zones. Within the slab there is water — both water that seeps into the rocks through faults, and water within the crystal structure of certain minerals. Where does this water end up? In the podcast, Geoff Abers explains how we can probe the subduction zone with seismic waves to answer this question. The results are surprising — over geological time, the amount of water in all of today’s oceans may have been mixed into the deep mantle by subducting plates. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e072e22f-c319-4910-83b1-8671e336a2ad/Dr.McNamara12CROPPED.jpg Home - Maria McNamara on Seeing the Ancient World in Color Popular reconstructions of ancient environments, whether they be in natural history museum dioramas, movies, or books, present a world of color. But are those colors just fanciful renderings, perhaps based on the colors we see around us today? Or is there evidence in the fossil record that we can use to determine the actual color of plants and animals that lived in the geological past? In the podcast, Maria McNamara explains that such evidence is indeed present in certain exceptionally well-preserved fossils. And she describes how she is using it to reveal the vivid colors of insects and vertebrates that lived in the geological past. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8cefc148-ed17-44a5-bb08-04d27864590e/Phil+Renforth+%281+of+2%29.jpg Home - Phil Renforth on Carbon Sequestration As it becomes increasingly unlikely that human greenhouse gas emissions will slow rapidly enough to avoid serious climate change, mitigation efforts are growing in importance. A promising approach to mitigation is the removal of carbon dioxide from the atmosphere. Phil Renforth is developing the science and practice of large-scale carbon dioxide removal using geochemical methods. In the podcast, he describes several such methods, focusing on enhanced weathering of rocks and industrial waste, and the liming of the oceans. In the image, he is using a borehole to sample slag, which is one of our most voluminous industrial waste materials. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f221916a-fd7d-42ba-9012-dc82de281d82/TW+at+sea+Fig.+1+in+persepctives+paper.jpg Home - Tony Watts on Seamounts and the Strength of the Lithosphere Although to a first approximation, tectonic plates move like rigid caps over the asthenosphere, they are not, in fact, totally rigid. They flex in response to loads placed upon them at plate interiors and stresses that impinge upon them at their margins. Tony Watts uses the observed flexure of oceanic plates in response to loading by seamounts to determine how strong the plate is below the seamount. He discovered that less than half of the plate’s thickness supplies the elastic strength that supports the seamounts. The rest is brittle (top layer) or ductile on the relevant timescales (bottom layer). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/32d67f62-da4d-4622-a320-eac0ea529ba9/NSD2.jpg Home - Neil Davies on the Greening of the Continents Life only emerged from water in the Ordovician. By that time, life had been thriving in oceans and lakes for billions of years. What did the colonization of the land look like, and how did it reshape the Earth’s surface? Neil Davies describes how we can decipher the stratigraphic sedimentary record to address these questions. Perhaps surprisingly, it’s easier to recognize small and fleeting events than to recognize large-scale features such as mountains, valleys, and floodplains. He also describes his remarkable 2018 discovery of the largest known arthropod in Earth history — a 2.6-meter-long millipede. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7c500f1b-d31d-48d7-9050-276afcf7a79d/Ben+Weiss+landing+page.PNG Home - Ben Weiss on the Mission to Psyche To unravel the early history of the solar system, we need to look beyond the Earth, since any evidence of such a distant past has been thoroughly erased by the Earth’s active geological processes. Asteroids, and the meteorites they spawn, have been useful in this regard, as they are thought to be unaltered scraps left over from the earliest stages of planet formation. In this episode, we focus on a very special asteroid called Psyche that will be visited by a spacecraft to be launched in August 2022. Ben Weiss explains why we want to know how it formed, not only to understand Psyche’s history, but also because it will shed light on the history and structure of the inner planets of the Solar System. It may also help us understand some of the dense bodies we’re rapidly discovering around other stars. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5201dac4-516d-454a-a112-9306373b53dc/RB+at+temple.png Home - Roger Bilham on Himalayan Earthquakes As the Indian Plate grinds inexorably northwards into Tibet, its movement is accommodated, in part, by large earthquakes. Many faults showing evidence of past earthquakes run along the Himalaya, but it is the Main Frontal Thrust that is currently the most active. The surface expression of this fault runs along the foot of the Himalaya in northern India. To the north, the fault plunges below the Himalaya and Tibet. As Roger Bilham explains in the podcast, we now have evidence of a zone of partial seismic coupling along the fault plane at intermediate depths. This can store hidden reservoirs of elastic energy that can be released during an earthquake, amplifying it into one of the devastating megaquakes that can wreak so much damage. In the image, Roger Bilham is excavating beneath temple blocks thrown from the wall of an 8th century temple in Kashmir by an earthquake in 1123. The blocks have been undisturbed since they fell, trapping soil beneath them. Using carbon 14 dating of charcoal in the soil, he was able to date the earthquake. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0f21a432-2790-44f7-9425-a76de8a18d8c/SP+Revised.jpg Home - Susannah Porter on Tiny Vampires in Ancient Seas The fossil record of complex life goes back far beyond the Cambrian explosion, to as far back as 1,600 million years ago in the late Paleoproterozoic with the first appearance of eukaryotes. But these creatures only started to diversify much later, around 750 million years ago. What enabled this evolutionary change has been a puzzle, but one idea is that it reflects the appearance of microscopic predators. In the podcast, Susannah Porter tells us how she discovered incontrovertible signs of predation in vase-shaped microfossils dating from this period. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87ff042a-9131-4a48-b77b-f5788a02fba5/AF+on+a+tourist+boat.jpg Home - Ana Ferreira on Seeing Flows in the Mantle Does the pull of a subducting slab drive plate motions? Or is it the upwellings of convection cells in the mantle? We now have a new way to shed light on this question. It's called seismic anisotropy, which is the spreading out of seismic waves according to their direction of polarization. This happens when the mantle through which the waves travel has crystals which are preferentially aligned, and that occurs when there is deformation or flow going on. So we can work backwards to use the observed dispersion of seismic wave arrival times to infer flow patterns in the mantle. In the podcast, Ana Ferreira explains how she used this to reveal an interaction between a mantle plume pushing up into and flowing around a subducting plate in the southwest Pacific. But, despite the vigor of such plumes, she concludes that it is probably the pull of the sinking slabs that is still the primary driver of plate motions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3c1665f9-9f63-45d2-b9b1-c0de0d87b061/PG+Castleton+21+ex-MikeSarginson.jpg Home - Phil Gibbard on the Anthropocene There’s no question that Homo Sapiens is having a major impact on the Earth. The question is, though, should this qualify for a new formal chronostratigraphic unit in the Geological Time Scale? Phil Gibbard describes the various proposals for the base and time scale level of such a new unit. After 13 years of work, the group formally charged with the official determination on the Anthropocene has made progress on when such a unit would start (mid-twentieth century) and what its status should be (epoch), but has yet to decide on whether such a unit should exist at all. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/65774865-372e-4ba0-8bae-03de3d58782f/Bercovici-Action5.jpeg Home - David Bercovici on How Plate Subduction Starts Subduction zones are a fundamental aspect of plate tectonics, yet we still don't really understand how subduction initiates. It's a tough problem because as oceanic plates move away from a mid-ocean spreading center and cool, they get stiffer and should become more and more resistant to bending and sinking down into the mantle. But recent work suggests that the clue to this puzzle lies in the physics of grains at the microscale. In the podcast, David Bercovici explains how the behavior of stressed mineral grains can radically affect the strength of oceanic lithosphere on the plate scale. In the picture, he is discussing the equations that govern the progressive damage of grains in a conglomerate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6d762726-0034-4721-b91d-57886492fc1c/YouTube+talk.JPG Home - Bob Hazen on the Evolution of Minerals During the course of Earth history, new types of rock have appeared on the scene as the Earth cooled and plates formed and started to move and interact in accordance with plate tectonics. The different rock types reflect the particular assemblage that composed them, and each tectonic environment favors the formation of a particular rock type, such as granite or basalt. But what about the minerals themselves? Have they been present since the Earth formed, or did they, too, only appear when certain conditions were met? In the podcast, Bob Hazen discusses mineral evolution, which turns out to be fertile ground for probing the deep history of Earth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ed83df7e-82f1-4206-8fb2-0b119c7f9673/IMG_2940.jpg Home - Matt Jackson on the Inhomogeneity of the Mantle Although we can’t sample the Earth’s mantle directly, we can learn about its composition from lavas thought to originate there that are erupted at mid-ocean ridges and at hot-spots. Kimberlites, which are xenoliths sourced from the mantle, also give us information. The data reveal a picture of a mantle that is compositionally and isotopically inhomogeneous at scales as big as a hemisphere and as small as a few centimeters. In the podcast, Matt Jackson describes the latest findings and suggests how they might be understood. Just after the interview, he boarded a research vessel (pictured) sailing for the western Pacific to sample ancient lavas from a chain of hot-spots there on the so-called “hot-spot highway.” https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d5c19786-e0f7-4b09-bc93-d778b54afd4f/portrait.jpg Home - Carmie Garzione on Reconstructing Land Elevation Over Geological Time Throughout geological history, various points on the Earth’s surface have been lifted up to great elevations and worn down into low, flat-lying regions. Determining surface elevation histories is difficult because rocks that were once on the surface are usually eroded away or buried. Furthermore, most rock-forming processes are not directly affected by elevation. But it turns out that we can overcome these challenges, as Carmie Garzione explains in the podcast. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/daf393f4-9d83-430a-9edb-eb3fdd17c762/CDM+Poas+edited.jpg Home - Chuck DeMets on High-Resolution Plate Motions The magnetic stripes frozen into the sea-floor as it forms at mid-ocean ridges record the Earth’s magnetic field at the time of formation. Reversals in the Earth’s magnetic field define the edges of these stripes, in effect time-stamping the sea floor position. Until recently, the reconstructions of plate motions relying on this giant natural tape-recorder were limited to a temporal resolution of about 5 million years. In this podcast, Chuck DeMets explains how he obtained a five-fold increase in resolution to reveal some totally unexpected plate speed variations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b683ce0d-7d3b-4fe2-be14-8b7313425b29/Mike+inspecting+pillows+-2.jpg Home - Mike Searle on Ophiolite As the name implies, oceanic lithosphere underlies the oceans of the world — except when they form ophiolites. Then oceanic lithosphere is thrust on top of a continental margin. Are ophiolites a special kind of oceanic lithosphere? Or are there peculiar tectonic circumstances that emplace denser oceanic rocks on top of lighter continental ones? Mike Searle addresses these questions, and reveals the sequence of events that created the world's most extensive and best-preserved ophiolite — the Semail ophiolite in Oman. Here he is framing a pillow of the lavas at the top of the ophiolite crustal sequence in Oman. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/45be8211-a3eb-46b5-861c-a4e2e59ecd81/MD+edited-1.jpg Home - Mackenzie Day on Dunes Some of the most extensive sandstone deposits in the world were deposited by wind. How do such aeolian rocks differ from water or ice-deposited rocks? And what do they reveal about the environments in which they formed? Mackenzie Day is an expert on aeolian processes. In the podcast, she describes the dunes we see in the geological record on Earth, as well as on Mars and on a comet, and explains how they formed. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8e2e19cc-105c-4740-b4b7-1e7a0d337aad/SS+in+HI+edited.jpg Home - Sue Smrekar on the VERITAS Mission to Venus The best maps we have of Venus were made by Magellan, a space probe that flew in the 1990s. NASA has just approved a new mapping mission that will produce radically improved maps of the topography, radar reflectivity, and gravity field, and the first-ever global map of surface rock type. Sue Smrekar, the mission Principal Investigator, explains why this will revolutionize our understanding of Venus and perhaps also throw light on the early history of Earth when processes analogous to those happening on Venus today may have occurred. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c7bc249-0cec-4785-9c2f-a31f7ac5c93a/FB+pic.jpg Home - Rick Carlson on Probing the Early Solar System Almost all the evidence about the nascent solar system has been erased by processes accompanying the formation of the Sun and the bodies that formed out of the circumsolar disk about 4.6 billion years ago. But some meteorites and the tiny dust grains contained within them have anomalous compositions that can be understood only by invoking a history going back to the giant molecular cloud progenitor of the solar system, and to the stars that ejected the material that formed the cloud. Rick Carlson is an isotope geochemist who measures such anomalies and uses them as clues to the birth of the solar system. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/06c31749-3d3c-4965-8af0-d2a0ed4584f1/EM+with+volcano+background.jpg Home - Ed Marshall on Iceland’s 2021 Eruption Eruptions whose magma comes from the asthenospheric mantle generally occur at mid-ocean ridges. But from March to September 2021, such an eruption took place on dry land on Iceland’s Reykjanes peninsula. This provided a rare glimpse of the processes occurring at the mantle-crust boundary. And, according to Ed Marshall, the lava tells a story of vigorous mixing of a highly heterogenous mantle. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8c148b75-92cc-4d8c-ba77-daf9f31fe4cc/Richard+Fortey+holding+Calymene.jpeg Home - Richard Fortey on the Trilobite Chronometer Long before radiometric dating appeared on the scene, the geological time scale was defined by the sedimentary record, and particularly by key fossils preserved within them. Throughout the Cambrian, and to a lesser extent until the end-Permian extinction about 300 million years later, trilobite fossils served as some of the most useful of these key fossils. Richard Fortey explains why. Here he is holding a trilobite from the calymene genus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635776943273-V9M0OR13OFVU9IM6FH0Z/PFH+in+Mackenzie+mtns.jpg Home - Paul Hoffman on the Snowball Earth Hypothesis The history of the Earth is marked by many ice ages. But according to the Snowball Earth hypothesis, the ice almost blanketed the entire globe at least twice in the Neoproterozoic and Archean. Paul Hoffman explains the mechanisms that could have brought this about, and describes the extensive evidence that has now been amassed in support of two snowball periods in the Neoproterozoic, about 720 and 650 million years ago. Courtesy of Sasha Turchyn https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635005983198-ULIRJ8OPJBYML20P69J3/thumbnail_Peter+Cawood+5443m+%281%29.jpg Home - Peter Cawood on When Plate Tectonics Started We know that the Earth was formed as a ball of molten material and quickly differentiated into a metallic core and a rocky mantle. We also know that at some point, the Earth’s surface formed itself into the rigid blocks we call plates, and that these plates started moving and interacting as part of a global process we call plate tectonics. But when was this point reached? Peter Cawood explains how five quite different types of evidence preserved in the geological record all point to the same answer. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634421919485-2R6UAP1XLMQRHEZYVJL8/Becky+Flowers+cropped.jpg Home - Becky Flowers on Deciphering the Thermal History of Rocks Many processes in geology affect the temperature of rocks. Erosion is one example — as a surface is eroded, the rocks below get closer to the surface, cooling as they go. So if we know the temperature history of a rock, we can infer its erosion history. Becky Flowers has a thermochronology lab in which she determines the cooling history of rocks as recorded in specific crystals they contain, such as zircon and apatite. She explains how this works, and how she has used her results to unravel histories such as that of the Grand Canyon, the South African plateau, and even that of the lunar surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633747816083-EBKGZTEECRABDQ9QHVAL/Linnemann+Ulf.jpg Home - Ulf Linnemann on the Assembly of Central Europe in the Paleozoic The geological history of Europe is quite complicated. Several continental blocks came together after oceans that separated them disappeared down subduction zones. Ulf Linnemann explains how zircon crystals that were eroded out of igneous rocks and then recycled into sedimentary rocks can reveal the sequence and timing of the events that led to the final assembly of Europe in the Paleozoic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632002152359-IC8EXGNOXQUZV7N8QZHC/Douwe+2018.jpg Home Douwe van Hinsbergen on What Drives the Motions of Tectonic Plates We’ve known that blocks of the Earth’s surface move with respect to each other since Alfred Wegener proposed the theory of continental drift in 1912. But we still don’t really know what drives these motions. Douwe van Hinsbergen argues that if we juxtapose reconstructions of plate motions over geological time with modern observations of the mantle from seismic tomography and from mantle geochemical signatures in volcanic rocks, we can infer that the mantle is relatively quiescent. Does that mean the plates cannot be riding on convection cells in the mantle? https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629379206534-3HDXZAKUS49N2NSUZR6P/photoMathilde_Mahato_recadree.jpeg Home - Mathilde Cannat on Mid-Ocean Ridges Oceanic plates are continually manufactured at mid-ocean spreading ridges. But exactly what processes go on at these ridges? It turns out that it depends on what type of ridge it is—fast-spreading or slow-spreading. And that our traditional view of vanishingly thin plate thickness at ridge axes is inaccurate. Mathilde Cannat describes our modern understanding of mid-ocean ridges and the observations that led us there. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628517086463-LENZ9EKDKGVO9XF6WG1Y/edited-1.jpg Home - Kathryn Goodenough on Sources of Lithium for a Post-Carbon Society As we decarbonize and electrify our economy, new raw materials move center-stage. One of these is lithium, whose singly charged ion drives the increasingly ubiquitous lithium-ion battery. Kathryn Goodenough presents the geology of our lithium sources, and the state of our knowledge as to the processes that concentrated the lithium in these sources. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627477643009-FZFTOMPGSV7DV27T5596/edited+portraits-2.jpg Home - Steve D’Hondt on Reviving a 100-Million-Year-Old Bacterial Colony How long can living cells survive in buried sediments? It turns out that bacteria, at least, can survive for at least 100 million years in sediments below the sea floor with barely any access to food. Had they been alive and reproducing all that time, or were they in suspended animation in a kind of hibernation? Steve D’Hondt explains how any plausible explanation pushes the boundaries of what we previously believed about how long cells can survive. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620868629706-8R7QMEKX5J1K13ND9YNE/Molnar+2012+processed.jpg Home - Peter Molnar on Why the Tibetan Plateau is So High How can we tell what is happening at the bottom of the lithosphere, especially in one of the most remote places on the planet? Peter Molnar describes how many diverse lines of evidence, from the fossil record to normal faulting point to abrupt elevation changes in Tibet, both before and well after India collided with it. He thinks this tells us that the bottom of the thickened lithosphere there is gravitationally unstable and hot enough to literally drip off into the asthenosphere below, after which the remaining lithosphere becomes more buoyant. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1623519173061-CXR16CVP01TTF1IE8TJ4/soccer+ball.jpg Home - Harriet Lau on the Motions of the Solid Earth on Timescales from Hours to Millennia The motions of plate tectonics occur on timescales of millions to billions of years. But there are forces acting on the Earth that cause motions on much shorter timescales, from hours to millennia. Harriet Lau analyzes such motions with the goal of extracting information about the structure and composition of the deep mantle. Here she is using a soccer ball to teach rotational dynamics. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622727351135-EYKKL2J5DXP8OEN1AUH9/CJ-skis-cropped.jpg Home - Craig Jones on the Iconic Landscapes of the American Westerns Some of the most dramatic scenery on the planet has literally set the stage for hundreds of American Western movies. What is the origin of the rocks in these photogenic locations, what happened to them in the tens and hundreds of millions of years since they formed, and what circumstances give us such an unimpeded view of them today? Craig Jones explains. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621997195912-VZ91LHKB0T3N9K0KAXUQ/CJ+close+crop.jpg Home - Claude Jaupart on Whether the Earth is Cooling Down The Earth is losing heat. Claude Jaupart wants to know how much, and so he has measured the heat flowing up through the top layers of the crust by making measurements down hundreds of boreholes. But the Earth continues to generate heat through radioactive decay of elements such as potassium, uranium and thorium. He calculates that for the past two billion years at least, the radioactive heat generation has not kept up with heat loss, and that the Earth is therefore cooling down - though at the extremely slow rate of 100 °C over a billion years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620434486178-WME78HF0F6SYAKAYIOSR/kstack_jezeroposter.jpg Home - Katie Stack on the Geological Mapping of Mars with the Perseverance Rover Katie Stack’s research focuses on the Martian sedimentary rock record, using orbiter and rover image data to understand the evolution of ancient surface processes on Mars. She describes what we are learning with the powerful instruments aboard the Perseverance rover as it traverses an ancient Martian river delta deposit. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620073951878-WCFZLBAMO6VIHFSASP03/KT+boundary+in+the+Raton+basin%2C+New+Mexico.jpg Home - Jan Smit on Resolving a Single Hour of the Cataclysm That Ended the Cretaceous 66 Million Years Ago Jan Smit is a paleontologist who specializes in abrupt changes in the geological record. After the discovery of an end-Cretaceous surge deposit in North Dakota, he was part of the team that pieced together the striking evidence it contained, particularly its perfectly preserved fossils and tiny glass spherules called tektites. He describes how this led to a detailed picture of the dramatic events that unfolded within an hour or two following the asteroid impact. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619825098644-22I6YKX611GV0MH8Z6YY/Marie+Edmonds.jpg Home - Marie Edmonds on Volcanic Gas Marie Edmonds has studied the gas emitted by volcanos in subduction zone settings, at mid-ocean spreading ridges, and in continental rift zones. She measures the concentrations of the various gas components and uses this to infer what is occurring at depth. She is especially interested in deep carbon recycling from the atmosphere to the mantle and back out into the atmosphere at volcanos. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619466536564-QSENBFY5C27CHN2OCJ9O/IMG_9217+%281%29.jpeg Home - Gillian Foulger on Explaining Intra-Plate Volcanism Without Mantle Plumes Gillian Foulger is a leading proponent of the plate hypothesis of volcanism, which posits that volcanism away from plate boundaries can be explained by extensional deformation of the lithosphere with melting of the upper mantle. The plate hypothesis uses plate tectonic theory to explain all volcanism without invoking plumes or hot-spots that originate in the lower mantle. She hosts a lively debate on whether mantle plumes exist at mantleplumes.org. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1618882775696-MMULJBZF8YIVNL5WYJSP/102209_Compression_141.jpg Home - Sarah Stewart on a New Scenario For How the Moon Formed Sarah Stewart uses computer-based dynamical simulations and lab experiments to create scenarios for the collision of a massive body with the Earth that can reproduce the composition, orbits, and spins of the Earth and Moon today. She believes a new kind of object called a synestia formed in the immediate aftermath of such a collision. Here she is in her lab with an instrument that can generate very high temperatures and pressures in a target to simulate conditions after the impact. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617639485003-YZNMMWFFX02ZF92YEVZA/Dietmar_at_work.jpg Home - Dietmar Müller on Reconstructing Plate Motions Over a Billion Years of Earth History Dietmar Müller and his team have built interactive software to combine hundreds of diverse geological research studies into a single self-consistent picture of the plate-tectonic motions over deep time. He explains how this astonishing feat was accomplished and points out salient features in the results. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616897350493-KK6CS1Q1Y1DT4VRHFXY1/bob%26blackburn_cropped+copy.jpeg Home - Bob Anderson on How Geology Affects Landscape Bob Anderson is fascinated by patterns in landscape and has devoted his research career to understanding the physical and chemical processes that generate these patterns on scales from the microscopic to the continental. He uses the Sierras as a classic example of how the nature of the bedrock shapes landscape, and explains how the use of cosmogenic radionuclides has revolutionized our ability to uncover the timing of the processes shaping the Earth’s surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616613115290-YSMWS8CUWI1BIQPA1JJG/DE+in+VT.jpg Home - David Evans on Supercontinents David Evans is a tectonic jigsaw puzzle-master. Using a wide diversity of geological clues, he reconstructs the supercontinents into which almost all of the Earth’s landmasses were joined at various points in Earth history. His own observational work focuses on magnetism imprinted in ancient rocks, which can tell us the latitude at which these rocks formed. To measure these magnetic signals, he has a specialized paleomagnetism lab at Yale. Courtesy of Saran Morgan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615679170694-5HVLINZ2EFDKQLQW9CIS/Portrait.PNG Home - Mike Howe on the UK National Geological Repository The UK National Geological Repository is a 16-million-strong collection of fossils, rocks, and cores from boreholes across Britain and the UK Continental Shelf. Mike Howe explains the significance of some noteworthy items in the collection, such as a conodont fossil that resolved the long-standing enigma of their origin, and a mysterious ring-shaped fossil that led to the discovery of new species from the Ediacaran period. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612051833297-FWEFEA7FN5M7LDRBUQ8U/RW+in+Namibia-2.jpg Home - Rachel Wood on the Emergence of Complex Life in the Precambrian Rachel Wood is a field geologist who searches for the very earliest evidence of complex life in the fossil record. Together with her colleagues, she has established direct evolutionary connections between life in the late Precambrian (Ediacaran) and that of the Cambrian, suggesting that complex life emerged earlier than previously thought. Here she is on a geological field trip in Namibia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615159632203-QSRSB8060T930KBGNWOH/Lee+in+the+Field+cropped.jpg Home - Lee Groat on How Gemstones Form Through a combination of field and lab studies, Lee Groat unravels the precise geological histories that result in the formation of gemstones. He explains how emeralds and sapphires form, including those of a spectacular occurrence in Baffin Island that yielded 40 sapphires selected for a brooch presented to Queen Elizabeth II on the occasion of her Sapphire Jubilee. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614470393893-C570JWNS9N3FAAXERJXX/McNamara-portrait.jpg Home Allen McNamara on the Deep Mantle Structure of the Earth Allen McNamara develops sophisticated computer-based fluid-dynamical models of the deepest mantle to simulate the chemical and thermal structures that could give rise to the striking features revealed by seismic tomography. His models predict the shapes of the thousand-kilometer-scale low-shear-velocity provinces as well as those of the much smaller ultra-low-velocity shear zones that can barely be resolved in today’s seismic imagery. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613084991484-B798ZDCQCQ164NT70B31/selected_P3129862.JPG Home Tomo Usui on the Mission to the Martian Moon Phobos Tomo Usui is leading the science team for the 2024 Japan Aerospace Exploration Agency’s mission to Phobos, which will land, collect samples, and return them to Earth in 2029. He is especially excited about ejecta from Mars that are expected to be present in the sample as these will be our first-ever non-meteoritic Martian samples. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611085571488-NM6L8GGIQCY70O72EZPV/Carolina+Lithgow-Bertelloni.png Home Carolina Lithgow-Bertelloni on Dynamic Topography Carolina Lithgow-Bertelloni models the effect of mantle currents on the overriding tectonic plates. Her models predict that the mantle can deflect the plates up or down by as much as a kilometer and explain otherwise anomalous topographic features seen both today and in the geological record. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610223554724-V101IQIEG730AV8AD8VU/Web+portrait.png Home - Cathy Constable on Mapping the Earth’s Magnetic Field in Time and Space Cathy Constable reconstructs global maps of the Earth’s magnetic field over timescales from millennia to millions of years using the remnant magnetism “frozen” into human artifacts and rocks. This has revealed surprising patterns of variation that in turn cast light on the processes in the Earth’s core that are responsible for generating the field. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1608246306816-XW7N576IEMVY2AD3RF3L/F_Fiondella-0634.jpg Home - Bärbel Hönisch on Reconstructing Climate in the Distant Past Bärbel Hönisch uses the skeletal remains of foraminifera as her raw material in reconstructing ocean and atmospheric conditions that prevailed in past geological periods. Trace chemical constituents in these creatures can record the temperature of the ocean and carbon dioxide of the atmosphere. Climate models being applied to the present day are being validated by what she is discovering about the planet’s past evolution. Courtesy of Francesco Fiondella https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607031839614-BTIP0DVY2OEF4XKQMKFK/DSC01534.jpg Home - David Rothery on Volcanism in the Solar System David Rothery investigates volcanism on Earth and elsewhere in the Solar System using remote-sensing Earth-orbiting satellites and space probes. Mercury is his present focus, and he is lead co-investigator for geology on the X-ray spectrometer aboard BepiColombo, an ESA mission currently on its way to Mercury. He describes some intriguing puzzles about Mercury that he hopes BepiColombo will resolve, as well as a type of volcanism occurring on some icy bodies in the outer solar system called cryovolcanism. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606584729615-V4IIJFF919MI2NV11LMC/Connolly_Paris+copy+2.jpg Home - Harold C. Connolly Jr. on Bringing an Asteroid Sample Back to Earth Harold C. Connolly Jr. studies the origin of the oldest materials in the solar system, especially the small spherical igneous rocks called chondrules that are the main structural component of stony meteorites. He explains what we hope to learn from a sample of the asteroid Bennu that is being returned to Earth by the OSIRIS-REx spacecraft. In the background of the photo is a backscatter electron image of the carbonaceous chondrite meteorite Jbilet Winselwan showing several chondrules. Courtesy of Roger Hewins https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605971921050-DYRUYOH1B3RCLARWPCP6/LJ+in+Andalucia-2.jpg Home - Laurent Jolivet on the Origin of the Mediterranean Laurent Jolivet is an expert on the dynamics of tectonic plates and the mantle. He combines satellite measurements, seismic tomography, field observations, and computer modelling to reconstruct plate motions, even in some of the most complicated parts of the world. Here he unravels the tangled evolution of the Mediterranean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605743165420-MKUF54NN9KHA5Q95Q559/image-asset.jpeg Home - Sir Mark Moody-Stuart on Transitioning to a Post-Carbon Economy After training as a field geologist, Sir Mark Moody-Stuart joined Shell in 1966, rising through the ranks to become chairman from 1998 to 2001. He is now a board member of Saudi Aramco, the world’s largest oil-producing company. When the danger posed by global warming became apparent, he became a leading voice for change in the oil industry. He argues that the major oil companies are uniquely positioned to play a key role in the transformation of our energy industry. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604248136565-JH7QHIWGKXNQUMJSMX6M/John+Marshall+Ella+island+%281%29.jpg Home - John Marshall on the Riddle of the Mass Extinction 360 Million Years Ago John Marshall studies fossils, especially ones that coincide with mass extinctions. He recently discovered a Devonian lake-bed deposit in Greenland containing malformed fossil spores. He explains how this points to a new kill mechanism that could be the cause of the mass extinction at the end of the Devonian period. Photo courtesy of Sarah Finney https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604009171318-ZOOU0NRPAPN782NLMHRT/LJR+Burma+2-2.jpg Home - Laurence Robb on Where Our Mineral Resources Come From Laurence Robb is an expert on the origin of mineral deposits, principally in Africa and Asia. He uses our latest understanding of plate tectonics to unravel the processes that formed some of our most important mineral deposits. Here he reveals a range of mechanisms by which minerals are concentrated into economically valuable resources. Photo courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603307050053-NEZ9X148EMGCXBP7MJE7/HeadShot.png Home - Bruce Buffett on Probing the Earth’s Core Bruce Buffett matches computer-generated simulations of the Earth’s core to the observed magnetic field of the Earth to investigate the motions and magnetic fields within the core. Here he explains how he does this, and discusses the complex plume structures revealed by this research. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601494369638-XU8I4VTA8NVUOJDW1NIV/David+Sandwell+pic.jpg Home - David Sandwell on Seeing Plate Tectonics Under the Oceans David Sandwell uses satellites to make accurate measurements of the shape of the ocean surface. He explains how this enabled him to create a global map of the topography on the sea floor. This revealed the global extent of classic plate-tectonic features, such as spreading ridges and transform faults, but also intriguing new features we still do not understand. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601321760885-S1I2A13ED85QDPSG2VIG/Barbara+Romanowicz+The+Wall+Papers.jpg Home Barbara Romanowicz on Seeing Deep into the Earth With seismic tomography, we can use the seismic waves triggered by earthquakes to make images of the Earth’s mantle. Barbara Romanowicz explains how this is possible, and that we can even see relics of ancient sea-floor plates that have subducted and sunk almost all the way down to the Earth’s core. Photo courtesy of the University of British Columbia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600442430600-9LFL6JLCCUNYZQJ8OXMD/JV+with+the+SIMS.jpg Home John Valley using the ion microprobe at the University of Wisconsin in Madison to date a zircon crystal, with Takayuki Ushikubo and Noriko Kita. Photo courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600456890390-2K5Z62GRZ1W770B41DVR/Sara+Russell+cropped.jpg Home - Sara Russell on What the Asteroids Can Tell Us About the Earth The asteroid belt is a region lying between the orbits of Mars and Jupiter that contains billions of asteroids, ranging from some as small as pebbles to as large as nearly 1000 km across. Sara Russell explains how we can use asteroids to help us unravel how the solar system formed and to cast light on questions such as how the Earth got its water and organic materials. Photo courtesy of Tammana Begum https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597071454243-UB6W64IMOV1K6HBV3WN9/C_Warren.jpg Home - Clare Warren on Divining the History of a Rock Most rocks were formed many millions of years ago. Since then, some have been largely left alone, while others have been baked at high temperatures and buried at great depths. Clare Warren explains how we can now uncover remarkably precise histories of such rocks, even if they have been through more than one episode of such extreme treatment. Photo courtesy of The Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596055112987-QXWURDOLBMD5ZYKII80G/DSCN1393.jpg Home - Steve Sparks on What Makes a Volcano Erupt Steve Sparks has turned our ideas about volcanoes upside down. Not quite literally, but by applying the physics of fluid motion to the rocks and magma below volcanoes, he discovered that magma forms slowly at much greater depths than previously thought, eventually forming an unstable blob that forces its way up through the overlying rocks to erupt from a volcano. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596054937759-BN7SPV8EB10IIA1QZANV/Iceland-2.jpg Home - Dan McKenzie on What Venus Tells Us About the Earth Why look to another planet to reveal something new about the Earth? Dan McKenzie describes an ingenious way of using the data sent back from the Magellan Venus orbiter to discover that Venus is covered with an elastic plate about 30 kilometers thick. Explaining this very unexpected result revealed something extraordinary about the Earth. Photo Courtesy of James Jackson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596054365781-Q0EMEEJCAFCGE6MKOZB5/2011_bam_1.jpg Home - James Jackson on the Fatal Attraction Between Cities and Earthquakes In this episode, James Jackson explains what happens, geologically-speaking, during an earthquake, why they strike where they do, and why earthquake-prone places are such attractive places to live. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596055640669-XFA4C5NZ7ERN7XAAYWCD/IMG_5309.JPG Home - Mike Searle on Why Mountains Exist Mike Searle applies the theory of plate tectonics to explain what causes mountains of all kinds to form. They range from enormous mountain belts such as those that stretch from the Himalaya to the Alps, to mid-ocean volcanoes such as Hawaii. https://www.geologybites.com/jamesjacksondiagrams daily 0.75 2020-07-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595366072812-KOTQDJFVACOIDBCK3ZRI/world_eqs.jpg Diagrams for James Jackson The world distribution of earthquakes. Each earthquake indicates an active fault. The faults occur in narrow bands in and on the edge of the oceans and are dispersed throughout the Alpine-Himalayan belt. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595366400121-E5X9JGM2M659SB52V0DG/asia_eqs.jpg Diagrams for James Jackson The distribution of earthquakes in Asia indicating a complex network of active faults. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595367149744-ZSJY1ES6UMSM6H6LOP6Y/historical_1.jpg Diagrams for James Jackson Earthquakes that killed more than ten thousand people in the last 1,000 years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595367238026-9HD6DMSCU829REAJRZK1/historical_2.jpg Diagrams for James Jackson Earthquakes that killed more than ten thousand people from 1000 to 2008 AD with trade routes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595367698498-HXQR486CTE6GS42X26UB/historical_3.jpg Diagrams for James Jackson Histogram showing the number of earthquakes for each century of the last millennium that killed more than ten thousand people. https://www.geologybites.com/danmckenzie daily 0.75 2025-04-16 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595445938862-VG6S77EY6PUHGAI45NF1/Iceland-2.jpg Dan McKenzie Dan McKenzie at a fault fissure splitting apart earlier basalt lava flows at Grjotágrá, NE Iceland. Courtesy of James Jackson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596157480181-GQPDHMBQMHT9MD84GUAH/1292_Magellan_deploy.jpg Dan McKenzie - The Magellan spacecraft being released from the Space Shuttle in 1989. All the topographic measurements were made by the altimeter, which is the conical object attached to the side of the dish antenna. It pointed directly downwards, and the dish pointed to one side when it was mapping. The dish was used both to capture radar data for imaging the Venusian surface, and also to transmit the data back to Earth. Dan McKenzie used the Doppler fluctuations in this signal to determine the local gravity field. Image courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596157572292-DJ7HY49V9ZWKOPV7BOX3/radar+image+of+Venus.jpg Dan McKenzie - Radar image of Venus from Magellan showing a perspective rendering of the topography data that was correlated with the gravity field data as described in the podcast. The image shows two craters formed by the impact of meteorites. Courtesy of NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596157648219-LWUG5TUWAVMWCRZT66AI/A55.jpg Dan McKenzie Rendering of the topography of Venus and the Earth. The two planets are roughly the same size. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596157745862-D66BXHS6T40MKA5R3D3Y/Venuspioneeruv.jpg Dan McKenzie Ultraviolet image of the atmosphere of Venus showing the dense clouds of sulfuric acid droplets. Taken by Pioneer Venus Orbiter in 1979, courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596674939580-D5Q2RHTIQ1W1JI07Q67T/venus_alt_19.jpg Dan McKenzie The large-scale (more than 700 km) topography of Venus from the Magellan spacecraft. At these larger scales, the effect of elastic support on the topography disappears. The box indicates the Atla region shown in the images below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596675032984-9C6X0TNYON6P8O13HFEJ/venus_grv_19_v2+box.jpg Dan McKenzie The large scale (more than 700 km) gravity field of Venus inferred from the Doppler measurements of the radio signals from Magellan. At these scales, the effect of elastic support on the gravity disappears, so what remains is the gravity field caused by convection of the underlying mantle. It reveals a pattern of convection cells. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596675077202-TEZD1MNPFARRDSWMHPEA/venus_resid_alt_19_v2+box.jpg Dan McKenzie Map of the large-scale topography with the effect of convection of the mantle below the elastic plate removed. Since elastically supported topography is not significant at these scales, what remains is the topography supported by buoyancy - like a floating iceberg, but here it is the Venusian plate (the layer of crust and mantle that does not take part in the convective flow) floating in the mantle below. Most of the topography in the Atla region has disappeared, indicating that Atla is almost entirely supported by mantle convection. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596721808336-Y4LC3L8MEJKPYXR33BD9/venus_topo_to_360-2.jpg Dan McKenzie Atla region topography at all scales. One degree of latitude is approximately 100 kilometers, and the map covers an area of about 3,700 km square. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596721840910-6DWXL16AP4Y3W6LJ3TA5/venus_grav_to_60-2.jpg Dan McKenzie Map of the large-scale (more than 700 km) part of the gravity field, revealing the pattern of convection in the interior of Venus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596721883296-QSV0M6L1SI1RC2GYSSJK/venus_elastic_topo-2.jpg Dan McKenzie Map of the elastic topography, which is the real topography minus the topography caused by convection of the mantle below the surface plate. The map reveals the downward flexing of the plate around the big volcano towards the lower left (around 0, -165) where it elastically supports the extra mass of the volcano. The linear features in this map look like a map of rift valleys in Africa, suggesting that in these regions the plates of Venus and the Earth have similar elastic thicknesses. All maps courtesy of Dan McKenzie https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597267137903-6Y9BC8FWPUU2NL8LILTA/Gravity+anomaly+drawing.png Dan McKenzie Diagram contrasting the relationship between the topography and the gravity field for a thick elastic plate and for a thin elastic plate. For the thick plate, the topography is fully supported by the plate, resulting in a gravity field that follows the topography. For a thin plate, in which the topography is fully compensated (no elastic support), the topography has no effect on the gravity, as with a floating iceberg. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597268642209-X89P5NZQ5DIUA87LBV29/regimes+curve.jpg Dan McKenzie Graph showing how the relationship between the gravity field and elastically supported topography differs in each of three scale ranges. At large scales (i.e., long wavelengths) where convection and crustal thickness dominate, the expected relationship is shown on the left of the graph. The intermediate scales where elastic support dominates are shown in the middle of the diagram. At the small scales shown on the right of the figure, there is no compensation at all, and the curve flattens out, indicating that the gravity follows the topography. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597269606015-24CFBRYS3DZVB7G42QJ3/different+thickness+curves.jpg Dan McKenzie Graphs showing the theoretical relationship between the ratio of gravity to elastically supported topography at different size scales for plates of different elastic thicknesses. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597267383986-RMRMLHCWUNSYDPVZ4EVD/Admittance+vs+wavelength+plot.jpg Dan McKenzie This is the graph that enabled Dan McKenzie to estimate the thickness of the elastic plate on Venus. It shows the scale above which elastic support is no longer important, i.e., where convection causes the observations (shown as circles) to depart from the curve expected for elastically supported topography, which occurs above about 700 km. The curve that best fits the observations in the elastically supported domain is that calculated for a 28 km thick plate. All figures courtesy of Dan McKenzie https://www.geologybites.com/about daily 0.75 2026-01-04 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612497122340-YS5JVNJS1KKLTZFT06V6/Blue%2Bquartz%2Bon%2BAndrews%2BPoint-2.jpg About About this Podcast Series In learning about the geology of our planet, I have been struck both by the story we have uncovered and by the theoretical and experimental ingenuity of those who have got us to this point. I hope these podcasts reveal pieces of the story in digestible bites as told by those who discovered (and continue to discover) them. I aim to make this series accessible to curious listeners, even those who do not have a formal scientific background. But some of the ideas are quite subtle or intricate, and this might turn out to be a bit optimistic. Give me feedback, either by submitting the form on the Contact page, or by email, so I can adjust things to make the series better. Oliver geologybitespodcast@gmail.com X: @geology_bites Bluesky: GeologyBites Instagram, Facebook: geologybites https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596150779466-64V7SOO2SAU7W7RT7RBD/Oliver+Strimpel+In+Zanskar%2C+Northern+India About Above the Parkachik glacier below the peak of Nun (7,887 m) in Zanskar, in the far north of India, on a 2018 geological field trip. https://www.geologybites.com/about-1 daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-2 daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-3 daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-4 daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-5 daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-zdjxy daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/about-38t7z daily 0.75 2020-07-21 https://images.squarespace-cdn.com/content/v1/5cee9df5880cbc000150d93b/1561902574874-0TNHDCEXEFFAEJPP4GP2/fran.jpg About https://www.geologybites.com/donate daily 0.75 2020-07-22 https://www.geologybites.com/contact daily 0.75 2023-03-07 https://www.geologybites.com/dan-mckenzie-pictures-and-diagrams daily 0.75 2020-07-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595469130463-X4VJWXMOGEDYHSXSRMDQ/1292_Magellan_deploy.jpg Dan McKenzie pictures and diagrams The Magellan spacecraft being released from the Space Shuttle in 1989. All the topographic measurements were made by the altimeter, which is the conical object attached to the side of the dish antenna. It pointed directly downwards and the dish pointed to one side when it was mapping. The dish was used both to capture radar data for imaging the Venusian surface, and also to transmit the data back to Earth. Dan McKenzie used the Doppler fluctuations in this signal to determine the local gravity field. Image courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595469404507-ANXEI2GE42YYK1Q693Q9/radar+image+of+Venus.jpg Dan McKenzie pictures and diagrams Radar image of Venus from Magellan showing a perspective rendering of the topography data that was correlated with the gravity field data as described in the podcast. Courtesy of NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595780348909-5ATTY5BOOCLRDHER8VVJ/A55.jpg Dan McKenzie pictures and diagrams Rendering of the topography of Venus and the Earth. The two planets are roughly the same size. Courtesy of Dan McKenzie https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595780852082-JALRV9NTQ3DM7M1SEGLY/Venuspioneeruv.jpg Dan McKenzie pictures and diagrams Ultraviolet image of the atmosphere of Venus showing the dense clouds of sulfuric acid droplets. Taken by Pioneer Venus Orbiter in 1979, courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595781119783-0OLCXCJF3DLQQ0UDJPDR/venus_alt_19.jpg Dan McKenzie pictures and diagrams Map of the topography of Venus from the Magellan spacecraft. Courtesy of Dan McKenzie https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595781223932-BJDOJK7EHBNDAKV0WI37/image-asset.jpeg Dan McKenzie pictures and diagrams Map of the gravity of Venus inferred from the Doppler measurements of the radio signals from Magellan. Courtesy of Dan McKenzie https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595781341635-C4WD6S0Z6D32T15QHED1/venus_resid_alt_19.jpg Dan McKenzie pictures and diagrams Map of the topography with the effect of convection of the mantle below the elastic plate removed. What remains is the topography that is supported by the plate. Dan McKenzie analyzed this to determine that the thickness of the Venusian elastic plate is 20-30 km. Courtesy of Dan McKenzie https://www.geologybites.com/stevesparks daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595902804969-XNQ8CNG3XS3M6D3PYBJY/DSCN1393.jpg Steve Sparks Steve Sparks at the Erciyes volcano, one of the largest active volcanoes in Turkey. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596156663030-NJVOYPUBSEZGWYTBU6I4/Figure+1.jpg Steve Sparks - Classical model of a volcano with a permanent shallow magma chamber. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596156972774-H4VJ9QCW3QXJT7VQXJU7/Figure+2.png Steve Sparks - Current model of a volcano in which melted material is stored between the crystals of an extensive mush. The melt separates out from the mush very slowly. Because it is lighter than the surrounding rock, it is unstable, and rises to the surface, with only transient storage in a shallow magma chamber. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1596157052110-B4XUC9PQTRVJBXJMY43K/Instability+experiments.jpg Steve Sparks Lab experiments show how an instability forms between liquids of different densities and viscosities. In this experiment, the denser, less viscous material (analogous to the melt) is placed above the denser more viscous material (analogous to the crustal rocks). This is upside down compared to the real world, in which the melt is produced below the rocks, and finds its way to the surface when an instability forms at the melt/rock boundary, causing a blob of melt to pinch off and rise. All images courtesy of Steve Sparks https://www.geologybites.com/stevesparksdiagrams daily 0.75 2020-07-28 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595904254058-C4COAAJQSVFR430O8UHI/Figure+1.jpg Steve Sparks diagrams Classical model of a volcano with a permanent shallow magma chamber. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595904482401-S7VDH2QP7FAVRQYA3Y64/Figure+2.png Steve Sparks diagrams Current model of a volcano in which melted material is stored between the crystals of an extensive mush. The melt separates out from the mush very slowly. Because it is lighter than the surrounding rock, it is unstable, and rises to the surface, with only transient storage in a shallow magma chamber. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1595904692881-DSVGSB15D0PG5ZLN1LIS/Instability+experiments.jpg Steve Sparks diagrams Lab experiments show how an instability forms between liquids of different densities and viscosities. In this experiment, the denser, less viscous material (analogous to the melt) is placed above the denser more viscous material (analogous to the crustal rocks). This is upside down compared to the real world, in which the melt is produced below the rocks, and finds its way to the surface when an instability forms a blob to rise. All images courtesy of Steve Sparks https://www.geologybites.com/clarewarren daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597073186268-QR5AM67SS3VM5DDU8XHH/C_Warren.jpg Clare Warren Clare Warren with a petrological microscope for looking at thin sections of rocks with polarized light, which reveals optical properties that can distinguish minerals clearly. Clare Warren is Senior Lecturer in the School of Environment, Earth and Ecosystem Sciences at The Open University. She investigates how, when and why metamorphic rocks record their history, and, specifically, when different geological clocks start and stop 'ticking'. Using such clocks, together with detailed geochemistry, she uncovers the temperatures and pressures experienced throughout a rock’s history. She applies this knowledge to work out just what happens when continents collide and mountains form. Photo courtesy of The Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597071576230-RIOSNVA5KPJT97DIFL3J/Bhutan+valley+C+Warren.jpg Clare Warren Masang Kang Valley in northwest Bhutan where Clare and her team collected the rocks discussed in the podcast. The glacially carved valley is 4,000 meters high, and sits at the base of Masang Kang, Bhutan’s highest mountain. Photo courtesy of Clare Warren https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597071670345-81RF7JEMBGUJDTH2CVJD/Outcrop+metabasite+C+Warren.jpg Clare Warren An outcrop of the high-pressure rock discussed in the podcast in the Masang Kang valley, Bhutan. This rock was formed as a basalt that intruded into the Indian continent about 800 million years ago, long before the collision with Asia. That collision, which started about 50 million years ago, metamorphosed this basalt at great depths, turning it into a metamorphic rock called eclogite. Photo courtesy of Clare Warren https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597094408123-9IVHE61JKOLSPF3ZT91O/Close+up+metabasite+C+Warren.jpg Clare Warren Closeup of the eclogite shown in the picture above. The red mineral is garnet, the white mineral is plagioclase, and the grey/green/blue mineral is hornblende. This rock tells us about the lower crust of the Himalaya. It was metamorphosed at temperatures of around 650 C and pressures corresponding to a depth of 42 km about 15 million years ago. How it was brought back to the surface so quickly, geologically speaking, is still unclear. Photo courtesy of Clare Warren https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597153753376-8QRYY3FI8HLVP8DHW8IE/Thin+section+E+Wood+annotated.jpg Clare Warren When rocks are cut into slices about 30 microns thick, they become transparent. In this thin section of the eclogite shown in the previous photos, garnet (pink), quartz (colourless), iron oxide (black) and hornblende (green) can be identified. There are other minerals in the rock too small to be seen at this scale. The relative abundance and juxtaposition of the garnet, hornblende (which has formed by replacing another mineral called pyroxene) and quartz tells us about the high pressure history of this rock. The field of view is 1 cm across. Photo courtesy of Eleni Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597071899154-LT7BP2NXEDF0P2FK3U13/False+Colour+SEM+E+Wood.png Clare Warren Scanning electron microscope image of the rock shown in the previous images. Minerals are colored by density, with the darker green minerals the least dense, going through blue, pink, orange, and red to the densest. The image is 80 mm across. Photo courtesy of Eleni Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597096001605-OOBWX6C7N25SZ7GSZK03/Outcrop+metapelite+C+Warren.jpg Clare Warren The lower-pressure rock (a garnet-bearing gneiss) discussed in the podcast, found about a kilometre away from the high-pressure eclogite shown above. Clare Warren and her team proposed a way in which rocks with such diverse histories could end up so close to each other - see below. Photo courtesy of Clare Warren https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597098260745-BZN4IAZ7BTG2ZDM887CG/Tectonics-Bhutan.jpg Clare Warren This diagram shows how the low-pressure rock (red star) and the eclogite (green star) came from different levels of the Indian continental margin and were metamorphosed in different parts of the Himalayan system at different times. During their transport towards the surface, they ended up next to each other. The red hashed zone is the partial melting zone, where rocks get so hot they partially melt to form the big granite plutons that are dotted around the Himalaya. Although the low-pressure rock revealed a history spanning 34 million years, it was never pushed down deep enough to be converted into eclogite, remaining stuck in the middle Himalayan crust. (The blue star indicates a rock with yet another, even shallower, history that is also juxtaposed with the other two rocks today.) Courtesy of Eleni Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597025809193-VDSVUBB529BRGQ6OUR5E/zircon.png Clare Warren Images through the cores of two different zircon crystals showing tree-ring-like growth rings. The cores are 800 million years old, but the brighter outer rims of these grains record growth during metamorphism accompanying the formation of the Himalaya 20 million years ago. Zircon ages are obtained from the decay of uranium to lead. These grains were extracted from rocks similar to those shown above, but in Sikkim, about 100 km to the southwest of the Masang Kang Valley in Bhutan. Photo courtesy of Catherine Mottram https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1597072058605-ORSICF9ICHO1KA3FLAVS/LA-ICP-MS+B+Kunz.jpg Clare Warren One of the instruments used to measure the elemental and isotopic composition of a mineral to very high accuracy. A laser in the black instrument to the left acts like a tiny drill that excavates 10 micron wide pits in the sample, which sits in the yellow box. The excavated particles are sucked into the mass spectrometer (white box on right). A plasma torch ionizes the particles and breaks them down even further. The ions then pass between powerful magnets that separate them by mass, and the different masses are measured on a sensitive detector. Photo courtesy of Barbara Kunz https://www.geologybites.com/johnvalley daily 0.75 2025-04-16 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600444740168-81G8DLTFHLSQ5201MB1Y/JV+on+his+own+at+SIMS.jpg John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600445994023-3RG5MNWUVK15VDZI8O1P/Bonesal.jpg John Valley Artist’s impression of a hot Hadean, with magma oceans, floating “rockbergs,” and meteor bombardments. The Moon’s orbit was closer to the Earth, and there was a dense steam atmosphere. Image courtesy of Chesley Bonesal https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600630958907-R75U3FR6DRT348GH9N6X/Dixon+early+cool+Earth.jpg John Valley Artist’s impression of a cool Hadean, with liquid water oceans, a basaltic shield volcano, and clement conditions. Image courtesy of Don Dixon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600448428640-CMWERSIBH9V3MCLEPP80/timeline.png John Valley The Earth’s history is divided into four eons - the Hadean, the Archean, the Proterozoic, and the Phanerozoic. The Phanerozoic was named after the Greek word for life, but microorganisms originated much earlier, and even the animal fossil record starts in the late Proterozoic. Timeline courtesy of Andrée Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600720386731-ZS26FW7XNH0HM1YLM8H8/All+Australia.jpg John Valley The Hadean eon zircons were found in the Jack Hills region of Western Australia. Image courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600720109949-THDSPHSQV8BDKJN01ZNX/Jack+Hills+satellite+2+w+captions.jpg John Valley False color satellite image of the Jack Hills region where the oldest known zircons are found. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600447355032-HEJBVPLQXMU7TINFKHAN/Jack+Hills+road.jpg John Valley The Jack Hills region of Western Australia is not all hilly, but arid and unpopulated. Photo courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600447540229-Q2X815Z0TNYQIWB4LOTQ/Zircon+outcrop+in+the+Jack+Hills.jpg John Valley The “discovery outcrop” where Hadean age zircons were first found in these conglomerates by Simon Wilde (right) and others in the 1980s. (John Valley, left; Aaron Cavosie, center) Photo courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600448113384-JDSE83UZA2E1HJREUKE6/Jack+Hills+hand+samples.jpg John Valley Samples taken from the Jack Hills conglomerates. The pits are 5 mm drill holes where samples of quartz were taken for analyzing oxygen isotope ratios. (Quartz is silicon dioxide.) The zircons are concentrated in the dark layers, most clearly visible in the top left sample. Photo courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600449045442-IGIDIUB4W6RR2CPAB8MA/optical+photo+of+zircons.png John Valley Zircon crystals extracted from the Jack Hills conglomerates. Some are smoothed by abrasion, but others have retained their crystal faces despite their great ages. Photo courtesy of Jack Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600449213222-XY0J4DTIFBJGMJAY582P/SIMS+diagram+slide+with+sample+detail.PNG John Valley Diagram of an ion microprobe similar to that used to date the zircons. An ion gun (yellow) fires a beam of ions onto the zircon sample where it sputters some ions off the surface. These secondary ions are then directed into a mass spectrometer (green) where a strong magnetic field separates the ions out according to their mass. The relative amounts of each ion species is measured with an accuracy of nanograms (blue). The ratio of a parent isotope, such as uranium to a daughter isotope, such as lead, resulting from radioactive decay of the parent yields the age of the sample. Diagram courtesy of Cameca and John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600450366651-5JZF0NP9I9YP20O4XDBU/b-w+CL+image+of+zircon+in+concordia.jpg John Valley Image of a zircon crystal using cathodoluminescence (CL). The crystal is placed in an electron microscope and “illuminated” with an electron beam. The electrons cause the crystal to emit light that reveals its internal structure. The CL image here shows that the zircon is zoned, each zone reflecting a growth phase when the crystal accreted more material from a surrounding melt. By directing the ion probe beam onto different portions of the crystal, we can date the various phases of the crystal’s growth. This particular grain has a history that spans almost a billion years. Image courtesy of John Valley, Valley et al., Nature Geoscience, 2014 Vol. 7, 219 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600451145868-7Y775VP2X4HR818XGS8P/concordia+diagram.png John Valley The results from measuring the uranium lead isotope ratios in the zircon crystal shown above. This is a concordia diagram, since it shows whether the ages derived from each of two independent uranium to lead decay pathways are consistent with each other. Concordant ages must fall on the solid line. Each probe of six different probe beam locations were analyzed and plotted on this concordia diagram together with their error ellipses. All three of the ages obtained from the core region are concordant, with ages just below 4.4 billion years. Measurement #4 on the crystal rim is concordant, with an age of 3.4 billion years. Diagram courtesy of John Valley, Valley et al., Nature Geoscience, 2014 Vol. 7, 219 https://www.geologybites.com/sara-russell daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600457369083-BPREZDSUE4S2EFEWPBXM/Sara_Russell_on_The_Moon_Landings_%26_Cosmic_Mineralogy.jpg Sara Russell Sara Russell is a professor of planetary sciences and leader of the Planetary Materials Group at the Natural History Museum in London. She is a member of the science team for both of the current space missions to obtain samples from an asteroid and return them to Earth. She even has an asteroid named after her. Using asteroids as snapshots of the early solar system, her research seeks to unravel how the solar system formed and cast light on questions such as how the Earth got its water and organic materials. Photo credit: Ubiquity Press https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600459429935-OHFPKKWUVOV4IQ7XM5EQ/Asteroid+Belt.jpg Sara Russell Although the majority of asteroids lie in a belt just beyond the orbit of Mars, there are a few that lie farther out along the orbit of Jupiter called the Jupiter Trojans, and some farther in that are referred to as the near-Earth asteroids. The targets of both the current sample return missions - Bennu (OSIRIS-REx mission) and Ryugu (Hyabusa 2 mission) are near-Earth asteroids. Diagram courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600457751885-88QRX1WSU8FXLSVIXZN0/Bennu.png Sara Russell Asteroid Bennu is the target of the NASA OSIRIS-REx sample return mission. It is about half a kilometer across at its equator. Bennu makes one orbit around the Sun every 1.2 years. It makes one full rotation on its axis every 4.3 hours. Image courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600458265857-C3TVSNQSQSJHZDBULP8M/Bennu+size+comparison.PNG Sara Russell Courtesy of the University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600458863464-GBR0LY8CPZ3V7031GWUC/Touchdown+simulation.png Sara Russell OSIRIX-REx simulation of touchdown on Bennu to obtain a sample from the surface. Image courtesy of NASA https://www.geologybites.com/barbara-romanowicz daily 0.75 2021-03-31 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601322659274-2S8G4RMQH0PBJXAHRX0K/Barbara+Romanowicz+The+Wall+Papers.jpg Barbara Romanowicz Barbara Romanowicz is a Professor of the Graduate School at the University of California at Berkeley, and Chair of Physics of the Earth’s Interior at the Collège de France in Paris. She uses the seismic waves triggered by earthquakes to probe the interior of the Earth. Using her training as a mathematician, she has forged new techniques for analyzing these waves to give us a much sharper view of the deep structure of the Earth. Photo courtesy of the University of British Columbia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602253567561-7Q29GBDFSKZKES6RZR6B/tomography+principle.jpg Barbara Romanowicz Tomography relies on “illuminating” inhomogeneities within the Earth using seismic waves from as many directions as possible. The time taken for a seismic wave to travel from its source, e.g., S1, which is usually an earthquake, to each receiver in a network of receivers (R1, R2,…) depends on the path it follows and its speed along that path. The speed of a seismic wave depends on the temperature of the material it is passing through - the hotter it is, the slower it travels. By measuring enough travel times, we can map the temperature inhomogeneities within the Earth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602254602940-3IQC7LRXD4R91O9WSHRB/network+of+stations.jpg Barbara Romanowicz The seismic waves detected by this network of seismic stations are used to synthesize tomographic images of the Earth’s mantle, such as those shown below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601476691593-B6L4CQOBGVXRFD02TLGG/Japan+w+Key.png Barbara Romanowicz - Japan Section under Japan using two different models showing seismic wave velocity, which is an indicator of temperature with fast velocities being colder. The black lines indicate depths of 400, 600, and 1,000 km. The subducting slab of the Pacific plate is clearly visible. The sinking of the slab appears to stagnate at a depth of 660 km. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601476770404-PVOYJG1X1LV5D2MB608A/Tonga+w+key.png Barbara Romanowicz - Tonga The seismic wave velocity section also shows a subducting slab beneath Tonga, which appears to stagnate at a depth of about 1,000 km. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601345865494-XOJAN3GJATXVYVEFAF8X/Encyclopaedia+figures+-+modified+for+website.png Barbara Romanowicz Cross-sections through the whole mantle along the plane indicated at right for two different models. The colors indicate shear wave velocities, with low velocity regions (blue) indicating cooler regions and high velocity regions (red) indicating hotter regions. Both models show a broad plume of hot material below Samoa and Hawaii (which is off-path). The locations of major hot spots are shown as green circles. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601345912821-K2H6PNQ0JDIJIZF72QOB/Cape+Verde+and+Darfur.png Barbara Romanowicz Cross-sections through the whole mantle for the same two models used for the figure above for the section shown at left. Hot plumes that appear to extend to the core-mantle boundary are revealed by both models below Cape Verde and Darfur. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603649480772-FD32MUCUW4F3CZI4UFQJ/mantle-models+%281%29.png Barbara Romanowicz Shear wave velocity maps at four different depths. The cross sections are keyed into their locations on the map at the depth where each of the subduction zones is most pronounced. Thus, the top left section, which cuts through Japan, is keyed to the 600 km depth map where the cold material of the stalled slab shown in the section shows up most clearly. Similarly, the more recently subducted material along the southwest coast of S. America is keyed to the 600 km depth map, while the material subducted longer ago, which has had time to sink further, below central S. America, is keyed to the 1000 km depth map. https://www.geologybites.com/david-sandwell daily 0.75 2021-02-02 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601495491410-3ZDTBAN17646UU6BKGPZ/David+Sandwell+pic.jpg David Sandwell - David Sandwell is a Professor at Scripps Institution of Oceanography at the University of California San Diego. He has been a leader in using satellite measurements to map the sea floor, which has given us our first global sea-floor map. David Sandwell deploying a GPS receiver in Baja, Mexico. Courtesy of David Sandwell https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601507030147-HCC6IKMKG43KFFINWGHM/CryoSat2_Auto1A.jpg David Sandwell The European Space Agency’s CryoSat-2 satellite. Though its main purpose is to use radar altimetry to map polar ice, the altimetry measurements are conducted throughout its orbit, providing high-quality sea-surface data for the bathymetry mapping described in this podcast. Courtesy of EADS Astrium https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601507573472-J4L7M2NGEWQD796AQAKJ/Principles+of+radar+altimetry.png David Sandwell The satellite measures distance to the sea surface by timing the round-trip travel time of radar pulses emitted by the satellite. The results are beamed down to a ground station. The diagram shows in exaggerated form how the extra gravity from a mountain on the sea floor piles up the water above it to produce a corresponding bump on the surface. In reality, the surface bump is about 10,000 times smaller than the sea-floor bump. Thus, a seamount 1 km high produces a surface bump of about 10 cm. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601590087314-XHUKIOQOI58JSEGSZI5Y/upward_seamount.jpg David Sandwell The effect of sea-floor features on the gravity at the sea surface for three different ocean depths. It shows that the two seamounts are smeared into a single gravity anomaly when the sea is 4 km deep, but they are resolved into two peaks if the depth is 3 km or less. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601516158419-P7H9005MCCIODGMZSP46/Ship+sonar.PNG David Sandwell In contrast to the bathymetry from satellite altimetry (contours), the measurements from ship-borne sonar cover a much smaller area, but at a resolution of 100 meters, i.e., about 40 times sharper than the satellite map. Ship captain Chris Curl and researcher JJ Becker aboard R/V Melville crossing over Discovery Seamounts in the South Atlantic ocean. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601513615238-WPUISCEQW29C76XSPL4U/plate+tectonics.png David Sandwell Diagram illustrating sea floor spreading along mid-ocean ridges. The ridges are displaced sideways at transform faults. Stretching away from the ridge are fracture zones that record the spreading of the sea floor. Abyssal hills form parallel to the ridge axis. The plate motions are driven by the pull of the cold and dense subducting lithosphere. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601512647763-GWZUTK0QOBCNBQVTVK0H/global+bathymetry+20MB.jpg David Sandwell Global bathymetry map obtained from satellite altimetry and ship depth soundings. The red dots show the locations of major earthquakes. The sea-floor spreading ridges and transform faults and fracture zones perpendicular to them are clearly visible. Many of the major features in the the southern oceans were largely unknown prior to mapping from satellite altimetry. This includes the Louisville Ridge and Foundation Seamounts in the South Pacific, and the ridge transform structure of all the southern hemisphere spreading ridges. Today, data from CryoSat-2 are revealing previously unmapped seamounts, microplates, and abyssal hills on the older sea floor away from the spreading ridges. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601508341497-NGQGVUO78GT0CL7MJYB7/Uncharted+seamounts+over+3+km+high.png David Sandwell The satellite altimetry produced the contour map, which reveals the approximate location of the seamounts. These are used to guide a ship-borne survey to the locations marked by the red dots to obtain actual depth measurements to calibrate the altimetry data, and to map out the seamount summits in detail. The uncharted seamounts marked by red dots are predicted to rise more than 3,000 m from the surrounding sea floor. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601514468766-12RM3JO6RYIFXK6PVNOZ/Mamerickx+new+plate.PNG David Sandwell The altimetry-derived bathymetry uncovered a microplate (labelled MP in the images) in the Indian Ocean. The microplate is about 150 km across. The areas of chaotic sea floor are thought to be caused by large changes in spreading direction associated with the collision between India and Asia about 50 million years ago. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601515318350-V5L9DLM0E567VCQC7U8C/Gulf+of+Mexico+-+sediment.PNG David Sandwell The sea floor in the Gulf of Mexico basin is very flat because the original topography is covered by thick sediment (6-12 km). The density contrast between the base of the sediments and the original topography produces gravity anomalies associated with the extinct sea-floor spreading ridge and the continent-ocean boundary (COB). The exact location of the extinct ridge was unknown prior to the mapping by CryoSat-2. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601517354517-JU3K173B6KCIE7RV9ZP3/See-saw.png David Sandwell When a transform fault, which manifests as a sideways displacement of a spreading ridge, propagates along the ridge, it leaves behind a diagonal shear zone and a pseudofault - analogous to the wake of a boat. The sheared zone is crust that formed on the right plate, was sheared by the moving transform fault, and deposited on the left plate. The pseudofault is an age offset on the right plate and has the characteristics of a standard fracture zone. When a propagating transform fault reverses direction, it creates a zig-zag pattern. The satellite-derived global bathymetry map showed that such “see-saw” propagators are ubiquitous. What makes the transform faults propagate or reverse direction is not understood. Courtesy of Scripps Institution of Oceanography https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1601518314276-TTZYJD2EP6V6DJKDL8EO/Atlantic+with+see-saw+from+snip.PNG David Sandwell Gravity field of the mid-Atlantic ridge. The active spreading boundary (red) includes orthogonal ridges and transform faults. The straight fracture zones (yellow) record the opening direction of the Atlantic basin. The wiggly magenta lines are newly-discovered see-saw propagating transform ridges. The wiggles are symmetric about the spreading ridge, indicating that they formed as part of the sea-floor spreading process. Courtesy of Scripps Institution of Oceanography https://www.geologybites.com/john-marshall daily 0.75 2021-02-06 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602014356040-E5EU2E3YW2H6KYE4B2DY/John+Marshall++boating+East+Greenland+%281%29.JPG John Marshall John Marshall is a Professor at the School of Ocean & Earth Science at the University of Southampton. He is a fossil expert specializing in mass extinction events. He explains how his recent research has uncovered new evidence that may finally explain what caused the mass extinction at the end of the Devonian period. Here he is on his way to a field location in East Greenland. Photo courtesy of Jon Lakin https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604263724285-6SGLOIQTRKFQG05XIL9P/Helicopter-Leaving-Team-on-Rebild-Bakker-scaled.jpg John Marshall Dropping off equipment and supplies for John Marhsall’s team on Rebild Bakker, the East Greenland island on which the Devonian lake-bed sediments were discovered. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015384165-VCEYBW4SX0TPGCK4IUQH/field+location+in+East+Greenland.jpg John Marshall The ravine on Rebild Bakker in East Greenland where the malformed spores were discovered. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015468263-MRM21DXUYLF4TQHPLHWF/IMG_5142.jpg John Marshall The end-Devonian period (360 million years ago) lake-bed mudstone in East Greenland in which well-preserved malformed spores were found. The huge ancient lake bed was in the arid interior of the Old Red Sandstone Continent, made up of Europe and North America. This lake was situated in the Earth’s southern hemisphere and would have been similar in nature to modern-day Lake Chad on the edge of the Sahara Desert. Though the surface is shattered by freeze-thaw cracking, there are good unweathered samples just below the surface. The boundary between the Devonian and Carboniferous Periods lies at the base of the yellow notebook. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605037026877-JZ88USSU6WXUM426JKNA/Middle-Devonian+with+present-day+coastlines++C.R.+Scotese.JPG John Marshall Disposition of the continents in the mid-Devonian period, about 30 million years before the end-Devonian extinction. The present-day coastlines are shown, with Greenland being a part of a large continent, called the Old Red Sandstone continent, located just south of the equator. Courtesy of C.R. Scotese https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605037251892-3YEW5JDC0GF77T7DME3P/Torsvik+%26+Cocks+2017+Earth+History+%26+Palaeogeography.jpg John Marshall More detailed reconstructed map of the Old Red Sandstone continent of the late Devonian period showing the location of the crust that make up present-day Greenland. Courtesy of Trond Torsvik and Robin Cocks https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015629339-Q1YK08VCBQJ45G4EYL1L/normal+spore+cropped+%281%29.jpg John Marshall Photomicrograph of a normal Grandispora Cornuta spore, which is the Latin for a big spore with horns, i.e., spines. Though the spore is somewhat squashed and folded, the spines are all the same, regularly distributed, and end in identical points. The diameter is 75 microns, i.e., less than a thousandth of a millimeter. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015681106-NY6P38EOMBQLQ1RQFVH1/malformed+spore+cropped+%281%29.jpg John Marshall The same species of spore, Grandispora Cornuta, but with significant malformation. The evenly spaced spines are reduced to irregular blobs with an irregular overgrowth at the top of the specimen. The spore has also turned a darker color, which may be a response to increased radiation with the growing plant able to increase the amount of UV-absorbing chemicals in the spore wall, akin to a sun-tan in humans. Same scale as above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604363804789-ZS59OUTOI7CJ7Z3KD22Q/aba+0768+Marshall+ozone+cartoon.jpg John Marshall Cartoon illustrating how an initial warming event causing an initial reduction in the ozone layer is in turn amplified by the resultant collapse of the forest ecosystem. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015750104-IQ0PYKHY0VKRRMD16Z2O/eccentricity+figure.gif John Marshall Changes in the eccentricity, i.e., in how much the orbit departs from a perfect circle, affects the strength of the incident solar radiation at any given latitude. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602015969731-BHZOFMILBIEV5G3Y8JCY/obliquity+figure.gif John Marshall Changes in the tilt (obliquity) of the Earth’s axis of rotation with respect to the plane of the Earth’s orbit around the sun (the ecliptic) vary the severity of the seasons. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1602016125655-815SRP4XVQDTTSXEOLH8/precession+figure.gif John Marshall Precession changes the timing of the seasons with respect to the orbit of the Earth around the sun. For example, if at the start of a precessional cycle, summer in the northern hemisphere occurs when the Earth’s orbit is at its closest point to the sun, then in the middle of the cycle, 13,000 years later, summer in the northern hemisphere will occur when the Earth is at its furthest point in its orbit. About every 41,000 years, the effects of the changes in orbital eccentricity, axial tilt (obliquity) and precession align with each other, causing climate changes, such as ice ages or periods of global warming. John Marshall suggests that changes in incident solar radiation caused by these orbital effects, together with a planet that was unusually susceptible to being tipped into an extreme warm state, undermined the forest ecosystem which in turn released methyl halogens that damaged the ozone layer, thus letting more ultraviolet from the sun reach the Earth’s surface and cause the end-Devonian mass extinction. https://www.geologybites.com/bruce-buffett daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603306033076-QS6G8AKMMHKQLZP4RVYM/HeadShot.png Bruce Buffett Bruce Buffett is a Professor in the Department of Earth and Planetary Science at the University of California, Berkeley. He investigates the structure and motions within the Earth’s core by matching physics-based simulations of the core to the observed magnetic field of the Earth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603230174271-FI8X5PMG4I7KQZNV4BV6/EMK_Earth_interior.jpeg Bruce Buffett Diagrammatic cross-section of the Earth showing the very thin crust, the mantle (orange) and the core, with a solid inner part and a liquid outer part. Courtesy of Eric King https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603230407786-4QHLAKZOQPC3HILXZ7LL/Artist_s_view_of_Swarm_pillars-1.jpg Bruce Buffett Artist’s impression of two of the three ESA Swarm satellites which have been surveying the Earth’s magnetic field since 2014. Each satellite has two magnetometers. One sits on the end of the boom and measures the absolute magnitude of the field. The other is located about halfway down the boom and measures each of the x, y, and z components of the magnetic field. Bruce Buffett is using Swarm measurements of the 10-60-year period variations in the Earth’s magnetic field to improve our understanding of the core. He thinks these variations might be caused by physical wave motions in a layer of the outer core. Courtesy of ESA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603231768922-UE5NSJIPYQVS7BX5YKSE/800px-TolucaMeteorite.jpg Bruce Buffett An iron meteorite composed of an iron-nickel alloy, similar in composition to that of the Earth’s core. Such meteorites originated from the cores of planetesimals - small bodies formed during the process of planet formation. This example shows Widmanstätten patterns, whose shapes are caused by long iron-nickel crystals. Courtesy of H. Raab https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603232619307-PURHWC5X0ODU454ADG5O/Screen+Shot+2020-10-16+at+10.21.09+AM.png Bruce Buffett Computer simulations of the Earth’s liquid outer core generated by numerically integrating the equations of fluid motion (Navier-Stokes equations) and electromagnetism (Maxwell’s equations). The colors indicate the radial velocity of the core material on the plane of the Equator. The two calculations differ in the assumed value of the core viscosity. The simulation on the right assumes a viscosity 500 times smaller than that on the left (corresponding to the viscosity of asphalt) but that is still many orders of magnitude higher than the actual viscosity of the core. The calculation gets more compute-intensive as the viscosity is reduced, but it becomes more realistic. Courtesy of Bruce Buffett https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603233468222-CBMPMLHYI84B871EHF95/INCITE_Earth.png Bruce Buffett Higher-resolution image of the results of the simulation at top right. The broad features, such as the scale of the plumes around the inner core (the black disc) and the outwardly decreasing scale of the motions, are thought to represent the actual core correctly, but a simulation that uses a lower viscosity (closer to that of water) would show much smaller scale structures. Nonetheless, the broad features seen in existing simulations can explain the observed magnetic field. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1603306256903-7LIC5WATIKB60S8Y2RZG/Earth%27s+Field+simulation.png Bruce Buffett Simulation of the radial magnetic field at the core-mantle boundary. The overall structure is that of a dipole (yellow in Northern Hemisphere, and blue in the Southern Hemisphere) but there are also smaller-scale features. It is the small-scale structure that disappears when the stratified layer at the top of the core gets too thick. The simulation shows a slight weakening of the magnetic field at the North Pole. This is probably a transient feature, but it may reflect the present-day field at the core-mantle boundary since the field at the North Pole is, in fact, quite weak. This simulation uses a viscosity value intermediate between those used in the two simulations shown above. Courtesy of Bruce Buffett https://www.geologybites.com/laurence-robb daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604008841805-YILNZFF013FVOYJ2BB0G/LJR+Burma+2-2.jpg Laurence Robb Laurence Robb is a Visiting Professor at the Department of Earth Sciences at the University of Oxford. He studies the processes by which mineral deposits form and the factors that control their distribution in space and time. He is pictured on a field trip in Myanmar to study its tin deposits. Photo Courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604008678620-S6OTE885F976RECAZF2N/03-21-2.jpg Laurence Robb Diagram illustrating how hydrothermal vents form on mid-ocean spreading ridges. Courtesy of Laurence Robb https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604007526820-4EVDXPADODG41NO70899/Kimberlite_Pipe_Interpretation.jpg Laurence Robb Diagram of an idealized kimberlite intrusion. Courtesy of the Colorado Geological Survey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604006925800-THK7W5ASC3005CFFLZN3/botswana-diamonds-mine.jpg Laurence Robb Kimberlite pipe at Ontevreden, Botswana, being mined for diamonds. Courtesy of the Mozambique Resources Post https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604007181211-FQLFUI4PGQABO9ZKJNP7/Chromitite+seams+Bushveld+Complex.jpg Laurence Robb Chromite seam in the Bushveld Complex in South Africa. Chromite is an iron chromium oxide, and is our principal source of chromium. Courtesy of Laurence Robb https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604007708155-SXT3GL99Q9Q01W51MHR9/1024px-BlackSmoker.jpg Laurence Robb A hydrothermal vent (black smoker) in the East Pacific Rise, a mid-ocean spreading ridge that runs south from the Gulf of California. Courtesy of the USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1604008306453-GUPQGUBHPGVUW5NY0694/Lithium+extraction.jpg Laurence Robb Lithium extraction in a shallow salt pan at Salar de Uyuni, Bolivia. Brine is pumped out of a nearby lake into a series of evaporation ponds. Over a period of 12-18 months, the water evaporates and salts precipitate, including lithium in the form of lithium carbonate. Courtesy of Matjaž Krivic/INSTITUTE https://www.geologybites.com/mark-moodystuart daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605738375557-OIFQXR6TS2H28ZBEWU6F/image-asset.jpeg Mark Moody-Stuart Sir Mark Moody-Stuart is a former chairman of Royal Dutch Shell and is a director of Saudi Aramco, which has the largest daily oil production of any oil-producing company. He obtained a PhD on the Devonian sediments of Spitsbergen before joining Shell, where he started his career as a geologist in Spain, Oman, Brunei, and Australia. After recognizing that our response to global warming demands a transformation of our energy strategy, he became a prominent voice for change in the oil industry. Here, he discusses how he sees this change coming about. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605739557432-3EU84D4P61CCYBRNAJY5/OECD_consumption.png Mark Moody-Stuart This chart shows that overall, demand for oil has been shrinking in the OECD countries since 2000. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605740082849-BSAFDQUO3BEM1LUOK2AD/nonOECD_consumption.png Mark Moody-Stuart https://www.geologybites.com/laurent-jolivet daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605901974669-BWFS2RPDDFFVB713IZYZ/image-asset.jpeg Laurent Jolivet Laurent Jolivet is a Professor at the Institute of Earth Sciences at the Sorbonne University. He is an expert on the motions of the lithosphere and the mantle, and has studied the Mediterranean in particular for 30 years. He explains how the Mediterranean formed as a temporary ocean that will eventually be swallowed up by the collision between Africa and Europe. Courtesy of Damien Do Couto https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606146186447-2Z4RZG5LK9D6DXIM0RH1/Slab+retreat+Mediterranean-simple.gif Laurent Jolivet The animation shows a reconstruction of the Mediterranean region from 35 million years ago to the present. The bold lines represent the subduction zones, with the triangles indicating the overriding plate. All the subduction zones are retreating. For example, the Hellenic subduction zone in the eastern Mediterranean retreats to the south from the latitude of present-day Turkey to just off the coast of Africa. Blue domains are oceanic lithosphere with the rest being continental. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605967552391-9PMYWADZCUI76PKUSJSN/Hellenic+subduction+zone+cross+section.jpg Laurent Jolivet Seismic tomogram of a section running through the Hellenic subduction zone. The fast seismic velocity regions shown in blue reveal the Hellenic slab, which plunges down below the Aegean at about 15 degrees north. Courtesy of Wim Spakman https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605969149563-AP5XUDV6J2MP6YWN0WBX/Line+of+Section.PNG Laurent Jolivet Map showing the line of the cross-section illustrated in the time series reconstruction below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605904643778-KDP9FKE5H7LXT5ZF4LBQ/Mediterranean+figures+-Geology+Bites+-slab+retreat.jpg Laurent Jolivet Reconstruction of the retreating slab along a section from the Pyrenees to Calabria from 35 million years ago to the present. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605900388313-8DDXB7ZN1WVK2B0EXLH8/Slab+retreat+Mediterranean-Tyrrhenian.gif Laurent Jolivet Animation of the slab retreat shown in the four still frames shown above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605968388888-88VUW219KZDNXXCWCMC8/Gibraltar-slab+tear+still+images1024_1.png Laurent Jolivet Reconstruction of the evolution of the Gibraltar slab from 50 million years ago to the present. It shows the progressive tearing of the sinking lithosphere. The four images are shown in sequence in the animation below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605968447883-UQ95564OOEC2P4LQEJGR/Gibraltar-slab+tear+still+images1024_2.png Laurent Jolivet https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605968480949-8M3V39PLRU4HY7NUL2IE/Gibraltar-slab+tear+still+images1024_3.png Laurent Jolivet https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605968502963-E0WCXQS2EAB5HSTN3G6M/Gibraltar-slab+tear+still+images1024_4.png Laurent Jolivet https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605900617142-W7W43JOY3AO07FLIT8WQ/Slab+tearing+Gibraltar.gif Laurent Jolivet https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605901771824-BVVFWEUZ8KYAVXUTY6DK/Present-day+geometry+of+slabs+under+the+Mediterranean.png Laurent Jolivet Three-dimensional rendering of the present-day slabs underneath the Mediterranean, showing the main subduction zones (red lines) and mantle flow (pink arrows). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606146563480-M4U0M51XL9SR1G4CBDBS/Africa-Eurasia-reconstructions+%281%29.gif Laurent Jolivet Reconstruction of the movement of Africa with respect to Eurasia. The animation also shows the simultaneous evolution of the microcontinent Apulia and of the Mediterranean region. Note that in the podcast, Apulia is referred to as a promontory of Africa, but in this reconstruction it appears to be an island. However, after the Late Jurassic (about 150 million years ago), once the sea-floor spreading ridge that made Apulia rift away from Africa had become extinct, Apulia became part of the African plate, and moved together with it. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605901098815-UK96E619AFM42TSLN9JI/image-asset.gif Laurent Jolivet This animated reconstruction from 70 million years ago to 10 million years ago shows the slab subducting below the Apennines and retreating to the northeast (i.e., towards the right in the animation). At the northern edge of the subducting slab, anticlockwise toroidal flow in the mantle (shown by the red arrows) pushes the Alps towards the west into France. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605903701616-OI2CZX19NDBZRQ9RLS4P/Fault+Plane+for+Appenines.png Laurent Jolivet This map shows the locations of recent earthquakes in the Mediterranean region, with each circle indicating whether the earthquakes resulted from extensional faulting (blue), compressional faulting (red), or lateral (strike-slip) faulting (yellow). The black lines indicate the main subduction zones. The earthquakes in the Apennines are extensional in nature because the subducting slab to the northeast of the Apennines is retreating, which puts an extensional (stretching) stress on the overriding plate in front of the retreating slab where the Apennines are located. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605819169122-OVO5LF6KMQBFADY9RR3A/Toroidal+flow+in+the+E+Mediterranean.png Laurent Jolivet Anti-clockwise rotation of the eastern Mediterranean and the Middle-East is the result of the lithosphere’s coupling to the mantle below, which is flowing in an anticlockwise toroidal motion. As explained in the podcast, toroidal motion occurs at the edge of subducting slabs that are retreating. Motion indicated by the arrows is obtained from satellite GPS measurements. Image courtesy of Xavier Le Pichon and Corné Kreemer https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605901242032-VZZLWDUGJ1I088RRRJ8Z/image-asset.png Laurent Jolivet The map shows the locations of volcanos during the Quaternary Period (i.e., the past 2.6 million years), with Mount Etna (blue) and Santorini (red). Santorini and the other Aegean volcanos lie above the subducting Hellenic slab which plunges northwards under the Aegean. The lines indicate the locations of the subduction zone trenches, with the triangle denoting the overriding plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1605898860625-LJ5AUBY2DKBPGN32PBBW/Volcanos+and+Seismic+Tomography+-+slide+8+not+sure+if+relevant.png Laurent Jolivet The position of the volcanos is superposed over a seismic velocity map. The colors indicate the seismic wave velocity at a depth of 200 km, with red representing slower speeds implying warmer regions, and blue representing faster velocities implying colder regions. The subduction trenches are shown by the pink lines. Both the volcanic arcs along the Apennines and in the Aegean are located above subducting slabs. Mount Etna (blue triangle) is nearly above the southern edge of the Ionian slab shown by the blue patch below Calabria and the northern part of Sicily, placing it above a window between slabs where the magma from the upper mantle (asthenosphere) can reach the surface. Santorini (red triangle), by contrast, is above the middle part of the Hellenic slab sinking below the Aegean region, which corresponds to the normal context for a subduction-related volcano. Courtesy of Wim Spakman and Laurent Jolivet https://www.geologybites.com/harold-c-connolly-jr daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606342368422-KD3VSCZE2YEVEUM2KSKW/26854_1383203894627_2724712_n+copy.jpg Harold C. Connolly, Jr. Harold C. Connolly Jr. is Founding Chair and Professor at the Department of Geology at Rowan University. His research focusses on the very oldest materials in the solar system, especially the tiny igneous rocks called chondrules that are the main structural component of stony meteorites. He explains what we hope to learn from a sample of the asteroid Bennu that the OSIRIS-REx spacecraft will return to Earth in 2023. Here he is holding an example of a chondrite (stony) meteorite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606334752032-WZDGFFTMVZV56LCLBNDV/Bennu+mosaic+-+credit+NASA-Goddard-U+Az-EPA.jpg Harold C. Connolly, Jr. Asteroid Bennu is about half a kilometer across at its equator. It makes one orbit around the Sun every 1.2 years and completes a rotation on its axis every 4.3 hours. Each pixel in the image corresponds to 1/3 of a meter on Bennu’s surface. Image courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606334916960-U24OE1G5CIYSWKIOQXAZ/image-asset.png Harold C. Connolly, Jr. Size comparison courtesy of the University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606335037852-15VH65550X3021OA9X1P/Bennu+orbit+-+2+Lauretta+et+al.jpg Harold C. Connolly, Jr. - Bennu’s orbit intersects that of the Earth and is inclined to the ecliptic (the plane of the Earth’s orbit). Courtesy of the Meteoritical Society https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606343266486-312U0AVVHGNYRWGTDBVT/OSIRIS-REx+with+arm+extended+courtesy+Goddard+-U+Az+-+NASA+See+IEEE+Spectrum.jpeg Harold C. Connolly, Jr. Artist’s impression of OSIRIS-REx with the collector arm extended. Courtesy of Goddard Space Flight Center, University of Arizona, and NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606343577750-DN4UTRUCH3ZXP9FKYJXB/image-asset.gif Harold C. Connolly, Jr. Captured on Oct. 20, 2020, during the OSIRIS-REx sample collection event, this series of 2 images shows the surface of Bennu just before and after touchdown. Courtesy of NASA, Goddard Space Flight Center, and the University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606343887284-ZSK6BP3O2ZAJ1B9YNA0Z/Asteroid+Belt.jpg Harold C. Connolly, Jr. The main asteroid belt lies just beyond the orbit of Mars. Ceres and Vesta are the two largest bodies in the asteroid belt, the former actually being classified as a dwarf planet. Diagram courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606411581255-2SK3ZKXAKEVZZ66W7WN0/DSCN0626+copy.JPG Harold C. Connolly, Jr. Thin section of the meteorite Allende, a carbonaceous chondrite that is similar to Bennu. The arrow points to a calcium-aluminum-rich inclusion that represents the oldest solids in the solar system, with radiometrically-determined ages going back to 4.567 billion years. The one shown here is not igneous, but rather an accumulation of accreted minerals, some of which are igneous minerals, i.e., crystallized from a melt. The round objects are chondrules, which are rich in olivine and pyroxene. Chondrules are igneous rocks that constitute the dominant structural component of chondrites (stony meteorites). The dark matrix is composed of micron-sized minerals, which can sometimes contain presolar grains. The slide is 2 cm in diameter and seen here in plane polarized light. Courtesy of Dolores Hill and Harold C. Connolly Jr. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606410634574-EXTFCIDJIYJIFOPG6BEJ/Horus-2+copy.jpg Harold C. Connolly, Jr. The same thin section seen with crossed polarizers. The olivine and pyroxene crystals display bright high-order interference colors. These minerals, which are common on Earth and constitute a major component of the mantle, are also common in the oldest rocks of the Solar System. Courtesy of Dolores Hill and Harold C. Connolly Jr. https://www.geologybites.com/david-rothery daily 0.75 2023-10-29 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606776319210-DQX9MFR0YNH5CWUUKCPL/DSC01744.jpg David Rothery David Rothery is Professor of Planetary Geosciences at The Open University. He studies volcanism here on Earth and throughout the Solar System. He is an accomplished educator and has written popular books on geology, volcanism, and moons; authored university courses; and led numerous field trips. The photo shows him leading a field trip in Hawaii. Photo: Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606778101673-65SUN06B2OY8J8Y6LW2Q/lava+flows+on+Venus.jpg David Rothery Magellan radar image of a 300 x 230 km region of Venus showing lava flows and volcanos. The dark flows probably represent smooth lava flows similar to 'pahoehoe' flows, which have a smooth or ropey surface on Earth, while the brighter lava flows are rougher flows similar to 'aa' flows, which have a rough, clinkery texture on Earth. The rougher flows are brighter because the rough surface returns more energy to the radar than the smooth flows. Courtesy of NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606777743510-D2H4N2P1M43A3F8I7MS2/lunar+maria.jpg David Rothery A view of the Moon looking south across Oceanus Procellarum, with an artist’s impression of how the edges of the dark volcanic plains called maria may have looked while active. The evidence for this comes from gravity studies, which indicate that the structures at the maria edges are ancient, solidified, lava-flooded rifts that are now buried beneath the surface of the maria on the near side of the Moon. Courtesy of NASA/Colorado School of Mines/MIT/JPL/GSFC https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606785559011-BKRO0MI41FIZX395Y9V0/Tvashtarvideo.gif David Rothery Eruption from a volcano on Jupiter’s moon Io imaged by New Horizons during its Jupiter fly-by en route to Pluto. The plume is 330 km high, though only its uppermost half is visible in the image as its source lies over the moon's limb on its far side. The images were captured over the course of eight minutes. This is an example of silicate volcanism, similar to that occurring on Earth except that the explosion is taking place into a vacuum. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606778545145-8DXO88T18WKIDD24EX3O/Enceladus+model.jpg David Rothery Diagram illustrating the cryovolcanic processes thought to be happening on Enceladus, an icy moon of Saturn. Cracks in the ice shell enveloping the moon allow water and other compounds to escape into space. The lack of confining pressure causes them to vaporize instantly. Courtesy of NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606779631288-SBZCT8SCKVJH2Y581BYY/Fig1_Rachmaninoff_crop.png David Rothery Exaggerated color image from MESSENGER centered on Nathair Facula, the diffuse-edged yellow spot about 260 km in diameter that dominates this view. It is interpreted as the explosive deposit from a series of eruptions from the compound volcanic vent labeled in the image. When active, it would have resembled a present-day explosive eruption on Io. Also appearing in the image is Copland, a lava-flooded impact crater 208 km in diameter. Courtesy of NASA/JHU APL/Carnegie Institute Washington https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606779941605-AGNDFPKUL7O1NE9VFXY8/MIXS_engineering_model.jpg David Rothery David Rothery with a full-size engineering model of the X-ray spectrometer assembled at Leicester University that is aboard the BepiColombo spacecraft. The spectrometer will analyze the surface of Mercury by collecting fluorescent X-rays emitted by the surface rocks after stimulation by high-energy solar X-rays. On the right with the square aperture is a collimator (MIXS-C) that collects X-rays efficiently over a broad range of energies with a wide field of view (~10°). On the left with the circular aperture is an X-ray telescope (MIXS-T) for high-resolution, narrow field (1° field of view) mapping of the planetary surface. Courtesy of David Rothery https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606780284714-TSV8WVRRN8HEKC3VS1QO/Bepi_in_orbit.png David Rothery Artist’s impression of the BepiColombo Mercury Planetary Orbiter as it will look free-flying in Mercury orbit. The X-ray spectrometer telescope (MIXS-T) and collimator (MIXS-C) apertures are labeled. Courtesy of ESA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1606778782786-FTFGRG7BNJO47RF3U7S2/Miranda.jpg David Rothery Cryovolcanic landscape on Miranda, an icy moon of Uranus about 500 km in diameter. These cryovolcanic lava flows are well over a billion years old. If David Rothery could pick the next space mission, he would go there to see this landscape in greater detail, as well as the as-yet-unseen terrain that was in darkness when Voyager-2 flew past in 1986. Courtesy of JPL https://www.geologybites.com/barbel-honisch daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607828192330-2AP14BPOFQ6E872M9KWW/F_Fiondella-0634.jpg Barbel Honisch Bärbel Hönisch is Professor of Earth and Environmental Sciences at the Lamont-Doherty Earth Observatory at Columbia University. She reconstructs past Earth environments over geological time using a number of tell-tale signatures in the geological record. Courtesy of Francesco Fiondella https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607985366737-CMA28AC9KM7F30JIRSP1/Screen+Shot+DSC_0593+2.png Barbel Honisch Photomicrograph of a living Orbulina universa foraminifer consuming a brine shrimp (left) captured by its sticky filaments. The brown circle is the calcium carbonate shell, about half a millimeter in diameter, which is what is preserved in ocean sediments when the organism dies. Courtesy of Howie Spero https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607983390718-GVC3YZ38BWOEILSSQYEL/Morozovella+velascoensis+credit+Olsson+et+al.+1999+Paeocene+Atlas.PNG Barbel Honisch Photomicrograph of a skeleton of a foraminifera species called Morozovella velascoensis from the eastern Indian Ocean. Bärbel Hönisch used this species in her work to reconstruct ocean acidification that took place about 56 million years ago during an event known as the Paleocene-Eocene Thermal Maximum. Courtesy of Olsson et al. 1999 from the Paleocene Atlas https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607829402992-OH64J3RCTD6B8N6Z8TGK/image-asset.jpeg Barbel Honisch Planktonic foraminifera from a Pleistocene sediment taken from a core drilled on the Sierra Leone Rise. It includes several different species. A single species and a restricted size range are selected for the quantitative analyses of climate proxies. Courtesy of Bärbel Hönisch https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607829596234-KYW4CHGDKRS23BZ2LI41/Seep-sea+sed+core+of+Paleocene-Eocen+boundary.jpg Barbel Honisch Deep-sea sediment cores cut in half to show sections of the Paleocene-Eocene boundary - 56 million years ago. Such cores are a common source of the foraminifera used by Bärbel Hönisch in her climate reconstructions. Courtesy of James Zachos https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607985589941-SN440DAKG0JRJGHI7UTM/JOIDES+Drill+Ship%2C+credit+International+Ocean+Discovery+Program.jpg Barbel Honisch The JOIDES Resolution is a research vessel that drills into the sea floor to obtain sediment cores, such as the ones illustrated above. Most of the sediment cores that Bärbel Hönisch works on have been drilled by this ship. Credit: International Ocean Discovery Program https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1607985870816-IWJVTXRTFVQZ85YRA6V4/IMGP1509.JPG Barbel Honisch The mass spectrometer that Bärbel Hönisch uses to measure the ratios of various isotopes such as boron 10 and boron 11 in foraminifera skeletons. Courtesy of Bärbel Hönisch https://www.geologybites.com/cathy-constable daily 0.75 2021-02-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610665707774-9A5IWLGAWT0DJROZ35B1/CathyBloodyCanyon_MonoLake-2.jpg Cathy Constable Cathy Constable is a Professor at the Scripps Institution of Oceanography. She measures the remnant magnetism of rocks and human artifacts around the globe to reconstruct not just the variations of the Earth’s magnetic field as a whole, but also its spatial variations from place to place over geological time. Here she is in Bloody Canyon with Mono Lake, California, in the background. Nearby sediments record a geomagnetic excursion. Courtesy of Steven Constable https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610669422666-LOWA4T5RBHR07TD6OMM0/Sea-floor+stripes.PNG Cathy Constable A ship-towed magnetometer is used to measure magnetic anomalies and reveal magnetic stripes as sea-floor is created at a mid-ocean ridge and transported away. The Earth’s field is frozen in when magma solidifies as it erupts from the mid-ocean ridge. The stripes are good at recording the changing intensity of the Earth’s magnetic field, but less good as records of the contemporary direction of the field. Courtesy of Jeff Gee https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610666854536-732SEH8B9SF4IQ75P5KP/Stalagmites.jpg Cathy Constable Stalagmites from Pau d’Alto cave in Central South America in which previously magnetized particles preferentially align with the magnetic field as the layer is deposited. As shown in the graphs at far right, the layers can be dated very accurately. Courtesy of Trindade et al., 2018 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610667517781-JOZME9FVOIUST3UIR89L/Varves.jpg Cathy Constable Sediments that are probably varves from Lake Bosumtwi, Ghana, with each layer representing an annual seasonal cycle. The sediments contain preferentially aligned magnetized particles that indicate the direction of the magnetic field at the time they were deposited. Courtesy of Koeberl et al, 2005 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610667908600-DNWLVRZNFMF0GTFRFT5H/Pot.jpg Cathy Constable Fired materials such as bricks, pottery, kilns and hearths, as well as a pot such as the one shown, also retain a remnant magnetism frozen into place when they cooled, which can indicate the intensity of the Earth’s field at the time. Courtesy of Agnès Genevey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610668338692-Y3QAWJRBGZAL3X6O68U6/Lava.jpg Cathy Constable Lava flows are imprinted with the magnetic field that prevailed at the time they solidified from the molten state. The image shows a lava from on Hawaii’s big island. Courtesy of Cathy Constable https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610666026789-HY76XK9GE9D6DU41R8OB/Spitsbergen_pmag_sampling-2.jpg Cathy Constable Paleomagnetic samples taken from a lava flow above Woodfjord in Spitzbergen, Norway, are oriented so as to record the absolute direction of their remnant magnetism. Courtesy of Hubert Staudigel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611688582244-EP4GUMOF7F292POT1WEL/OutcropOnSteensMountainFromReversalDrilledSection.jpeg Cathy Constable This lava flow section at Steens Mountain in southeastern Oregon records a magnetic reversal at 16.7 million years ago. Courtesy of Nick Jarboe https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610668821054-RLXTWR3AWQ43E75HMU1Y/MonoLake_WebBook3375x.png Cathy Constable The Wilson creek sediment section north of Mono Lake records a geomagnetic excursion indicated in the graphs at right. The rock thickness whose magnetic field is shown in the graphs represents 23,000 years of deposition. Courtesy of Lisa Tauxe, 2020 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611690136136-V79PC6OIKU26D9W7WK9Y/Fields+for+dipoles+and+quadrupoles.PNG Cathy Constable Magnetic field strength and field direction dip relative to the horizontal for three idealized fields: (i) a pure dipole field with the dipole parallel to the Earth’s rotation axis and about the same strength as the modern field (bottom); (ii) a quadrupole field parallel to the Earth’s rotation axis (middle); and (iii) an example of a quadrupole field that is not aligned with the Earth’s rotation axis (top). Courtesy of Cathy Constable https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611690608203-LHQ9JOY7UONYAHWOJ9KQ/Actual+field+maps.PNG Cathy Constable Snapshots in time of the actual geomagnetic field. (i) Field strength and inclination for 2020; note the low field strength over the south Atlantic and South America, known as the South Atlantic Anomaly, and the deviation of the magnetic equator (line of zero inclination where the field is horizontal) from the geographic equator (top); (ii) field strength and inclination from 1000 CE when the overall field was appreciably stronger than today, and more dominated by a dipole field (middle); and (iii) geomagnetic field during the Laschamp excursion 41,000 years ago when the field strength was much lower and its direction was complex (bottom). Courtesy of Cathy Constable https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611691531080-LW5W11WTC0JZ22KGKAJQ/Screen+Shot+2021-01-26+at+11.11.18+AM.png Cathy Constable Reconstructions of variations in axial dipole strength with time from 100,000 years ago to the present. Black arrows indicate times when magnetic field excursions have been observed either regionally or globally, as in the case of the Laschamp excursion. Courtesy of Cathy Constable https://www.geologybites.com/carolina-lithgowbertelloni daily 0.75 2021-09-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610400690129-MJCR6QHQWYYD12BNK829/Carolina+Lithgow-Bertelloni.png Carolina Lithgow-Bertelloni Carolina Lithgow-Bertelloni is a Professor of Geosciences at the University of California, Los Angeles. She views the Earth’s large-scale topography as an expression of the interior processes of the Earth, and in particular of the currents in the mantle. She describes how this works, and gives examples of major topographic features that are best explained by invoking vertical motions of the mantle. Courtesy of Carolina Lithgow-Bertelloni https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610403759048-0G0RM5XSI0KG4ZDX0LHA/Dynamic+Topography+diagram.PNG Carolina Lithgow-Bertelloni Diagram illustrating the principle of dynamic topography. Differences in density in the mantle induce the flow indicated by the arrows. This flow exerts forces on the base of the overriding tectonic plates, causing a deflection in the surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610401911743-53D1S7CK2GVS3KMM0TGF/PastedGraphic-1.png Carolina Lithgow-Bertelloni Cartoon showing the two main contributions to topography: isostatic, which is a result of variations in thickness and density of the crust and lithospheric mantle; and dynamic, which is caused by deflection of the Earth’s surface by vertical forces imposed on it by mantle convection. The two inset columns illustrate isostatic topography, and dynamic topography is shown above a subduction zone (left, blue arrows) and an upwelling under a continent (right, yellow arrows). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610404357532-P95EBE4KP09L7II86CN7/LLVSW+from+McNamara.PNG Carolina Lithgow-Bertelloni Maps of the large low-shear-velocity provinces detected by seismic tomography. The top figure shows a 3D rendering of the boundary of the provinces. The lower figure is a map of a slice through the lowermost mantle at a depth of 2750 km. They show that the low-velocity regions lie primarily below Africa and the Pacific. The low-velocity regions are interpreted as higher temperature regions that are expected to generate upward convective flow patterns. Courtesy of Allen McNamara, based on the S20RTS tomography model by Ritsema et al., 1999, 2004 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611069844531-ABDE7A8Z1H7982DEW5LV/Residual+topography+from+CLB%27s+models+of+isostatic+topography.png Carolina Lithgow-Bertelloni Map of the residual global topography after the isostatic component caused by the thickness and density of the lithosphere is subtracted from the present-day observed topography. The major cause of this topography is thought to be the dynamic topography discussed in the podcast. Prominent high regions (red) are seen under the Western Pacific, the Eastern Africa, Antarctica, and the North Atlantic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1610405640933-VHYYEIBQH759E87C6KDP/Farallon+Plate+effect+on+dynamic+topography.PNG Carolina Lithgow-Bertelloni Reconstruction of the effect of subduction of the Farallon plate off the west coast of North America about 60 million years ago. The shaded region labeled dynamic subsidence would have been sufficiently depressed to allow incursion of the shallow inland seas for which there is ample evidence in the fossil record. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611070209623-L5EATYFQLSXBV5VTYBJ2/Nazca+subduction.PNG Carolina Lithgow-Bertelloni Schematic illustrations showing how a change in subduction style could have driven the topographic and sedimentary evolution of western Amazonia in South America since the Miocene (23 million years ago), eventually shaping the present day landscape. Figures (a) and (c) map the topography predicted by flexural and dynamic calculations both before and after the arrival of the flat slab. Turquoise arrows represent drainage directions. Gray dotted regions indicate sedimentary infill, with region 1 being the oldest deposits and 3 the youngest. Figure (e) is a similar cross-section extending from the offshore trench to the Atlantic Ocean, showing the present day configuration of drainage and the location of the sedimentary deposits that preserve the record of landscape evolution hypothesized in figures (b) and (d). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611071411937-A8M0GRDDW4P09C0A0DTG/Flat+and+30+degree+slab+modelling.PNG Carolina Lithgow-Bertelloni Comparison of dynamic topography predicted by two different slab models for the Peruvian subduction zone, shown in 3D (top row) and 2D (bottom row). The left-hand side (a and c) represents the present-day 3D flat-slab morphology determined from local seismicity (small black circles give individual earthquake locations), whilst the right-hand side (b and d) reflects the uniform 30◦ dip slab model akin to ‘normal’ subduction before the onset of slab flattening. (a–b) Dynamic topography (blue mesh surfaces) has been vertically exaggerated for illustrative purposes. The slab surfaces are color-coded according to the density assigned in the models. (c–d) Same as figures (a–b) but now in map view, comparing the dynamic topography with the slab contours (white dashed lines). https://www.geologybites.com/rachel-wood daily 0.75 2022-01-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e593dc23-fe00-49b6-9a75-405c1a797640/IMG_2642.JPG Rachel Wood Rachel Wood is Professor of Carbonate Geoscience at the University of Edinburgh. She has uncovered fossils that suggest that the fuse of the so-called Cambrian explosion of life was lit in the Ediacaran, the geological period that preceded the Cambrian. Here she is on a geological field trip in an extremely remote part of Siberia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235172464-ZRZVAR2W7CPFO0NO1RJJ/IUGS+Time+Chart.PNG Rachel Wood Geological time scale spanning the entire 4.56-billion-year history of the Earth. This podcast focuses on events that took place at the very end of the Precambrian during the Ediacaran period and in the first period of the Phanerozoic eon - the Cambrian. Courtesy of IUGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611703173992-WYXBS2LNK6KHXNABXAWJ/IMG_2350.JPG Rachel Wood Rachel Wood and her team travelled down the Yudoma River to reach the key outcrops with Ediacaran fossils. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611703746341-RUBTUA2VNR6F6SIV3BOH/IMG_2430.JPG Rachel Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611704040800-SW7Y2MSVTYKZT3JZHRPT/IMG_2390.JPG Rachel Wood Outcrop of lower Cambrian rocks with abundant conical-shelled fossils. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611704076358-7DAREF03F1R44GE1LLHE/IMG_2292.JPG Rachel Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235266068-36S30CN3SRA5XVUU7WT3/Cambrian+skeletal+fossils.JPG Rachel Wood Closeup of a fossil-rich exposure in the Cambrian outcrop shown above. These fossils are known as Hyoliths, and are probably related to brachiopods and bryozoans. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611704290269-I5YMLULDTE88WJQ7F82C/IMG_0582.JPG Rachel Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235416082-DU3K339K0NU6FXXELZRV/Swartpunt.JPG Rachel Wood The Swartpunt site records the youngest rocks close to the Precambrian (Ediacaran)/Cambrian boundary. The site is famous for the preservation of soft bodied Ediacaran fossils, as well as the skeletal fossils Cloudina and Namacalathus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235474365-WQT5VII9AOBF9SOESP74/Grens.JPG Rachel Wood At this site, called Grens, Rachel Wood collected soft-bodied Ediacaran fossils, as well as samples for carbon isotope and redox analysis. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235531278-R5ID6JJMJF2IISECAQ4G/IMG_2473.JPG Rachel Wood Cloudina – a skeletal fossil that appears in rocks globally around 550 million years ago, and goes extinct around 540 million years ago. There is debate as to whether it was related to cnidarians or annelid worms. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235585052-TSDPI0880O3TK0G74HKC/image-asset.jpeg Rachel Wood Exceptionally well preserved Cloudina fossil from Namibia. Courtesy of Geoff Wood https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235658174-P5TQRHHOK4260X9GG8XL/Namacalathus+-+exceptional+soft-tissue+preservation.jpg Rachel Wood Namacalathus - with excellent preservation of soft body parts. This is the creature described in the podcast as being goblet-shaped. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612235764671-L51YXFYJYWINBF17FJX0/Namapoikia.jpg Rachel Wood Namapoikia, an Ediacaran sponge, often found together with Cloudinia. It has only been found in a single locality in Namibia, and has an age of 547 million years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611704495696-BI2RMA3H7ANUOKF9GJ0O/Ediacaran+soft-bodied+fossils+Newfoundland.JPG Rachel Wood The pale structure in the foreground is an Ediacaran soft-bodied fossil in this Newfoundland outcrop. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1611704573654-NN3ZRZZ4JWBLYFOAVAHG/Modern+stromatolites+Carbla+Point+-+similar+to+Edicaran+soft-bodied+fossils.JPG Rachel Wood Modern stromatolites growing at Carbla Point, Australia. Shallow seas may have looked like this before the rise of animals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612236020855-YI7XR0WCA55S4W1BZXIP/image-asset.png Rachel Wood Timeline spanning the latest two periods of the Precambrian (Cryogenian and Ediacaran) and the Cambrian (shaded green) showing examples of animals found in the fossil record at various times (a). Middle track (b) shows carbon isotope variations, which indicates that the carbon cycle was unstable and in a state of flux. Bottom track (c) shows ocean oxygenation levels obtained by analyzing iron compounds in the rocks with oxygen-deficient (anoxic) water shown in black, anoxic and sulfidic (euxinic) water shown in red hatch, and oxygen-rich (oxic) water shown in blue. Dissolved oxygen in the oceans probably reached a threshold, or series of thresholds in the Ediacaran that allowed animals to diversify by meeting their increased metabolic demands as they became more active. The blue “spikes” labeled OOE1-4 (ocean oxic events) indicate oxygenation episodes that appear to coincide with the carbon isotope variations. The episodic increase in oxygenation continued throughout the Ediacaran and probably well beyond. Wood et al., Nature Ecology & Evolution, Vol. 3, 528, 2019 https://www.geologybites.com/tomo-usui daily 0.75 2021-02-15 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612469398475-N6J4SFPDOADBL2DA2F1Y/selected_P3129862.JPG Tomo Usui Tomo Usui is a professor in the Department of Solar System Sciences at the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency. He leads the science team for the next Japanese sample return mission, which will launch in 2024 and return a sample from the surface of Phobos in 2029. He describes how this feat will be accomplished, and what we hope to learn about Phobos, Mars, and the early Solar System. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612470517264-ZZFV8WZP1LMNCXPZVKY7/Phobos_colour_2008.jpg Tomo Usui Phobos, taken by NASA’s Mars Reconnaissance Orbiter in 2008. The larger of Mars’s two moons, it is 13 miles across. The most prominent feature is Stickney, the large crater in the lower right. The series of troughs and craters are thought to have formed when material ejected from impacts on Mars later collided with Phobos. It is hoped that a portion of the sample returned to Earth by the Martian Moons Exploration (MMX) mission will include some of this material. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612905777255-ZTBOQJFNVO7J9WYP0K3O/Mmxspacecraft_0.jpg Tomo Usui Artist’s impression of the MMX spacecraft in front of Phobos with Deimos, Mars’s second moon, at upper right. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613409481657-KBRQIHWA63IIVRV9WMGG/MMX+Component+Diagram.png Tomo Usui The spacecraft consists of propulsion, exploration, and return modules. The total launch mass is 4,000 kg, of which 1,900 kg is propellant. Mounted on the platform supported by the landing gear are two cameras, an infrared spectrometer, a mass spectrometer, a laser ranger (LIDAR), dust sampler, and neutron and gamma ray instrument. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613410771592-SQMUPASQZMO0PBVG812Y/Sampling+Systems.JPG Tomo Usui MMX is equipped with two sampling systems - a core sample to access samples 2 or more cm below the surface, and a pneumatic sampler that samples the surface material, which is hoped to include ejecta from Mars. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612471785840-QAYCXLOS8CMTPDX8KNIP/Rover+-+credit+CNES+2019.PNG Tomo Usui Artist’s rendering of the rover that will be deployed by MMX by allowing it to free-fall onto the surface from a height of a few meters. The rover, which weighs 25 kilos on Earth, will weigh just 1.5 grams on Phobos. Courtesy of CNES https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612480471342-MDEDSY57GRZ960038AFH/Hayabusa+sample+return+capsule.PNG Tomo Usui Capsule for holding the sample to be returned to Earth. The capsule is 16 inches in diameter and has a heat shield enabling it to survive re-entry into the Earth’s atmosphere. The image shows a capsule from the prior Hayabusa 2 mission to the asteroid Ryugu. The capsules for the Phobos mission will be very similar in shape but larger in size and able to carry 50 grams of sample. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612480747351-DGPBBWJ6L6DKZ5VCW2QX/Capsule+recovery-2.PNG Tomo Usui Hayabusa 2 capsule with its parachute as it landed in the Australian desert in December 2020. The capsule, to the right of the parachute, is 16 inches across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612481067478-5DO7BAYPNHNH77QW5RH7/Origin+of+Phobos+1.PNG Tomo Usui The capture theory of the origin of Phobos posits that Phobos originated as an asteroid farther away from the Sun in the asteroid belt and was captured by Mars when its orbit brought it close to the planet. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612481402162-6HFG72BWL3ZCCUR7BKCY/Origin+of+Phobos+Impact.PNG Tomo Usui The impact theory of the origin of Phobos invokes the collision of a massive body with Mars, which threw off ejecta that coalesced to form Phobos as well as Mars’s second moon, Deimos. By obtaining an isotopic fingerprint of the sample returned from Phobos, we will be able to tell whether Phobos has more affinity to an asteroid or to Mars, and therefore determine which origin theory is more likely. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1612481578762-ZHHM8DIHCDL803ML6E8L/Sample+curation+facility.PNG Tomo Usui The capture curation facility is a clean-room laboratory with instruments for analyzing the sample. The capsule is disassembled and opened inside the vacuum chamber shown in the image, where it can be manipulated without risk of contamination. https://www.geologybites.com/mike-howe daily 0.75 2021-03-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613148841043-QRU3XQRGKC32J67EKN1V/Portrait.PNG Mike Howe Mike Howe is Head of the UK National Geological Repository. He explains what distinguishes the repository from a museum collection, and picks out some special examples from the collection, such as cores from the largest North Sea oil field, and the fossil that resolved a long-standing riddle as to the nature of the conodonts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613150353478-LNIFJN39MJA8SRXOIYQE/P545362.png Mike Howe The National Geological Repository houses its 16 million specimens in its Keyworth, Nottinghamshire facility. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613150671661-736H4TNONWOPBD3QI60H/P612497.png Mike Howe The portion of the Rookhope borehole from a depth of 1,460 feet that revealed the granite with the unexpected erosive surface (unconformity). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613150887406-E0BJ7LMJZ16ICFW7P3ZB/P618525.png Mike Howe Complex veining of sphalerite (zinc sulfide) and fluorite in a Carboniferous limestone from a depth of 690 feet in the Rookhope borehole. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613151075141-VH6S25WF784ZP1AU03XA/P832070.png Mike Howe Ammonite fossil. Dactylioceras anguiforme From the Jurassic of Barrington, Somerset. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613151633279-2PPF5DY331KY4GQJ7QN1/graptolite.jpg Mike Howe Graptolite fossil. Graptolites are a marine, free-floating colonial animal. Their morphology evolved rapidly during the Paleozoic, which makes them very useful for correlating and dating rocks, especially during the Ordovician and Silurian periods. Diplograptus (Orthograptus) rugosus apiculatus Elles & Wood From the Ordovician of Laggan Gill, Scotland https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613170320431-TZHLHCX8FGF9D5039KHJ/abt_4142940560635531788MzM3MzM.jpg-l.jpg Mike Howe The Ring Pit Quarry with slates showing concentric rings. The photograph was taken in 1894, but it was not until 1958 that the rings were conclusively identified as a newly-discovered frond-shaped Ediacaran fossil species. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615682453997-U9W21YXN7OJWKY5L79GH/Ring+Fossil.jpg Mike Howe One of the large “ring” fossils from the Ring Pit quarry. It is now recognized to be the holdfast structure of a rangeomorph informally termed “the dumbell.” Wilby, P.R, John N. Carney, J.N., and Howe, M.P.A., Geology (2011) 39 (7): 655–658. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613405190484-LA8N4FN4YPACZEGNAH88/GB3D+Screenshot.PNG Mike Howe Screenshot of a search result for a trilobite using the National Repository’s GB3D fossil database. The database includes three-dimensional scans and high-resolution photographs of 2,000 type fossils. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613405538578-XHIYSGGE1TPP9TH6BKXG/GeoIndex+Screenshot.PNG Mike Howe Screenshot from GeoIndex, a geographical information system enabling the public to choose from over 200 layers of data. Examples of the data layers include bedrock geology, boreholes, hazards, geochemistry, contaminants, geophysics, minerals, and environmental designations. https://www.geologybites.com/allen-mcnamara daily 0.75 2021-03-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613357444990-0V2UZ0LJ87TZ4FP527DL/McNamara-portrait.jpg Allen McNamara Allen McNamara is a Professor of Geological Sciences at Michigan State University. He explains how his computer-based fluid-dynamical models of the mantle help distinguish between competing theories about the nature and origin of the large low-shear-velocity provinces near the core-mantle boundary under Africa and the Pacific. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613358753933-5CZFC70V9ONC1MD62WUN/LLSVP+animation.gif Allen McNamara Animation showing the extent of the large low-shear-velocity provinces (red) inferred from seismic tomography. The dark red ball represents the Earth’s core. Courtesy of Sane Cottar https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613359096078-USFLQ0Q6W7YZOZBL0WXK/LLSVP+3D+Tomography.jpg Allen McNamara 3D rendering of seismic tomography of the lower mantle: low-shear-velocity regions are shown as red and high-shear-velocity regions are shown as blue. The large red regions lying below Africa and the Pacific are the large low-shear-velocity provinces. Ritsema et al., 2004 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614113576667-3DEQFOT5HGI1C22FJTBN/Slide+6+-+map+of+LLSVPs.jpg Allen McNamara Map of the large low-shear-velocity provinces (red) for a layer 200 kilometers above the core-mantle boundary. Ritsema et al., 2004 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614031791363-R0DGX12CRFODNGAKU9CE/Spherical-parallel-processing-mesh.JPG Allen McNamara Example of a mesh used in the computer-based fluid dynamical models created by Allen McNamara and his colleagues. The red ball in the center represents the core. The mantle is divided into 12 caps, each of which is handled by a different processor. The mesh extends from the core-mantle boundary at the bottom to the overriding lithosphere at the top (not shown). As computer performance increases, it becomes practicable to use ever-finer meshes. In 2021, 144 processors work in parallel using mesh elements representing a radial increment of 25-50 kilometers. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614032497545-G6WRVO6K329VIDB7NGOJ/Thermochemical-Piles.jpg Allen McNamara Prediction of the present-day shape of a primordial compositionally differentiated dense layer (orange) at the bottom of the mantle that has been perturbed from an initially smooth layer by the flows induced by plate tectonics acting over the past 120 million years. In the podcast, compositionally differentiated regions are called compositional reservoirs. The image also shows the observed seismic tomography, with blue and red representing faster seismic velocity (i.e., cooler) and slower seismic velocity (i.e., warmer) regions respectively. The following set of images show the seismic tomography predicted by the model. Hernlund & McNamara, 2015 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614035618870-CL5N8OP1OV7UTOOZDN32/Synthetic+resulting+from+primordial+thermochemical+piles+slide+29.JPG Allen McNamara The top left image shows the temperature field that would result from the computer-generated compositional reservoir shown above. If seen through the “eyes” of present-day seismic tomography, the results would be as shown at bottom left. This bears considerable resemblance to the observed seismic tomography shown at bottom right. All maps are for a layer about 200 kilometers above the core-mantle boundary. Bull et al., 2009 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614033768397-18D97FXJYVBPAQHKZP3J/Plume+clusters+from+plate+tectonics+thermal+only+slide+16.jpg Allen McNamara This 3D map shows clusters of plumes that result from modeling the effect of plate motions over the past 120 million years on a primordial, initially uniform layer of cooler mantle without any compositional differentiation from the rest of the mantle. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614035658727-LWBN6H4O8WO1FIORLAGH/Synthetic+tmoography+from+geodynamic+model+with+plume+clusters+slide+17.JPG Allen McNamara The top left image shows the temperature field that would result from the plume cluster prediction shown above, with its corresponding hypothetical seismic tomography (bottom left). This bears much less resemblance to the observed seismic tomography (bottom right) than the first example shown above. Thus, according to these models, if the large low-shear-velocity provinces are primordial, an initial smooth layer would have been chemically differentiated as well as cooler, not just cooler. All maps are for a layer about 200 kilometers above the core-mantle boundary. Bull et al., 2009 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614037794517-YLI3WHYB6RU4TNK5QC9Q/Two+ways+to+form+thermochemical+piles+slide+21.JPG Allen McNamara There are two main hypotheses as to how compositional reservoirs at the base of the mantle formed: (i) a primordial, intrinsically denser layer continually erodes as it gets caught up in mantle flows (top); and (ii) an intrinsically denser material, such as basalt, subducts and accumulates through time (bottom). Each of these can produce the same present-day result, which makes it hard to determine which is more likely to have occurred. The series of models shown next simulate subduction of various thicknesses of crust to see if the second, i.e., the accumulation hypothesis, is plausible. Garnero et al., 2016 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614031448294-NJOZL97ZQYEQIJTH59K5/Updated+Map+of+ULVZs.jpg Allen McNamara Map of ultra-low-velocity zone detections and non-detections. The background shaded regions show the shear-wave tomography of the lowermost mantle. Most of the mantle has not yet been mapped with respect to ultra-low-velocity zones. McNamara et al., 2010 https://www.geologybites.com/lee-groat daily 0.75 2021-03-09 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614900274165-9GDUROWTOBHG8LWUIXZL/Me+at+Logtung.JPG Lee Groat Lee Groat is a Professor in the Department of Earth, Ocean, and Atmospheric Sciences at the University of British Columbia. He studies the mineralogy of gemstones and also works in the field, having conducted surveys of parts of northern Canada looking for emeralds. Here he is doing fieldwork at a giant molybdenum and tungsten deposit on the British Columbia/Yukon border. Courtesy of Allison Brand https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615329912800-XZ6Y6GAO1U5Q94EOCCEL/Emeralds+In+Situ.jpg Lee Groat Emeralds in a quartz vein with at the Tsa da Glisza occurrence in the Yukon Territory. The image is approximately 4 cm across. Courtesy of Lee Groat https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615330059386-BMRD03X28K3EUJZQ4VVZ/Figure+11a.jpg Lee Groat - Faceted emeralds about 3mm in length from the Tsa da Glisza occurrence. Courtesy of Bradley S. Wilson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615330315667-6WNJG338JJUMFLSPE6IH/Figure+11b.jpg Lee Groat Melee-size (2.5-3.5 mm) emeralds set in gold and silver. Courtesy of True North Gems, Inc. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615327736484-17GOT1DDCNJ7F8RDODIB/Emerald+from+a+pegmatite+in+N+Ontario+%28Taylor+2%29.jpg Lee Groat Emerald in a pegmatite from northern Ontario. Courtesy of Lee Groat https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613851839365-196J9RBGGH7PDIFAYFBV/Baffin+Island+spinels.jpg Lee Groat The vivid blue spinels on Baffin Island that are the most impressive gems Lee Groat has seen in the field. The chromophore responsible for their color was probably already present in the sediments before they were metamorphosed into these gem-bearing rocks. The gems occur with white carbonate in a calc-silicate rock composed of the green amphibole pargasite. Belley & Groat, 2019 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614901917770-HHFJU6W8YWKLJQVWW7MP/LAG+with+saw+Baffin+Is-2.jpg Lee Groat Lee Groat wielding a diamond saw at the Beluga sapphire outcrop at Kimmirut on Baffin Island. The brooch presented to Queen Elizabeth II on the occasion of her Sapphire Jubilee included sapphires from this occurrence. Courtesy of Allison Brand https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613851449762-XHFZ5MRHJTT2UDY8WOFY/Baffin+Island+sampling+edited.jpg Lee Groat The dark parts are diopside plus phlogopite plus feldspar, and the light parts are calcite, scapolite, and nepheline. The sapphires occur in the white material. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1614902075361-E6ESCWAYDJOMTW8TJC99/Sapphire+Baffin+Is-2.jpg Lee Groat Sapphires in situ in a calc-silicate rock at the Beluga occurrence. Courtesy of True North Gems, Inc. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613851956935-2ZIOJZYZD3KLSUF59UK3/Figure+9.png Lee Groat Colorless, blue, and yellow sapphires from Kimmirut on Baffin Island where the Beluga sapphires were found. Courtesy of True North Gems, Inc. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613852197645-MYADZBDRAMKYS6UDLRBH/Sapphires+and+Queen.JPG Lee Groat Brooch presented by the Canadian Governor-General to Queen Elizabeth II on the occasion of her Sapphire Jubilee. The brooch contains 48 pale blue sapphires from the Beluga occurrence on Baffin Island together with more than 400 Canadian diamonds. Brooch Image courtesy of Hillberg & Berk https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1613853034671-6F6YFRLUXUFZF5X5UU45/tectonic+gems+-+cross+section.JPG Lee Groat Gems can form at plate boundaries where an oceanic plate subducts below a continental plate (A) or two continental plates collide (B). Stern et al. 2013 https://www.geologybites.com/david-evans daily 0.75 2021-03-31 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615074236413-W9F4Y1JBU6S0ZDR6LFW4/DE+at+Bathhurst+Inlet.jpg David Evans David Evans is Professor of Earth and Planetary Sciences at Yale University. He uses magnetic fields frozen into rocks when they formed to deduce where they were and, together with uranium-lead dating, to reconstruct the supercontinents that assembled about every 600 million years over most of Earth history. Courtesy of Page Burt https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615074688765-O23AH107CUXUT948DST0/Supercontinent+Timeline.JPG David Evans Timeline of the supercontinents in millions of years ago (Ma). Black lines represent rift zones associated with supercontinental breakup. Red stars in the Superia supercraton (lower right inset) indicate possible mantle plume focal points of radiating swarms of mafic dykes. Evans et al., 2016 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616613906086-KJYM2I3SJW7BW51QUAHY/Baddeleyite+e-Rocks.jpg David Evans Crystals of baddeleyite (zirconium oxide) occur in the basalt dyke swarms that form when a supercontinent breaks up. Just as with zircon, these crystals trap uranium in their crystal lattice, and can therefore be used to obtain accurate ages of such swarms. Since zircons are generally absent from mafic rocks such as basalt, the advent of baddeleyite dating opened up a powerful new geochronological tool. The crystals shown here are about 3 cm long - much larger than most crystals used for dating. Courtesy of e-rocks https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615074865078-O1N18I561YQ8UIBD28LV/Geomagnetic+Field.jpg David Evans Although the magnetic poles wander, over the long term the Earth’s magnetic field is aligned with the geographic poles. The field adheres approximately to a magnetic dipole. When a rock forms, the ambient magnetic field is frozen into it. If we can measure the angle of the magnetic field with respect to the horizontal, we can determine the latitude at which the rock formed. Original source unknown https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615075150719-YBBV5A58FCKT8GC3MU2L/Magnetometer+and+shilded+oven.jpg David Evans The barrel-shaped object at right is a magnetometer, and the horizontal cylindrical-shaped object at left is a shielded oven for heating the rock samples during partial demagnetization. All of the instruments are housed within a shielded room that blocks out over 99 percent of the Earth's magnetic field, so that demagnetization of the rocks can be achieved in a magnetically neutral environment. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616612077992-87IDPBNQDPO3OGY9DBMX/Western+China+-+Rodinia+breakp.jpg David Evans Western China is one of David Evans’s field locations. The grey band of rock in the hillslope consists of layers of basalt that attest to the breakup of Rodinia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615076398810-T7SM56PJDRWXHE79DODD/Paleoproterozoic+Conceptual+Model.jpg David Evans A hypothetical example shows how, among the various geological features that can be used to reconstruct an ancient supercraton, dyke swarms provide the most convincing evidence. (a) A hypothetical supercraton with various geological elements, just prior to breakup. A large igneous province (green) with flood basalts and associated dykes and sills is emplaced along the incipient rift. (b) Breakup of the supercraton has spawned two cratons (A and B). If the cratons are not too modified, as with present-day South America and Africa, they are easily fitted together again using the shape of their margins (P-R and PM), and the matching up of the LIP (P1), older sedimentary basins (P2), and ancient orogenic front or fold-thrust belts (P3). (c) The more general case in which further breakup and relative translation and rotation has occurred (Craton C) and craton margins have been modified, and differentially uplifted. Dykes related to the LIP, however, remain on all three cratons and precise age dating yields a critical clue that they might be part of a single event. Paleomagnetic data may yield additional geometrical clues (north arrows), and paleolatitudes. (d) Reconstruction of the original supercraton, based only on the matching of the dyke swarms. Bleeker & Ernst, 2006 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615133450577-SJY2S6KDRIC1Q3KWAK21/Paleoproterozoic+Conceptual+Model+synthesis.jpg David Evans Reconstruction of the Superia supercraton before rifting and breakup of various blocks on its southern margin between 2,500 and 2,080 million years ago. The red star shows the initial location of a hotspot, 2,075 and 2,065 million years ago, and the other colored stars show the inferred location of the hotspot at the indicated time intervals. Ernst & Bleeker, 2010 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1615075716943-VH6S167NG2628JKFW9HC/Nunavut+central+Canada-2.jpg David Evans The great roadless barrenlands of Nunavut, central Canada, are one of David Evans’s field sites. The rocks he measures and samples there testify to the unification of Laurentia, the ancestral North American continent about 1,800 million years ago. Sites such as these are accessible only by helicopter. Courtesy of Rob Rainbird/Theresa Raub https://www.geologybites.com/bob-anderson daily 0.75 2021-04-13 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616889789397-HBA34UKGSEJMYD05HNKO/rsa_on_lrb_pillar_DSC2142.png Bob Anderson Bob Anderson is chair of the Department of Geological Sciences at the University of Colorado Boulder. He is a geomorphologist who has studied many diverse aspects of the landscape, focusing recently on Alpine and Arctic landscapes in which ice plays a prominent role. It was his sense of awe and aesthetic appreciation of patterns in nature that drew him into the field. Here he is in eastern Greenland near the outlet of the Helheim ice stream. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616698110266-4BRO1QHLCWYXFWA37IBZ/el_cap%26cloud1_300dpi.jpg Bob Anderson The 3,000-foot granite wall of El Capitan in Yosemite National Park, California, characterizes the western edge of the Sierras, which consists of rocks with a very low density of flaws. Climbing routes on El Capitan, which make use of cracks, are widely spaced. This also gives the rock great strength and the ability to sustain tall walls. The valley itself, from which the photo was taken, has been deepened by numerous glaciations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616698484100-EM1AFE7L0TQIGSJTWK3P/Glacial+polish+2.jpg Bob Anderson A glacially polished valley wall in Yosemite National Park. The patterns in the rock indicate that the glacier was sliding away from the viewer, aligned with the flutes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616698555026-N4GFNI1UUHWWN03DV4OF/Glacial+polish+1.jpg Bob Anderson Close-up of a polished granite surface in Yosemite National Park. The width of the view near the camera is about 2 feet. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616704145763-J212A3GA2WMJ7TV2NNOR/Google+Earth+image+of+E+Sierras.jpg Bob Anderson Google Earth perspective image looking west at the eastern Sierra front and moraines bounding each valley. The hundred-meter scale of these moraines is in great contrast to the tiny moraines in valleys draining westward on the west edge of the Sierras. Courtesy of Google https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616704907504-4AKWDLK48R4XZ9MP4Q8S/cosmogeneic+production+sketch.jpg Bob Anderson High-energy cosmic rays enter the Earth’s atmosphere and collide with atoms in the atmosphere, which produces cosmogenic radionuclides, such as carbon 14 and beryllium 10. Of interest here, however, are the high-energy particles that hit the Earth’s surface and collide with atoms in rock to create the cosmogenic radionuclides beryllium 10 and aluminum 26. Since cosmic rays do not penetrate far below the surface, the abundance of these radionuclides is an indicator of how long a rock has been on the surface and exposed to the incident cosmic rays. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616889183369-XAOKPPILABNEA663DUQC/cosmogeneic+graph.jpg Bob Anderson This graph shows that when exposed to cosmic rays, the concentration of beryllium 10 atoms in quartz increases at first, and then flattens out as equilibrium is reached between the beryllium production rate and radiogenic decay rate. The sloping part of the curve is the range of time over which the beryllium 10 concentration varies with time, and therefore the timescale when it can be used to date how long the quartz has been on the surface and exposed to cosmic rays. As the graph shows, this timescale is several million years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616713843200-0R75EDZIK66YGPHCDVTA/mudcrack_puddle1.jpeg Bob Anderson In this desiccated mud puddle, the cracks are spaced by about 2 cm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616708642672-H6DW4ZAJUUC912GWPMFY/cracks_briggsdale+sign+DSC_5286.jpeg Bob Anderson The cracks in this road sign have a spacing of about 5 cm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890000745-PT63Y927JNG31QFCOB27/caution_sign_red_escape_DSC_2877_7x6.jpg Bob Anderson The cracks in paint on caution sign meet at right angles to each other. The bolt head in the center is 1 cm in diameter. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890527850-LUQLQKSO3R5EVZB9G70D/mudcracks_roberts_lake_h_DSC_0237+copy.jpg Bob Anderson Mud cracks in a desiccated lake bed on Alaska’s North Slope. The caribou and geese tracks indicate that the cracks are spaced by about 30 cm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616708710104-D0RU6DOKH9919TKNXYDW/Arctic+ice+wedge+polygons.png Bob Anderson Arctic ice wedge polygons with a spacing of about 30 meters. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890182005-JCU8KFJEPY5YBNMTTI4F/patterned_ground_1_DSC_0277+copy+copy.png Bob Anderson These frost wedge polygons on Alaska’s North Slope are about 40 meters across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890285898-788WS5XDNNQJ22LI1K5J/rsa_on_overhang_DSC_0225+copy.jpeg Bob Anderson Bob Anderson on an eroding permafrost clifftop at the edge of the Beaufort Sea on the North Slope of Alaska. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890370303-XFCS3OO47H9NUW9TMVPR/Seven+Sisters.jpg Bob Anderson The Seven Sisters form an eroding chalk sea cliff edge on the English Channel. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890401115-TF7O657ZGP31L08B6RMS/Tors+on+Dartmoor.jpg Bob Anderson The tors of Dartmoor in Devon, England, form edges on hill slopes. The blocks tumble off the downslope sides of these outcrops. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616890439196-4MUJEC4YC3MC42WVCGOE/River+nick+point+Grand+Canyon.jpg Bob Anderson Sharp steps in the dry channel bed of a river course draining toward the Grand Canyon are an example of knickpoints, which are edges in river channels that move through the landscape. https://www.geologybites.com/dietmar-muller daily 0.75 2021-05-12 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617387013045-CJ74UKJ4WKWT5MYT561E/IMG_9817.jpg Dietmar Muller Dietmar Müller is Professor of Geophysics at the University of Sydney. He and his team built GPlates, a powerful software tool enabling researchers to synthesize diverse sets of geological data into a self-consistent reconstruction of the Earth’s tectonic history. In February 2021, his team published an animated billion-year plate reconstruction, which has had an enormous impact on the public. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617379656132-SDJW5YKSIS26RXF3VLPX/G-Plates+Main+Window.JPG Dietmar Muller The main screen of GPlates showing plates and plate boundaries. Researchers all over the world use GPlates to reconstruct plate-tectonic positions, orientations, and motions through geological time in an interactive manner. The software also functions as a geographic information system and a way of visualizing image data. Geological, geophysical, and paleo-geographic data may be attached to the simulated plates, enabling researchers to trace the motions and interactions of these data through time. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617635025005-EYDBB56UGFO3OZJJX0P0/GPlates+screenshot+w+age+legend.jpg Dietmar Muller GPlates screenshot, with seafloor age data superposed onto the reconstructed oceanic plates. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617380543672-18A2OUBOR2ECL5T5TACJ/Reconstruction+of+continents+from+EGU+blog+-+colors+are+amalgamation+of+diff+models-when+slab+at+sfc%2C+must+be+a+SZ+there..jpg Dietmar Muller A map of reconstructed plate locations 120 million years ago. The continents are shown in grey and white and the color shading indicates the seismic velocity of the mantle at a depth of 1,400 km obtained from seismic tomography. The seismic velocity is an indicator of mantle temperature, with the coldest regions suggesting the presence of subducted slabs of oceanic crust. Because it takes about 120 million years for a slab to sink to a depth of 1,400 km, and assuming the slabs sink vertically, the presence of these slabs are markers of active subduction zones in these locations 120 million years ago. This information serves as a constraint on valid tectonic reconstructions. Courtesy of Grace Shephard (CEED/UiO) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617458597463-DAGNXN3KGHA80LBV1Y2U/1000+Ma+snapshot.JPG Dietmar Muller 1000 Ma Snapshot: The distribution of continental crust, ocean basins, and plate boundaries used in the plate model at one billion years ago. Continental lithosphere is shown as tan, blue, and green. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617459734203-PC3REUKUBZ3J97KAKMO8/500+Ma+snapshot.JPG Dietmar Muller 500 Ma Snapshot: Selected abbreviations: A-C Avalonia-Cadomia; Af Afghanistan; B Baltica; C Congo; CM Central Mogolian Terrance; I India, S Siberia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617471548826-NXH556HIQS6P0RZ8FF6Y/0+Ma+snapshot.JPG Dietmar Muller Present-day snapshot: distribution of continental crust, ocean basins, and plate boundaries used in the model. https://www.geologybites.com/sarah-stewart daily 0.75 2021-05-12 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617762432018-TKKSXEXX77I01V59KP5O/Sarah+stewart+-+whiteboard.jpg Sarah Stewart Sarah Stewart is a Professor in the Department of Earth and Planetary Sciences at the University of California Davis. She explains how, following a massive impact with another body, the Earth formed a synestia - an inflated disk of gas in which the impacting body and Earth were thoroughly mixed, and out of which the Moon and a new Earth solidified. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617762737293-OCPOPKH2JI2L54K134D5/Press_release_cartoon3.png Sarah Stewart A post-collision synestia is much bigger than a planet, as this image shows. Its initial shape is a biconcave disc, which evolves as it cools. The Moon accretes within the synestia over a period of about 1,000 years following the impact. Courtesy of Simon Lock https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617849671359-3QEV6UWHQ7EUTM20VM0P/Three+lunar+orbit+tilt+angles.JPG Sarah Stewart A. Sarah Stewart’s model begins with a giant impact that tilts the Earth’s spin axis between 60 to 80 degrees from the ecliptic and leaves the Earth with a 2- to 3-hour day. The Earth is spinning so quickly that its equatorial axis is twice the length of its polar axis. B. After the Laplace plane transition (shown in this simulation), angular momentum is transferred away from the Earth-Moon system, and the Earth becomes spherical. The Earth’s obliquity is near present day, 23.5 degrees, and the inclination of the Moon’s orbit is 30 degrees. C. After the Cassini state transition (shown in this simulation), the Moon’s orbit is lowered to the present-day 5 degrees from the ecliptic plane. Animations based on Ćuk et al. Nature 539, 402–406(2016) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617762884280-DKXIO7S1IRM5CMDLFOJP/Z+Machine%2C+Sandia+Arts+%26+Sparks.jpg Sarah Stewart The Sandia Labs Z-machine, located in Albuquerque, New Mexico, concentrates electrical energy and turns it into short pulses of enormous power, which are then used to heat a target to as high as 1.8 million degrees C. Sarah Stewart and her colleagues use this machine with Earth minerals at the target to simulate conditions following a Moon-forming Earth impact. Courtesy of Randy Montoya https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617762598695-YILFI5NWASL7WURBHF4N/natgeo-moon.jpg Sarah Stewart Artist’s impression of a collision with a Mars-sized body based on impact simulations. Impact simulations described in Canup & Asphaug, Nature (2001) 412, 708, and Canup, Icarus 168 (2004) 433 Courtesy of National Geographic https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1617762796481-SDPQZV5CJDVHH5F4C1OX/moon-sequence2.gif Sarah Stewart Simulation showing the accretion of the Moon within a synestia. Initially, the synestia is larger than the Moon’s orbit. As the synestia cools and contracts, the Moon emerges and becomes a separate body in orbit around the synestia. Eventually, the synestia cools to form the Earth. The Moon’s chemistry can be explained by formation at the high pressures and temperatures of the synestia. Courtesy of Sarah Stewart and NASA PIA 20700 https://www.geologybites.com/gillian-foulger daily 0.75 2024-02-22 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619391868198-OKOM3FUKNH998BE6WM1L/IMG_2393+%281%29.jpeg Gillian Foulger Gillian Foulger is Emerita Professor of Geophysics at Durham University. She points out the lack of evidence in support of the mantle plume hypothesis and describes an alternative - the plate hypothesis. A key prediction of the plate hypothesis is that the lithosphere should be extending wherever we see intra-plate volcanism. She explains that many of the observations we already have can be reinterpreted as consistent with the plate hypothesis, and suggests new experiments that could clearly distinguish the competing hypotheses. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619392719979-C4QEXTJDYVSV1Y8TPQ5P/Pacific+Island+Chain.jpg Gillian Foulger The map shows the actual position and age (yellow boxes) inferred from the seafloor magnetic anomalies of the Hawaiian islands and the Hawaiian-Emperor seamount chain. The diamond-shaped points and ages (black boxes) are the positions of the islands and seamounts that would be expected if the source of volcanism was a fixed plume and the present-day locations were determined purely by motion of the Pacific plate. The red and yellow diamonds reflect uncertainty about the motion of the Antarctica plate used to determine the fixed frame of reference for the plume. Raymond, C.A., Stock, J.M. and Cande, S.C., 2000. Fast Paleogene motion of the Pacific hotspots from revised global plate circuit constraints. In: M.A. Richards, R.G. Gordon and R.D. van der Hilst (Editors), History and Dynamics of Plate Motions. AGU Geophysical Monograph Series. AGU Geophysical Monograph, pp. 359-375. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619462848098-X1576NK9SV3PM2C7LPCC/69f7908ccd003bf32bc8784997f58b10.jpeg Gillian Foulger The map shows that the western Pacific is bordered by subduction zones, with the Aleutian trench to the north, west Pacific subduction zones off the coasts of Japan and China to the west, and between Java and Samoa to the south. This results in a radial-outward extensional force on the west Pacific lithosphere. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619462810399-RAFTYOTL69B449HH8D45/Stress+map.jpg Gillian Foulger Global map of the tectonic stress field induced by horizontal tractions derived from the history of subduction. The arrows show the relative strengths of the extensional (outward-pointing arrows) and compressional stresses (inward-pointing arrows). Hawaii (red circle) is located at a point where the extensional forces are equal in all directions. In the podcast, Gillian Foulger suggests this may be causing lithospheric extension in Hawaii, which, according to the plate hypothesis, would cause volcanism from melting in the upper mantle. Lithgow-Bertelloni & Guyunn (2004), Origin of the lithospheric stress field, J. Geophys. Res., 109, B01408, doi:10.1029/2003JB002467 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619530649883-YHHHZO2BC049BA80F5IN/Eastern+Snake+River+Plain+hotspot+trace.jpg Gillian Foulger The location and time progression of volcanism in the eastern Snake River Plain. The prevailing view is that this traces the path of the North American Plate over a hotspot or mantle plume, now centered below Yellowstone National Park. Courtesy of Kevin Case https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619392845059-6WKKMO96YHN0T34988HV/Basin+and+Range+JPG.jpg Gillian Foulger - Plate Hypothesis Explanation According to the plate hypothesis, the time-progression of east-west extension of the volcanism in the eastern Snake River Plain is explained by the progression of lithospheric extension. While the plume hypothesis explains the trail of volcanism by the motion of the North American plate over a hot spot, Gillian Foulger points to the lack of evidence for a hot spot, and suggests an upper mantle origin of the volcanism following waves of lithospheric extension. Christiansen, Foulger, & Evans (2002), Upper mantle origin of the Yellowstone hotspot, GSA Bulletin, 114, 1245 https://www.geologybites.com/katie-stack daily 0.75 2021-05-08 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619619488311-XIT546DXOCX8F967VD3J/kstack_marsyard.jpeg Katie Stack Katie Stack is Deputy Project Scientist for the Mars 2020 Rover Mission and an expert on the Martian sedimentary rock record. She leads a large team of scientists that will combine orbiter and rover image data to investigate processes that took place on the the ancient surface of Mars. Here she is testing a prototype in the “Mars Yard” at JPL in Pasadena, California. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619620458638-S5EUKBAPQ25E706HOPHF/25045_Perseverance_Mars_Rover_Instrument_Labels-web.jpg Katie Stack In the podcast, Katie Stack discusses the imaging instruments on the mast (Mastcam-Z and SuperCAM) and the close-up camera on the arm (WATSON), as well as the subsurface radar (RIMFAX) and the UV (within SHERLOC) and X-ray (PIXL) spectrometers. NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619621109744-2LPF1GWAKO6O6KNGNBOO/pia24542-perseverances-selfie-with-ingenuity-1041.jpg Katie Stack Perseverance and the helicopter (left) 13 feet from the rover captured by the wide-angle camera (WATSON) located at the end of the rover’s arm. The pale-colored rocks have yet to be identified. NASA/JPL-Caltech/MSSS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619621513296-57K8CSX13ANJJ0XAQEV5/PIA23491_1_MSR_a_Mars_2020_collecting_sample.png Katie Stack Artist’s impression of Perseverance drilling to obtain a rock sample. Soil and rock samples collected by the rover will be retrieved and returned to Earth by a future mission. NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619624564185-4YR1792HGCB2HJ63KJZI/PIA23976.png Katie Stack Simplified map of the regions in and around Jezero Crater prepared before landing. The green circle shows the rover’s landing ellipse. As part of Perseverance’s primary mission, samples will be collected from the crater floor, the delta, the marginal deposits, and the crater rim. Each of these areas may contain different kinds of evidence of the environment on Mars over 4 billion years ago. The region outside the crater, called Midway/Northeast Syrtis, might be explored after completion of the primary mission if the rover is still operational. NASA/JPL-Caltech/USGS/University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619627251559-KQIMMFPRGYG49FP0TW6U/2b-Ellipse_Map_v3_NoAnnotation.jpg Katie Stack Perseverance landed within Jezero crater, just beyond the end of the fan-shaped river delta deposited by the ancient river bed that cuts through the crater rim on the left. The crater was once filled with a lake several hundred feet deep. The image is 31 miles across, and the crater in the middle of the delta deposit (red arrow) is about 0.6 miles across. The image was taken by the ESA Mars Express orbiter. ESA/DLR/FU-Berlin/NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619621986726-CVAB7P1B81EW5K5DZ03X/PIA24331_landing_site_full_res.jpg Katie Stack The green dot shows where Perseverance landed in Jezero Crater on an image taken by NASA’s Mars Reconnaissance Orbiter. NASA/JPL-Caltech/University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619624398055-FN73YOB34FYJLSFQLTO4/Stack2020_Article_PhotogeologicMapOfThePersevera+-+Fig+6.jpg Katie Stack A photogeological map showing bedrock and surficial units mapped by the Mars 2020 Science Team in and around the Perseverance landing site. Kathryn Stack et al., Space Science Reviews (2020), 216:127 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619625295332-MNUN0R4ZC9E22MHZ4RB3/PIA24264-Panorama-supplemental-image-wind-carved-rock.jpg Katie Stack A rock carved by wind first noticed in the Mastercam-Z panoramic camera. NASA/JPL-Caltech/MSSS/ASU https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619625423742-CC5EKRZT2SPHIHPP0RE5/PIA24492_annotated_Diapositive4.jpg Katie Stack A rock named “Yeehgo” (a Navaho word for “diligent”) 11 feet away from the rover. As Katie Stack explains in the podcast, even with the state-of-the-art instruments aboard Perseverance, identifying rock types on Mars is difficult, and it is not yet known whether Yeehgo has a sedimentary or an igneous origin. NASA/JPL-Caltech/LANL/CNES/CNRS/ASU/MSSS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619625851148-UFUZ93RZVT99Y11PJIT4/PIA24486-Drive-Map.png Katie Stack This image shows two possible routes (blue and purple) from the landing site (white dot) to the fan-shaped delta deposits. The yellow line marks a possible subsequent traverse across the delta. The base image is from NASA’s Mars Reconnaissance Orbiter. NASA/JPL-Caltech/University of Arizona https://www.geologybites.com/marie-edmonds daily 0.75 2021-05-10 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619743784539-1BM03GD4HRFXEJ0RR9DT/Kilauea.JPG Marie Edmonds Marie Edmonds is Professor of Volcanology and Petrology at Cambridge University. She studies the cycling of volatile elements such as carbon between the atmosphere and the mantle and the role that volatiles play in melting, magma transport, and the style of volcanic eruptions. She describes how all volcanos emit gas and how the gas can reveal a lot about the origin of the magma and also forewarn of eruptions. Here she is using an infrared spectrometer to monitor gases emitted during the 2018 eruption of Kilauea on Hawaii. Courtesy of Richard Herd https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619744460775-34VRW7CUOTLNRF1RKDBV/SoufriereHills.JPG Marie Edmonds After a long period of dormancy, the Soufrière Hills Volcano on the Caribbean island of Montserrat became active in 1995 and has continued to erupt ever since. The image shows the lava dome with a gas plume shortly before the large dome collapse and explosion sequence of July 12-13, 2003. Marie Edmonds has made detailed measurements of the gas emitted by this subduction-zone-related volcano. Courtesy of Richard Herd https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619745298998-LGZDHQH35T97Z5AUCQ5F/Hunt_2017_GCubed.jpg Marie Edmonds Diagram illustrating the processes involved in continental rifting. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619746876501-8BG28E4Q9MV7PDABJOE8/wong_2019_Frontiers.jpg Marie Edmonds The various processes that continually cycle carbon from the atmosphere into the ocean where it is deposited in sediments and subducted. Subducted carbonates are then released back into the atmosphere by volcanos at subduction zones, , at mid-ocean ridges, mid-ocean volcanic islands, and in rifting continents. LAB = lithosphere-asthenosphere boundary. Carbon fluxes given in millions of tons per year. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1619747540549-482ZELW100FKA8NKVDLR/carbonisotopes.jpg Marie Edmonds The ratio of carbon 13 to carbon 12 in various settings compared to a standard ratio. DOC = dissolved organic carbon. https://www.geologybites.com/jan-smit daily 0.75 2021-05-28 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620046875867-9VLAVMEXUYUIIJ21S7UG/IMG_8536.jpeg Jan Smit Jan Smit is Emeritus Professor of Event Stratigraphy at the Free University of Amsterdam. Initially a paleontologist studying planktonic foraminifera, he became intrigued by what appeared to be extremely sudden events in the fossil record, especially at the boundary between the Cretaceous and the Paleogene, known as the KT boundary. He describes the unprecedented discovery of a thick surge deposit in North Dakota containing an extraordinarily well-preserved assemblage of fossils that document the final moments of the Cretaceous. He is pictured (left) at the Tanis site with Robert DePalma, who first identified the site and is pointing to the gills of a paddlefish lying upside down and containing numerous tektites. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620331632714-E5LAIM6EJF2FXK1L8NV4/Map+of+Deccan+Traps.jpg Jan Smit The Deccan traps are extensive thick sequences of lava that were erupted at the close of the Cretaceous. Before the asteroid impact hypothesis, the climatic cooling and atmospheric toxicity resulting from the gases emitted during this prolific series of eruptions were thought to be the principal cause of the end-Cretaceous mass extinction. Courtesy of Courtney Sprain https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620331953225-JGY47B895JRU8QQ7MC8E/deccan_16x9.jpg Jan Smit The sequences of lava within the Deccan Traps near Mahabaleshwar are over 3,300 meters thick. Courtesy of Gerta Keller, Department of Geosciences, Princeton University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620006195619-5P0K7DD1EJY5EPNQOFLQ/PNAS+Fig.+1.jpg Jan Smit Maps of the Tanis site in North Dakota. A: Regional context showing the large sea covering central North America during the Cretaceous. The map shows previously known tsunami locations (black dots) and the Tanis site (star) on an ancient river draining into the inland sea. B: Photo and interpretation showing the 2.5-meter-thick surge event deposit overlying sandstone deposited as a point-bar in the Tanis river. C: Diagram (not to scale) of the event deposit setting. The event deposit (1) covers the slope of a sandy bar of a meander (2). The densest carcass accumulations (3) were found just below Cretaceous-Paleogene boundary deposits (4) that directly overlay the event deposit. DePalma et al., PNAS, (2019) 116, 8190 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620047575407-HVYFN5PXXNSBLQ6U41FP/PNAS+Fig.+2.jpg Jan Smit Graphic log of the Tanis surge deposit showing the distribution of the tektites (ejecta spherules) and fossils. The Iridium layer is indicated at the top, just below the 1-2-cm-thick clay layer (tonstein) that is a global marker of the Cretaceous-Paleogene boundary. DePalma et al., PNAS, (2019) 116, 8190 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620049259510-34VVAK3AKDI9UJPSP3YY/PNAS+Fig.+7.jpg Jan Smit A: Freshwater paddlefish just below a nacreous marine ammonite shell (inset). B: Diagram showing the fish carcasses oriented by the flow direction. C: Mass grave of fish carcasses. DePalma et al., PNAS, (2019) 116, 8190 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620050288594-6TJQT6FQ59MHR2LNSBDT/Image.jpeg Jan Smit Jan Smit’s rendering of a paddlefish swallowing tektites suspended in the water. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620163400775-A7FQP7JAGD4C1WIRYIUA/Tektites.jpg Jan Smit Closeup of the fish that Robert DePalma is pointing to in the top image on this page. The curved bones are the upper and lower jaw of a paddlefish, which was buried upside down. The small light spherules within the red circle are tektites caught in the gills. Courtesy of Jan Smit https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620049837049-IBUST0C13DPQXRTZE4FA/PNAS+Fig.+6.jpg Jan Smit Detailed images of tektites in the fish gills. A & B: X-ray of a fossil sturgeon head. C & D: Microtomography images of another fish specimen with microtektites embedded between the gill rakers. DePalma et al., PNAS, (2019) 116, 8190 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620050456755-WD1WMMIZBM5J15N6YVIQ/Spherules+in+amber.jpg Jan Smit A: Spherules within amber found at Tanis. B: An exposed unaltered spherule stuck within amber. DePalma et al., PNAS, (2019) 116, 8190 https://www.geologybites.com/peter-molnar daily 0.75 2022-07-28 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620761941730-VZQAFNK9CT2F94JEF3WG/PM%26GrossGluckner.JPG Peter Molnar Peter Molnar is a Professor of Geological Sciences at the University of Colorado at Boulder. He has worked on a great many subjects, but especially on how mountain ranges are built and how climate is affected by topography and crustal movements over geological time. His research on mountain ranges has focused on the high terrain in Asia - the Himalaya, Tibet, and the Tien Shan, all of which he has studied extensively in the field. He explains why he thinks that bits of hot mantle are dripping off the bottom of the Tibetan lithosphere and how this can account for the 4,500-meter height of the Tibetan plateau. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620837626621-RGKPMV4XZ4HIR4XWVM69/Tibet_and_surrounding_areas_topographic_map.png Peter Molnar The elevation map shows the enormous extent of the high Tibetan plateau. Generic Mapping Tools, GLOBE & ETOPO1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620846290640-25QKTQADB61H7ZGXAOLK/DSC_0197.JPG Peter Molnar Geological field trip campsite in Tibet, with part of Bukadaban (6,860 m) in the Kunlun mountains in northern Tibet. This series of three images were all captured north of the Jangtang mountains in the Hoh Xil basin (see topographic profile below). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620846638555-TUS3HZYLA1QQ7QSJ0U1T/Tibet+landscape.jpg Peter Molnar Bukadaban, looking northeast across LiXie Wudan lake in northern Tibet. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620846396111-GGC4UK4KQZG2UKR5LO5Y/DSC_0342.JPG Peter Molnar Driving along the shore of Yinma lake. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620846959657-D6QP0W9DUWV7IYU1U6JZ/Folded+red+beds+processed.jpg Peter Molnar To the west of Lhasa, these folded sedimentary rocks overlain by volcanic rocks from the late Cretaceous provide evidence for the formation of the Transhimalaya mountain range well before India collided with Tibet around 50 million years ago. Courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620837963231-AZSFZRZLDO14PQ8YF47F/Paeloelevation+profiles.JPG Peter Molnar Hypothesized topographic profiles across Tibet based on a range of paleoaltimetry indicators. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620769658950-LLT54XVBH8DCQ7O37ZX3/Palm+Fossil.jpg Peter Molnar Palm fossil found in the Lhunpola basin between the Transhimalaya and the Jangtang mountain ranges. It was recovered in a 25 million-year-old ancient lake sediment at a present-day elevation of 4,655 meters. Since such tropical plants cannot withstand the cold climate at high elevations, the fossil indicates the basin was no more than about 2,000 meters in elevation at the time. Courtesy of T. Su https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620770584399-22QOJAT6LSJMEYUZAIJG/Fossils+-+leaves+PNAS20Su.jpg Peter Molnar Fossil plants from the Middle Eocene (about 47 million years ago) in central Tibet at a present-day elevation of 4,850 meters. They represent a humid subtropical ecosystem that would have flourished at a land surface height of up to 2,400 meters with a monsoon season and a mean temperature of about 19 °C. The scale bars are 10mm (A,C,D,H,N,O,R,S), 5mm (B,G,I,J,P,Q), and 2mm (E, F, K, L, M). Su et al., PNAS (2020), 117, 32989 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620914917061-ICNTEMJY3AOHI1WIJBVR/normal+fault+Tibet+-jessup_gsa_fig_5.jpg Peter Molnar Pervasive north-south normal (extensional) faults indicate that the Tibetan plateau is extending in an east-west direction and subsiding, perhaps by as much as about 1,000 meters over the past 15 million years. This suggests that the plateau may have been as high as about 5,500 meters in the mid-Miocene. The image shows recent normal faulting in the Ama Drime massif in southern Tibet. Jessup et al., (2008) Geology, 36, 587-590 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620835775933-9C7UTW81K8MN4KELF3G5/Lithosphere%2C+mantle%2C+crust.JPG Peter Molnar The crust is less dense than the mantle. The lithosphere consists of crust and lithospheric mantle. Below the lithosphere is the asthenosphere, which is mantle that is hot enough to convect. The crust and the mantle are distinguished by their composition, i.e., they have different mineral assemblages. The crust contains silica-rich minerals, such as feldspar and quartz, and the mantle contains minerals rich in iron and magnesium, such as olivine and pyroxene. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620836461011-BFDMXWODWLI0J6SQB3FZ/Isostasy+Diagram.jpg Peter Molnar Vertically exaggerated cross‐section through the upper mantle, showing crust and mantle. The asthenosphere is a weak layer that underlies the stronger mantle lithosphere. The lithosphere includes the coldest uppermost part of the mantle and the crust on top. The thicknesses of both crust and mantle lithospheres vary from place to place but, in general, where the crust is thick, the surface stands high to form a mountain belt or high plateau. The gradation in tone through the lithosphere indicates a downward decrease in strength to the asthenosphere. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620836715512-TGRFAES370ULHVNHMTDK/Growth+and+collapse+of+mountain.JPG Peter Molnar Sequence of cartoons showing the growth and collapse of a mountain range built by horizontal compression and thickening of the lithosphere (b). The lithospheric root, composed of thick, cold, dense mantle lithosphere, breaks off and sinks. It is replaced by the ambient hotter mantle of the asthenosphere, indicated by the light shading in (c) where thickened mantle is shown in (b). The remaining lithosphere then rises, with the surface rising as indicated by the dark shading at the top of the thick crust. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1620837105233-22EQPE0AA82KQENS6KW7/Blobs.JPG Peter Molnar The cartoon shows how horizontal compression induces thickening of the crust and mantle lithosphere. Since the mantle lithosphere is denser than the underlying asthenosphere, it is gravitationally unstable, and blobs of mantle lithosphere detach and sink. https://www.geologybites.com/subject-index daily 0.75 2021-05-20 https://www.geologybites.com/claude-jaupart daily 0.75 2021-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621994296340-7VMY72014U875EYWDDD6/CJ+with+over+borehole.jpg Claude Jaupart Claude Jaupart is Professor of Geophysics at the University of Paris and the Institut de Physique du Globe. His research aims to understand the physics of igneous processes in the Earth, such as those occurring in volcanic eruptions, magma chambers, and the mantle. He reveals how heat flow out of the Earth is highly variable on all spatial scales and that Earth has been cooling slowly for the past 2 billion years at least, which still leaves plenty of heat to drive today’s plate motions and volcanism. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621995212155-L3037BP52Q2SXZ3XVEI3/Field-remote-place-2.jpg Claude Jaupart - Make it stand out Making a heat flow measurement down a deep borehole in the far north of Canada. Claude Jaupart describes the steps that need to be taken to ensure that an accurate measurement of the Earth’s heat flow is obtained. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621995307852-U92NDUG4JCDVCW7RSRLL/Field-collecting-samples-2.jpg Claude Jaupart - Make it stand out Collecting borehole rock samples for thermal conductivity measurements back in the lab. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621995427422-EC76DU5VDOSZYJBB4I2M/Raglan-site-Hudson-Strait-2.jpg Claude Jaupart - Make it stand out Borehole site in northern Canada on the Hudson Strait. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621995596233-945JHAQ17Q579UOROMTA/Raglan-Hudson-Strait-cable-3.jpg Claude Jaupart - Make it stand out Borehole at the Hudson Strait site showing the cable that connects to the temperature-measuring device that is lowered down the borehole. While most borehole measurements are conducted at depths of a few hundred meters to a thousand meters, the deepest boreholes reach depths of 2.5 km. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621995806918-R9H999HPA75W2NIHTSSX/Raglan-Hudson-Strait-visitor-2-2.jpg Claude Jaupart An Artic fox keeps Claude Jaupart and his team company for a day. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621996042127-JWHTJ0M3WP38FMMOPMJZ/Bullard+Probe.JPG Claude Jaupart - Make it stand out Deploying a Bullard probe for measuring heat flow in sediments on the sea floor. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621996225753-OGZODPJA3TQOHKZQU1QL/History+of+Earth%27s+Temperature.JPG Claude Jaupart History of the Earth’s mantle temperature as determined from analysis of lava compositions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621996396945-8GSS37CEUKVJ5YH4FYXN/N+American+heat+flux.JPG Claude Jaupart - Make it stand out Map of the heat flux in North America. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621996572980-67AFF3CYK2BCV4EYSNPS/Borehole+T+depth+profiles.JPG Claude Jaupart Temperature profiles down two deep boreholes in Canada. https://www.geologybites.com/craig-jones daily 0.75 2021-06-04 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622645537454-ZN58FSPXXP2CV19V829Y/Craig+skiis+cropped.jpg Craig Jones Craig Jones is a Professor in the Department of Geological Sciences at Colorado University at Boulder. He studies elevated topography in continents, primarily in the western United States, using seismology, gravity measurements, paleoaltimetry, and petrology. He explains how the rocks forming the iconic landscapes of the American West were deposited, what happened to them over the subsequent hundreds of millions of years, and how present-day climate has laid them bare. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622559038361-IX84HNAO07W4VWFALYJ8/Map+of+Colorado+Plateau+on+map+of+whole+USA.JPG Craig Jones The Colorado Plateau spans the states of Colorado, New Mexico, Utah, and Arizona. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622559071859-2FV4IGEXAZ09E4J5FFWV/Map+of+Colorado+Plateau+with+immediate+environs.png Craig Jones https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622559675088-E9B5DQL9ZD4C9017EH09/Map+w+4+locations+annoated+enhanced.jpg Craig Jones - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622558887930-BESZF81W5Q7WPVPTHEJI/John-Ford-Scene-Stagecoach-Arizona-Monument-Valley+credit+Walter+Wanger+Productions.jpg Craig Jones A scene from the 1939 movie Stagecoach, the first major motion picture to be shot in Monument Valley. Courtesy of Walter Wanger Productions https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622600159473-3NCHGR43E85LCVV6NOVC/MonumentValley+2002+Pano.jpg Craig Jones - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622557748563-PCBCKIIH2PTUFRI3XCFY/Stratigraphy+Monument+Valley.png Craig Jones - The Monument Valley buttes result from the erosion of various layers of sedimentary rock having differing strength. The sheer cliffs comprise the De Chelly Sandstone, originally formed as sand dunes, with the Organ Rock Shale, consisting of tidal mudflats, forming the gentler slopes, the base, and much of the intervening flats. The underlying Cedar Mesa Sandstone, which forms the erosion-resistant plains between the buttes, was a marine shoreline sand deposit. Thus, the sequence of rocks here reflects the emergence of this landscape as material eroded from the Ancestral Rockies covered this region. Present-day erosion eats away at the shale, undermining the sandstone, which falls away in blocks. Craig Jones uses the analogy of dominos on a beach falling away when the underlying sand is disturbed. Courtesy of Wayne Ranney https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622563262005-SD4O3O4WCGF11XXFTF3Q/The_Three_Patriarchs_in_Zion_Canyon.jpg Craig Jones - Make it stand out Cliffs in Zion National Park of the Navajo Sandstone. The gentler slopes at the base are the Kayenta Formation, which consists of river and floodplain deposits. Note the lower Navajo is red and the higher part is white, which probably reflects changes to the rock long after it was deposited, most likely bleaching by organic fluids trapped for a time in these rocks. Courtesy of Daniel Mayer https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622601004616-1IGL9MODC576TW4TVQBF/Cross-bedding+at+Zion.jpg Craig Jones - Make it stand out In Zion National Park cliffs, horizontal lines are old erosion surfaces; inclined lines are crossbeds, formed by slight differences in the amount of silt in sands on the lee slopes of ancient sand dunes. These are truncated at the top when the dunes moved on but left a thick deposit of sand. Winds would have been from left to right here, as the crossbeds, which were the lee slopes of the dunes, are inclined to the right. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622564004395-CURV9NMOVJNEOM9SFASA/1920px-Inspiration_Point_Bryce_Canyon_November_2018_panorama.jpg Craig Jones - Make it stand out The colorful cliffs and hoodoos of the park are made up of the Claron Formation, which consists largely of lake deposits of silt, lime, and sand. Some layers are more resistant due to their chemistry, and they protect the rock below. Because these rocks are cut by vertical joints that permit erosion of the rock beneath, as erosion proceeds, pillars of protected rock are left behind. Courtesy of Tony Jin https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622677053241-VULCG21AA0XD4HXTQR9S/Grand+Canyon+-+vibrance-reduced.jpg Craig Jones - Make it stand out The Grand Canyon with the Colorado River. Courtesy of Lennart Sikkema https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622677244080-8BY8U2X0T1MHSFSGC1Z1/Stratigraphy_of_the_Grand_Canyon.png Craig Jones - Make it stand out The stratigraphy of the Grand Canyon. Courtesy of the National Park Service https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622645292206-2CELC3Z9N4O62ST5ZUST/Map+of+Alabama+Hills.JPG Craig Jones - Make it stand out The Alabama Hills lie on the eastern edge of the high Sierra Nevada and about 50 km west of Death Valley. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622644911760-FH0HWL0KPTO493WZJ4CL/Farallon+plate+-ancient-subduction-zone-diagram-10x.jpg Craig Jones The long-lived subduction of the Farallon plate created the Sierra Nevada, whose granites were intruded at a depth of 5-30 km below a chain of volcanos. The volcanic carapace has been eroded away, exposing the granite below. Courtesy of Robert J. Lillie and Wells Creek Publishers https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622599934563-5FYASU9DYAWDX2GPWPG4/CJ+at+Great+Western+Divide.jpg Craig Jones - Make it stand out The glacially sculpted landscape in the background is the Great Western Divide within the Sierra Nevada and Sequoia National Park. The image shows avalanche chutes that terminate along a line corresponding to the top of the glaciers that once flowed through the valley. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622600408067-BDCSA9UCW9CD8I3NTF5M/N+from+Mt+Whitney+processed.jpg Craig Jones - Make it stand out Sunrise view from the summit of Mt. Whitney reveals the jagged and diverse forms of erosion along the crest of the Sierra Nevada. This is a landscape shaped by ice, as evidenced by the glacial lakes, U-shaped valleys, and cirque headwalls visible here. Owens Valley (home to the Alabama Hills) is at the right, largely lost in haze. Nearly all the rock here is a form of granite emplaced about 82 million years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622600829435-LFTSXFCYF82HBE5FDOWB/Soda+Creek+to+Whitney.jpg Craig Jones - Make it stand out View of the Sierra crest from the Great Western Divide illustrating landforms of the glaciated Sierra. Mt. Whitney is at upper left, Mt. Langley at upper right. The U-shaped canyon at the bottom center is a classic glacial landform, and is truncated by the Big Arroyo cutting across the view, with the far wall of that canyon forming the edge of the Chagoopa Plateau, an older landscape now dissected by these glacial canyons. On the far side, the Sierra crest has glacial cirques, most evident near the center of the photo. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1622601312186-KF1JO1Y2I5O5J5CGCIF9/Alabama+Hills.jpg Craig Jones - Make it stand out The lumpy “Oldest Hills” of the Alabama Hills in the foreground lie below the petrologically similar rocks of Mt. Williamson in the upper left. The dry environment of the Alabama Hills leads to a form of physical weathering common to granitic rocks, where the mineral grains within the rock (quartz, feldspar, and mica) break apart at grain boundaries, leaving granitic sand, which is easily carried off by wind or water. In contrast, rocks high in the Sierra are dominantly broken apart by ice freeze-thaw weathering. https://www.geologybites.com/harriet-lau daily 0.75 2021-06-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1623008584700-8GOG84DV5OTYWXWANJHQ/looking+at+olivine.jpg Harriet Lau Harriet Lau is an Assistant Professor in the Department of Earth and Planetary Sciences at the University of California at Berkeley. She studies the motions of the Earth over intermediate timescales, from the diurnal ones induced by tidal forces to millennial accommodations to the arrival or disappearance of ice sheets. She views these intermediate timescale responses of the Earth as manifestations of the interior structure and composition of the deep Earth. Here she is looking at large olivine crystals in a sample of the San Carlos Olivine from Arizona. She describes experiments performed on samples such as this to measure deformation in conditions that mimic deep Earth conditions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1623251197252-913JTBW1GO01L9ZT5SHO/fig1.jpg Harriet Lau The timescale of the motions in the mantle determines the nature of the mantle’s behavior - from elastic at the second timescale at one end, to viscous at the million-year timescale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1623009274695-06GWGU0HPB9UJD3XI8J8/Hudson+Bay.JPG Harriet Lau The rate of change in sea level today due to the large Laurentide ice sheet that completely melted by ~ 7,000 years BP. Sea-level change is negative in places that are rebounding today. In other places, the land is sinking as a bulge caused by the weight of ice in a neighboring area relaxes. https://www.geologybites.com/steve-dhondt daily 0.75 2021-07-29 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627477189865-BN2ASOEQ8QKT2C86VYRX/edited+portraits-1.jpg Steve D'Hondt Steve D’Hondt is Professor of Oceanography at the University of Rhode Island. He studies life beneath the sea floor, and was a part of the team that discovered bacterial cells living in 100-million-year-old sediment. He explains how the bacteria managed to eke out a living for such a long time with barely any access to nutrients. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627050228349-AW4OY8VZP1P0FZ5Z8PA6/South+Pacific+Gyre.png Steve D'Hondt The sediments containing the 100-million-year-old bacteria were found in the abyssal clay on the sea floor in the South Pacific Gyre. In this region, the deposition rate is extremely slow, being of the order of centimeters over a million years. This means that the supply of nutrients to any life forms there would be extremely limited. Courtesy of Education Development Center, Inc. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627050631345-BKOUEIJ115JDCH1LQ29H/JOIDES+Resolution+By+IODP%2C+Attribution%2C+httpscommons.wikimedia.orgwindex.phpcurid%3D76114907.jpg Steve D'Hondt The JOIDES Resolution research vessel was used to drill into the abyssal clay at a depth of 6 km in the south Pacific Gyre to obtain the samples containing the ancient bacteria. Courtesy of IODP https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627074011903-RIV0ZEHL23F5S5IPLHIQ/PC050866.JPG Steve D'Hondt - Make it stand out Cores of the abyssal clay being prepared for geological sampling. The cores were sampled for microbiology (i.e., the bacteria) before they were split in order to minimize the chance of contamination. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627053691272-G0OWCSW5K1EKYGORMHAC/Fig.+1+A+SYBR.JPG Steve D'Hondt Photomicrograph of the cells from the ancient bacterial colony. The cells have been treated with a reagent that binds to DNA and fluoresces green under UV illumination. The scale bar represents 5 microns. Morono at al., Nature Communications 11, 3626 (2020) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627054048587-V2YRP6BBYQ52Z143PSK8/Fig.+1C+13C+and+15N+incorporation.JPG Steve D'Hondt In this sample, compounds labeled with stable carbon and nitrogen isotopes have been added to the bacterial incubations. The yellow, red, and blue in this image show that the cells have incorporated nitrogen from the ammonia, i.e., that they are actively metabolizing nutrients https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1627073163152-EW9CJ15MMG8IPNLAT66V/Fig+5-3.jpg Steve D'Hondt Graph showing the population of the ancient bacterial colony over time. The time is shown in days after the addition of nutrients. The number of cells increases from about 1,000 per cubic centimeter to about a million per cubic centimeter. https://www.geologybites.com/kathryn-goodenough daily 0.75 2023-07-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628431473716-RLXJLJW8FKTTZ9C477NF/edited-2.jpg Kathryn Goodenough Kathryn Goodenough is Principal Geologist at the British Geological Survey. She studies the geology of critical raw materials, and particularly of lithium. In the podcast she describes the three different lithium source types: granitic pegmatites, sedimentary rocks, and brines. She explains the geology of these source types, and the incomplete state of our knowledge as to just how lithium is concentrated in these sources. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628433997810-IJ08Q0I536T1BF0NKBZJ/Spodumene-usa59abg.jpg Kathryn Goodenough Lithium occurs within a number of minerals. Spodumene is a pyroxene mineral consisting of lithium aluminum inosilicate. Much of the world’s lithium is extracted from this mineral. Courtesy of Rob Lavinsky, iRocks.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628434548928-6PXQ6D8PO8ABD5T2M57E/petalite-1.jpg Kathryn Goodenough Petalite, another common mineral containing lithium, is a lithium aluminum phyllosilicate mineral. Courtesy of Jorge Moreira Alves https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628434691422-E9F0COEB6GMTT7O3RW7C/lithium+ine+in+Zimbabwe.jpg Kathryn Goodenough Bikita lithium pegmatite mine in Zimbabwe. Courtesy of LiFT https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628435574911-KIGJVPW3MCSEX3YQ1L5O/Li+evaporation+ponds+at+San+Pedro+de+Atacama.jpg Kathryn Goodenough - Make it stand out Lithium brine evaporation ponds in the Atacama desert, Chile. Courtesy of Bloomberg.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1628435833557-MVCCWX5FHDQ65RLJW9FT/serbia_jadar_resources.jpg Kathryn Goodenough Large deposits of lithium in sedimentary rocks have been found at Jadar in Serbia. The rocks contain jadarite, which is a sodium lithium boron silicate hydroxide. Courtesy of pixabay.com https://www.geologybites.com/mathilde-cannat daily 0.75 2021-08-19 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629125919468-VIXPBJDKF08FDGXGG4AX/photoMathilde_Mahato_recadree.jpeg Mathilde Cannat Mathilde Cannat is a research director at the Institut de Physique du Globe of Paris. Her research on mid-ocean ridges has fundamentally changed our understanding of the geological processes that create new oceanic crust at these ridges. She describes how both volcanism and faulting play a role, their relative importance depending on the spreading speed and supply of melt from the underlying mantle. Especially in slow-spreading ridges, the ridge axis behaves like a factory, underplating a 10-15-km-thick plate with new lithosphere, while faulting acts like a conveyor belt, transporting away the newly formed plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629126841755-EYYKRX7XN0121ORT3NQP/20180814_121807.jpg Mathilde Cannat - Make it stand out One of the research vessels Mathilde Cannat used to map mid-ocean ridges, especially in the Atlantic. For several studies, the vessel was used to launch a submersible that carried Mathilde Cannat to the sea floor. Courtesy of @lfremer-CNRS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629134065255-X0P7A6ZBGVV6BO8TNDSB/Map_JdFR_EPR_MAR_SWIR.jpg Mathilde Cannat - Make it stand out Map showing the spreading ridges Mathilde Cannat refers to in the podcast. EPR: East Pacific Rise, a fast-spreading ridge. MAE: Mid-Atlantic Ridge, a slow-spreading ridge. SWIR: Southwest Indian Rise, an ultra-slow-spreading ridge. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629163279656-G8S5XOTAZJHN75JQLONW/Searle+Oman+Ophiolite.jpg Mathilde Cannat - Make it stand out The rock succession through the Oman ophiolite, a slice of oceanic crust and mantle from the Tethys Ocean (now disappeared) formed 95 million years ago above a subduction zone and subsequently emplaced onto the continental margin of Oman. The ophiolite section may be a useful proxy for oceanic crust formed at mid-ocean ridges. Courtesy of Mike Searle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629130215768-KJE2J1BDB1ONSNL3QB85/161227014954983_15_1080i+copie.jpg Mathilde Cannat - Make it stand out Photo taken from a submersible of mud-covered serpentinized peridotite along an extensional fault at the Southwest Indian Ridge. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629130389189-Y3PX3J4LRP1S9516P9S3/HTWN011-large-4K.jpg Mathilde Cannat - Make it stand out A “black smoker” hydrothermal vent at the Lucky Strike hydrothermal field in the Mid-Atlantic Ridge being studied with a temperature probe (right) and a microbial sampler (left). Courtesy of @lfremer-CNRS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629238333186-8DEHEO8YQ4RAPA1K1UXW/Thick+and+Thin.jpg Mathilde Cannat - Make it stand out Diagram showing a thin axial lithosphere at a fast-spreading, magma-dominated mid-ocean ridge (top), and a thick axial lithosphere at a slow-spreading, fault-dominated mid-ocean ridge (bottom). Courtesy of Mathilde Cannat https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629238583836-CU8PFEEECK92WSRU2D0N/IODP+Proposal.JPG Mathilde Cannat - Make it stand out Diagram of a slow-spreading mid-ocean ridge in which the extension is primarily accommodated by faulting. As the plate is transported up and away along the detachment fault footwall (left), new mantle material rises, cools, and solidifies at the base of the brittle lithosphere, thus maintaining the same thickness as long as the heat balance is unchanged and the line of constant temperature (isotherm) stays fixed. Courtesy of Mathilde Cannat https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629130908237-IILR66WA1UO1F4X35XDR/Faults.JPG Mathilde Cannat - Cross section across the Southwest Indian Ridge showing how faulting dominates in this ultra-slow-spreading ridge. The divergence of the African plate and the Indian Ocean plates at this spreading ridge is dominated by faulting, with new faults developing ever ~10 km, sometimes reversing polarity. Cannat et al., 2006, Modes of seafloor at melt-poor ultraslow-spreading ridges, Geology, 34, 605 Cross section across the Southwest Indian Ridge showing how faulting dominates in this ultra-slow-spreading ridge. Each line is a fault, with the numbers indicating the faulting sequence, from 1 (presently active) to 8 (initiated about 11 million years ago). The divergence of the African plate and the Indian Ocean plates at this spreading ridge is dominated by faulting, with new faults developing every ~10 km, sometimes reversing polarity. Note that the vertical scale is exaggerated. Cannat et al., 2006, Modes of seafloor at melt-poor ultra-slow-spreading ridges, Geology, 34, 605 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1629132580383-1WAT62YSGUXJ4LBQP8RV/Along-ridge+sketch.JPG Mathilde Cannat - Make it stand out Sketch of a spreading ridge showing along-axis variation from spreading that is magma-dominated (yellow/orange) to fault-dominated (green). Cannat et al., 2019, On spreading modes and magma supply at slow and ultra-slow mid-ocean ridges, Earth and Planetary Science Letters, 519, 223 https://www.geologybites.com/douwe-van-hinsbergen daily 0.75 2021-09-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632145934085-QYOQC9A6XD5XO9I2PRVR/Douwe+cropped+Borneo-1.jpg Douwe van Hinsbergen Douwe van Hinsbergen is Professor of Global Tectonics and Paleogeography at the University of Utrecht. He has reconstructed the plate movements over the past 250 million years of the regions that contain today’s mountain belts. He explains how these reconstructions appear to be consistent with seismic tomography of the mantle and the geochemical signatures of lavas at mid-ocean ridges, above subductions zones, and at hot spots only if the mantle is relatively static over geological time. This in turn suggests that plate motions are not driven by a vigorously convecting mantle. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146140251-0ZX2O4RTSDJPU3VV1OQG/geo-Subduction-EN-edited.jpg Douwe van Hinsbergen - Make it stand out Diagram of a subduction zone showing slab pull and ridge push, the main gravitational forces invoked to explain plate motions. Slab pull is caused by the negative buoyancy of the old, cold, dense oceanic lithosphere, which becomes denser still as it descends into the mantle when basalt transforms into eclogite. Ridge push arises from the gravitational pull of the lithosphere down the slope at ridges and down the gentler slope as the lithosphere cools and sinks before it subducts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146199113-KFIA1ZITMBWDB56UT34J/Globe_View_Greater_Adria_Europe_Fixed.jpg Douwe van Hinsbergen Plate reconstruction showing the presence of a former continent called Greater Adria in the Mediterranean region between Northern Africa and Southern Europe. Douwe van Hinsbergen used reconstructions such as this one to predict the location of past subduction zones. Van Hinsbergen et al. (2020), Gondwana Research 81, 79-220 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146252746-T4PI8HPGSMC50YPHVX8W/Press_Release_figuur_EN.png Douwe van Hinsbergen Enlarged detail of the Mediterranean region shown in the above reconstruction. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146320283-GVE8WZHPDG3WKFQJ3OS0/Grasberg+coutesy+of+Freeport-McMoRan.jpg Douwe van Hinsbergen The Grasberg gold, copper and silver mine in Papua New Guinea. These magmatic rocks display a geochemical signature associated with subduction zones, but there is no subduction occurring there. Douwe van Hinsbergen’s research suggests that the mantle below the mine was enriched by subduction of a slab (the Arafura slab) 30-25 million years ago, whose relics appear in seismic imagery of the mantle 500-650 km below the mine. As the Australian plate moved north over the Arafura slab, it “ploughed” through the mantle, with the leading edge causing melting of the mantle and forming the magmas that carry the signature of the past subduction. The magmas ascended to the surface and cooled to form the rocks of the Grasberg mine. Courtesy of Freeport McMoRan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146506845-SXVURQCKUP59EWT5LQQH/Fig+1+cropped-1.jpg Douwe van Hinsbergen - Make it stand out These diagrams present the evidence for the suggestion that the geochemical signature of the rocks in the Grasberg gold mine of Papua New Guinea results from a subduction zone in the region 30-25 million years ago. The chemical imprint of that subduction on the mantle remained stationary to the present day, when the northward movement of Australia triggered mantle melting that brought material sourced from the mantle to the surface, thus providing a window into the composition of the mantle below. A: absolute motion of the Australian plate. B: plan-view seismic tomogram at a depth of 586 km. Blue areas are regions of higher seismic velocities and are interpreted as lithosphere of the Australian continent and of the Arafura and Halmahera slabs. C: location of the seismic tomogram cross section of D. Gr/Er refer to the Grasberg and Erstberg magma bodies. D: Seismic tomogram of a vertical section parallel to the direction of the absolute motion of the Australian plate over the past ~25 million years. White dots represent earthquake locations. E: Interpretation of the seismic tomogram of D, indicating the locations of the Arafura and Halmahera slabs and Australian continental lithosphere. Van Hinsbergen et al., (2020), Geophysical Research Letters, 47, e2020GL087484 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632146600942-I5W87QK64TB53STKJFMM/Figure+2+New+Guinea.jpg Douwe van Hinsbergen - Make it stand out The diagrams present a model of how the rocks bearing the imprint of a subduction zone might have formed in New Guinea. A. An edge of the Australian lithosphere was formed when a slab broke off 50 million years ago. B. Australia moves north, pulled by an intra-oceanic subduction zone to the north that creates a subduction zone signature in the mantle. C. Over the period from 25 to 8 million years ago, the northern continental edge of Australia reaches the mantle region enriched by the subduction zone to the north. D. The continued ploughing of Australia through the enriched mantle causes melting, and magmas rise through the faults associated with a plate boundary. Van Hinsbergen et al., (2020), Geophysical Research Letters, 47, e2020GL087484 https://www.geologybites.com/ulf-linnemann daily 0.75 2021-10-16 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632869944400-N6R73FF4IKZ95HRP6Y22/Ulf-Linnemann.jpg Ulf Linnemann Ulf Linnemann is Leader of the Geochronology Lab at the Senckenberg Collections of Natural History in Dresden. He has developed the systematic dating of detrital zircon populations into a powerful tool for reconstructing tectonic plate movements through geological time, and the paleogeography that led to the transport of zircons from one plate to another. He explains how he identified distinct detrital zircon provinces in Europe and used these to work out how the plates of modern-day central Europe came together. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632870932300-5LODGIQ8Y78NQVSQMNQP/Linnemann_Dublin_OS+selection-edited_Page_01.jpg Ulf Linnemann Zircons crystallize out of a cooling magma. The illustration shows one such setting — in a magma chamber under a volcano. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633189855976-5SLV9KX2TQC1ROOTWLY3/Linnemann_Dublin_OS+selection-edited_Page_03.jpg Ulf Linnemann - Make it stand out The various steps required to extract zircon crystals from rocks before they can be dated. These steps are very labor-intensive. At the end of the podcast, Ulf Linnemann says how much it would enhance his research if these preparatory steps could be made faster and more efficient. The zircon crystals suitable for detrital zircon analysis are between 65 and 125 microns across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633189561916-ZZS84C1J2H0JA292F79J/Linnemann_Dublin_OS+selection-edited_Page_04.jpg Ulf Linnemann Zircon crystals can be imaged by using a method called cathodoluminescence. A beam of electrons in a scanning electron microscope is directed onto a crystal, causing the crystal to luminesce. The luminescence is sensitive to small variations in the internal structure of a zircon, and so it can reveal the various zones within a zircon. These may reveal that a zircon formed in more than one phase of crystallization. The images are used as a guide for the ion probe or laser instruments that can then be targeted to the different regions to obtain the ages of the various zircon zones. The average grain used in detrital zircon studies is about 100 microns across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632871790068-1W4RXRE39GWAZAU43J6D/Linnemann_Dublin_OS+selection-edited_Page_05.jpg Ulf Linnemann - Make it stand out The zircon provinces of Europe when it was a part of the Gondwana supercontinent, which in turn was part of Pangea. Each of these provinces is characterized by a distinctive age distribution of detrital zircon ages. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872083958-8IJU2BET9PZ7D5XEUY7Y/Linnemann_Dublin_OS+selection-edited_Page_06.jpg Ulf Linnemann - Make it stand out A quartzite sampled by Ulf Linnemann on the island of Bornholm in the Baltic Sea. The detrital zircons in this sedimentary rock of Neoproterozoic-Cambrian age are representative of the southern margin of the Baltica craton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872226962-I8OW0VP4AJO761VRLWWF/Linnemann_Dublin_OS+selection-edited_Page_07.jpg Ulf Linnemann - Make it stand out The detrital zircon population that characterizes the South Baltica zircon province. This population is found all along the so-called Tornquist Zone, which marks the southern boundary of Baltica and extends 2000 km from the Baltic Sea to the Black Sea. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872445349-BE93VKCP0U3Y751KLJZQ/Linnemann_Dublin_OS+selection-edited_Page_08.jpg Ulf Linnemann - Make it stand out Ulf Linnemann sampled these sandstones in the Brabant Massif in Germany as representative of Middle Cambrian rocks of Avalonia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872539779-47JOPDQ1R883I3MGTP66/Linnemann_Dublin_OS+selection-edited_Page_09.jpg Ulf Linnemann - Make it stand out The detrital age distribution that characterizes the Avalonian zircon province. As explained in the podcast, parts of this age distribution bear the signatures of other tectonic plates — mainly that of Baltica. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872745396-4D1GRVKDAIMATQSF2LYA/Linnemann_Dublin_OS+selection-edited_Page_10.jpg Ulf Linnemann - Make it stand out Ulf Linnemann sampled sandstones from the Cliff of Atar on the Reguibat Shield of Mauretania as representative of the Northwest African craton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632872955148-QM17SGJJ0FXB63BAORTH/Linnemann_Dublin_OS+selection-edited_Page_11.jpg Ulf Linnemann - Make it stand out Detrital zircon age distribution characteristic of the Northwest African zircon province. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873042190-EM9VZS33KY6QCKQG7X13/Linnemann_Dublin_OS+selection-edited_Page_12.jpg Ulf Linnemann - Make it stand out These Neoproterozoic rocks were sampled in the Saxo-Thuringian Zone of the Lausitz Block as representative of Cadomia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873183089-A4VXDVZKYOWYFEG9XY9E/Linnemann_Dublin_OS+selection-edited_Page_13.jpg Ulf Linnemann - Make it stand out Detrital zircon population characteristic of the Cadomian zircon province. The population of zircons from 2 billion years and older is derived from the Northwest African craton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873383816-UE4G0TOG7GL2KAVC548U/Linnemann_Dublin_OS+selection-edited_Page_14.jpg Ulf Linnemann - Make it stand out The detrital zircon age distributions (grey histograms) of all four blocks (Baltica, Avalonia, Cadomia, and West Africa) are shown side by side in a single diagram to make it easier to compare them to each other. The figure shows that the detrital zircon age distributions of the four zircon provinces are very different from each other. As Ulf Linnemann explains in the podcast, the ability to characterize a block by its detrital zircon population age distribution makes this a valuable tool for reconstructing the relationships between the plates and hence inferring their relative positions during the Paleozoic. In addition to the zircon populations, the diagram shows how a different set of measurements — that of hafnium isotopes in the rocks — can also serve to characterize the different tectonic blocks. The colored bands, lines, and arrows relate to the hafnium analysis. (MORB = mid-ocean ridge basalt; εHf = a measure of the difference between the hafnium isotope ratios in the rock and that of the Earth as a whole; CHUR = chrondritic uniform reservoir, which is assumed to be representative of the bulk Earth.) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873596450-WB22PD0LZY490EWUZJSD/Linnemann_Dublin_OS+selection-edited_Page_15.jpg Ulf Linnemann The various geological zones that make up present-day Germany include basement rocks from three tectonic blocks — the Baltica craton, and the Avalonian and Cadomian terranes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873826958-VVCIOC5X9OOZ1LAS1JZB/Linnemann_Dublin_OS+selection-edited_Page_18.jpg Ulf Linnemann - Make it stand out The present-day distribution of Avalonian and Cadomian basement rocks. Younger, Mesozoic rocks cover the white areas in between the exposed outcrops. The Avalonian terrane extends as far as the Appalachians on the other side of the Atlantic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632873936170-C33H1FMUQ66WO0943KZR/Linnemann_Dublin_OS+selection-edited_Page_19.jpg Ulf Linnemann - Make it stand out Classification of the detrital zircon record of Avalonia in the early Paleozoic as preserved in sandstones of the Brabant Massif in Germany. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632874055721-WXO9FJ2URWPNLK7FD1ZD/Linnemann_Dublin_OS+selection-edited_Page_20.jpg Ulf Linnemann This series of plate location reconstructions is based in part on the detrital zircon analysis described in the podcast. In a given time slice defined by the age of a sedimentary rock, the relative proportions of its detrital zircons characteristic of each of the zircon provinces indicate how close to the sedimentary rock the blocks corresponding to those zircon provinces were. Thus, 330 million years ago, the presence of detrital zircons from Baltica in each of the Avalonian, Cadomian, and even Northwest African blocks indicates that the plates had docked with each other by that time. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632874090372-P77ADD9NMJ1DZC2V1YIR/Linnemann_Dublin_OS+selection-edited_Page_21.jpg Ulf Linnemann https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632874117564-3YLPA9WVZJDP2M9UK2ME/Linnemann_Dublin_OS+selection-edited_Page_22.jpg Ulf Linnemann https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632874145652-SEEENEZYM8U8X5MNKF75/Linnemann_Dublin_OS+selection-edited_Page_23.jpg Ulf Linnemann https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1632874171614-QHBQS62TVS08C4DEF6MM/Linnemann_Dublin_OS+selection-edited_Page_24.jpg Ulf Linnemann https://www.geologybites.com/becky-flowers daily 0.75 2021-10-18 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633462301396-G25YSN60EZ7GHWSSSG8Q/Becky+Flowers+cropped-2.jpg Becky Flowers Becky Flowers is a Professor of Geological Sciences at the University of Colorado, Boulder. She uses the abundances of retained helium in minerals to determine the cooling history of the rocks containing these minerals. As she explains in the podcast, knowing the cooling history gives us a powerful tool for investigating erosion histories, enabling us to date when erosion surfaces were formed, even when the rocks overlying the erosion surface are absent from the geological record. Courtesy of Christine Siddoway https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633789418133-UHEZBUSR1FJN2FP0HRXD/Closure+temperature+concept+Metcalf+and+Flowers+2021+Fig+2.JPG Becky Flowers - Closure Temperature Helium is continuously produced by radioactive decay of uranium and thorium, but at high temperatures the crystal acts as an open system, enabling the helium to diffuse out. At lower temperatures, the helium is “stuck” in the lattice, and the daughter-to-parent ratio increases linearly with accumulation time. The temperature at which the crystal transitions from open to closed behavior is called the closure temperature. Metcalf and Flowers (2021), Encyclopedia of Geology, p. 69 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633448608129-AQUNI04L3Y0KSVYYFKYN/closure+temps+of+diff+He+thermochronometers+Ault+et+al+2019.JPG Becky Flowers Closure temperatures for a variety of minerals used in uranium-thorium-helium thermochronometry. Ault et al. (2019), Tectonics, 38, 3705 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633790121770-WYR3V43ZPNXMIKDYGI3V/Apatite+in+erosional+setting+Ehlers_Farley_Fig+1.jpg Becky Flowers - Make it stand out In an erosional setting, apatite crystals approach the surface as erosion removes overlying material. The cooling associated with this exhumation process is revealed by uranium-thorium-helium thermochronology. Ehlers & Farley (2003), Earth and Planetary Science Letters 206, 1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633790492490-G1QP733XQNQNKF86SVCL/apatite+crystals.jpg Becky Flowers Apatite crystals selected for uranium-thorium-helium dating. The crystals are 50-100 microns long. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633790861872-ZCJYSGKITKRWUAJSVHJM/heatnig+chamber+cropped.jpg Becky Flowers - Make it stand out One instrument in Becky Flowers’s thermochronology lab. The rock samples are heated in the black heating chamber at top right, reaching a temperature above the closure temperature for helium in the mineral of interest, such as apatite. The released helium is directed via the cylindrical valves to the left of the heating chamber into a compact mass spectrometer located behind the control panels. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633460712248-5HUNBXPJC8RVFBV4GRPX/Southern+Africa+-+Stanley+et+al+2015+1A.JPG Becky Flowers - Make it stand out Relief map of southern Africa showing the high plateau studied by Becky Flowers and her team by using the kimberlite pipes within and on the margins of the plateau. Stanley et al. (2015), G-cubed, 16, 3235 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634419743433-BMFG6YLJAEOLRW6P0D2C/Stanley+et+al+2015+Fig+2A-1.jpg Becky Flowers - Make it stand out This map shows the locations of the kimberlite pipes studied by Becky Flowers and her team. The two study regions discussed in the podcast are indicated by the dashed rectangles. “Previous Work” rectangle marks the region in which the results showed a pronounced phase of erosion coincident with substantial lithospheric alteration and thinning, suggesting lithospheric processes contributed to elevation gain here. “Study Area” rectangle marks the region with a more protracted history of erosion and more subdued lithospheric alteration, suggesting that in this region the elevated topography was caused in part by another process, such as flow in the convecting mantle below the lithosphere, giving rise to dynamic topography. Stanley et al. (2015), G-cubed, 16, 3235 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633461083203-HG14O16X7WRIPF1VOTBG/craton+stability+-+burial+and+erosion+McDannell+and+Flowers+2020+Fig+2.JPG Becky Flowers - Make it stand out Becky Flowers has measured the thermal history of rock samples from cratons that show multiple cycles of cooling and reheating. The diagrams show a geological history that could have caused such a history. (A) Early-middle Proterozoic: rapid cooling of the rock during a continental collision and the associated active mountain-building and metamorphism. (B) Middle Proterozoic: the rock sample was exhumed to near the surface. (C) Paleozoic: The sample is reheated by subsequent burial by sediments. (D) Present day: the overlying sediments are eroded away, causing cooling of the sample, and exposing the bedrock of the cratonic shield containing the rock sample. SL = sea level. McDannell and Flowers (2020), Elements, 16, 325 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633462339896-X91DMOC76ENKGHFXB59Q/BarraPeak_GrandCanyon_GreatUnconformity.jpg Becky Flowers Barra Peak, a PhD student in Becky Flowers’s group, with her left hand resting on the Great Unconformity in the Grand Canyon. The beds below the Great Unconformity are dipping, while those above are generally flat-lying. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633463091874-0Y0TVTCEFE8WITR5WM50/Peak+et+al.+2021+-+Fig.+1+section+great+unconformity-Grand+Canyon.JPG Becky Flowers - Make it stand out Stratigraphic column of the Grand Canyon Supergroup in the Upper Granite Gorge of the Grand Canyon. Unconformities are marked in red. The thermochronology studies of Becky Flowers and her team suggest that these unconformities are amalgamated into the single Great Unconformity in other locations. This indicates that the Great Unconformity developed in multiple phases corresponding to the amalgamation of Rodinia before 800 million years ago, the subsequent break-up of Rodinia, and Snowball Earth glaciations during the Cryogenian (717-645 million years ago). In the western part of the Grand Canyon, the entire Grand Canyon Supergroup is absent, highlighting the heterogeneity on the local scale. Peak et al. (2021), Geology, 49 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633644281052-5V2OACR2LFYDC36EITHX/Grand+Canyon+Great+Unconformity.JPG Becky Flowers Image from Karlstrom et al. (2012), GSA Special Paper, 489 Cross-section through the eastern Grand Canyon. Here, the three major sets of Grand Canyon rocks are: (1) upper horizontal layers of Paleozoic sedimentary strata (blue), (2) tilted sedimentary strata of the Grand Canyon Supergroup (green, yellow, orange, purple), and (3) metamorphic and igneous rocks of the Vishnu basement (grey). The red squiggly lines mark multiple unconformities that formed at different times during a several-hundred-million-year interval. In the time column at right, the time gaps across the unconformities are shown in black, with the estimated duration of each unconformity gap labeled in red within the figure. Although the Grand Canyon Supergroup is preserved in the eastern canyon, it is missing farther west. In the middle left of the cross-section where the Cambrian Tonto Group (blue) sits directly on the basement (grey), the Grand Canyon Supergroup is missing. Here, immediately adjacent to the preserved Grand Canyon Supergroup, Supergroup deposition and associated unconformity development (tilted red squiggly lines) probably occurred, but it is likely that the Supergroup sequence at this location eroded away to form a composite unconformity. Based on thermochronology work, Becky Flowers and her team infer that the Grand Canyon Supergroup was never deposited in the western Grand Canyon. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633463855533-5K5TT07VOI7IOKNK1X6H/Conodont+images_large_cjes-Zhang+et+al+2017+Canadian+jounral+of+Earth+Sciences%2C+54%2C+936.jpeg Becky Flowers Conodonts are extinct vertebrates that resemble modern-day eels. Fossils of their tooth-like mouth parts occur widely in the geological record in shales and limestones, which are rocks that lack minerals, such as zircon and crystalline apatite that are amendable to uranium-thorium-helium thermochronometry. In order to obtain thermal histories of such sedimentary rocks, Becky White attempted to apply the methods of thermochronometry to biologically produced apatite found within conodont fossils. The mobility of the parent uranium in conodont apatite makes this very challenging, but she has not given up on this. Zhang et al., (2017) Canadian Journal of Earth Sciences, 54, 936 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633465782307-9H7LA3FOGNANWNXCQWC6/Moon+craters%2C+NASA.jpg Becky Flowers Since rocks undergo extreme heating during a meteor impact, thermochronology can be used to date the history of the meteor bombardment of the Moon. Becky Flowers and her group have dated the impact history of samples brought back to Earth by the Apollo missions. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633791478949-PIHT1F8MHR9ASO4ZZ58U/slunar+sample+location.jpg Becky Flowers - Make it stand out Location from which the Apollo 14 sample was taken. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1633791535295-OP38CRNB602F3QHMZT97/lunar+sample.jpg Becky Flowers - Make it stand out The Apollo 14 sample that Becky Flowers analyzed with uranium-thorium-helium thermochronology. Her results revealed that the rock had been subject to extreme heating 3.95 billion years ago and 110 million years ago. Kelly et al. (2018), Earth & Planetary Science Letters, 482, 222 https://www.geologybites.com/peter-cawood daily 0.75 2021-10-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634855239156-ZKR8IXPYRLNA4AMN9UM7/Peter+Cawood+Argentina+cropped.jpg Peter Cawood Peter Cawood is a Professor in the School of Earth, Atmosphere, and Environment at Monash University. He studies the origin and growth of the Earth’s continents, especially the ancient cores of continents called cratons. These hold clues as to how and when plate tectonics started. In the podcast he explains how we can examine many aspects of the geological record to look for signs that plate tectonics was operating. Using inference from five main proxies of plate tectonics, he presents compelling evidence that plate tectonics goes back as far as the Archean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634321943824-GO3P2K84FJXY9NYP8SXE/Age+range+of+PT+start+estmiates.jpg Peter Cawood Estimates of the various researchers as to when plate tectonics started vary hugely from as early as over 4.2 billion years ago in the Hadean to as recently as about 850 million years in the Neoproterozoic. Korenaga (2013), Annual Reviews of Earth and Planetary Science 41, 117 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634320658219-R9O49AVYERGEOIXJRB9P/Earth+at+4.5+Ga.jpg Peter Cawood - Artist’s impression of the Earth 4.55 billion years ago After the cooling of an initial magma ocean, a layer of partially solidified crust is thought to have covered the Earth. Heat traveled through this layer, referred to as a stagnant lid, by localized magmatism. Eventually the lid became sufficiently hot to suffer a catastrophic overturn. This process then repeated itself until the Earth had cooled by several hundred degrees when it transitioned to plate tectonics. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634859984842-3KYYII5C3XAA3Q4RCVP9/stagnant%2Blid%2Btectonics.jpg Peter Cawood - Make it stand out Summary of the different modes of cooling of the Earth. (A) In the Hadean, there is localized melting of the lithosphere (dark and light green), which emplaces the granitoids and greenstones seen in ancient cratons. (B) In the Archean, the lithosphere may have formed coherent, rigid sections akin to the lithospheric plates of today, but they did not form a global network, and they did not subduct. (C) Plate tectonics on the modern Earth, in which the lithosphere includes thick continental plates and a thin oceanic lithosphere that subducts when it cools and sinks. Capitanio et al. (2019), Earth and Planetary Science Letters, 525 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634321331403-7JFG3DGYFOWSNP0KMS7X/possible+stages+of+evolution+of+a+silicate+planet.jpg Peter Cawood - Make it stand out Plate tectonics requires certain conditions of lithospheric strength and density to be possible. The arrows between “Plate Tectonics” and the intermediate stagnant lid stages referred to as “Drips & Plumes” and “Delamination and Upwellings” indicate that changes in the tectonic regime of a silicate planet between the two types of stagnant lid and plate tectonics are possible, but that transitions back and forth from “Heat Pipe” and “Terminal Stagnant Lid” are not expected. Stern (2016), Geoscience Frontiers 7, 573 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634906314588-9UM3YIHQQNMHEXFR5763/summary+of+modes.jpg Peter Cawood - Make it stand out Diagram of the three cooling modes: pre-plate tectonics, transition phase, and plate tectonics. (A) Pre-plate tectonics: Small wavelength convection in the mantle causes the lithosphere to form drips down into the asthenosphere, while blobs of melt rise and emplace granitic rocks — tonalites, trondhjemites and granodiorites (TTG). (B) Transition phase: Localized subduction causes fluid flux melting, which generates magmas with modern-day chemical composition, and portions of the lithosphere become thickened. (C) Plate tectonics: Subduction becomes sustained, the plates form a single global network, and thick, stable continental lithosphere is formed. Cawood et al. (2018), Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, v. 376 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634998878429-M1R11957S3B40L21OFLE/Current+plates.JPG Peter Cawood - Make it stand out Modern-day plate tectonics requires a globally linked system of plates. It is possible that some of the evidence of the very earliest subduction zones, such as those in Western Greenland and Arctic Canada, reflect localized plate-like behavior without a globally linked network. Cawood et al. (2018) Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, v. 376 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635000208927-XK2XX73116HAM9Y97LUF/IMG_20180527_101628.jpg Peter Cawood - Magmatic Activity Before Plate Tectonics As Peter Cawood mentions in the podcast, the felsic (i.e., silica-rich) rock record shows pulses of magmatic activity that emplaced the so-called tonalite-trondhjemite-granodiorite (TTG) rocks, which are types of granite, into the cratons before the magmatic patterns characteristic of plate tectonics emerged. The picture shows complex cross-cutting relationships in a TTG outcrop in the Kaapvaal Craton in southern Africa. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634322499350-SZGPDG0YTB3XHCR8MERT/Great+dyke+in+Zimbabwe.jpg Peter Cawood The occurrence of dykes along large-scale brittle fractures is strong evidence for rigid plates, which is one of the requirements for plate tectonics. One of the most striking of these dykes is the Zimbabwe dyke, which is 550 km long and 4-11 km wide and is clearly visible from space. It was emplaced 2.57 billion years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634856611506-QSZK27UUR5IPNKOFC36U/Dike+swarm+in+Yilgarn+craton-edited.jpg Peter Cawood The Yilgarn craton in southwest Australia contains swarms of dykes that fractured the craton 2.4 billion years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634322640606-E9D7322UY154TG6KGW0G/dykesi+n+first+supercontinents.png Peter Cawood Possible correlation of dyke swarms across cratons indicate brittle fracturing of rigid plates in the late Archean, which may be related to the breakup of the first supercontinents. Söderlund et al. (2010), Precambrian Research, v. 183, 388 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634323924187-FQS3A2BQFLFNOU5NLA45/sed+basin+in+Pilbara.jpg Peter Cawood The presence of large expanses of thick sedimentary successions in sedimentary basins is evidence for a rigid lithosphere since mechanical strength is needed to support such a weight of rock. The base of the Fortescue Group in Western Australia, which Peter Cawood mentions in the podcast, has been dated as being 2.7 billion years old. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634999330446-ZQYXWFL7BT6UYI5FELJF/Fig.+4+-+passive+margin+%26+foreland+basin+simplified.jpg Peter Cawood - Types of Sedimentary Basin (a) The edge of continent that is formed when it rifts is called a passive margin. The margin forms in a two-stage process. Initial stretching of the continent results in faulting and produces a rift basin. Eventually the extending continent is broken into two parts separated by oceanic crust forming at a mid-ocean ridge. As the continents drift apart, they cool and subside, forming a passive margin. Sediments accumulate during both phases of margin formation, forming thick sedimentary successions. (b) Where two continents collide, the loading of the over-riding plate on top of the down-going plate depresses the surface, forming a region known as a foreland basin. Sediments accumulate in these basins. The different types of sedimentary basin in the geological record are taken as evidence of lateral motion of rigid plates undergoing extension and rifting on the one hand, and collision on the other. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634857873828-CYNGBY144ASB7G37HQ04/metamorphic+record+-+low+t+high+p.jpg Peter Cawood - The Metamorphic Record The graph shows the incidence of the three different kinds of metamorphism discussed in the podcast: high-temperature/low-pressure characteristic of mantle plumes and volcanic back-arc settings (red dots), intermediate-pressure and temperature characteristic of converging plates (green dots), and low-temperature/high-pressure characteristic of subduction zones (blue dots). The latter kind only becomes common in the record in the Neoproterozoic (NP). Since low-temperature/high-pressure metamorphism is characteristic of the metamorphism experienced by cold slabs of oceanic crust subducting intact deep into the lithosphere before returning to the surface, some workers have taken this as evidence that plate tectonics only started as late as the Neoproterozoic. Brown et al. (2018), American Mineralogist, 103, 181 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634999552739-XC8FDIJFYU202IH2ES2N/Fig.+7+-+Archaean+plaaeomag.jpg Peter Cawood - Paleomagnetism Paleomagnetic studies have shown convincing evidence that the Superior, Kaapvaal, and Kola-Karelia cratons moved with respect to each other around 2,700 to 2,440 million years ago, and the Kaapvaal craton moved with respect to the Pilbara craton at about the same time. Cawood et al. (2018), Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, v. 376 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1634858576384-H9ITN2U54SOKF5UUEC61/Modelling+T%3D1550.jpg Peter Cawood - Mantle Temperature = 1,550 °C (right) Numerical models suggest that when the mantle is about 200 degrees hotter than it is today, lithosphere sinking into the mantle at a subduction zone heats up and breaks apart before it gets very far. Mantle Temperature = 1,350 °C (left) When the mantle cools to its present-day temperature, the subducting slab takes longer to heat up and is able to remain intact as it sinks down to the mantle transition zones at depths of 400 km and 600 km. Such subducting slabs become denser as they sink, and their increasing negative buoyancy causes “slab pull,” which is thought to be the major driver of plate motions. Moyen & van Hunen (2012), Geology, 40, 451 https://www.geologybites.com/paul-hoffman daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635515961316-FT9DJNHB3O8V3IX412JM/PH+w+Dan+Schrag+edited.jpg Paul Hoffman Paul Hoffman is Emeritus Professor of Geology at Harvard University. His research on the sedimentary rocks of Namibia revealed compelling evidence of glaciation at sea level in the tropics about 650 million years ago. In the podcast he explains what convinced him that the Earth was almost completely glaciated twice in its history. Here, Paul Hoffman (right) and Dan Schrag point to the contact between the end-snowball glacial deposits with dropstones and the 635-million-year-old dolomite that caps the glacial deposits in Namibia. Dan Schrag is a geochemical oceanographer who reconciled the cap carbonates with the Snowball Earth hypothesis. Courtesy of Gabrielle Walker https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635626189390-C00YYYXXLHPNZZ66IBXG/SnowballEarth680Ma%2528H%2529.jpg Paul Hoffman The Snowball Earth is a climate state in which the oceans are covered by a continuous ice shelf and continents are mostly buried by ice sheets. In the ablation zone, ice sublimates directly into the atmosphere. Dust or volcanic ash accumulate on the glacier as dark ice-dust (called cryoconite). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635626376888-YBM45XLOEKXGR8YB91H5/cryoconite+distribution.jpeg Paul Hoffman Sea glacier on a Snowball planet with a sublimation zone (in red) where dark ice-dust collects and a layer of compressed snow (meteoric ice) accumulates. Sublimation of meteoric ice and melting of marine ice at low latitudes are balanced by an accumulation and freeze-on outside the inner tropics. At the ELL (Equilibrium Line Latitude) the sublimation and deposition are equal. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635622210415-I3G379FB7UYOIB4MMW6M/IceAgeHistory8%2528H%2529.jpg Paul Hoffman Glacial epochs in Earth history from 3.5 billion years ago to the present day. The Sturtian and the Marinoan are the only two periods in which the ice sheets extended from pole to pole. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635517121294-YVIYJZY7GTHYHJ1NXL8B/balance+of+processes.gif Paul Hoffman The geochemical carbon cycle, showing major sources and sinks of carbon dioxide to the ocean and atmosphere. As carbon dioxide accumulates and the planet warms, the weathering of rocks containing silicate minerals increases, which increases the rate of removal of carbon dioxide from the atmosphere, which counteracts the warming. This negative feedback adjusts the amount of carbon dioxide in the atmosphere so as to balance the carbon dioxide sources and sinks, maintaining a steady state. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635531071317-KW869AN2TL7Z9FWO7NT5/another+process+diagram+Ch8-6b.gif Paul Hoffman The geochemical cycle on a Snowball Earth. Volcanic and metamorphic carbon dioxide sources continue unaffected, but removal of carbon dioxide from the atmosphere is limited by the absence of rainfall. In addition, silicate weathering is reduced by ice cover and cold ground temperatures. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635531653511-1VSADFQ8TWJ5D0ZJFTKR/temp+vs+time+Ch8-8.gif Paul Hoffman Hypothetical depiction of the Sturtian Snowball Earth scenario in terms of global mean surface temperature and ice cover (pale blue) on the Earth with the continents of 750 million years ago. The temperature plot shows that the onset (purple dot) and termination (blue dot) of glaciation near the equator were very abrupt. It also shows a hot aftermath caused by high carbon dioxide levels. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635721114363-DW1UBUTRG40SGNO3RFFG/CryogenGlacDist6%28H%29.jpg Paul Hoffman - Global Distribution The present global distribution of Cryogenian glacial formations corresponding to the Marinoan glaciation (651-635 million years ago) and the Sturtian glaciation (717-661 million years ago). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635967576543-8ZJEPJMJ8ZPHA54VMJS7/1.MoonlightValleyTillite.jpg Paul Hoffman - Distinctive Glacial Features Tillite deposited by the Marinoan glaciation with rounded and polished boulders dispersed in an unstratified silty claystone matrix. Glaciers erode by abrasion and quarrying, and deposit unsorted debris when they melt or sublime. As the glacier flows, boulders are rounded and polished by milling caused by shearing of the substrate below the glacier and the sediment carried by the ice. Hammer (circled) is 32 cm long. Moonight Valley Tillite (Marinoan), East Kimberley Region, Western Australia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635968202773-B0FBIHXGNYO6A18SPZTC/2.BiggenjargaGrooves%28H%29.jpg Paul Hoffman Grooves in a sandstone were produced by northwest-directed (arrow) glacial flow. This glacial pavement is overlain by a moraine composed of glacial till (upper right), onlapped and buried by shallow-marine clastics, implying a former tidewater ice margin or grounding line. Smalfjord Formation (Marinoan), Bigganjar’ga, Varangerfjord, Finnmark, NE Norway https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635968620285-U8S08OQKYDSAFD8JKGSN/4.GroundLineFacies.jpg Paul Hoffman The diagram shows how a distinctive wedge of sediment is deposited at a grounding line, which is where a grounded ice sheet becomes a floating ice shelf. Massive diamictite (a sedimentary rock with a wide range of particle sizes) is deposited on the landward side of the grounding line (brown), and a stratified diamictite is deposited on the seaward side of the grounding line (orange). The stratified diamictite combines material falling out of a plume of meltwater, ice-rafted debris, and deposits from density flows and bottom currents. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635969449025-I1SNFJUO8KOEKY4OWVXS/6.GhaubDropFlapWide.jpg Paul Hoffman An ice-rafted dropstone impacted the underlying stratified deposits (carbonate turbidites, debrites and plume fallout), which were punctured and deformed by the impact. Below the 2-cm coin (top right) is a doubly-folded sediment flap that was ejected by the impact site. Ice-rafting is a key criterion for glacial action in marine paleoenvironments. Ghaub Formation (Marinoan), Fransfontein Ridge, NW Namibia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635970062965-12C628CYPZ9ETE18ST56/8.GhaubDebrite.jpg Paul Hoffman A graded debrite (debris-flow deposit) in the proglacial sediments deposited within a Marinoan grounding-zone wedge in northern Namibia. Coarse debris flows can be triggered by excess debris pile-up at the ice grounding line and by oscillatory movement of the grounding-line ice-front itself. Ghaub Formation (Marinoan), Fransfontein Ridge, NW Namibia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635970831486-YH2B0E55DQDP6EDCEOAV/HoloceneCarbonates.jpg Paul Hoffman - Carbonate Platforms Distribution of recent marine carbonate reefs, platforms (e.g., Great Bahama Bank), and continental shelves. Most marine carbonate production occurs in shallow waters and latitudes less than ~35° because of carbonate saturation chemistry. Calcium carbonate is more soluble in colder and deeper water than in warm, shallow water. Certain organisms precipitate skeletal carbonate in colder, deeper water by controlling carbonate saturation in intracellular fluid, but skeletal carbonate is absent in Cryogenian deposits. On tropical coasts near major deltas (e.g., Amazon, Congo), carbonate production is inhibited or diluted by terrigenous sediment input. Modified after Rodgers (1957) in Le Blanc RJ et al. eds., Regional Aspects of Carbonate Deposition. Sp. Publ. 5, SEPM (Society for Sedimentary Research) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635722505005-Y0I7DJM926UEE34RE3HO/CUP_Fig.4.11_HostFacies%2B%25281%2529.jpg Paul Hoffman The strata underlying the glacial deposits represent ambient ocean conditions at or close to the time of glacial onset. The figure shows carbonates underlying glacial deposits in several locations (e.g., North and South Namibia), which provide evidence of glaciation at sea level in the tropics. In other locations, the glaciers formed at mid-latitudes where carbonate is uncommon, or were formed in the tropics but near deltas where carbonate production was swamped by detritus from land erosion (terrigenous), such as in the present-day Amazon or Congo River deltas. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635971257945-I98IZ1HT39I52MAXL7Q3/Nam-Mong%28H%29.jpg Paul Hoffman Generalized stratigraphy and rock types of carbonate-dominated platform successions of Neoproterozoic age in northern Namibia and western Mongolia. Glaciomarine formations and postglacial cap carbonates of Sturtian and Marinoan age are well developed and exposed in both areas. They indicate glaciation at sea level in the warmest zones and in the absence of mountains. If the warmest areas were glaciated, colder areas must have been frozen as well. This was the rationale for the Cryogenian Snowball Earth hypothesis (Kirschvink 1992). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635624354029-Z954330ODV0CVMZ1XGZ9/TwityaCapStoneknife%28H%29.jpg Paul Hoffman The Rapitan Group (716-663 million years old) is a glacial sequence sandwiched between carbonate units in the Mackenzie Mountains of northwest Canada. The rocks get younger from right to left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635624829802-X8MQIISLFVRMYW3U05BV/Spitzbergen+DitlovSection.jpg Paul Hoffman The Marinoan Wilsonbreen Formation (W) in Spitsbergen (Svalbard) is a 135-meter-thick glacial sequence bracketed by carbonate units (S and D). The much more recent Carboniferous-Permian limestone (CP) is visible in the far distance. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635723332658-AQ99MN7MPW7XZ9VGRQOU/Paleomagnetism%2BCh2-3.jpg Paul Hoffman - Paleomagnetic Evidence The right side of the figure shows how the inclination of the magnetic field frozen into a rock at the time it formed tells us its latitude at that time (paleolatitude). The left side of the figure shows histograms of the paleolatitudes of glacial deposits for various periods of geological history. It indicates that in the Neoproterozoic there was an anomalously high number of glacial deposits in equatorial regions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635533599081-W8HQV3R9LEARM9WETLXW/Melting+at+end+of+snowball.jpg Paul Hoffman - Glacial Meltdowns and the Cap Carbonates Contact between the younger (Marinoan) Cryogenian cap carbonate (CD) that overlies ice-rafted debris (IRD) and glacial debris flows (DF) in Namibia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635975139362-5P6J8L4YHCXQSIK3R4HK/3.CranswickCap.jpg Paul Hoffman Marinoan cap carbonate (dolostone) and underlying Stelfox glacial diamictite in the northwestern Mackenzie Mountains, Northwest Territories, Canada. The Stelfox diamictite is ~40 m thick and disconformably overlies a carbonate-dominated marine shelf sequence (Keele Fm). The cap dolostone is 12 m thick and is conformably overlain by deeper-water marls (Hayhook Fm) and organic-rich black shale (Sheepbed Fm) that yielded a radiometric age of 632 Ma. The pale color of Marinoan cap dolostones is globally distinctive, and those in the Mackenzie Mountains feature giant wave ripples indicating enhanced trade winds during snowball deglaciation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635975449605-0VB2YPOWA53KCE1NUBAT/4.CanyonCap.jpg Paul Hoffman 10-m-thick cap dolostone conformably overlies the Marinoan Storeelv diamictite-rich formation in Tillite Canyon on Kap Weber near the head of Keiser Franz Joseph Fjord, central East Greenland. The cap dolostone is conformably overlain by deeper-water multicolored argillite and marlstone (Canyon Fm) of the postglacial maximum flooding stage. The base of the cap dolostone defines the Cryogenian−Ediacaran boundary. Glacial deposits were first recognized and described at this location by Christian Poulsen during Lauge Koch’s first ship-based expedition to East Greenland in 1929. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635975650061-78CK43527CFE8JXX0Q1L/5.MaiebergWall.jpg Paul Hoffman Post-Marinoan cap-carbonate sequence on the Otavi/Swakop Group carbonate platform in NW Namibia. The anomalous thickness of cap-carbonate sequences in many areas was an early indication of glacial longevity before radiometric ages were available. Maieberg Formation (early Ediacaran), upper Hoanib River, NW Namibia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635975896666-OLWVW15OMEOW24DTCU5D/6.TapleyHillCap.jpg Paul Hoffman An unusually well-developed post-Sturtian cap dolostone sharply overlies the terminal siltstone of a Sturtian tillite. The siltstone contains ice-rafted dropstones (inset). In this area, the post-Sturtian cap dolostone is better developed than its post-Marinoan equivalent. Tapley Hill Formation (Cryogenian), Kingsmill Creek, Arkaroola Wilderness Sanctuary, northern Flinders Ranges, South Australia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635774265927-S2PDKPQR7VK4N06IG52S/ThreeEons3%28H%29.jpg Paul Hoffman - Phylogenetic Evidence The time scales of fossil records over three eons. Though most of the pre-snowball fossil cyanobacteria are found in marine formations, the mapping of habitats onto molecular phylogenies indicates that they originally evolved in freshwater habitats before Cryogenian time. pO2 = partial pressure of oxygen in the atmosphere. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635775061710-0L72R7YSZ8OMKVJP05Y9/SanchezBaracaldo_FreshwaterOrigins2%28H%29.jpg Paul Hoffman An example of habitat mapping onto a phylogenetic tree for living cyanobacteria and archaeplastida (red, green, and glaucophyte algae, and derived plants). Orange and blue dots on the branching points give the relative proportions of freshwater and marine correlates respectively. The dots are mostly orange (freshwater) before the Cryogenian snowballs. Sanchez-Baracaldo et al. (2017), PNAS 114, E7737 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635775584591-DJ2UENTX6NEVMYCG87XS/McMurdoRefugiaDiversity%28H%29.jpg Paul Hoffman Table summarizing polar-alpine habitat diversity for phototrophs (organisms that obtain their energy from sunlight) in terms of temperature, sunlight intensity, nutrient availability, and redox state. The salt-stratified (meromictic) lake habitat refers to deep waters (over 40 m) that have dim light but are warm (+24 C in Antarctica) and relatively relatively nutrient-rich. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635718598320-NPOME1YVG419AU01BHIX/Li14_720.635Ma_4%28H%29.jpg Paul Hoffman - Rifting Rodinia Reconstruction of the Rodinia supercontinent at 720 (bottom) and 635 (top) million years ago. The presence of a supercontinent at equatorial latitudes and its subsequent break-up may have brought higher precipitation to previously arid regions, increasing silicate weathering, and thus drawing down atmospheric carbon dioxide, which in turn would have cooled the Earth. Large Igneous Province The 720 Ma reconstruction also shows the large igneous province (Franklin LIP) that erupted at the equator at the start of the Sturtian glaciation. According to one theory, the magma erupted through sulphur-rich deposits, lofting sun-reflecting sulphur particles into the stratosphere, which increased the Earth’s albedo. According to another theory, the large area of freshly exposed lava at equatorial latitudes increased silicate weathering, drawing down atmospheric carbon dioxide. Either mechanism would cause cooling. Glaciation that is rapid enough to overcome the geochemical carbon negative feedback is easier to envisage if the Earth is already cool when the glaciation begins. https://www.geologybites.com/richard-fortey daily 0.75 2021-11-13 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7f741115-7212-42be-8e68-eab2777dde23/RAF+at+desk+edited.jpg Richard Fortey Richard Fortey is formerly head of arthropod paleontology at the Natural History Museum in London and is visiting professor of paleobiology at Oxford University. He has devoted much of his research career to the study of trilobites — their systematics, evolution, and modes of life — and has named numerous trilobite species. He outlines their extraordinary 300-million-year history and explains what made them such excellent markers of geological time. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1636063034884-2C0D4VART98HMAOJLMK8/Trilobite+timeline.JPG Richard Fortey - Trilobite Family Diversity Over the Paleozoic Although trilobites are the signature organism of the Paleozoic, first appearing in the Early Cambrian, their peak diversity was in the early Paleozoic. They began a general decline in the upper Paleozoic (despite bursts of adaptive radiations in the Ordovician, Silurian, and Devonian periods) that ended with their extinction at the end of the Permian. Courtesy of S.M. Gon III https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1636066412563-F76ULJTLVUH40Z4VE0AJ/Spiny+Phacopid.jpg Richard Fortey Spiny phacopoid. This is one of many species recently discovered in the Devonian strata of Morocco that have evolved spectacular spiny exoskeletons. These are presumed to have protected the trilobites from attack from the cephalopods that are found in the same strata, and probably from fish as well. Although the number of trilobite families had declined by the Devonian, some of the most bizarre trilobites appeared during that time period, including sightless forms that lived in deep-sea strata. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1636066778434-WTVG5WAO0WEDAWWTN1WZ/one+of+the+last+Permian+trilobites+from+Oman.jpg Richard Fortey One of the last Permian trilobites from Oman was fossilized when it had curled itself up into a ball. Scale is one cm. across. Note how the tips of the thoracic segments can slide past one another as the animal enrolled (a piece of the ‘cheek’ has broken off to show this) to produce a very tight state of enrollment. Many trilobites developed an additional “lock” to secure them in the enrolled position. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1d1bb23a-0f4a-4787-bebe-720bb2f5650d/Olenoides+edited.jpg Richard Fortey The Middle Cambrian trilobite Olenoides may have been an early predatory trilobite. It is one of a few trilobites for which the limbs are known from examples preserved in the Burgess Shale of western Canada. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/79b22005-e320-4d10-b501-675449048dea/Harpetid+edited.jpg Richard Fortey An extraordinary harpetid trilobite from the Devonian of Morocco with a concave brim surrounding the head shield. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7ecaae07-c8c6-4df8-b75a-15e614d9242b/Trident+trilobite+-+Walliserops+trifurcatus.jpg Richard Fortey A trident-bearing trilobite from the middle Devonian in the Atlas Mountains of Morocco. Courtesy of the Colorado School of Mines Geology Museum and Ron Wolf https://www.geologybites.com/ed-marshall daily 0.75 2022-01-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f93840d-08e7-465c-ad63-f9c09ce84bf2/EM+with+gas+mask.jpg Ed Marshall Ed Marshall is a postdoctoral research fellow at the University of Iceland in mantle geochemistry and igneous petrology. The Fagradalsfjall eruption in the southwest of Iceland provided him with a once-in-a-lifetime opportunity to study lava sources almost directly from the asthenospheric mantle. He describes how he collected lava samples frequently enough to measure the geochemical evolution of the eruption with fine temporal resolution. Preliminary results provide strong evidence for a lava source at the base of the crust where vigorous mixing of a heterogenous mantle is occurring. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/af7d1eee-5e6e-4dbe-a72d-8b06dd3a1daf/EM+with+pole.jpg Ed Marshall - Make it stand out Ed Marshall wearing protective gear for sampling lava flows. The gear consists of a leather apron, shin guards, sleeves, and gloves. He also wears a specially designed heat-resistant face plate and helmet. He is holding a steel pole with a small scoop welded to the end. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e1d0c114-2bd0-4855-bdab-c24920a00700/2021-04-12+15.37.53.jpg Ed Marshall The lava is scooped up and immediately dunked in a bucket of water to convert it into a glass. This inhibits crystallization, preserves any volatiles present in the melt, and ensures that the entire sample is representative of the melt as a whole. If crystals form, the composition of the melt and the crystals would diverge from the original composition of the magma. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/278f5bf5-a21a-49b5-8c78-291109d31401/Layers+of+the+Earth.JPG Ed Marshall The lithosphere is the rigid upper-most layer of the Earth. It is the lithosphere that is broken up into the large rigid plates whose motions are governed by plate tectonics. In most places, the lithosphere is composed of two compositionally distinct layers - the crust on top, and the lithospheric mantle below. Below the lithosphere lies mantle that is hot enough to flow, i.e., the convecting mantle, the upper-most part of which is the asthenosphere. At rifting plate boundaries and under hot spots, the lithosphere is thought to be thin, and in some cases to comprise only the crustal layer with little or no lithospheric mantle. In the podcast, Ed Marshall suggests that the erupted lava in Iceland comes from a source at the boundary between the asthenosphere and the 15-km-thick crust, there being little or no lithospheric mantle present under the volcano. Courtesy of the USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a5b7f77d-abdf-4dbb-a21e-9ab79760c4b1/Lavafield+evolution_20211115_with+samples.png Ed Marshall A map of the lava distribution over time. Each color represents the farthest extent of the lava at a given date. The first vent opened in the evening of March 19, 2021. Several new vents opened up on April 5, but by April 27 only a single vent was still active, and remained the only active vent until the end of the eruption. The stars indicate where Ed Marshall sampled the lava. Map by Gro Pedersen. Data from Landmælingar, Icelandic Institute of Natural History and University of Iceland Institute of Earth Sciences https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a6b84cb-5adc-4623-b72f-a1949c8b75ba/time+vs+La-Sm.png Ed Marshall A time plot of the ratio of the concentration of two trace elements contained within the lava — lanthanum (La) and samarium (Sm). The ratio changes most rapidly at the beginning of the eruption and then stabilizes. These changes are thought to reflect a mixing process in which a batch of melt with high La/Sm mixes with a batch with low La/Sm. The low and high La/Sm melts can be produced from the same mantle by extracting melts from different depths. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/89846967-efea-4c39-9f59-81536fbc5130/Schemaic+diagram-01.png Ed Marshall A figure depicting mixing within a crust-mantle magma reservoir in which both depleted and enriched melt are introduced to the reservoir and mixed. In another plausible scenario, a "pulse" of enriched melt was injected into the magma reservoir, which then mixed and homogenized during the course of eruption, causing the abundances of trace elements in the lava to stabilize. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2672796-ea03-416c-9fe1-7196f3c803da/2021-04-24+12.29.31+gabbro+xenolith+within+lava.jpg Ed Marshall Gabbro xenolith included within the lava. Minerals visible within the coarse-grained xenolith include plagioclase (light-colored flecks) and clinopyroxene (dark-colored). These xenoliths are derived from the gabbroic lower crust and the margin of the mantle magma reservoir. The image is about 5 cm across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/24f1c0de-f609-4435-9468-ded26cdba42d/2021-11-03+16.53.21.jpg Ed Marshall Picked olivine crystals from very gas-rich, foamy lavas. The olivines are 'wet' with a thin coating of volcanic glass over their surface. They are derived from deep within the magma system and contain melt inclusions having a wide range of compositions that illustrate the wide range of magma types present at the crust-mantle boundary. Each olivine is about 2mm in size. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c82512a-9f35-4fc4-b979-daac940f4298/photomicrograph-4.jpg Ed Marshall Olivine crystal with melt inclusions (circled). Such inclusions preserve pristine samples of the deep melts out of which the olivines formed. The field of view is 5 mm across. https://www.geologybites.com/rick-carlson daily 0.75 2021-12-01 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/76ff1530-cf2d-49a2-b5d2-48226ed8754f/RC+pic.jpg Rick Carlson Rick Carlson is Director of the Earth and Planets Lab at Carnegie Science in Washington, DC. He uses mass spectrometers to measure the ratios of various isotopes in meteorites and in the tiny pre-solar grains often contained within them. He explains how variations in these ratios point to different pre-solar-system origins for these bodies. The challenge then is to infer what was going on in the solar nebula as the sun and planets were forming to result in these unexpected observations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/55b3f2ac-0118-4d91-8a8a-2a1528fe1141/The+Eagle+Nebula.jpg Rick Carlson The solar nebula formed out of a giant cloud of dust and gas such as the Eagle Nebula, which lies at a distance of 7,000 light years and is about 70 light years across. It is illuminated by stars that are forming within it. Courtesy of NASA, ESA and the Hubble Heritage Team (STScI/AURA) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b08d9fe6-6e7e-44cd-a1f3-3221cc03b610/Evolution+of+molecular+cloud.jpg Rick Carlson The series of diagrams (not to scale) illustrate how the solar system was formed. A. A giant molecular cloud starts to collapse. B. The solar nebula is formed with the young Sun surrounded by a circumstellar disk. C, D. Planets start forming out of the circumstellar disk, sweeping up material in their “feeding zone” as they grow. E. The gas and the smaller bodies have been accreted into the planets and the asteroid belt. Courtesy of Plymouth State University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/283b6a26-d997-4a3e-a3d8-c6834310b3c0/Crab+Nebula.jpg Rick Carlson According to some theories, the formation of the solar system was triggered by the arrival of a shock wave from a nearby supernova, such as the Crab Nebula pictured here. The nebula corresponds to a bright supernova seen by Chinese astronomers in 1054. Courtesy of NASA, ESA and the Hubble Heritage Team (STScI/AURA) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec789c65-c085-4591-9fdb-bb50fdb2ef2d/Pre-solar+grain.jpg Rick Carlson Photomicrograph of a silicon carbide pre-solar grain. Courtesy of Zinner (2003), Treatise on Geochemistry https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/da04ff5b-3b1f-4c2b-8a9c-6ed8d49dd21e/Ba+isotope+graph.jpg Rick Carlson Barium isotope abundances of a pre-solar silicon carbide (SiC) grain compared to the solar barium isotope abundances. The scale on the left shows that for some of the barium isotopes (e.g., those with masses of 130 and 132 atomic units), the abundances in the pre-solar grain are 80% lower than in the sun. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dd4be92e-2718-49a5-ac09-23198f513a94/Residue+vs+leach.jpg Rick Carlson These plots illustrate what happens when isotopic anomalies get diluted by mixing with other materials. Both the plots show the abundances of barium for material from the primitive Murchison meteorite. The plot on the left shows the results for residue that does not dissolve in acid. It looks similar to the pattern for the pure pre-solar grain above, though with a much smaller range of variation. The right figure shows the same plot for what is dissolved, i.e., leached out by the acid. The leach includes a range of pre-solar grains, and its pattern is complementary to that of the silicon carbide grain shown above. If the residue and the dissolved material are added together, the result is an isotopic composition for barium similar to that of the sun. This implies that the Murchison meteorite sampled a mixture of different types of pre-solar grains that on average provide a barium isotopic composition similar to the average solar composition. Murchison Leach image from Qin et al. (2011), Geochimica et Cosmochimica Acta https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/edb4a91d-40f6-4901-8b1a-2b5959670bb9/Oxygen+isotopic+composition+of+presolar+grains.jpg Rick Carlson The plot shows the oxygen isotopic composition of a range of pre-solar grains. Each grain is shown as a blue dot. The shaded regions show the isotopic compositions resulting from nucleosynthesis in supernovae, novae, and stars in the later stages of their evolution (AGB stars). The total range of oxygen isotopic composition of all Earth materials would fit inside one of the dots, and would sit where the dotted lines cross. Courtesy of Larry Nittler https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9add34d2-7d98-43dc-a234-16bbc3709aed/ALMA+image.jpg Rick Carlson This image was produced by the Atacama Large Millimeter Array (ALMA), and shows a disk of dust 2,000 astronomical units across orbiting a young star called HL-Tau. The black rings are gaps in the red dust, and are probably regions of the protoplanetary disk where planets are forming and scooping up the dust. Courtesy of ALMA (ESO/NAOJ/NRAO) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4dd82bee-4cbb-4323-b5dc-b3c0df44a653/Vistas-Ae%CC%81reas-27-scaled.jpg Rick Carlson The ALMA radio telescope consists of an array of 66 antennas, each of which is a dish 12-meters or 7-meters across. The telescope operates at wavelengths of 0.32 to 3.6 mm and, depending on how the antennae are positioned, has a resolution between 0.004 and 0.2 arcseconds. Courtesy of Clem & Adri Bacri-Normier (wingsforscience.com/ESO) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87794d58-6f0a-4871-80f5-eb17b6cc850b/Allende.JPG Rick Carlson Chondritic meteorites provide us with samples of primitive solar system material. Their name comes from the small circular objects called chondrules that are the crystallization products of small melt droplets that were rapidly melted and cooled ”dust balls” in the early solar system. The white objects are called Calcium-Aluminum Inclusions (CAI) as they are composed of minerals rich in those elements that are some of the most refractory minerals – think of ceramics. CAIs are often regarded as the first objects to form from a cooling solar disk and yield the oldest ages of any material in the solar system at 4.568 billion years. The matrix in between the chondrules and CAIs consists predominately of hydrated magnesium silicates. Most of the presolar grains are found in the matrix, which is regarded as material that may never have reached high temperatures during accumulation of the meteorite parent body. A primitive meteorite such as this can be thought of as a sediment that is simply a collection of the various types of solid objects in the circumstellar disk at the time that planet formation began. The image shows a piece of the Allende meteorite, which is the largest carbonaceous chondrite found on Earth. The chondrules are about 2mm in diameter. Courtesy of the National Museum of American History https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/23f84d65-9dee-4c63-9146-0c7312c3a4b8/Ru+and+Mo+plot.jpg Rick Carlson Plot of titanium isotope ratios versus chromium isotope ratios for the Earth and different types of meteorite. It shows that for these isotopes, Earth sits in between the carbonaceous chondrites and the non-carbonaceous chondrites (colored points). SNC = Martian meteorites. The epsilon prefix on the axis legends indicates parts per 10,000 difference between the measured ratios and the corresponding ratio in terrestrial materials. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/808e9600-397d-41f4-a2d0-0269019ee414/Ru+and+Mo+isotopic+compositions.jpg Rick Carlson - Make it stand out A plot of ruthenium and molybdenum isotope ratios as a function of distance from the Sun. The left plot indicates that terrestrial materials may be at the end of the range of solar system ruthenium isotopic composition, but in the podcast, Rick Carlson suggests that we may be missing a population that would lie beyond the Earth in such a plot. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f8c2d791-cf41-42cf-af29-f171b66c249c/Jupiter+cartoon.jpg Rick Carlson In some early solar system scenarios, Jupiter formed early enough to effectively isolate the inner non-carbonaceous chondrite meteorites (red, NC) that were concentrated in the inner solar system from the carbonaceous chrondrites (blue, CC) in the outer solar system. As discussed in the podcast, Jupiter may also have blocked newly arriving supernova shock-wave material from penetrating the inner solar system, thus enabling inhomogeneities to develop in the solar disk. Kruijer et al. (2017), PNAS, 114, 6712 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e18f73a5-a1aa-4324-8156-73caa598b7a9/mass+fractions+accreted+to+Earth.jpg Rick Carlson - Make it stand out The graphs illustrate how the isotopic composition of different elements can be used to determine which type of meteorites accumulated to Earth during various stages of its formation. Lithophile elements are those that concentrate in the silicate portion of the planet, so their isotopic composition averages all the material from which Earth was made because they were not sequestered in the core. Elements that are strongly siderophile, meaning that they concentrate in iron metal, would have been sequestered into the core as Earth grew. The more an element is concentrated in the core, the more likely its isotopic composition in the mantle reflects only the latter stages of accretion, whereas elements that are only somewhat siderophile will track longer periods of Earth accretion. Consequently, the isotopic composition of a highly siderophile element like Ru in the present Earth’s mantle will be controlled by the small amount (~0.5%) of Earth’s mass that accreted after core formation was complete. Elements with intermediate siderophile tendencies will average periods of Earth accretion that vary by how much of the element is sequestered into the core. Thus, the isotopic composition of a moderately siderophile element such as Mo will reflect the average of the last few percent of accreted material, whereas a weakly siderophile element such as Cr will average most of accretion with a slight bias towards the material accreted in the latter stages of Earth formation. Dauphas (2017), Nature 541, 521 https://www.geologybites.com/sue-smrekar daily 0.75 2021-12-06 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cbccd1ea-876f-4436-88b5-d2a5cf0c10a5/Sue_headshot1_orange_2020+small.jpg Sue Smrekar Sue Smrekar is Principal Investigator of the VERITAS mission to Venus. She has played leading roles in previous planetary exploration missions, including the Mars InSight Lander and the Mars Reconnaissance Orbiter. VERITAS is the first mapping mission to Venus since Magellan in the 1990s. In the podcast, she describes the instruments that will produce maps having orders of magnitude better resolution than previous maps. She explains how the Venusian surface features and interior properties VERITAS should discern will address the following first-order questions: (1) What processes shape rocky planet evolution; for example, are there mantle plumes or subduction zones; (2) What geological processes are currently active; for example, is there ongoing volcanism that is resurfacing the planet today; (3) Is there evidence of past and present interior water either in surface features or within the rocks. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a448164f-dfbf-4a05-9dd4-3843a911be23/Mission+Overview.JPG Sue Smrekar VERITAS Mission Overview. In addition to the mapping performed by the VEM and VISAR instruments, the Science Phase II will include a gravity experiment in which the orbit of the spacecraft is tracked to high precision. Perturbations in the orbit are used to measure the local gravity field, which in turn provides information about the interior structure of the planet. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8fcd760f-21c6-4fa9-9694-5f8ada0018ea/Space+probe+rendering.jpg Sue Smrekar Artist’s rendering of the VERITAS spacecraft and the kinds of topographic and surface rock type maps it will produce. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4219cdf0-df2e-41df-9918-edad1829e892/Payload.JPG Sue Smrekar - Make it stand out The VERITAS payload includes two instruments and a gravity experiment. VISAR will produce a digital elevation map having two orders of magnitude better resolution than the Magellan maps. By making repeated measurements of the surface, VISAR will also reveal whether the surface is currently deforming. VISAR is being built by JPL and the Italian Space Agency. VEM is a passive detector in the near infrared with wave bands selected to minimize the confounding effects of the dense Venusian atmosphere. VEM is contributed by the German Space Agency. The gravity experiment will determine the gravity field around Venus to an accuracy of 3 milligals with a resolution of 155 km. For comparison, the gravity at the Earth’s surface is 976 to 983 gals. The telecommunications system on which the gravity experiment relies is contributed by the Italian and French space agencies. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c38b11d8-2d2d-41a9-bd50-89dc8833bb50/VEM+bands.JPG Sue Smrekar The 14 wavebands of the VEM fall into four categories. The radiation of the surface bands originates from the surface and is selected to reveal rock type as well as the thermal signature of active volcanism. The radiation in the water vapor bands originates in a layer close to the surface and is sensitive to the abundance of water vapor. Volcanic outgassing could cause short-term variability in the water vapor. In the cloud bands, radiation originates at an atmospheric layer above the surface but below the clouds. Because the signal in the cloud bands has no surface or water vapor contributions, the measurements in these bands can be used to remove cloud-induced variability from the other bands. Finally, the background bands (not shown) are sensitive to spectral regions in which the atmosphere is opaque, thus allowing the background signal to be removed from the other bands. The scattering of the outgoing radiation by the high density of clouds places a 50-100 km limit on the resolution of the VEM maps. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a5f66311-81a4-4d94-965d-87991511a652/Distinguishing+rock+type+with+VEM.JPG Sue Smrekar - Make it stand out These graphs show the emissivity of basalt and of felsic rocks such as rhyolites and granites at the wavebands of the VEM. The shaded red and blue regions show the range of emissivity variation seen in lab samples, while the instrumental uncertainties are shown by the purple bands in the middle of the diagram. The figure shows that the VEM will easily be able to distinguish the rock types on the surface of Venus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/83e58a6b-5c1a-4d24-8fab-66dde516fe80/Magellan+radar+image+NASAJPL-Caltech.jpg Sue Smrekar - Make it stand out Radar map of the Venusian surface from the Magellan mission. The resolution is 25 km. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c23c9335-b107-4ff9-8a25-7a661ca3bf4e/San+Andreas+Fault.jpg Sue Smrekar - Make it stand out Simulated radar imager of Southern California and the San Andreas fault at the 250 m resolution of VERITAS (left) and the 25 km resolution of Magellan (right). The San Andreas fault would not be visible in Magellan imagery. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d054e994-719a-4d2d-b3bc-9ff14162f0a5/Havaii+at+VERITAS+resolution.jpg Sue Smrekar Topographic map of the island of Hawaii at the 25 m resolution expected from VERITAS. The island is about 115 km across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bcd426ab-1f11-454a-9335-3fdf892691c0/initiation_subduction_HD.JPG Sue Smrekar Artist’s impression of a subduction zone induced by a plume beneath the erupting volcano. The maps produced by VERITAS will have sufficient resolution to detect structures such as subduction zone trenches, faults, and fracture zones. https://www.geologybites.com/mackenzie-day daily 0.75 2021-12-11 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/598de224-7964-4891-9464-1dbd0a910df2/MDay_Headshot.jpg Mackenzie Day Mackenzie Day is an Assistant Professor in the Department of Earth, Planetary, and Space Sciences at the University of California, Los Angeles. She studies aeolian processes in the field and with wind tunnel experiments. In the podcast, she explains how dunes can reveal ancient wind speeds and directions, as well as how much sediment was available when the dune formed. She also describes the dunes we have seen on Mars, Titan, and even on a comet. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bdbb50ec-0053-4c63-a919-26524a62d3bb/Stacked+Aeolian+sets+-+Zion+National+Park-2.jpg Mackenzie Day Stacked sets of aeolian cross-strata in the Jurassic Navajo Sandstone in Zion National Park, Utah. The horizontal features are bounding surfaces between different individual dune deposits. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9aa03087-94a9-4e56-9b5f-6473feb139c3/Rainbow+over+Cedar+Mesa+-+Canyonlands+NP%2C+Utah-2.jpg Mackenzie Day Cedar Mesa formation in the Canyonlands National Park, Utah. This Permian aeolian sandstone is about 500 m thick. The colors were imparted to the sandstone after deposition, and indicate the concentration of iron in subsurface water. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/715a3d26-0508-40c8-a526-77534b6e2452/The+Wave%2C+AZ.jpg Mackenzie Day The Wave, in Arizona, consists of large-scale sets of cross-bedded aeolian sandstone. The bedding features were formed by a cycling between the flow of grains down the slope of a dune and rippling by the wind. This indicates there were periodic changes in the prevailing winds during the Jurassic as large sand dunes migrated across a sandy desert. The thin ridges and ribbing are caused by differential erosion resulting from the variation in the strength of the sand cementation as a function of grain size. Courtesy of Brian Passey/The Spectrum & Daily News https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8414f83b-9191-487c-9126-f364eccbdac7/Sunset+over+gypsum+dunes+-+White+Sands%2C+NM-2.jpg Mackenzie Day Gypsum dunes, White Sands, NM. Gypsum dunes are unusual since most sand dunes are made of quartz, feldspar, and iron oxides. Being very soft, gypsum does not survive transport well, and so such dunes can form only when the source of the gypsum sand is nearby. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cc3c3c1f-a4af-46c5-be90-ab82d61c0ae1/Grainflow+on+the+lee+face+of+a+modern+dune+-+Oregon-2.jpg Mackenzie Day Grain flow on the lee face of a modern dune in Oregon. Each lobe is a grain-flow avalanche. The cumulative effect of such avalanches is to migrate the dune in the down-wind direction. Wind ripples in foreground indicate the effect of turbulent eddies, which cause ripple branches to veer to the left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/85f684e1-a8d0-462e-8f2b-e778aea8dbaa/Wind+ripples+-+Algodones%2C+CA-2.jpg Mackenzie Day Wind ripples on the stoss (upwind) side of a dune in Algodones, Californa. The parallel ripple crests are perpendicular to the wind, with characteristic tuning-fork branching. Such active ripples are preserved in the rock record as pin-stripe laminae, which are the thin layers left behind by the migrating ripple. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/885ac348-e6e5-49fb-98cf-e9e0c6968fa4/Wind+Ripples+-+Arches+National+Park-2.jpg Mackenzie Day Wind ripples in the Jurassic Navajo sandstone at Arches National Park, Utah. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3564346f-b367-49bf-84d2-e5f7b50948d5/Grain+flow+filled+with+concretions+toeing+into+wind+ripples+in+Page+SS+-+Page%2C+AZ-2.jpg Mackenzie Day Jurassic Page sandstone, with intermediate-scale wedges in the upper part of the image formed by grain flows (avalanches) down the lee side of a dune. At the smaller scale, wind ripples appear in the lower part of the image. The passage of a dune leaves the largest-scale structures in the sandstone, as seen, for example, in the Zion National Park image which appears as the first illustration above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/27af631e-b895-4271-ac93-f4ce4d9bc6ce/Mars+dune-2-annot.jpg Mackenzie Day - Make it stand out Aeolian sandstone with large-scale crossbedding on Mars's Mount Sharp as seen by the Curiosity rover. The beds slope towards the left indicating that the prevailing wind was from the right. Courtesy of NASA/JPL-Caltech/MSSS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/14a956d3-c50d-4bfc-956f-cf8303195f29/Sand_Dunes_on_Mars.jpg Mackenzie Day Barchan dunes on the Martian surface taken in December 2013 by the Mars Reconnaissance Orbiter. Each dune is about 100 m across. They were formed by wind blowing from top to bottom. Courtesy of NASA-JPL-University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/663edad8-3dfb-463c-9b80-d3a4ead4d885/Edited+comet.JPG Mackenzie Day Ripples on the surface of comet 67P/Churyumov-Garasimenko as seen by the Rosetta spacecraft. In the upper image, the central bedform (yellow arrow) has a length of about 20 m and a height of about 2 m. In the lower image, the crest-to-crest distance ranges from about 7 m for the emergent ripples (orange arrows) to about 18 m for the larger bedforms (yellow arrows). The picture was taken on September 18, 2014, which was before perihelion. Superimposed in yellow are the positions of ripples from a photo taken 16 months later, which was after perihelion, revealing activity in the dunes. Jia et al. (2017), Proceedings of the National Academy of Science, 114, 2509 Image Courtesy of ESA/Rosetta/MPS https://www.geologybites.com/mike-searle-2 daily 0.75 2023-09-09 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/82fedcb4-1850-498b-95ee-68e7e76c9603/IMG_7707.JPEG Mike Searle 2 Mike Searle is Emeritus Professor of Earth Sciences at the University of Oxford and at the Camborne School of Mines in Cornwall. In his second Geology Bites appearance in this 50th episode, he describes what ophiolites are, and how they present us with a unique opportunity to see oceanic crust and upper mantle at close quarters. So close, in fact, that in this image, he has his finger on the Moho, the lithological boundary between the crust and mantle in the Semail ophiolite in Oman. He explains the evidence that enabled us to reconstruct the sequence of events that placed the Semail ophiolite on top of the Arabian continental margin. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fc3818cd-791a-4f00-999c-6c0ad78c27c3/Arabian+continent.JPG Mike Searle 2 Landsat satellite image of the Arabian plate. The large yellow swirls in the central and southern regions of the Arabian peninsula are sands in the Empty Quarter covering an area about the size of France. The Oman ophiolite comprises the dark-colored rocks exposed along mountains of northern Oman. DSF = Dead Sea Fault Image Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/62610408-db92-4ec6-9554-8901cb2f65c5/Ophiolite+map.JPG Mike Searle 2 Geological map of the Oman mountains showing the extent of the Semail ophiolite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a4b59b93-f095-49fd-9eb5-122342d5c5bb/Ophiolite+stratigraphy.JPG Mike Searle 2 - Semail ophiolite “stratigraphy” Idealized section through the Semail ophiolite showing all the elements of the mantle and crustal sections separated by the Moho Transition Zone. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0f8f937f-1189-472f-9ddc-6e06c4d5f53b/Back-arc+OU+diagram.JPG Mike Searle 2 Diagrammatic section through an arc system at a subduction zone, showing the relationships between the fore-arc, volcanic (island) arc, and back-arc basin with a back-arc spreading center. As the oceanic lithosphere subducts, dehydration reactions in the subducted basalts release water, causing partial melting of the mantle above, which in turn feeds the volcanism on the upper plate. As discussed in the podcast, the evidence suggests that ophiolites formed at a spreading center in a back-arc basin. The metamorphic sole discussed in the podcast corresponds to the top of the subducting oceanic lithosphere where the earthquake dots are shown. The metamorphism was caused by the exposure to the hot wedge of mantle material that lies immediately above it. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4e782975-3bd3-43bd-b203-706e07eafdd4/Supra-subduction+zone.JPG Mike Searle 2 - Make it stand out In the podcast, Mike Searle describes the evidence that supports this model for the formation of the ophiolite rocks. Radiometric dating of the ophiolite and of the metamorphic sole reveal that they were formed simultaneously. The metamorphic sole is the purple-shaded layer (amphibolite sole). The inverted metamorphism of the sole is explained by heating of the subducting oceanic lithosphere by the hot wedge-shaped mantle material lying above it. The trace element geochemistry matched the ophiolite with lavas formed in island arcs and back-arc spreading centers, as depicted here. In the case of the Semail ophiolite, though, the erupted lavas consist only of pillow lavas formed under water, since the erupted volume was not sufficient to reach the ocean surface and form the volcanos of an island arc. The subduction zone initiated in the middle of the Tethys ocean about 95 million years ago. After about 15 million years of subduction, i.e., at 80 million years ago, the Arabian continental margin arrived at the subduction zone trench from the southwest (i.e., the left side of the figure), and its leading edge was pulled down to a depth of about 100 km, causing the overriding oceanic plate to be obducted onto Arabia. This is the mechanism of ophiolite emplacement. After the subducted oceanic slab broke off, the subducted continental rocks, which are much less dense than the mantle, “floated” back up to the surface, where they appear today, for example as the coastal eclogites at As Sifah described in the podcast. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/10354fb2-4a7f-4a8f-a294-97d0400c1c35/Airial+view+with+annot.jpg Mike Searle 2 - Make it stand out Aerial view of the Oman ophiolite. The ophiolite has been thrust over the Mesozoic limestones of the Arabian plate margin seen in the distant mountains. The carbonate minerals of the limestones weather much more slowly than the olivine and pyroxene of the mantle harzburgite, which is why they are topographically much higher than the ophiolite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/accf5b3a-4ac6-4d28-b5f0-29146b78db76/peridotite+mantle+sequence+edited.jpg Mike Searle 2 Highly eroded mantle peridotite sequence of the Semail ophiolite. In the podcast, Mike Searle describes this “Lord of the Rings” landscape, and how he often scratched his knees while scrambling over these very crumbly rocks. They have survived being eroded away completely only by virtue of the extremely dry desert climate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/609b8a2d-2a6f-4493-922d-55d683b1f5d8/Ophiolite+hill.jpg Mike Searle 2 The mantle portion of the ophiolite is composed mainly of harzburgite, a variety of peridotite largely composed of the minerals olivine and clinopyroxene. In dry climates, olivine weathers to form a brown crumbly material. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/57ec9c49-4781-4c87-90d9-f60dc77e1401/Sequence+photos.JPG Mike Searle 2 - Make it stand out The sequence from the metamorphic sole (left) to the lowermost layer of the ophiolite (right). The metamorphic sole comprises rocks of the Triassic-Jurassic oceanic lithosphere that have been metamorphosed by the overlying mantle as they subducted at depths of 38-45 km. The metamorphism is inverted, with the highest-grade metamorphic rocks on top (garnet & clinopyroxene amphibolite) and the lowest-grade metamorphic rocks on the left (marble and quartzite). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd2bd7c9-06d8-4aa6-b398-7f6a0d013e4e/Mike+among+pillow+lavas.jpg Mike Searle 2 Mike Searle among the giant pillow lavas of the upper crust of the Semail ophiolite. As explained in the podcast, the lavas were formed above a subduction zone that was active 96-80 million years ago in the Tethys ocean. The pillows erupted underwater, causing them to cool rapidly and form the characteristic nested pillow shapes. The lava did not build up sufficiently to rise above the surface and form the volcanos that constitute the island arcs commonly produced above subduction zones. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5ac51420-a670-4ebe-9827-ca854fb09cb6/As+Sifah+beach.jpg Mike Searle 2 As Sifah eclogite beach, showing the dark-colored eclogites beneath pale-colored metamorphosed Permian limestones. The eclogites are ultra-high-pressure rocks exhumed from a depth of about 100 km after the subducting oceanic slab is thought to have broken off, releasing these lighter continental rocks to return to the surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1efe5d79-ac00-4de9-b0ab-7bd200b8954a/eclogite-2.jpg Mike Searle 2 The As Sifah eclogite beach at high tide. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a3a06088-a3b2-41e4-9ba6-13fcabeae302/eclogite-1.jpg Mike Searle 2 The eclogites contain giant garnets (dark spherical minerals), as well as blue glaucophane (a sodic amphibole), and green pyroxenes. The metamorphic petrology indicated that metamorphism peaked at a depth of about 100 km. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/63e75c62-b2cd-40c1-a94d-ac2bdb575904/As+Sifah+eclogite+rock.jpg Mike Searle 2 A sample of the eclogite studded with dark garnets. Photo by Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f68b4356-dd08-4631-b2c2-da442d1a31d4/Landsat+of+Oman+-+1.jpg Mike Searle 2 As mentioned in the podcast, Mike Searle has promulgated a proposal for a set of GeoParks to protect and highlight the extraordinary geology on display in Oman. Landsat image of Oman with box indicating the region covered in the map below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/86aa1e13-459d-4cc7-bc6c-a44661508454/northern+region.JPG Mike Searle 2 Landsat image of northern Oman showing locations of proposed GeoParks in northern Oman. The As Sifah eclogites are shown just south of Muscat as park number 4. https://www.geologybites.com/chuck-demets daily 0.75 2021-12-28 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d1ba7f73-4d9d-416b-b9e2-b6a5343f88fc/demets2021.jpg Chuck DeMets Chuck DeMets is Emeritus Professor of Geoscience at the University of Wisconsin, Madison. He studies the magnetic anomalies in sea-floor rocks to reconstruct plate motions at a temporal resolution five times better than has been done hitherto. This has revealed unexpected speed-ups and slow-downs in plate motions that provide juicy puzzles for geodynamicists. In the podcast, he focuses on the detailed motions of the Indian plate that show, among other things, that its northward movement actually sped up for a period after the collision with Eurasia before it settled down to a steady slower speed. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/beee9207-bc71-449d-b297-995f93c631d9/Lecture23_Slides+%28dragged%29+%281%29.jpg Chuck DeMets Magnetic stripes are created symmetrically on each side of a mid-ocean ridge spreading center as illustrated in (b). When the melt emerges from the ridge, the Earth’s field aligns the magnetite crystals it contains. When the rock solidifies, the aligned magnetite crystals are frozen in and thus preserve a record of the field, indicated by the black and white shading. Since the age of the magnetic field reversals of the Earth are known accurately from radiometric dating and the effect of periodicities in the Earth’s orbital motions (Milankovitch cycles), the age of each stripe edge can be determined. This is the principle used by Chuck DeMets to obtain his high-resolution reconstructions of plate motions. An example of measured sea-floor anomalies on either side of the Reykjanes ridge, which is part of the mid-Atlantic ridge just south of Iceland, is shown in (c). In order to determine exactly where the reversals are located in the noisy magnetometer measurements, the measured field is compared with an idealized profile of the known reversals to find the optimal alignment as shown in (a). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2bbe597-55a1-4029-ba13-3fa0a83692e3/Screen+Shot+2021-11-29+at+9.07.52+AM.jpg Chuck DeMets Magnetic anomaly measurements measured by Russian ships across the Carlsberg ridge. The observed profile extends northeast from the ridge, and the synthetic magnetic anomaly profile below the map shows the magnetic anomaly pattern resulting from an assumed 30 mm/yr full spreading rate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a4cdc62d-34bf-4501-b000-fc3a0cd530fd/MerkDeMets_2011.jpeg Chuck DeMets Chuck DeMets with his Russian collaborator, Sergey Merkouriev. The high-resolution reconstructions of the Indian plate motions relied on the detailed magnetic surveys performed by Sergey Merkouriev aboard a Russian navy ship during the 1990s. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4e555555-a018-4495-91a4-ac199f434678/2021.jpg Chuck DeMets The map shows the Indian plate with the three ridges discussed in the podcast: the Carlsberg Ridge, the Central Indian Ridge (Central IR), and the Southwest Indian Ridge, as well as the Sumatra trench where the Indian plate is subducting to the northeast. The map shows how movement of the Africa (Somalia) plate would cause an anticorrelated change in spreading rates at the Carlsberg Ridge, which lies on the northeast side of the plate, and at the Southwest Indian Ridge, which lies on the southeast side of the plate. The black dots indicate the locations of earthquakes with foci shallower than 60 km depth from 1963 to 2003. The shaded areas show diffuse plate boundaries where the deformation that accommodates the plate motion is distributed across many faults in a broad area, as opposed to by a single feature such as a mid-ocean ridge. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/daa5d418-2a74-4a51-802b-7c03e678afe9/Fig.+1+-+study+area.JPG Chuck DeMets The area covered by high-resolution plate motion studies performed using the magnetic survey data from the Russian navy. Plate boundaries are shown in red. AN, Antarctic Plate; AR, Arabia Plate; AU, Australian Plate; CIR, Central Indian Ridge; CP, Capricorn Plate; FZ, fracture zone; SM, Somalia Plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0c86ca96-dadc-4b8b-9802-3e990afb92e7/Fig.+2+-+survey+tracks.JPG Chuck DeMets Ship and airplane magnetic profile tracks used to perform the high-resolution plate motion analysis. The red, blue, and black lines, respectively, indicate tracks from Russian vessels, from a 1990 aeromagnetic survey, and all other sources. The bold lines indicate active plate boundaries. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1567f41b-649a-47e5-922d-9251886df260/Fig.+3+magnetic+anomalies.JPG Chuck DeMets The magnetic anomaly grid derived from dense Russian and other magnetic data for the region shown in the figures above. Reds and blues indicate areas of positive and negative magnetic anomalies, respectively. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4de60de4-a5d5-4ee5-be03-5544a76d428b/Fig.+13.JPG Chuck DeMets - Make it stand out Results of the high-resolution study of the Carlsberg Ridge showing the motions of India relative to Somalia over the past 60 million years. (a) The spreading rate showing the 100% speed-up at about 50 million years ago followed by a steep slow-down to about 45 million years ago, assumed to reflect the effect of the collision with Eurasia. The plot also shows the short-lived small speed-up at about 18 million years ago, after which the plate motion is a fairly constant 22 mm/yr. (b) Plate slip directions. CIR, Central Indian Ridge; IN, India; SM, Somalia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/29219a08-2a83-4554-a7c5-498b6ae22978/Fig.+19.JPG Chuck DeMets - Make it stand out Sea-floor spreading rates (a) and slip directions (b) between the Somalia-Antarctic (Sm-An), Somalia-India (Sm-In), and Somalia-Capricorn (Sm-Cp) plates since 52 million years ago. The plots reveal the anticorrelation between the Sm-An spreading rates (red) and the Sm-In spreading rates (black) that would be expected if the variations were caused by motion of the Somalia plate. The results are based on the high-resolution determinations of the spreading rates at the Carlsberg Ridge, the Southcentral Indian Ridge, and the Southwest Indian Ridge. https://www.geologybites.com/carmie-garzione daily 0.75 2022-01-01 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5fc8ce18-2d0b-4ff2-8a3b-5c3070c8683a/portrait+-+U+Az.jpg Carmie Garzione Carmie Garzione is Dean of the College of Science at the University of Arizona. The past elevation of various points on the Earth’s surface is one of the hardest environmental parameters to reconstruct. But Carmie Garzione has managed to pin down the history of elevation changes by analyzing stable isotopes of carbon and oxygen in carbonate rocks. In the podcast, she describes how the method works, and presents her findings for the Tibetan plateau and the Andes. They show pulses of very rapid (geologically speaking) uplift. She explains what this might be telling us about what has been going on in the lower crust and upper mantle in these regions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6fafda84-88f6-42e7-bc5a-50c3c9fa023c/O+isotoe+fractionation.jpg Carmie Garzione One method Carmie Garzione used to determine the elevation at which a sedimentary rock was formed relies on the fractionation of oxygen isotopes. Water vapor containing the heavier oxygen 18 isotope forms stronger H-O bonds and therefore preferentially precipitates out as water. As water vapor in clouds is blown progressively up a slope, it becomes more and more depleted in oxygen 18. When the water is captured in carbonates, either within lake deposits or in paleosols, the ratio of oxygen 18 to oxygen 16 can be used as a proxy for elevation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cd0f7637-24f9-4492-ae2e-2bed944bd2b9/O+isotope+vs+elevation.jpg Carmie Garzione Empirically determined relationship between elevation and the depletion of oxygen 18 in rain water. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2ce4a0b2-14a9-41dd-a06b-b622e49809fe/Western+Cordillera.jpg Carmie Garzione The Western Cordillera is an active volcanic arc that lies above the subducting Nazca plate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/28ebcc37-b1ea-4c24-825b-031054db7556/Altiplano+edited.jpg Carmie Garzione The Altiplano is a sedimentary basin. It was from this basin that many of Carmie Garzione’s carbonate samples were collected. The samples were analyzed using the stable isotope methods described in the podcast to determine the elevation history of the Altiplano. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4dd27199-a98b-4e47-add4-ca7b0860b698/Eastern+Cordillera.jpg Carmie Garzione The Eastern Cordillera lies to the east of the Altiplano and consists of a fold and thrust belt https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87599174-2b0b-4f51-ab64-0c6e6e1488b6/Questions+3.jpg Carmie Garzione This diagram illustrates the four geodynamic processes that may have played a role in building the Andean plateau. (1) Long-term lateral shortening and vertical thickening of the crust, which causes the surface to “float” higher, i.e., isostatic uplift. (2) Isostatic surface uplift by the addition of magma above the subducting Nazca plate. (3) Surface uplift by removal of dense lower lithosphere, i.e., foundering of lower crust into the mantle. (4) Redistribution of crustal material by mid to lower crustal flow. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0305f5c5-2825-4641-8a3c-e09ba883ccdd/Context+2.JPG Carmie Garzione The geological setting. The Central Andes overlie a zone where the Nazca plate subducts at a dip angle of 30°. The Altiplano is an internally drained sedimentary basin with low relief topography and an average elevation today of about 4 km. It is flanked by a chain of volcanos on its west called the Western Cordillera, and a fold and thrust belt on its east called the Eastern Cordillera. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58650e82-812b-4f65-aad6-4feba0931adf/Alitplano+region+studues+slide+16.jpg Carmie Garzione The central Altiplano is one of the regions studied by Carmie Garzione to determine its elevation history. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c27d41d5-dc16-4bb7-ab6a-90d25c05cf6f/Uplift+history+slide+16.jpg Carmie Garzione Elevation histories for the central Altiplano region shown above as determined using various methods for determining paleoelevation. The results suggest a period of rapid surface uplift between 10 and 6 million years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/787528ed-5b3a-4600-87ab-32c32d34b5ae/Region+studied+E+Cordillera+17.jpg Carmie Garzione The Eastern Cordillera region is another region that was part of the Andes paleoelevation study. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e251552-413a-4cd0-8a40-03f8a6b4c255/uplift+central+E+Cordillera+slide+17.jpg Carmie Garzione The paleoelevation history of the Eastern Cordillera shows a period of relatively rapid uplift between 24 and 17 million years ago. Blue = oxygen isotope data; yellow = clumped isotope data. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/af88f3fd-10d7-486e-b4fb-961196ebbee5/Along+strike+variations+-+3+studied+regions+18.jpg Carmie Garzione A comparison of the paleoelevation results for the three indicated regions of the Andean Altiplano are compared in the plot below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/706ec6b8-45f6-4afe-8c74-19e5d32fc3f8/Elevation+histories+compared+18.jpg Carmie Garzione The paleoelevation studies suggest that the period of large-magnitude surface uplift of the Altiplano propagates from south to north from middle to late Miocene time (15-5 million years ago). Blue = oxygen isotope fractionation data; pale blue and red = clumped isotope data. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/442c8c68-c554-497e-b924-126c92c7d54f/Removal+of+lower+lithosphere+9.jpg Carmie Garzione In the podcast, Carmie Garzione describes a possible mechanism that would explain a rapid pulse of surface uplift. As the lithosphere is laterally compressed and shortened as a result of the subduction of the Nazca plate, it thickens. The dense lower lithosphere then heats up to the point where it can detach from the lithosphere and sink into the mantle. The loss of this heavy anchor causes the remaining lithosphere to become more buoyant and rise. https://www.geologybites.com/index daily 0.75 2026-03-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/66ea5455-cabc-4698-9962-edb15c0dfc87/Dixon+early+cool+Earth+%28John+Valley%29.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6508b946-734a-4d80-917c-25b0cb352cf0/time+vs+La-Sm.png Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/79295dda-c461-4bb4-bf9a-87e3b0f29a1f/b-w+CL+image+of+zircon+in+concordia.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f3fb5d95-3eaa-4494-a544-6a04e51c4fa8/1920px-Inspiration_Point_Bryce_Canyon_November_2018_panorama.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/71b595b6-9182-4d94-820d-138bc9321e3b/Geophysics.JPG Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cb51f10b-f8c4-4ec6-a31f-8dcfd1a4437a/Blue+spinels+%28Lee+Groat%29.png Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/05b6e49b-7055-4e9e-83d1-d18e5bc3b805/Trident+trilobite+%28Richard+Fortey%29.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2efecace-159d-4651-aef9-83b8312367c1/Petrology+Thin_Section_of_Hillhouse_Gabbro_-_geograph_5888115.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/decd3dcc-3a1e-4f25-8d5d-13dedffda9d1/pia24542-perseverances-selfie-with-ingenuity-1041.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6ffb7343-33b0-4205-9ba9-df382b7c3543/Plate+Tectonics.JPG Subject Index https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0f264c74-37e9-45a5-a893-d9b6123dce4c/Li+evaporation+ponds+at+San+Pedro+de+Atacama.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5bf17583-7730-47bc-aef4-9265c957c1b3/Fountain+still.jpg Subject Index - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/matt-jackson daily 0.75 2022-01-18 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ef36214f-5111-4d20-b952-e658ed58665a/image.png Matt Jackson Matt Jackson is a Professor of Earth Science at the University of California, Santa Barbara. He probes the chemical composition of the mantle by analyzing trace elements and isotopes in hot-spot lavas from around the world. In the podcast, he describes the intriguing heterogeneity among the hot-spots of the so-called “hot-spot highway” in the western Pacific. The heterogeneity there, as well as on larger spatial scales, is challenging our ideas about the motions of the mantle over the billions of years of Earth history. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d3e0163f-f0aa-4b62-b41a-0b9e6c2b34f8/R+slash+V+Kilo-Moana.jpg Matt Jackson The R/V Kilo Moana is an oceanographic research vessel with equipment for geophysical, physical oceanographic, meteorological, and radioisotope research. This is the vessel Matt Jackson used for his expedition to the western Pacific in early 2022 to sample deep-sea lavas from hot-spots of the “hot-spot highway.” Courtesy of the University of Hawaii https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/446ecf2a-7f0d-4d4a-ba08-476e6dd074f0/Sigsbee+dredge.jpg Matt Jackson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3d96e82e-b86b-4d1e-a267-3cd52f69fea5/Modern+dredge.jpg Matt Jackson Courtesy of Science party, RR1310 expedition https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dc51fc33-7889-4cf4-938a-2bbe359fee15/Dredge_Full+Evelyn+Mervine.jpg Matt Jackson - Make it stand out Courtesy of Evelyn Mervine https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d61b9a10-4fd4-468f-aeab-7f420c406b32/hot-spot+location+map.JPG Matt Jackson Hot-spot location map. The dot colors indicate how far each hot-spot is from a large low-shear-velocity province (LLSVP). Red, orange, and yellow dots lie within the LLSVP zone, and blue dots lie the farthest away. The LLSVPs are shown as the yellow regions. Jackson, M.G et al. (2018), Geochem. Geophys. Geosyst. 19 doi:10.1029/2018GC007552 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1065e814-439b-41af-929f-b17f7324f3c7/Pacific+hot-spots.JPG Matt Jackson Hot-spots in the Pacific. The trail of extinct volcanos from the Samoan hot-spot and the Rurutu hot-spot (also known as the Arago hot-spot) can be traced for at least 100 million years before they subduct at the Mariana Trench. The Hawaiian trail is cut off at an age of 78 million years by subduction at the Kuril–Kamchatka Trench. Courtesy of Jasper Konter and Matt Jackson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1c1e7abd-a014-462e-9c38-f8de0a76b098/hot-spot+highway.JPG Matt Jackson - Make it stand out Enlargement of a portion of the figure above showing the overlapping hot-spot trails of the hot-spot highway in the western Pacific. Using radiometric dating and geochemical analysis, we can associate each seamount to its parent hot-spot, as indicated with the color-coded diagram of the seamounts along the bottom of the map. Jackson, M.G. et al. (2010), Geochem. Geophys. Geosyst. 11, doi:10.1029/2010GC003232. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d3ffc289-d816-4b97-8afe-7e4cb3a25fe3/Sonar+map+with+possible+dredge+sites+Zach+Eilon+-+hotspor+highway+volcano+located+in+W+regin+of+Amercian+Samoa+EEZ.jpg Matt Jackson High-resolution sonar map of a seamount in the hot-spot highway region near American Samoa. The resolution and reliability are orders of magnitude better than that of the satellite gravity-based sea-floor surveys, but only small regions can be mapped in this way since the exercise is very time-consuming. Such maps reveal zones of high sonar reflectivity that indicate a relative lack of sonar-absorbing sedimentary cover. This in turn suggests that the bedrock lava may be exposed, and therefore accessible to the dredge. Steeply sloping areas are also preferred, since coral and other surface material are more likely to have been sloughed off there. The contour lines show 100 m depth intervals, and background color represents the product of sonar reflectivity and slope: Warm colors indicate surfaces that are both steep and reflective, representing ideal dredging targets. Four dredge targets are shown as red lines. This seamount is about 17 miles across. For comparative purposes, the R/V Kilo Moana is smaller than the degree (°) symbols on the axes of the figure. Courtesy of Zach Eilon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1a2806bb-ffca-40da-b22b-3ae1a59af038/Cartoon+of+recylcing+from+Workman+et+al+2004.JPG Matt Jackson The diagram illustrates the standard model whereby material from subducting plates mixes with regions of the mantle and imparts characteristic trace element signatures on them. HIMU is a mantle reservoir containing a high uranium-to-lead ratio arising from recycling oceanic crust over billions of years. Other signatures (EM1, EM2) reflect recycling and long-term storage of materials derived from continental crust. The recycled material constitutes anywhere from less than a percent to 10 percent of the enriched mantle region. Workman et al. (2004), Geochem. Geophys. Geosyst., 5, Q04008 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/400a63f0-f14c-455f-926f-db9b48ef5e3c/signatures.JPG Matt Jackson - Make it stand out Plot of strontium isotope ratios vs. lead isotope ratios for oceanic hot-spot lavas from various localities. The partitioning into the different regions of the plot provides one type of geochemical signature that distinguishes the different mantle reservoirs. MORB = mid-ocean ridge basalt. HIMU = high uranium-to-lead ratio from ancient subducted oceanic crust. EM1 and EM2 are associated with ancient subducted continental crust. Willbold et al. (2006), Geochem. Geophys. Geosyst. (2006) 10.1029/2005GC001005 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cc21c10f-d48e-4a5d-a993-f06b66144162/Figure+1+Jackson+and+McDonald+2021.JPG Matt Jackson - Make it stand out Positions of the continents at present and at 500 million years ago. A. Pre-Mesozoic (i.e., older than about 250 million years) continental plates are shown in dark grey with present continental outlines in light grey for reference. The location of oceanic enriched mantle (EM) hot-spots are shown as red circles, and the continental and non-enriched mantle oceanic hot-spots are shown as blue squares. The pink shaded regions delineate the large low-shear-velocity provinces. B. Reconstruction of continents at 500 million years ago showing that the distribution of continents was primarily in the southern hemisphere during the formation of the Gondwana supercontinent. In the podcast, Matt Jackson suggests that the hot-spots in the southern hemisphere may have enriched mantle signatures resulting from mixing with subducted continental or continent-derived material associated with the assembly of Gondwana. Jackson et al. (2021), submitted to Nature https://doi.org/10.31223/X5NP7V https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92c71568-9b1c-4584-b96b-42a8cac8af22/xenolith-edited.jpg Matt Jackson Xenolith from the Samoan hot-spot. The xenolith is primarily composed of the minerals olivine (large bright green minerals) with lesser abundances of orthopyroxene (large dark green minerals) and minor amounts of clinopyroxene (small apple green grains that are difficult to make out in the image) and spinel (small dark grains). Matt Jackson found an unexpectedly large variation in trace element and isotopic composition between different clinopyroxene crystals within this 3 cm sample. This tells us that inhomogeneities in the mantle exist on very small scales. https://www.geologybites.com/bob-hazen daily 0.75 2025-04-16 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a501092b-ceaa-431d-a4c7-cf655f51d4d1/2019-Hazen-DCO.jpg Bob Hazen Bob Hazen is Senior Staff Scientist at the Earth and Planets Laboratory of the Carnegie Institution for Science and Professor of Earth Sciences at George Mason University. At a Christmas party in 2006, a well-known biophysicist asked him the question: “Were there clay minerals in the Archean?” Apparently, nobody had given this much thought prior to 2006. The topic quickly became the focus of his research, rapidly blossoming into a whole new branch of mineralogy. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c3ba98fe-49c7-4b9a-a787-961cb69abe8f/Dana.JPG Bob Hazen - Make it stand out In 1850, James Dwight Dana developed a classification of minerals based on chemistry and structure. Today’s mineral classification system as standardized by the International Mineralogical Association (IMA) is still based on mineral chemistry and structure. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d9bac028-0729-4835-98aa-8fde6c17d9e6/Graph.JPG Bob Hazen In 2008, Bob Hazen and his collaborators proposed that the Earth’s mineralogical diversity has increased through 10 stages. Hazen et al. (2008), American Mineralogist 93, 1693 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e3140caf-b565-495a-b138-0c3104accf58/Stage+zero.JPG Bob Hazen - Stage zero Pre-solar grains contain about 20 mineral phases. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/64e36bb5-d73c-437d-b6e5-754b0769475e/Stage+1.JPG Bob Hazen - Stage 1 This stage occurred in the stellar nebula prior to planetary accretion about 4.56 billion years ago, when presolar “dust bunnies” were melted into droplets called chondrules by the early Sun. These droplets accumulated in the earliest generations of meteorites, called chondrites. Unaltered chondritic material with approximately 60 different refractory (high melting point) minerals represents the starting point of the mineral evolution of all planets and moons in the Solar System. A cumulative total of about 90 minerals were now present. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9760ce48-b03f-4b7c-af51-ca060bbb008e/Stage+2.JPG Bob Hazen https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/15885b92-dc9c-4851-9cfb-0461442ae062/Stage+3.JPG Bob Hazen - Stage 3 By the time a dry planet had formed, about 300 minerals were present. This is the endpoint for the Moon and for Mercury. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5705d1ee-7dc3-45b8-9976-af93ad62e30b/2_Black_Earth50.jpg Bob Hazen - Stage 3 (continued) When water appeared on the Earth between 4.55 and 4.35 billion years ago, about 450 mineral species formed, including hydroxides and clays. Thus, the answer to the question put to Bob Hazen by Harold Morowitz in 2006 — “Were there clay minerals in the Archean?” — is “yes.” https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02c8f7e6-f8d0-4996-b5a5-d9309e668433/Stage+3+-+Mars.JPG Bob Hazen - Stage 3 (continued) Once the oceans dried up on Mars, new mineral formation may have stopped, leaving Mars with just 450 minerals. These include minerals formed by volcanic processes, outgassing, surface hydration, evaporation, and freezing. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/54d33f1d-8caf-4a34-bed3-4f752f488b73/Stage+4.JPG Bob Hazen - Stage 4 Granite formed through partial melting of basalt and/or sediments. New mineral species include pegmatites. At 3.5 billion years ago, more than 1,000 mineral species had formed. Top left: granite; bottom left: a simple pegmatite vein in quartz with large crystals of quartz and feldspar; center left: spodumene, a lithium mineral (courtesy of Rob Lavinski); center right: tourmaline, a boron mineral (courtesy of Rob Lavinski); and right: beryl (courtesy of Ron Lavinski). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d10e8ed7-582d-415d-b41d-a92ae17fec06/Stage+5+revised.JPG Bob Hazen - Stage 5 More than 3 billion years ago, plate tectonics started, creating new modes of volcanism. About 3,000 minerals were present at this stage. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/385bd1b0-501b-4e38-9834-23619dd2a904/Stage+5-2.JPG Bob Hazen - Stage 5 (continued) Massive base metal deposits are created as a result of near-surface mineralization processes accompanying plate tectonics. The most abundant base metals are copper, lead, nickel, tin, aluminum, and zinc. About 1,100 new mineral species were formed by these processes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d29a2791-16a5-4eb6-ac10-2399305757f8/Stage+5-3.JPG Bob Hazen - Stage 5 (continued) Regional and high-pressure metamorphic suites are formed at plate boundaries. Metamorphic rocks include blueschists, granulites, and ultra-high pressure phases. The inset at right is the classic diagram showing the loci in pressure-temperature space of the various mineral assemblages formed under similar pressures and temperatures, which are known as the metamorphic facies. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3723efbb-c4bf-4726-994c-67365b5e0155/Life+Roles.JPG Bob Hazen - Make it stand out Stage 6 Earth’s chemical and physical processes resulted in about 3,000 minerals species. The remaining ~2,700 co-evolved with life. The figure shows the five key roles played by minerals and life forms during the course of this co-evolution: catalyst, reactant, template, container, and scaffold. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4cc102b3-4001-49a5-a780-3cd7fed851e5/Stage+6-2.JPG Bob Hazen - Stage 6 (continued) An anoxic biosphere existed in the Archean from 4 to 2.5 billion years ago, producing carbonates (left) and banded iron formations (right). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/46f8887b-26d5-4263-8e01-11bb24c4d64b/Stage+7.JPG Bob Hazen - Stage 7 In the Paleoproterozoic (2.5-1.85 billion years ago), the oceans and atmosphere became oxygenated during the Great Oxygenation Event resulting from the rise of oxygenic photosynthesis. The number of mineral species rose to over 5,000 with about 2,000 new oxide, hydroxide, and carbonate minerals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87c4b835-53ed-4972-8b4f-e0385cc78655/Stage+8.jpg Bob Hazen - Stage 8 From 1.85 to 0.85 billion years ago, an “intermediate ocean” existed with an oxygen-rich surface region and deep-ocean anoxia with sulfate-reducing microbes. Few new mineral species formed at this stage. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9bfdb4cc-984f-430f-87d6-297b7e435fd2/Stage+9.jpg Bob Hazen - Stage 9 Between 850 and 542 million years ago there were at least two periods of almost complete glaciation (the Snowball Earth) and further oxidation. Few new species formed at this stage. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fbaf5dc3-f07e-4067-ba08-a1b33b73f9bc/Stage+10.JPG Bob Hazen - Make it stand out Stage 10 In the Phanerozoic Eon (542 million years ago to the present), new minerals were formed through biomineralization and the rise of the terrestrial biosphere, bringing the total number of mineral species up to its present-day value of about 5,700. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92aa7f77-e002-4665-a110-0dd2f4e98779/Network+intro.JPG Bob Hazen Mineral network graphs provide an interactive way to explore relationships among groups of minerals. Minerals are plotted in a multi-dimensional space that includes the traditional axes of chemical composition and crystal structure, but also newly added mineral characteristics such as minor and trace element content, isotope content, fluid and solid inclusions, size, shape, optical properties, and magnetic properties. The networks are projected into a 2D or 3D space that best reveals the clustering in the so-called natural kinds. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2e45434-6f94-4f11-ba24-4b7222edb361/network.JPG Bob Hazen - Make it stand out A graphical representation of the relationships between all known mineral species and their modes of formation on Earth and other bodies in the Solar system. In this network, each mineral is represented by a brown dot with a link that connects it to a node that represents its mode of formation (paragenetic mode). Minerals having only a single paragenetic mode have only a single link and appear at the outer edges of the network, while those with many paragenetic modes are densely linked and appear near the center. Although Bob Hazen and his team identified a total of 57 paragenetic modes, the modes fall into 11 paragenetic mode groups. It is these groups that are shown in this network, with the legend on the left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d2425e1a-7a7c-4a8e-8c70-1a06a4aed36c/Splitting+of+diamond.JPG Bob Hazen In the new mineral system, diamond, which is a single mineral species according to the IMA classification, is split into five natural kinds, principally based on the formation environment. In the case of diamond, the principal formation environments are stellar envelopes, the mantle, and meteor impact sites. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e5e6efd7-54bf-4649-9f29-03d68dd3cddc/Splitting+of+pyrite.JPG Bob Hazen Pyrite is a single IMA mineral species, but is split into as many as 21 natural kinds. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/43fbf35e-d7d7-4dce-a974-612f40834ec2/Tourmaline+lumping.JPG Bob Hazen Tourmaline has over 30 different IMA species. But the clustering of the mineral network suggests they can be lumped into a much smaller number of natural kinds. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c2e14ff6-be8a-439d-acc5-9b7496e328fe/Amphibole+lumping.JPG Bob Hazen The amphibole group has over 100 IMA species, but the mineral network graph suggests they can be lumped into just a handful of natural kinds. https://www.geologybites.com/david-bercovici daily 0.75 2022-02-05 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ce556ef4-c19d-48ef-9060-bcf95d744ea5/Bercovici-Portrait6+copy.jpeg David Bercovici David Bercovici is a Professor of Earth and Planetary Sciences at Yale University. He tackles the problem of why Earth has plate tectonics by applying physics at the scale of individual mineral grains. In the podcast, he explains how the behavior of rocks at the microscale can lead to the plate-scale subduction zones that are the main driver of plate tectonics. Courtesy of Tony Fiorini https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5db79e58-64a6-4762-aab6-5cd180c0e4b5/PNAS+2021+Bercovici+et+al+Fig.+1.jpg David Bercovici - Make it stand out This sketch shows a spreading ocean basin with a passive margin and the direction of ridge-push stress. The three model scales are shown: the macroscopic scale of the lithosphere and ocean basin, the mesoscopic scale of the petrological heterogeneity (showing two phases, green and blue, in an unmixed conglomerate of olivine and pyroxene), and the grain scale of individual mineral crystals. On the grain scale, the grain size evolves, and the mixing of the mineral phases is driven by compressive stress. This causes dilation of grain boundaries that are oriented parallel to the compressive direction and constriction on orthogonal grain boundaries, as indicated by the pink arrows in the right inset. This dilation and constriction occurs by subgrains of one phase migrating mechanically or chemically along the other phase’s grain boundaries (green arrows, right inset). Courtesy of Elvira Mulyukova from Bercovici and Mulyukova (2021), PNAS, 118 (4) e2011247118 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/608611dc-cf90-4441-bdfb-7f0d35f40fd7/PNAS+Fig.+3.JPG David Bercovici The diagram shows the increasing thickness of an ocean lithosphere as its distance from a mid-ocean spreading center (left axis) increases with its age. The gray contours symbolize the temperature zones from the hottest at the bottom (pale blue) in contact with the mantle below, and the coolest (black) at the sea floor. The thick green lines bound the region in which weak bands accumulate. Below this region, the material is more uniformly weakened; above this envelope, the material is cold and remains poorly mixed, coarse-grained and strong, but also likely subject to brittle failure. The insets show examples of the model’s solutions within each of the domains. Top: little mixing and high strength. Middle: vertical weak bands. Bottom: uniform weakness. Just like the fish, the snapshots of the microstructure are not to scale. Model parameters include the fraction of the minor phase, which is pyroxene in the lithosphere (Φ), the minor phase grain size (R), and the viscosity (µ). Bercovici and Mulyukova (2021), PNAS, 118 (4) e2011247118 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fdec9b96-5cc9-4143-8a68-f3689ea7e91c/Tasaka+et+al..JPG David Bercovici - Make it stand out Photomicrographs of undeformed (left) and deformed (center, right) samples of an olivine and orthopyroxene conglomerate. These experiments show that deformation, which increases from (b) to (c), drives the mixing of grains with concurrent grain-size reduction and weakening of the rock. γ = shear strain; PT-x is the name of the sample. Tasaka et al. (2017), Journal of Geophysical Research: Solid Earth 122, 7584 https://www.geologybites.com/phil-gibbard daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cf21c661-e6f5-4ba1-a813-0bff020a3343/2008_0624Feltwell0030+PLG+copy.jpg Phil Gibbard - Phil Gibbard is Emeritus Professor of Quaternary Palaeoenvironments at the University of Cambridge and Secretary General of the International Commission on Stratigraphy (ICS). He is a founding member of the Anthropocene Working Group tasked by the ICS to examine the status, hierarchical level, and definition of the Anthropocene as a potential new formal division of the Geological Time Scale. As he explains in the podcast, no consensus on the Anthropocene has been reached, and it remains controversial as to whether there is even a need for such an epoch at all. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3073f3d0-3a29-419f-8438-fde99b2b8d3f/ChronostratChart2022-02.png Phil Gibbard - Make it stand out The International Chronostratigraphic Chart, updated as of February 2022. The timescale is updated from time to time by the International Commission on Stratigraphy (ICS). This version differed from the previous version with the addition of a new stage in the Permian, the Artinskian, and the alteration of the numeric ages of the bases of the Fortunian (Cambrian) and the Aptian (Cretaceous) stages. As Phil Gibbard explains in the podcast, while the numeric ages may be updated, the paleontological or climatological definition of the base of each stage is changed very rarely. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8874f28e-80a3-4464-903a-f5aa17e46cbb/Quaternary+time+chart.PNG Phil Gibbard The Quaternary time scale as preferred by the ICS Anthropocene Working Group as of February 2022, with the Anthropocene shown at the rank of series/epoch. Black type indicates names officially approved and ratified by the ICS/Executive Committee of the International Union of Geological Sciences (IUGS EC). Names in grey type have yet to be officially sanctioned by ICS/IUGS EC. Golden spike = approved/ratified Global Boundary Stratotype Section and Point (GSSP); grey spike = GSSP awaiting submission or approval. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aaee3628-1307-4074-a30e-4105604a0197/Gibbard_et_al_Anthropocene+Fig.+1%2813%2B1%29.jpg Phil Gibbard - Make it stand out Geological timeline compared to historical timeline. Scholars have proposed a number of different starting dates for the Anthropocene that correspond to different social and environmental changes evident in the stratigraphic record. Rather than focusing on a single moment of transformation, Phil Gibbard suggests that the Anthropocene denote an event encompassing the whole of human-induced global environmental change. Gibbard, P.L. et al. (2021), Episodes, Journal of International Geoscience https://doi.org/10.18814/epiiugs/2021/021029; figure adapted from Ellis et al. (2016), Nature, 540, 192 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c6aad7d4-6ec1-4c59-b659-b7bd39a94b2e/Steffen+et+al+2011+first+12+indicators.PNG Phil Gibbard The increasing rates of change in human activity since the beginning of the Industrial Revolution. Significant increases in rates of change occur around the 1950s in each case and illustrate how the second half of the twentieth century has been a period of dramatic and unprecedented change in human history. Steffen et al. (2011), Phil. Trans. R. Soc. 369, 842 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fe58368b-5387-4254-a837-e4f84f09f13d/Anthropocene+Series+-+The+Great+Acceleration.png Phil Gibbard Global scale changes in the Earth system as a result of the dramatic increase in human activity. Steffen et al. (2011), Phil. Trans. R. Soc. 369, 842 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e2425a0-80eb-4775-b93d-9be0fb1b3eb8/Great+Acceleration+2.jpg Phil Gibbard Superposition of the 24 indicators plotted above on a single chart. “The Great Acceleration” has been an important motivator for those advocating the establishment of an official Anthropocene epoch in the geological time scale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d8ceff11-8057-4d4c-8d22-2bab7fe1980f/Mass+Extinction.jpg Phil Gibbard Cumulative vertebrate species extinctions as a percentage of total species. Changes such as these have been considered as indicators of the Anthropocene. Waters et al. (2016), Science 351, 137 https://www.geologybites.com/ana-ferreira daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eb349f85-093f-4158-9a7b-4413483a610d/Af+on+research+ship.jpg Ana Ferreira Ana Ferreira is Professor of Seismology at University College, London. She collects and analyzes seismic data from around the world, focusing particularly on the anisotropy of seismic wave speeds, i.e., the variations in the speeds of differently polarized seismic waves. As she explains in the podcast, we can use observed anisotropy to infer alignment of crystals in the mantle, which in turn can reveal flow patterns in the mantle. She has new results that show how mantle plumes and subducting slabs can have a major effect on each other. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eda05c1f-3135-4a21-8a22-00e970f7d2ee/GSN_Stations_-_2020.jpg Ana Ferreira The Global Seismographic Network (GSN) is a 152-station, globally distributed, state-of-the-art digital seismic network that provides free, real-time, open access data. The map shows the distribution of the stations that contribute to the network. All the sensors are land-based. So far, Ana Ferreira has obtained her seismic data from GSN, but is now collecting data from ocean-based sensors in the area around the Canary Islands and the Azores. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cab836d7-6c84-4ba9-8f4e-ab513222758e/garnero_splitting.gif Ana Ferreira The splitting of seismic shear waves in anisotropic media. In an isotropic medium, all waves travel at the same speed, but in an anisotropic medium, the wave speed depends on the plane of polarization of the wave. By measuring the dispersion of arrival times of differently polarized shear waves emanating from a given earthquake, it is possible to perform an inversion and infer the location of anisotropic regions in the mantle and their degree of anisotropy. Courtesy of Ed Garnero https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/109aad30-d519-4f5a-9870-eb3e964f64f4/Bathymetry.JPG Ana Ferreira Bathymetry map of the region in the western Pacific where the Tonga-Kermadec trenches and the Samoan plume are located. The foci of earthquakes are shown as very small colored circles, which are coded according to their depth. Orange and cyan lines represent ridges and trenches, respectively. Regions that have the geochemical signature of the Samoan plume lie within the regions delineated by the magenta and yellow lines. The northern half of New Zealand’s North Island appears in the southwest part of the map. Chang, S-J, Ferreira, A, & Faccenda, M (2016), Nature Communications 7:10 799 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aebc7926-2d00-4a0c-b661-f4a53dc0aef7/Tomographic+sections.JPG Ana Ferreira Seismic tomography of the southwestern region of the Pacific containing the Tonga-Kermadec trench and the Samoan plume. (a, c) Vertical cross sections along the SW-NE and NW-SE directions, respectively. The images show the wave speeds for vertical shear waves, with the large reddish (slow seismic wave speed) region, especially visible in (a), indicating the hot Samoan plume, and the blue (fast wave speed) regions indicating the cooler subducting Tonga slab. (b, d) Cross sections showing seismic anisotropy down to a depth of 1,400 km, which is the maximum depth at which the anisotropy is resolvable in the data. The sections show a distinct region of anisotropy (blue) behind the Tonga slab where the horizontal wave speed is ~2% greater than the vertical wave speed. This is interpreted as mantle flow induced by the subducting slab. (e, f) Seismic wave speed (e) and anisotropy (f) from geodynamic modelling of the subducting oceanic plate, the Hikurangi Plateau, and the Samoan plume, all of which are shown in the map above. The model appears to match the observations qualitatively, and suggests that the Samoa plume is a large upwelling originating from the core-mantle boundary. When this plume reaches the slab, it appears to flatten it, causing the subduction to stagnate. The pronounced signature in the seismic anisotropy seen in (b), (d), and (f) and the clear interaction between the Tonga slab (blue) and the Samoa plume (red/orange) seen in (c) may be revealing the interaction of the plume with the subducting plate. The transition between the upper and lower mantle at a depth of 660 km is indicated by the dashed line. Chang, S-J, Ferreira, A, & Faccenda, M (2016), Nature Communications 7:10 799 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b8446f04-89d3-4a25-975a-a1f9c2cf1476/Cartoon+time+history.JPG Ana Ferreira - Make it stand out Illustration of the temporal evolution of the interaction between the Samoan plume and the Tonga-Kermadec slab. (a) The Samoan plume is generated at a large ultra-low-velocity zone (ULVZ) at the core-mantle boundary (CMB) and ascends to the surface. (b) The Samoan plume collides with the Tonga slab at the mantle transition zone about 10 million years ago. (c) The upward stress caused by the collision between the slab and the plume causes the slab to stagnate as well as intense seismicity (cross marks), which is further enhanced by fast slab retreat (red arrow) due to the subduction of the Hikurangi plateau. (d) A schematic diagram showing the slab-plume interaction beneath the Tonga-Kermadec volcanic arc. Cyan lines on the surface show trenches, as shown in the bathymetry map above. The Samoan plume originates from a large ULVZ within the south Pacific large low-shear-velocity province (LLSVP) at the CMB. The buoyancy caused by upward stress from the plume below the Tonga slab may contribute to the slab stagnation within the mantle transition zone, while the Kermadec slab penetrates into the lower mantle. At the northern end of the Tonga slab, plume material migrates into the mantle wedge via toroidal flow around the slab edge induced by fast slab retreat. HP, Hikurangi Plateau; KT, Kermadec Trench; TT, Tonga Trench. Chang, S-J, Ferreira, A, & Faccenda, M (2016), Nature Communications 7:10 799 https://www.geologybites.com/susannah-porter daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8de3018d-c25d-412e-95a2-222e404b8a1d/Susannah+Photo+1+2021-+cropped.jpg Susannah Porter Susannah Porter is a Professor in the Department of Earth Sciences at the University of California, Santa Barbara. She studies microfossils of eukaryotic life forms that lived in the Neoproterozoic, about 750 million years ago. In the podcast, she describes her discovery of conclusive evidence that these creatures were predating on each other. Did this predation lead to diversification and evolutionary innovation at this time? Was it a microscopic foreshadowing of the enormous diversification seen about 200 million years later in the Cambrian? https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/418c8b3d-1c20-47c8-bb59-3c906bea899b/Tanner+Mbr+in+foreground%2C+Lava+Chuar+Cyn+%281%29.jpeg Susannah Porter - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6ee2f7e6-5252-4c3f-b779-cbebbac21adc/Tanner+Mbr%2C+Lava+Chuar+Cyn+%281%29.jpeg Susannah Porter - The Chuar Group Susannah Porter found the microfossils she discusses in the podcast in the 1,600-meter-thick Chuar Group, which consists mainly of shales and siltstones exposed over 15 square kilometers in the eastern Grand Canyon. The rocks were deposited in a shallow marine seaway near the equator about 750 million years ago in the early Neoproterozoic, about 20 million years before the ‘snowball Earth’ glaciations. The people visible in the image above provide a sense of scale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5eb37c5b-d752-4f8b-912f-a56e8e138444/Holes+and+arrows.jpg Susannah Porter Drill holes in vase-shaped microfossils: Half-moon shaped holes (black arrows) and circular holes (white arrows) in 780–740-million-year-old fossils of shell-forming (testate) amoebae from the Chuar Group of the Grand Canyon, Arizona. The holes are approximately 15 to 35 micrometers in size, and the shells are 75 to 150 micrometers in length. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dfab4193-adad-4130-93a7-77ff7f9e4b79/Holes.jpg Susannah Porter Circular holes, thought to have been formed by predatory 'vampire-like' protists that drilled into the walls of their prey, in a 780–740-million-year-old microfossil from the Chuar Group of the Grand Canyon, Arizona. The holes are ~0.2 micrometers in diameter, and the microfossil is 50 micrometers in diameter. It was originally a spherical vesicle, but has been flattened by the pressure of overlying rocks. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bb67a9f0-e0bf-4a0e-88ae-465aea4c4604/Bonniea.jpg Susannah Porter Comparison of the vase-shaped microfossil species Bonniea dacruchares with a modern testate amoeba. The cell lived inside the test and extended its pseudopods through the circular opening. (Bonniea dacruchares is named in honor of Bonnie Bloeser, who first discovered vase-shaped microfossils in the Chuar Group. The specific epithet, dacruchares, is an ancient Greek word meaning 'the delight one gets from tears', — fitting for these fine, tear-shaped fossils.) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/307ffd0e-d06b-4b6b-94c7-9a68bdcdf02c/Fig.+4+modern+analog+copy.jpg Susannah Porter As explained in the podcast, it was her familiarity with the tiny holes made by modern amoebae that first made Susannah Porter suspect that the holes in the ancient microfossils were made by a predator. These images show perforations in spores of the fungus Cochliobolus sativus made by the modern vampyrellid amoebae. (a) Overview of spores, several showing circular perforations. (b) Close-up view of spore, showing several circular perforations, each approximately 0.2 mm in diameter. Scale bar is 20 micrometers in (a), 2 micrometers in (b). Old, K. & Patrick, Z. (1976), Ca. Bot. 54, 2798 https://www.geologybites.com/roger-bilham daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3406f501-7951-4f5a-b2f0-1ef9a352d507/RB+closeup+portrait.jpg Roger Bilham Roger Bilham is Emeritus Professor of Geology at the University of Colorado, Boulder. He has conducted a detailed study of the historical record of earthquakes in the Himalaya over the past millennium. He tries to reconcile what we’ve observed with our current understanding of the physical mechanisms at play. This in turn helps us assess future hazard potential. In the podcast, he discusses what we’ve learned about exactly where the earthquakes occur, how they occur, and what determines how much damage they inflict. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a61dacc9-3154-4075-afbc-a064fd000579/Motihari+1934.jpg Roger Bilham Damage caused by a 1934 Bihar/Nepal earthquake in Motihari, a few km south of the Nepali border in the Indian state of Bihar. This Magnitude 8.4 earthquake nucleated from a point just south of Mt Everest and ruptured all the way to the Main Frontal Thrust, roughly 30 km north of this location. Shaking for several minutes during the earthquake resulted in liquefaction of sediments in the Ganges Plains and the collapse of the banks of rivers and lakes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5df8e939-e003-4f73-9ba8-79886e92fc3c/Bajaura+temple+-+displaced+blocks.jpg Roger Bilham The blocks in the doorway of the Bajaura temple in Raujare in the western Himalaya were displaced laterally during prolonged slow shaking accompanying a violent earthquake, possibly in the 15th century. In 1905, it survived the magnitude 7.8 Kangra earthquake with relatively minor further damage. Some have argued that the survival of medieval temples, such as this one, implies that extreme shaking can never have occurred in parts of the Himalaya. However, although stone structures are generally vulnerable to shaking collapse, some resist the long-period shaking by absorbing the shaking energy within the stone work (hence the displaced blocks in the photo), and only those fittest to survive remain for us to see. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f56f2e24-252c-40b7-a107-9c668efed400/typical+village+damage+2015.jpg Roger Bilham Damage caused by the 2015 Gorkha earthquake in Nepal. This scale of destruction was typical for villages in the impacted area. The structures consist of field stones, often rounded river blocks, that are assembled to form the outer and inner faces of the wall of a village building. Wooden beams support a corrugated iron roof. The stones are bonded with wet clay that has poor cohesion with the stonework and crumbles during an earthquake. The walls collapse in the direction of arrival of the displacement pulse of the earthquake, or are reduced to a pile of rubble after a few minutes of shaking, bringing the roof with them. Earthquake-resistant buildings are often beyond the reach of villagers. Simple remedies to strengthen field-stone structures take the form of adding wire mesh (chicken wire) to the outside and inside wall linked through the wall by wire or plastic straps. Small amounts of concrete and steel in the form of embedded or capping ring beams can be added by those with the incentive and funding to do so. Programs to undertake such retrofits face an overwhelming inventory of building stock so that it will take many lifetimes to effectively reduce earthquake risk in Nepali villages. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8e581d8e-3af8-4efa-82d2-ec8dbf8466b3/interferogram-edited.jpg Roger Bilham - Make it stand out This image shows the depression (blue) of the mountains along the locking line and the uplift of the mountains near Kathmandu (red) over a 2-week period spanning the 2015 Gorkha earthquake in Nepal. The image is an interferogram created by comparing synthetic aperture radar captured during two passes of the ALOS-2 satellite over the region — one before the earthquake and one after. The depicted changes were imposed in less than one minute during the earthquake. Lindsay E.O.R. et al. (2015), Geophysical Research Letters, 42 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d19b2b20-e6d4-4825-9b00-a917a86a452a/Steve+in+trench+annotated.jpg Roger Bilham Excavated trench across the scarp of the Main Frontal Thrust at the foot of the Indian Himalaya. The earthquake thrust a wedge of dark organic soil containing charcoal 10 m southwards (towards the right) over a lighter-colored thin layer of soil. Carbon 14 dating of the charcoal enables us to date the earthquake to the 13th-15th century. The figure on the ladder searching for charcoal fragments is Steve Wesnousky, who pioneered excavations of the Main Frontal Thrust starting in the 1990s. Courtesy of Steve Wesnousky https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/af51d4cf-d926-467a-ad5c-ea59cb823eb8/Earthquake+map.jpg Roger Bilham The map shows the locations of recorded Himalayan earthquakes over the past 500 years. Each black blob represents an estimate of the rupture area of the earthquake, i.e., the area of the Himalayan carapace that abruptly moved southwards during the earthquake. Rupture starts somewhere along the northern edge of these rupture zones, and moves sideways and southwards. The largest of the ruptures extend all the way to the Main Frontal Thrust at the southern edge of the Himalaya, where they lift the Himalaya above the Ganges Plain in the form of an abrupt scarp (shown in the previous figure). A half dozen of the earthquakes shown, however, failed to rupture all the way to the Main Frontal Thrust. We now realize that these "failed" earthquakes (failed in the sense that they incompletely permit the northward movement of India beneath the Himalaya) deposited huge pools of invisible strain energy at their southern edges. These reservoirs of energy remain dormant until released by great future earthquakes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f005ca8-cce0-4e9e-99d4-4cbc921ba9ed/the+great+paradox.jpg Roger Bilham - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6f1b4a08-f4ce-4eb8-b650-3fa247ea5b4c/failure+strain+limit.JPG Roger Bilham The width of the zone of incomplete seismic coupling between the locked portion of the fault to the south and the creeping portion of the fault to the north determines how much movement can occur along the fault when an earthquake is triggered. Assuming the incompletely coupled zone can store a strain of up to one in 10,000 before rupturing, the amount of available displacement during an earthquake for a 10-km-wide zone is 1 m. Such displacements generate earthquakes of magnitude 7.5 or lower. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b5d6117b-af0d-451d-9701-9dc6e8629944/failure+strain+limit+2.JPG Roger Bilham Megaquakes are generated by displacements of about 10 m. For a maximum strain of one in 10,000, such earthquakes are possible only when the zone of incomplete seismic coupling is 100 km wide. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8b8c220d-bf9b-41a0-8b01-cdd16858048c/strain+transferred+up%3Ddip.JPG Roger Bilham - Make it stand out Cross section along a line shown in the interferogram image above. The earthquake dynamically transported the strain stored at the northern end of the zone of incomplete seismic coupling (purple bubble) southwards along the fault plane to the region around Kathmandu (beige bubble). MFT = Main Frontal Thrust. MDT = Main Dun Thrust. Mw = moment magnitude of an earthquake, commonly referred to simply as magnitude. The scale was devised to extend the Richter scale to magnitudes great than 8, which tend to become increasingly underestimated when using computations based on Richter's original definition of the scale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/36cce1f9-f1f7-4abb-8181-c9d629ba7eb3/bulge+diagram.jpg Roger Bilham Concept diagram showing how elastic energy built up over time at the edge of a creeping zone of the fault can be translated rapidly along the fault during an earthquake. The earthquake simply moves the reservoir of elastic energy from one location to another. The energy may be released eventually when an earthquake ruptures a fault all the way to the surface. In the top figure, the strain near the lower right edge has approached the failure strain in the rock. Suddenly, a small part of the Main Himalayan Thrust slips. If it slips too little, it may simply stop in the form of a magnitude 4 earthquake. If sufficient slip occurs, it causes an instability - flash heating, melting or dynamic separation of the lower and upper surface of the fault have been proposed. The sudden lowering of friction releases more elastic energy, and a ripple rapidly propagates southwards, at velocities of greater than 2 km/second. The rocks above are translated southward. The ripple continues southwards, either fizzling out through the absence of sufficient elastic energy, or, if sufficient energy is available, making it all the way to the Main Frontal Thrust of the Himalaya, where it offsets the surface fault in the form of a scarp. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd9d7890-7550-4e41-b950-eb645bc34cd2/critical+stress.JPG Roger Bilham Computer modeling of the transfer of elastic energy during an earthquake. The diagrams show a simple boundary element elastic model of the Himalaya before (top) and after (bottom) rupture. The Tibetan Plateau acts as a backstop, preventing the northward movement of the Himalaya, which, in the top model, are clamped to the Indian plate. The forces of collision cause the rocks in the 20 km layer above the transition zone to be squeezed and rise in the vertical dimension. Using realistic physical parameters for the rocks, the model emulates the observed 5 mm/year of uplift that occurs between earthquakes due to the 15-18 mm/year of horizontal compression. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4e81adf6-fe28-4407-84f2-7bb20f2268b3/Rupture.JPG Roger Bilham By setting the friction on the thrust fault beneath the Himalaya to zero, all the compressional strain to the north can be released in the form of slip of the Himalaya southwards. In the example, slip is terminated a few tens of km north of the frontal fault and appears as a bulge. The prominent regions of strain change in the Indian plate (red for extension and blue for compression) are ignored in interpretations of surface earthquake mechanics. The predictions for the strain changes at depth are correct only for a purely homogeneous elastic model, which we know is a poor representation of the rheology of the Indian plate at depths greater than 20 km. https://www.geologybites.com/tag-review-march-2022 daily 0.75 2022-03-29 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/69b2bf69-d3c1-4785-861b-fe71a69f9c9e/TAG+202+Feature+2+%3D+Cover_Page_1.jpg TAG Review March 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2d4ccf58-71b5-4670-ab33-0b197ccc6e7a/TAG+202+Feature+2+%3D+Cover_Page_2.jpg TAG Review March 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a05c9cce-f932-4b86-8cc7-70cd2db4aa62/TAG+202+Feature+2+%3D+Cover_Page_3.jpg TAG Review March 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fbf72783-5c61-4e3f-9e22-ed8b7b6dd21d/TAG+202+Feature+2+%3D+Cover_Page_4.jpg TAG Review March 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/ougs-proceedings-review-2022 daily 0.75 2022-04-05 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f958bf50-c41a-47bf-9b7d-ec6e606803ce/OUGS+Proceedings+8+2022-Geology+Bites+review_Page_1.jpg OUGS Proceedings Review 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/07d8c811-5509-45bb-a2f3-c47be4808ed0/OUGS+Proceedings+8+2022-Geology+Bites+review_Page_2.jpg OUGS Proceedings Review 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bade7c39-9b68-44c8-a03a-b50e83f02f60/OUGS+Proceedings+8+2022-Geology+Bites+review_Page_3.jpg OUGS Proceedings Review 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/ben-weiss daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eb92e415-8f39-4fb2-955e-556c935b3407/portrait.PNG Ben Weiss Ben Weiss is Deputy Principal Investigator and Magnetometry Investigation Lead on the Psyche mission. He is a Professor of Planetary Sciences at the Massachusetts Institute of Technology (MIT). His research focuses on the formation, evolution, and history of the terrestrial planets and small bodies, such as the asteroids. He has studied samples of extraterrestrial bodies that land on Earth as meteorites. He is especially interested in their remnant magnetism as a clue to where they originate and how their parent bodies formed. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92234fe9-7427-42de-a553-00ad32c0ef6c/Artist+impression+enhancerd.jpg Ben Weiss Artist’s impression of Psyche, showing a heavily cratered, metal-rich surface. It is thought that Pysche is largely composed of iron and nickel, which is similar to the composition of the Earth’s core. Courtesy of Peter Rubin https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c0e858a4-f37f-4a14-97ed-4aca8506f688/Size.PNG Ben Weiss If Psyche were a perfect sphere, it would have a diameter of 140 miles (226 kilometers), or about the length of the State of Massachusetts (leaving out Cape Cod). It is estimated to have a surface area of about 64,000 square miles, or approximately 165,800 square kilometers. Courtesy of Arizona State University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/841bc3f0-d4ca-46d4-9a90-4faca768a8c9/oribt+of+Psyche.PNG Ben Weiss Psyche follows an orbit in the outer part of the main asteroid belt, at an average distance from the Sun of three astronomical units (AU); Earth orbits at 1 AU. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f58cf78-d665-4be0-9f1d-684a80b05c4d/Psyche_Mission_Elevation_160812.jpg Ben Weiss Radar image of Psyche obtained with the 305-meter-diameter Arecibo radio telescope in 2017. The image provides evidence for two 50-70-km-wide depressions near its south pole, which we interpret as giant craters. Shepard et al. (2017), Icarus 281, 388 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7fd681d2-73e2-4739-902c-2c6a73ba0704/Psyche_Mission_Core_Image_180809.png Ben Weiss Interior view of the Earth to the solid metallic inner core (gray innermost sphere). With a diameter of around 1500 miles (2500 km), the inner core is surrounded by molten liquid iron, the outer core (orange sphere). The liquid and solid metal cores lie beneath the solid silicate rock mantle of the Earth (green shading). Image credit: Edward Garnero/ASU https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d8a0757d-92b1-4c9e-840e-346f23c701f7/1-PIA25231-spacecraft-16_M8OZNMb.width-1320.jpg Ben Weiss - Make it stand out The Psyche spacecraft has to undergo rigorous testing to ensure it can operate in the extreme conditions it will face on its trip. Here it is shown on its way to the vacuum chamber at NASA’s Jet Propulasion Laboratory in Southern California. Courtesy of NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1ace3860-7ffb-4689-83ff-cc8b36f8f2bc/magnetometer.PNG Ben Weiss Artist’s impression of the Psyche spacecraft with its solar panels deployed, showing the location of the magnetometer. This instrument is composed of two identical high-sensitivity magnetic field sensors located at the middle and outer end of a 6-foot (2-meter) boom on the spacecraft. Although the spacecraft was designed to create the smallest possible magnetic field of its own, the magnetometer’s boom mounting minimizes the effect of any such field, however small. The magnetometer team is based at MIT and the Technical University of Denmark. Courtesy of NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0be146a0-91a4-4172-bce9-59952c1ddf86/Artist+impression+spacecraft+over+Psyche.PNG Ben Weiss Artist’s impression of the Psyche spacecraft in a low orbit over the surface of the asteroid. Although it is difficult to maintain stable low orbits, the resolution of the images and magnetic data captured by the insturments on board improve as the spacecraft moves closer to the surface. Courtesy of NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/77d9071e-6783-40b8-832e-b2e38569a67b/Fatemi+et+al+Fig+1d-clean.png Ben Weiss - This run simulates a non-conducting body with a weak magnetic field of about 145 nT on its surface. By comparison, the surface magnetic field of the Earth is 30-60 μT, about 200-400 times stronger. The solar wind compresses the field on the upstream side of the body. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7e13b246-eaf4-4a52-a5c7-fdf4aeac70e4/Fatemi+Fig+2d-clean.png Ben Weiss In this run, the body’s magnetic field is four times stronger than in the run to the left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/599d1562-7c46-41f3-96e6-dc2ea2c62c32/Fatemi+Fig+3d-clean.png Ben Weiss A highly conducting body is simulated here with no magnetic field of its own. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00323b79-d487-476c-85b7-1c6681a1318d/Trajectory.PNG Ben Weiss The Psyche spacecraft is expected to launch on August 1, 2022, and travel to the asteroid using solar-electric low-thrust propulsion, arriving in 2026. In 2023, it will fly by Mars, where it will undergo a gravity-assist to speed it up. After arrival, the mission plan calls for 21 months spent at the asteroid, mapping it and studying its properties. If funding is forthcoming and the spacecraft continues to function, the mission may be extended, though it may have insufficient fuel left to visit another body. Courtesy of Arizona Sate University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f100f8b7-a277-4a74-a767-f1624859f3d3/orbits.PNG Ben Weiss Once the spacecraft arrives at the asteroid in 2026, the scientific observations will be conducted from from four staging orbits, which will become successively closer. In its lowest orbit, the spacecraft will be very close — only 80 km above the asteroid’s surface, which is less than the body’s radius. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ab9384fb-6d2a-4808-937d-141eb1168f71/2201_5000__Exoplanets_Found_-_infographic.jpeg Ben Weiss - Make it stand out The enormous number of recently discovered exoplanets, especially the Super-Earths, helps us position Psyche within the range of possible planetary body types. This may help us determine which of the three formation scenarios for Psyche discussed in the podcast is the most likely. NASA/JPL-Caltech https://www.geologybites.com/neil-davies daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/27d6585e-1edf-4f8a-969a-d2c70ea3b54b/NSD1.jpg Neil Davies Neil Davies is a Lecturer in Sedimentary Geology at the University of Cambridge. He studies the interconnections and feedback loops between life and sedimentation. His research aims to understand how such interactions manifest themselves in the rock record. He does this by combining analyses of sedimentary structures and textures, stratigraphy, and trace fossils. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/331214b7-7b8b-4cef-b7ca-b2599426819f/ChronostratChart2022-02.png Neil Davies - Make it stand out In the podcast, Neil Davies discusses the development of land-based plant life, starting on continental margins in the Ordovician, accelerating in the Silurian, and becoming widely established and diversified by the Devonian. © International Commission on Stratigraphy, February 2022 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd35cb7a-a784-44c8-8b55-4602608145cd/Devonian+plants+enhanced.jpg Neil Davies Remains of early Devonian zosterophyll plants from the Andréebreen Formation of northern Svalbard, Norway. The zosterophylls are a group of extinct land plants that first appeared in the Silurian. They were among the first vascular plants in the fossil record, and had a world-wide distribution. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/12dc2325-a64c-4424-99a7-8049d81496a1/1280px-Zosterophyllum_sp._-_MUSE_cropped.jpg Neil Davies Reconstruction of an Upper Silurian zosterophyll. Courtesy of Matteo De Stefano and Museo delle Scienze, Trento https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7ff6ae3b-42d0-4812-a53f-c3284034019b/lycopsid+1+enhanced.jpg Neil Davies Standing lycopsid trees in the late Carboniferous from the Sydney Mines Formation of Nova Scotia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cc95086d-b1b3-4023-b708-d985e7e5bd56/lycopsid+2+enhanced-2.jpg Neil Davies https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8a22d59f-81b9-457e-8143-e6baea46a246/Coal+swamp+reconstruction.PNG Neil Davies Diorama of a Carboniferous coal forest. The large trees with a grid-like pattern on their trunks are lycopsids. Courtesy of the American Museum of Natural History https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4d753cda-5dbc-47f4-905f-c23bb2ca6a73/Davies+and+Shillito+2021+Sedimentology+-+large+space+and+time+scale+view.jpg Neil Davies - Make it stand out In the podcast, Neil Davies discusses a class of features in the sedimentary record that he calls “true substrates.” These are sedimentary bedding planes that demonstrably existed at the sediment-air, or sediment-water interface at the time of deposition. He asks whether true substrates are characteristic samplings of their time and place, or whether they are freak accidents that escaped destruction through exceptional circumstances, which would make them unrepresentative anomalies within a recycled and lost norm. The images here show examples of physical sedimentary structures that provide evidence for true substrates in the sedimentary stratigraphic record (on the left), with modern analogues (on the right). (A) and (B) Raindrop impressions. (A) Silurian Sundvollen Formation, Kroksund, Norway. (B) Boom River, Kyrgyzstan. (C) and (D) Parting lineation developed in plane bed flow regime. (C) Devonian Escuminiac Formation, Miguasha, Quebec, Canada. (D) Alnmouth, Northumberland, England. (E) and (F) Rill marks formed by draining water. (E) Mississippian Shepody Formation, Peck’s Point, New Brunswick, Canada (hyporelief cast of true substrate). (F) Holkham, Norfolk, England. (G) and (H) Adhesion ripples. (G) Silurian Tumblagooda Sandstone, Kalbarri, Western Australia. (H) Holkham, Norfolk, England. (I) and (J) Water-level drainage marks on ripple flanks. (I) Mesoproterozoic Meall Dearg Formation, Rubha Réidh, Scotland. (J) Alnmouth, Northumberland, England. White scale bars are 10 cm long; black scale bars are 1 cm long. (G) and (H) from Kocurek & Fielder (1982) J. Sediment Res., 52, 1229 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ae20b3c8-6c49-45e7-b2d7-547fa4a1cd4e/Davies+and+Shillito+2021+Sedimentology+-+large+space+and+time+scale+view+-+biological.jpg Neil Davies - Make it stand out Examples of biological sedimentary structures providing evidence for true substrates in the stratigraphic sedimentrary record (on the left), with modern analogues (on the right). (A) and (B) Arthropod trackways crossing ripple mark crests. (A) Silurian Sundvollen Formation, Kroksund, Norway. (B) Rainy Cove, Nova Scotia, Canada. (C) and (D) Stellate form to aperture of vertical invertebrate feeding burrows. (C) Mississippian Horton Bluff Formation, Blue Beach, Nova Scotia, Canada (hyporelief cast of true substrate). (D) Hopewell Rocks, New Brunswick, Canada. (E) and (F) Reticulate marking due to tangling of biological filaments. (E) Neoproterozoic Diabaig Formation, Diabaig, Scotland. (F) Rye, Sussex, England. (G) and (H) Sand-filled impressions of stranded jellyfish. (G) Cambrian Potsdam Sandstone, Rainbow Falls, New York, USA. (H) St. Cyrus, Scotland. (I) and (J) Desiccated and dried-out microbial mat. (I) Pennsylvanian Parrsboro Formation, West Bay, Nova Scotia, Canada. (J) Stiffkey, Norfolk, England. White scale bars are 10 cm long; black scale bars are 1 cm long. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ccf441a9-e0fc-4f34-bdef-a5076d030043/arthopl+specimen.jpg Neil Davies The largest known arthropod in Earth history was discovered by Neil Davies and his students in January 2018, in a large fallen block of sandstone in a coast cliff at Howick Bay in Northumberland in northern England. The fossil consists of the remains of a giant Arthropleura that lived in the Serpukhovian age in the mid-Carboniferous, about 330 million years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a8e7297b-4e00-4e82-b730-7f6fa7b98f5a/View+of+block-fixed.png Neil Davies - Make it stand out View of the fallen block (white circle) and original position (black circle) in the context of the damage zone around the Howick master fault. HT= thickening of mudrock in the hanging wall of the fault. Red arrows = sense of fault movement. Blue dashed line = approximate position of the Lickar Limestone, which marks the onset of the late Serpukhovian. Scale bar = 5 m. Courtesy of Geospatial Research Ltd. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3825eeb1-40c4-4d04-b8d3-66bfa6d14bd4/arthopl+specimen+in+situ+2.jpg Neil Davies - Make it stand out Above: slab A of the fossil prior to extraction. Image width is about 60 cm. Right: slab B of the fossil. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a03f66a5-0579-4c54-b6bf-b7b9da2f9ecb/arthopl+specimen+in+situ+1.jpg Neil Davies https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cafa3c8c-0959-4f97-b14b-ff398e4dd93e/Largest+arthropod+in+Earth+History+2021.jpg Neil Davies - Make it stand out (a) Scale of the Howick Arthropleura relative to other articulated giant specimens (preserved remains highlighted in pink) and the largest arthropod trackways known from each Carboniferous-Permian stage. The previously known body fossils were both markedly smaller than the dimensions of Arthropleura revealed by trace fossil evidence. (b) Reconstruction of the Howick Arthropleura within its habitat of a lower delta plain with open woodland. https://www.geologybites.com/tony-watts daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e0e0c951-725f-4af9-84c6-be80f829483e/TW+small+portrait.jpg Tony Watts Tony Watts is Professor of Marine Geology and Geophysics at the University of Oxford, and a Fellow of the Royal Society. His research focuses on measuring and modeling the structure of the lithosphere, and the deformation it undergoes in response to stresses. Some of the clearest such deformations occur in the seafloor, and he has concentrated on these, both at plate margins, such as trenches, and at plate interiors, especially at seamounts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/67ee1158-62a3-43c7-a038-1f4c55a7a1c5/Distribution+of+seamounts+globally.PNG Tony Watts Global distribution of volcanoes, ocean islands, and seamounts. (a) Volcanoes less than ~ 12,000 years old, together with major plate boundaries (blue, subduction zones; orange, mid-ocean ridges; black, transform/strike-slip faults). (b) Ocean islands (solid circles), atolls (x), and guyots (open circles). (c) Seamounts with height above surrounding sea floor greater than height above sea level of Ben Nevis, the mountain with the highest prominence in the UK (1,344 m). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e878e14f-152b-4400-8d80-04f7108cb803/4.16+Simple+model+for+growth+of+seamount.jpg Tony Watts Simple model for the growth of a seamount on the sea floor by eruptions at the summit. The ages are estimates based on consideration of eruption rates and the timescales of stress relaxation in the oceanic lithosphere. The vertical and horizontal growth of the seamount is accompanied by down-sagging of the central part of the edifice, large-scale slope failures, and thrusting and seismicity along a décollement plane. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9864ea1a-f296-46ec-bab6-c745f8790e39/4.17+map+of+bathymetry%2C+topography%2C+free-air+gravity+anomaly.jpg Tony Watts - Make it stand out Bathymetry, topography, and gravity anomaly around the Hawaiian Islands. White lines show the modeled flexure (contour interval is 1 km) assuming that the Hawaiian Islands act as a load on the Pacific plate with an effective elastic thickness (Te) of 30 km. (a) Bathymetry and topography based on satellite altimetry and shipboard soundings. (b) Free-air gravity anomaly. Sandwell et al. (1997), https://topex.ucsd.edu/marine_topo/ V19.1 Sandwell et al.. (2014), https://topex.ucsd.edu/marine_grav/mar_grav.html V29.1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6824271a-1b3d-4202-b986-0c0c5efd3286/4.18+simple+model+for+gravity+anomaly+and+flexure+of+lithosphere+at+seamount.jpg Tony Watts There is a positive gravity anomaly above a seamount that is at least partially supported by the elastic strength of the lithosphere. If the lithosphere provided no support, the seamount would effectively be floating like an iceberg, and there would be no anomaly. The illustration shows a model for the gravity anomaly and flexure of the lithosphere at a seamount or oceanic island. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/34fec14c-9db5-4b00-b532-89bebd23fed2/Fig+5+Challenger+paper+perscpective+view+of+Hawaii.PNG Tony Watts Swath bathymetry reveals debris being carried down the slopes of Hawaiian Islands. As Tony Watts explains in the podcast, such debris obscures the surface of the seafloor crust, so one has to resort to seismic methods to determine its shape. (a) Southeast flank of Hawaii showing Loihi, the newest submarine volcano added to the island chain. (b) North flank of Maui, Molokai, and Oahu showing incised canyons, large-scale slope failures and debris-flow deposits with large blocks that overfill the ‘moat’ flanking the islands. Vertical exaggeration ×4. Scales are approximate. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/75d5f58e-e1af-41c2-bb7c-b586c2ebd495/4.26+comparison+of+observed+and+calculated+flexure+-+Te+%3D+25+os+best+fit.jpg Tony Watts Comparison of observed and calculated flexure to the northeast of Oahu and Molokai in the Hawaiian Islands. The observed data (black dots) are based on seismic reflection profiles. The calculated profiles (red) are based on an elastic plate model with surface topographic loading and modeled plate elastic thicknesses of 10, 25, and 50 km. An elastic thickness of 25 km provides the best fit. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00d30702-3d40-4def-81c8-2c52756e68b5/4.33+staircase.jpg Tony Watts - Make it stand out Perspective view (from the northwest) of the seafloor to the west of the island of Hawaii showing the ‘staircase’ pattern of marine terraces offshore of the flank of Mauna Kea, the largest dormant volcano on the island. Secular rises and falls in sea level would not produce such a pattern of former beach levels. Instead, the pattern indicates subsidence of the island as the lithosphere sagged in response to the load of the growing volcano. https://www.geologybites.com/phil-renforth daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/adfde23b-de7e-4e3c-9c65-33070fe64366/Phil+Renforth+%282+of+2%29.jpg Phil Renforth Phil Renforth is an Associate Professor in the School of Engineering and Physical Sciences at Herriot-Watt University in Edinburgh. His research focuses on geochemical techniques of removing atmospheric carbon dioxide from the atmosphere. He is especially interested in methods that sequester carbon dioxide by enhancing the weathering of rocks and human waste materials. The image was shot in Hawaii, which is covered in basaltic rocks that contain minerals that weather rapidly, such as olivine. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bed5ee2d-be54-44e2-9dee-09795ee1772b/Carbon+cycle.PNG Phil Renforth The main steps of the geochemical carbon cycle. Courtesy of The Geological Society of London https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f9da44e3-4c9a-40e0-9039-c90ef6c45d4b/Geochemical+carbon+removal.PNG Phil Renforth The diagram illustrates the various geochemical methods of removing carbon dioxide from the atmosphere. Hawrot et al., 2021 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ecd80f39-2fb2-4632-9605-29a992237f91/technology+evolution+slide+10.PNG Phil Renforth - Make it stand out The figure illustrates the phases of carbon sequestration and development, from bench-scale experiments, to pilot-scale projects, to demonstration at the field scale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d3d44e8a-b6a7-4ac9-a1b0-5e4eb04ecc08/Slide+12+ocean+liming.PNG Phil Renforth - Make it stand out In the podcast, Phil Renforth introduces the main approaches to carbon sequestration by enhancing the weathering of rocks. Renforth & Henderson (2017), Reviews of Geophysics, 55, 636 https://www.geologybites.com/maria-mcnamara daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e6a7b0cb-dc7d-4475-86e4-d176b55e9a58/56834121-0-image-a-29_1650461407911.jpg Maria McNamara Maria McNamara is Professor of Paleontology at University College Cork in Ireland. Her research focuses on the preservation of non-biomineralized ‘soft’ tissues, such as skin, muscle, and internal organs. She examines such tissues in exceptionally well-preserved fossils, including many that retain color-producing structures at the micron scale. In the image, she is holding samples of pterosaur feathers on a microscope mount. Courtesy of Daragh McSweeney/Provision https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aa88f36f-e671-4221-850d-6eff6f0f4f4f/Exceptionally+preserved+fossil+assemblages+through+geological+time+and+space+2017.jpg Maria McNamara - Exceptionally well-preserved fossils In order to see the fossilized structures at the micron scale, the fossils must be exceptionally well preserved. As Maria McNamara discusses in the podcast, soft tissues can be preserved in extraordinary detail when certain conditions prevail. These include oxygen-starved settings and rapid burial sites. As of 2022, about 600 sites of exceptional fossil preservation are known around the world. Such deposits are called Lagerstätten. Well-known examples include the Cambrian Burgess Shale, the Carboniferous Mazon Creek, and the Eocene Green River Formation. The image shows examples of exceptionally well-preserved fossils. (a) Phosphatized embryo Megasphaera from the Ediacaran Doushantuo Formation, China. (b) Silicified multicellular alga Wengania from the Ediacaran Doushantuo Formation, China. (c) Pyritized tubular metazoan Conotubus from the Ediacaran Dengying Formation, China. (d) Ediacara-type fossil Swartpuntia from the Ediacaran Nama Group, Namibia. (e) Aluminosilicified carbonaceous compression of arthropod Marrella from the Cambrian Burgess Shale, Canada. (f) Oxidized compression of a ctenophore (“comb jelly”) from the Cambrian Qiongzhusi Formation (Chengjiang Biota), China (Yunnan University specimen RCCBYU 10217). (g) Carbonaceous compression of eurypterid from the Silurian Bertie Waterlime (Fiddlers Green Formation), US. (h) Silicified mayfly from the Miocene Barstow Formation, US. (i) Carbonaceous compression of insect Fulgora from the Eocene Green River Formation, US. (j) Fish from the Eocene Green River Formation, US. Muscente et al. (2017), Gondwana Research 48, 164 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5cafc9ce-b1ad-4354-8398-aef886c41c91/melanosomes+electron+micrscope%27.png Maria McNamara - Pterosaur melanosomes Scanning electron micrographs of the soft tissues of a pterosaur’s fossilized skull reveal that different types of feathers contained different shapes of pigment-bearing melanosomes. As Maria McNamara explains in the podcast, melanosome shapes are linked to color. In the top row, whisker-like simple filaments contain elongated melanosomes, suggesting darker colors. In the bottom row, more complex branched feathers contain ovoid melanosomes, pointing to brighter yellows or reds. Scale bars all represent 2 microns. Cincotta, A. et al. (2022), Nature 604, 684 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ade94ef8-c105-4572-abcf-ba70fac756f4/Original+colors+of+47+Ma+moths+2011+PLOS.jpg Maria McNamara - Make it stand out Structurally colored fossil moths from the Eocene Structurally colored scales in fossil moths with striking metallic hues from 47-million-year-old oil shales in Germany. The original colors were altered during fossilization. Preserved details in the scales allow reconstruction of the original colors and show that the dorsal surface of the forewings was yellow-green. The optical properties of the scales strongly indicate that the color functioned as a warning signal during feeding but was cryptic when the moths were at rest. (A–C) Light micrographs with details of areas indicated in (B, C). (D–J) Scanning electron micrographs of scales. (D) Surface showing longitudinal ridges and transverse cross-ribs and micro-ribs. (E) Two overlapping scales showing windows, perforations, and internal laminae of the upper, fractured scale. Arrow indicates densely packed bead- to rod-like spacers in the uppermost internal lamina. (F, G) Windows and perforations in proximal (F) and distal (G) parts of a scale. (H) Oblique fracture through scale showing successive internal laminae. (I) Surface of internal lamina showing perforations and bead-like spacers. (J) Horizontally fractured scale showing connective tissue (trabeculae, fractured and lying parallel to the scale surface) and reticulate basal lamina with, inset, intact vertically orientated trabeculae. Scale bars: (A), 5 mm; (B, C), 1 mm; (D, E, H, J) (including inset), 2 mm; (F, G, I), 1 mm. McNamara, M.E. et al. (2011), PLoS Biology 9(11): e1001200 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b044e681-7e6e-4552-bdd8-f349435455cb/Original+colors+of+47+Ma+moths+2011+PLOS-1.jpg Maria McNamara - Make it stand out Transmission electron micrographs of the fossil moth multilayer reflector (A) Vertical longitudinal section through a stack of four scales; scales are fractured locally. r, resin; s, sediment. (B) Detail of multilayer nanostructure in a longitudinal section through a single scale. (C) Transverse section through a scale showing broad ridges and the concave geometry of the interridge surface and of the underlying multilayer structure. Scale bars: (A, C), 1 mm; (B), 500 nm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/281258a4-44d4-402a-98a4-7f7cf5c82c19/Original+colors+of+47+Ma+moths+2011+PLOS-2.jpg Maria McNamara - Reconstruction of the original colors of the dorsal surface of the fossil lepidopterans. The dominant hue of interior zones of the fossil wings are blue today (when viewed in air) but were originally yellow-green. The edges of the wing were originally green-cyan and blue, and the outer wing margin, brown. McNamara, M.E. et al. (2011), PLoS Biology 9(11): e1001200 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dec265dc-fb14-411a-93a3-d37367ac8ce7/Weevil+scale+colors+2020+Biology+letters.jpg Maria McNamara - Pleistocene Beetle In the podcast, Maria McNamara describes structural colors and photonic crystals in 700,000-year-old subfossils from the Pleistocene glacial deposits. These images show subfossil weevil scales from Swiss glacial deposits captured using a light microscope (a, b, e, f) and a scanning electron microscope (c, d, g, h). The images in the right column are enlarged and rotated versions of the regions bounded by white boxes in the corresponding image in the left column. The light micrographs show the preservation of scales with bright blue, green and yellow hues, while electron micrographs reveal three-dimensional photonic nanostructures. McDonald, L.T., et al. (2020) Biol. Lett. 16: 20200063 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f6f4a2c5-b90e-4eda-a455-57e82bacd234/Snaek+-1.jpg Maria McNamara - Make it stand out Fossil skin from a 10 million-year-old colubrid snake found in Teruel, Spain The color of a given region of skin depends on the relative abundance of the various pigment cells. (A) The entire specimen; inset shows anterior. Cream-colored material is fossil skin. Numerals 1–7 show the sample locations. (B) Overlapping scales. (C–E) Scanning electron micrographs of fractured vertical sections through the skin, showing epidermis (Epi), dermis (De), basement membrane (B), chromatophores (pigment cells - iridophores [I], melanophores [M], and xanthophores [X]), stratum spongiosum (Sp), stratum compactum (Sc), and collagen fibers (C). (F–I) Details of iridophore (F), xanthophore (G), and melanophores (H and I). (J and K) Transmission electron micrographs of xanthophore (J) and melanophore (K). McNamara, M.E. et al. (2016), Current Biology 26, 1075 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/691874cf-89b6-467b-9db9-13cbe6b0b9f7/snake+-+variations.jpg Maria McNamara - Make it stand out Variation in the relative abundance of different pigment cells in skin from different body regions of the Teruel snake Encircled numerals correspond to sample numbers in A of the previous set of images. (A–C and G–I) Scanning electron micrographs of vertical sections through the fossil skin. (A) Abundant xanthophores; common iridophores and melanophores. (B) Common iridophores and xanthophores; occasional melanophores. (C) Abundant iridophores; common melanophores and xanthophores. (G) Abundant melanophores; common xanthophores; rare iridophores. (H) Abundant xanthophores; occasional iridophores; rare melanophores. (I) Abundant xanthophores and iridophores; rare melanophores. (D–F and J–L) Interpretative drawings corresponding to (A–C and G–I). Epi., epidermis. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/23a15d66-f00e-447b-9b50-2767203a895b/snake+-+reconstruction.jpg Maria McNamara - Make it stand out Color reconstruction of the Teruel fossil snake (A) Schematic representation of the relative abundance and position of pigment cells in samples of skin from different body regions. (B) Artist representation of the color reconstruction. https://www.geologybites.com/geoff-abers daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/286672b8-155d-4b90-a374-d3034dad15f6/GA+Alaska.jpg Geoff Abers Geoff Abers is Professor of Geological Sciences at Cornell University. His primary research interest is in understanding processes that drive the recycling of material within the Earth, mostly at subduction zones. He has set up dense arrays of seismographs to make seismic images of features as small as layering within subducted crust to beyond 100 km in depth. He is actively working around Mt. St. Helens, Washington, and along the Alaska margin. In the image, he is installing a seismometer in Alaska to record the aftershocks of the 2021 magnitude-8.2 Chignik earthquake. The seismometer is in the ground at the end of the black cable. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1724262f-7003-4c72-985e-c4b5b1c95ff0/SZ+Diagram.PNG Geoff Abers - Make it stand out Diagram of a volcanic arc lying above a subduction zone. In most such arcs, the volcanos appear where the subducting plate has reached a depth of about 150 km. Courtesy of Schroeder, K.D., from Wikimedia Commons under CC-BY-SA4.0 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/98e9ecdb-60f7-417e-9b4e-65221f07a721/Wada+and+Wang.png Geoff Abers Diagram of a typical subduction zone at a continental margin, showing the crustal and upper mantle components and the processes that take place within them. As Geoff Abers describes in the podcast, water is released from the subducting lithosphere when the hydrous minerals break down. This is indicated as “fluid migration” in the diagram. The water rises into the mantle wedge where it lowers the melting temperature and causes partial melting. The melt rises and erupts from an arc of volcanos. The green circle indicates the location of earthquakes (episodic tremor and slip, ETS) that is observed in warm-slab subduction zones. Wada, I., & Wang, K. (2009), Geochem. Geophys. Geosyst.,10, Q10009, doi:10.1029/2009GC002570 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0585e31c-2c8d-4493-a304-b971f1f9b9e7/Fig+1+-+locations+of+SZ+segments+for+subway+map.jpg Geoff Abers - Make it stand out Geoff Abers and his colleagues made models of over 50 segments of subduction zones across the world. For each segment, they plugged in observed parameters, such as the convergence speed of the two plates and the age of the subducting plates. The trench segments, numbered from 1 to 56, are color-coded with a parameter (Φ) that is a measure of the thermal characteristics of the segment, from red (hot) to blue (cold). Φ (km) is defined as the product of the convergence speed (km/million years) and age (million years) of the subducting plate. van Keken, P.E.B.R., et al. (2011) J. Geophys. Res., 116, B01401, doi:10.1029/2010JB007922 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/db4aa53c-5900-47c7-9ec4-9766d740cdef/Tokyo+subway+map.jpg.png Geoff Abers - Make it stand out Geoff Abers refers to this figure as the Tokyo subway map. Each of the over 50 subduction zone segments shown in the map above is represented by a line that shows the predicted rate at which water is lost from the subducting slab as a function of depth. All the slabs lose a significant amount of water as soon as the slab gets into contact with the hot overlying mantle wedge, which is modeled to be a depth of 80 km. For many of the modeled slabs, such as Kamchatka and Calabria, further water loss is minor, as indicated by the vertical lines below 80 km depth. Other slabs, such as Chile, continue to lose water with increasing depth, mainly via dehydration of the uppermost mantle layer of the slab. A few slabs, such as the Marianas, are so cold that little water water is lost, even at a depth of 230 km. van Keken, P.E., et al. (2018), Geosys., 2934 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/68741632-03a2-4714-b8c6-1f323841ce2a/Eleutian+trench+slide+15.png Geoff Abers - Sonar image of the sea floor off the shore of Alaska The image looks east-northeast. The deepest sea-floor depths are shown in purple. The Aleutian trench runs along the left side of the image below the accretionary wedge, which is shown in green. In the podcast, Geoff Abers explains how water can penetrate the plate all the way down to the mantle via normal faults associated with the bending of the plate as it curves down into the trench. Such faults can be seen as dark lines running roughly parallel to the trench in the blue region on the right. From Alaska Amphibious Community Seismic Experiment (AACSE) recovery cruise, 2019, R/V Marcus G. Langseth https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d2eff881-18af-46cc-90f1-7c72290f23b5/Seismograms+showing+hydration+slide.png Geoff Abers - Make it stand out In the podcast, Geoff Abers talks about using seismic imaging to track the fate of water in a subducting oceanic plate. Two examples of such images are shown here. Regions that appear red indicate slower seismic wave speeds, which reflect the presence of water. Left: image of the Pacific plate subducting below Alaska. Right: image of the Pacific plate subducting below the Cascade mountains on the northwest coast of the United States. Rondenay, S., et al. (2008), Geology, 36, 275 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8ba60621-352c-4e43-a52f-fb9e8482200c/Thermal+model+slide+14.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00637a4b-26f6-49a9-9b27-bcc62682cb34/facies+and+water+content+for+thermal+model+slide+14.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1d0e399b-f9ce-4663-b99a-23f38da8272a/facies+key+slide+14.png https://www.geologybites.com/brian-upton daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d69be672-5434-426b-a70e-c3bc9be1723b/BU+in+Narsaq.jpg Brian Upton Brian Upton is Emeritus Professor of Geology at the University of Edinburgh. During his long and prolific research career, he has conducted field studies in many parts of the world, concentrating especially on the Arctic. But throughout his career he has continued to investigate the unique alkaline rocks of South Greenland. As he explains in the podcast, these rocks contain an unrivalled number of exotic minerals, many of them not known to occur anywhere else. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7271fa89-bad8-47c5-a99d-ba5a658c87c2/Basement+map+edited+Henriksen+p+30.jpg Brian Upton - Simplified Map of Greenland’s Basement Rocks The crystalline basement rocks of Greenland consist of Precambrian fold belts welded together. The rocks of the Gardar Province, shown in red near the southwestern tip, were intruded into rocks (the Ketilidian fold belt) that were formed about 1,850 to 1,725 million years ago during folding and mountain-building accompanying the assembly of the supercontinent Nuna (also referred to as Columbia). Courtesy of Thuesen, C.E, GEUS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e879300a-1333-4cda-ab3e-085135941cf8/Rogers+and+Santosh+Columbia+edited.png Brian Upton - Reconstruction of the Supercontinent Nuna/Columbia A reconstruction of the supercontinent Nuna/Columbia at about 1,500 million years ago showing Greenland (orange) in a block together with North America, Baltica, and Siberia. The lines annotated by triangles indicate subduction zones, and the double line indicates a rift zone. Rogers, J.J.W. et al. (2002), Gondwana Research, V. 5, No. 1, 5 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/01d7bd92-e441-46a2-8637-1550b1633372/Fig+2+from+S+Greenland+Geological+Guide+p21.jpg Brian Upton - Make it stand out Geological sketch map of the Gardar igneous rocks. The rocks intruded into the Julianehåb granite batholith (pink), which was itself emplaced during the assembly of the supercontinent Nuna/Columbia between 1,855 and 1,795 million years ago. In the podcast, Brian Upton first discusses the giant dykes, which are shown in blue on the island of Tuttutooq to the southwest of Narsaq. The major portion of the podcast is devoted to the one-of-a-kind Ilimaussaq intrusion shown in blue to the northeast of Narsaq. The intrusion is split into two parts by the Tunulliarfik Fjord. Sorensen et al. eds. (2016), Geological Guide South Greenland, pp. 20-21 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0b08df1b-cd40-441f-a82f-ed5e64e454df/Fig+3+age+distribution+edited.png Brian Upton - Timeline The age distribution of the Gardar intrusions as determined by radiometric dating. The intrusions discussed in the podcast are highlighted: Ivigtut (Ivittut in the map above) is the site of the extremely high fluorine concentration in the mineral cryolite; https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b98c5b78-f37c-4a40-918e-5ff702305f14/QAP+diagram.PNG Brian Upton - Syenites The rocks in the intrusive complexes of the Gardar Province are principally composed of syenites that are highly enriched by fractional crystallization and mineral separation in a magma chamber. Igneous rocks that were intruded at depth can be classified according to the proportions of quartz (Q), alkali feldspar (A), or plagioclase feldspar (P) they contain. This classification is commonly mapped onto the ternary QAP diagram shown here. Syenites are plutonic igneous rocks that consist mainly of alkali feldspar without much quartz or plagioclase, and so they occupy the lower left corner of the QAP diagram. Courtesy of the Open University, © Open University 2010 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a8543c9-12fe-4907-93b9-3e3bf2d9fafb/Magma+chamber+diagram.PNG Brian Upton - Crystal separation Schematic representation of crystal settling and floating in a magma chamber. Brian Upton describes this process in the podcast. The high-density minerals that sink are the ones that are rich in magnesium and iron, such as olivine and pyroxene. In the case of the magmas that formed the Ilimaussaq complex, the lighter minerals that floated to the top included sodalite, which has a high sodium content. See diagrammatic cross section of the Ilimaussaq complex below. Courtesy of Alex Strekeisen after Stephen A. Nelson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2c86f27f-f2eb-494f-afd6-cbe2855f88bf/Fractional+Crystallization+diagram+credit+Woudloper.PNG Brian Upton - Fractional Crystallization Schematic diagrams showing the principle of fractional crystallization in a magma. As it cools, the magma becomes depleted in the elements that enter the crystals. As Brian Upton explains in the podcast, the magma eventually becomes enriched in the most incompatible elements, so called because they do not readily fit into the crystals that are forming in the melt. Woudloper, CC BY-SA 3.0 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c90242cc-1d71-4c25-b767-0daf0c7b1dc6/Simplified+x-s+of+Ilimaussaq+Complex+Fig+92+p+72.PNG Brian Upton - Make it stand out Diagrammatic cross section of the Ilimaussaq complex. Naujaite, shown in beige at the top of the section, is a kind of enriched syenite, often containing the low-density sodium-rich mineral sodalite. Various outcrops of the Ilimaussaq complex show pale blocks of naujaite within the darker lujavrite (also a kind of enriched syenite). The blocks are thought to have foundered off the top layer of the magma chamber that formed the complex. Andersen, S., et al. (1981), Rapport Gronlands Geologiske Undersogelse 103, 39 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d82b7fbd-8781-40cd-946d-30b1eed4297a/Fig+94+p+74.jpg Brian Upton Polished slab of Ilimaussaq alkali granite. The green coloration is due to micro-inclusions of aegerine (the sodium endmember of the aegerine-augite series of pyroxenes) within the alkali feldspar crystals. Grey areas are quartz, and the black is mainly arfedsonite, a rare sodium amphibole that is abundant in the Ilimaussaq complex (see photo below). Courtesy of Brian Upton https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/90ae7d03-78eb-4ab4-88af-620326da2873/Fig.+107+-+hyperagpaitic+lujavrite+w+steenstrupine.jpg Brian Upton Photo micrograph of an extremely enriched rock in the Ilimaussaq complex. The rock is a lujavrite, which is colored green in the diagrammatic cross section of the complex shown above. The image shows albite (colourless), naujakasite (greenish-grey), and the uranium-containing mineral steenstrupine, mentioned in the podcast. Steenstrupine is both a silicate and a phosphate with the formula Na14(Ce,Th,U)6Mn2Fe2Zr(PO4)7Si12O36(OH)2·3H2O). Upton, B.G.J (2013), Geological Survey of Denmark and Greenland Bulletin 29, p. 88. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2bbc1b53-66fb-4db8-b1cb-7120fb0cb2d6/Fig.+12+p22.jpg Brian Upton Aerial photograph along the Young Giant Dyke looking east-north-east along the island of Tuttutooq. The northern part of the Ilimaussaq complex (with ice) is in the far distance. The valley to the right is excavated by weathering of the dyke’s gabbro. Upton, B.G.J (2013), Geological Survey of Denmark and Greenland Bulletin 29, p. 22. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/523e4de0-d4f4-40f9-9548-158eedae88ad/Fig.+91+p+71.jpg Brian Upton - The Ilimaussaq Complex The Ilimaussaq complex is cut by the Tunulliarfik Fjord. The image shows the northern part of the Ilimaussaq complex. The rocks comprise extremely enriched syenites resulting from high degrees of fractional crystallization from the parental magma. The extremely rare mineralogy results in a surface that is less hospitable to vegetation than the surrounding granite of the Julianhab batholith and the lavas and sandstones of the Eriksfjord formation (see timeline above). Courtesy of Brian Upton https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/822c95d1-7982-4d6a-a804-8808709968d4/Ilimaussaq+complex+with+pemgatite.jpg Brian Upton - Make it stand out The Ilimaussaq complex looking west along Tunulliarfik Fjord. In the foreground is a pegmatitic layer containing the largest crystals of the complex. These include white alkali feldspar crystals up to 0.5 meters long, and black crystals of the rare amphibole arfedsonite. Photo: Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58dacb16-cbd5-4f5c-b116-6ad2e2970856/Cryolite+mine+Ivigtut.jpg Brian Upton - Cryolite Mine at Ivigtut Circa 1941 picture of mining operations at Ivigtut, the site of the world’s only cryolite mine. Cryolite was used as a catalyst and as a source of aluminium. Aluminium was needed in large quantities to manufacture aircraft in the United States during the Second World War. The mine extended far below sea level, but was separated from the sea by only a thin wall of rock. Courtesy of the Arctic Museum, Bowdoin College https://www.geologybites.com/geoscientist-review-2022 daily 0.75 2022-09-13 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/49a23190-0d05-4a8c-a902-d83c42d5bcc6/Geol.+Soc.+GEOSCIENTIST+Autumn+2022+GB+review_Page_1.jpg GEOSCIENTIST Review 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec6957b7-a5ed-4785-9a9f-bc9a03643d61/Geol.+Soc.+GEOSCIENTIST+Autumn+2022+GB+review_Page_2.jpg GEOSCIENTIST Review 2022 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/anna-fleming daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2f0b31c7-23af-4266-a5b5-e2ada02e089d/Aberdour+-+credit+Murdo+MacLeod.JPG Anna Fleming Anna Fleming is the author of Time on Rock, a book about the experience of climbing rocks in England, Scotland, Wales, and the Greek island of Kalymnos. Through the story of her progress from terrified beginner to confident lead climber, she explores her subjective experience of the physical nature and history of formation of rocks such as granite, gritstone, rhyolite, slate, and limestone. Here she is climbing on the quartz dolerite Hawkcraig Crag at Aberdour in Fife, Scotland. Courtesy of Murdo McLeod https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02aedcef-c076-4a70-a06e-39fbd6094a2d/Gritstone.jpg Anna Fleming - Make it stand out The gritstone in Yorkshire, England, is a hard, coarse-grained siliceous sandstone formed during the Carboniferous period about 300 million years ago when northern England was near the Equator. Courtesy of Matt O’Brien https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0043d0a9-3452-4a94-b8e3-a30d4d30c24a/Gritstone+closer.PNG Anna Fleming - Make it stand out The cross-bedding is visible in this crag of Yorkshire gritstone. Courtesy of Mike Hutton https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a3b28791-1a75-42ec-9257-324d42fcdfbe/Slate+quarry.jpg Anna Fleming - Make it stand out Disused slate quarry at Dinorwig, Wales. In the 19th and early 20th centuries, the slates of North Wales provided most of the roofing slate used in Britain. They were originally formed as deep-water marine mudstones during the Cambrian around 500 million years ago and were later uplifted, folded, and metamorphosed to form slates about 400 million years ago. In the podcast, Anna Fleming describes her experience of the smooth texture of the slate. Slate splits easily into thin sheets because of the alignment of tiny mica crystals in the rock. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bbf9e672-99a6-412c-906c-847918a124de/IMG-20221015-WA0001.jpg Anna Fleming Slate whistles made by a former Dinorwig quarryman. Courtesy of Branwen Davies https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/473874c6-ffa4-4d4c-bc96-98d85d24cb03/Cuillin+-+credit+Anna+Fleming.JPG Anna Fleming - Make it stand out The Cuillin range on the Isle of Skye, Scotland, consists largely of gabbro, a coarse-grained rock that formed in magma chambers below volcanos that have now been eroded away. The rocks were intruded about 60 million years ago. The Cuillins are notorious among climbers as they present special challenges, as Anna Fleming describes in the podcast. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1df448a0-bb5f-49dc-b423-a7cbf79a9072/Cairngorm+granite+tor.JPG Anna Fleming - Make it stand out Granite tors on Bynak Mor in the Cairngorms, Scotland. After what is often a long walk to reach the summit, the granite tors in the Cairngorms present a sought-after challenge for climbers. Their coarse-grained texture provides good friction to the climber, though they often lack suitable hand or foot holds. The granites of the Cairngorms and Scottish Highlands were formed during the Silurian (440-419 million years ago) when the continent of Laurentia collided with Baltica to join Scotland to the area that would become England and Europe. The granites were originally formed at depth as magma chambers below volcanoes that have eroded away. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4b99f831-56a5-49ba-af61-d7ba7ea43b03/Glen+etive+granite+-+credit+Murdo+MacLeod.jpg Anna Fleming - Make it stand out Anna Fleming climbing on granite slabs above Glen Etive. The granite has been smoothed by the action of glaciers. Courtesy of Murdo McLeod https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5771323d-e428-4239-8907-27cfba6d65a9/moray+sandstone.JPG Anna Fleming - Make it stand out The Moray sandstone cliffs overlook the Moray Firth, a vast inlet that cuts into the east coast of northern Scotland. This sandstone was mostly formed by wind-blown dunes during the late Permian and early Triassic (about 250 million years ago). It preserves fossils of extinct reptiles, known as the Elgin Reptiles after the nearby town of Elgin. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dc46a972-51e6-4f93-8aa4-96a8b0148fa9/Moray+sandstone+%281%29.JPG Anna Fleming - Make it stand out Patterns sculpted into the Moray sandstone by weathering and fluids circulating within the rock. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f4bf7a9e-614c-423b-9989-263bf363ded4/Kalymnos.PNG Anna Fleming - Make it stand out Limestone cliffs with a climber (red shirt in center) on the Greek island of Kalymnos. Courtesy of Nick Weicht https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b79bcbed-4655-4546-9a62-886b23b041ce/Kalymnos+map.jpg Anna Fleming Kalymnos lies near the coast of Turkey. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c91482d9-562c-42b6-acf5-d430cb0d12e5/Lewis+-+credit+Wil+Treasure.jpg Anna Fleming - Make it stand out Climbing on the Lewisian gneiss, a suite of Precambrian metamorphic rocks, on the western coast of the Isle of Lewis in Scotland. Courtesy of Wil Treasure https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c2f86acc-0d87-4ac0-96a1-3c1af055befc/Mountain+of+books.PNG Anna Fleming - Make it stand out A small mountain of books that sustained Anna Fleming during the COVID lockdown. https://www.geologybites.com/martin-gibling daily 0.75 2025-10-31 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/63b13544-0371-4770-a7f8-b0650a3e807d/Bermuda.jpg Martin Gibling Martin Gibling studies rivers and river sediments around the world. His research has focused on how rivers evolved between the Cambrian and the Devonian when land-based life began to flourish. He has also surveyed the record left by humankind’s effect on rivers from the earliest civilizations to the present day. In the first of two Geology Bites episodes with Martin Gibling, he talks about fluvial deposits in the geological record and the impact of the break-up of Pangea on river systems. In the second episode, he talks specifically about the history of the rivers of Europe and the Americas, as well as the impact of recent ice ages. He ends by considering how humans have changed rivers and their deposits throughout human history. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec60fa6e-e8f1-43c7-b55f-98c10e419100/1.2+GeologicalTimeline.jpg Martin Gibling - Make it stand out Geological timeline for the evolution of the Earth's rivers and other key events. Age dates from Ogg et al. (2016), A Concise Geologic Time Scale, Elsevier https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8d0c2e37-f9f5-4cd0-83f9-f5d3e96cb11f/1.3+FlowDirections.jpg Martin Gibling - Make it stand out Various structures within fluvial sediments can indicate flow direction. Left: cross-beds from the Triassic Hawkesbury Sandstone, Australia. Right: imbrication of boulders in the Cenozoic terrace deposits of the Yellow River, China. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/41aeda19-bcf4-465f-8132-ad945992f5af/1.5+FluvialStyle.jpg Martin Gibling - Make it stand out The main types of river forms on modern river plains are the braided, meandering, and anastomosing rivers. A meandering river has a single sinuous channel. Braided rivers and anastomosing rivers both consist of multiple interweaving channels, but anastomosing rivers have semi-permanent channels separated by floodplain rather than channel bars. The front face of each illustration shows how deposits appear in a rock outcrop. As shown at bottom right, rivers running in valleys create structures that are tens of meters thick as compared to the 5-10-meter-thick features deposited by rivers in plains. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9da4f792-3e81-4d11-bc00-7e8432bf5ee9/2.1JackHillsZircon_JWValley.jpg Martin Gibling Zircon crystal from quartzite rock in the Jack Hills, Western Australia, shown in a colorized cathodoluminescence image. A date of 4.4 billion years based on U-Pb geochronology shows that the crystal is the oldest known piece of the Earth. The date confirms that a crust existed prior to 4.4 billion years ago, which supports evidence for a cool early Earth that was habitable by 4.3 billion years ago. John Valley talked about this in an earlier episode of Geology Bites. Courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/47fc47bc-f5cb-4986-8bc4-ce2c844bb623/3.5+JogginsCliff.jpg Martin Gibling The Joggins Fossil Cliffs, Nova Scotia, Canada, are an example of river and shallow marine strata from the Carboniferous. They include fossil lycopsid trees that were entombed in their growing position when sand from shallow river channels swept through wetland forests. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7106cf00-0512-4cb3-8a96-7e28d37c5ce7/3.7+Relationsships+in+Joggins.PNG Martin Gibling - Make it stand out Relationships between plants and rivers observed in the Joggins Formation of Nova Scotia, Canada. Ielpi et al. (2015), Journal of Sedimentary Research 85, 999 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e48563b3-f49c-49b4-ae9e-920736a5de03/4.2+Pangea.jpg Martin Gibling The supercontinent Pangea, 200 million years ago, with dates of breakup into separate continents. Modified from Seton et al. (2012). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f74ac883-f7f6-43cf-b89a-d417121c21c8/4.3+RiverTimelines.jpg Martin Gibling - Make it stand out The longevity of modern rivers that still flow broadly in their ancestral courses. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2f9353a-f277-4886-aabd-e39ffc9a5ee5/4.4+Modern+African+rivers.PNG Martin Gibling - Make it stand out The modern rivers of Africa. In the podcast, Martin Gibling explains the origin of the Niger’s unusual course (see below). He also suggests that as Pangea was breaking up, the Karoo (Jurassic) and Paraná (Cretaceous) mantle plumes caused southern Africa to dome upwards, with the effect that rivers such as the Zambezi, Limpopo, and Orange drained radially from the rising domes or were diverted around them. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8527355c-d954-4abd-a2b7-b5eb84c79206/4.8+NigerRiverEvolution.jpg Martin Gibling Evolution of the River Niger. During the Cretaceous, the Benue followed a failed rift and was the predominant drainage until the Niger progressively captured its middle and upper reaches, forming a connected river perhaps as recently as 10,000 years ago. Modified from Bonne, K.P.M. (2014), Geol. Soc., London, Special Publication 386, 327 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4e086102-da73-4b30-9760-144e15278ebd/4.6+Nile+History.jpg Martin Gibling Evolution of the River Nile. Through the Oligocene and Miocene, drainage flowed northwest and southwest from the rising rift flank of the Red Sea (top and middle), until the Nile settled into its northward course late in the Miocene (bottom). Modified from Goudie, A.S. (2005), Geomorphology 67, 437 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0f9bff44-4815-4595-ba48-60f21be59f3f/5.1+Modern+Australian+rivers.PNG Martin Gibling - Make it stand out Modern rivers of Australia, showing the rivers flowing into Lake Eyre that are mentioned in the podcast, as well as the Channel Country, which includes Martin Gibling’s favorite river system. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/102eb256-df53-4d04-9cd6-ce29cafa532d/5.2+CooperCreekObliquePhoto.jpg Martin Gibling - Make it stand out Anastomosing channels of Cooper Creek cut into tough floodplain mud near Windorah in central Australia. Courtesy of Google, CNES/Airbus Maxar Technologies https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b24223ba-189e-4554-a46e-f49e22ef2e43/6.2+Modern+rivers+of+Asia.PNG Martin Gibling - Make it stand out Rivers of modern Asia. Many of the depicted rivers are discussed in the podcast, as is the role of the Aravalli Range in northern India that diverted the Ganges away from the Indus, causing it to drain into the Bay of Bengal. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/022e5118-c21f-4dc9-a5a9-37a47344fb10/6.7+EvolutionAsianRivers.jpg Martin Gibling - Make it stand out The maps show the evolution of Asian rivers resulting from the ongoing collision between India and Asia during the Cenozoic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f27dda45-bf94-4416-b893-021ef7267518/6.6+FigureRiverChanges.jpg Martin Gibling Inferred river histories, based on concepts developed on the Colorado Plateau by John Wesley Powell and colleagues in the late 1800s. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/88ea4339-308c-4d43-88cd-d184d482a315/6.1%28A%29+KaliGandakiValley.jpg Martin Gibling - Make it stand out The Kali Gandaki Valley, more than 5 km deep, running south between the 8,000-m peaks of Annapurna and Dhaulagiri in Nepal. The river was antecedent to the most recent period of tectonic uplift, cutting down to keep pace with the rising mountains. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3d725a0c-7cbc-4ae7-b586-914b39e028d7/6.5+SiwalikGroup.jpg Martin Gibling - Make it stand out Former sandbed rivers (pale strata) and floodplain mudstones (red) of the Siwalik Group, laid down on Himalayan megafans and later thrust southward in the Siwalik Hills of India. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fcba083e-06c0-41dd-b2a9-7e75fa1f7eb3/7.4+EvolutionAlpineRivers.jpg Martin Gibling Evolution of rivers in the Alpine region, linked to the collision between Europe, Africa, and several small plates. As the mountain belts rose, rivers flowing south to Tethys were incorporated into the developing Danube, Rhine, and Rhone systems, and the Vistula flowed north from the rising Carpathians. Modified from Kuhlemann, J. (2007), Global and Planetary Change 58, 224 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3331fb0b-ea26-4a95-a112-2cdb7e048300/7.5+EvolutionDanube.jpg Martin Gibling Stages in the evolution of the Danube River. With a large load of Alpine sediment, the river delta advanced into a paleolake in the Pannonian Basin. After cutting gorges through the Iron Gates and elsewhere, the river connected to the Black Sea about four million years ago. Modified from Olariu, C. et al. (2018), Terra Nova 30, 63 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d24832c1-77e6-4bb7-835b-1d94e51d9035/7.7+EvolutionRhine.jpg Martin Gibling - Make it stand out Stages in the evolution of the Rhine River. For much of its history, the river was made up of disconnected drainages. A connected Rhine from the Alps to the North Sea may be as little as three million years old. Modified from Preusser, F. (2008), Netherlands Journal of Geosciences, 87, 7 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f27d33a8-3ae7-479d-b74a-28043e4a4366/8.3+EvolutionAmazonRiver.jpg Martin Gibling - Make it stand out Stages in the evolution of the Amazon and other rivers in the northern part of South America. The 'Sanozama' river initially flowed west along the line of the modern Amazon, but drainage reversed to form the Amazon system as the Andes rose, generating a transcontinental river by nine million years ago. Carme Garzione discussed the history of elevation changes in the Andes in a previous episode of Geology Bites. Modified from Figueiredo J. et al. (2009) Geology 37, 619 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/766cd415-b658-4059-bd83-2b8f07c8a654/8.1%28B%29+SantaremAmazon.jpg Martin Gibling - Make it stand out River Amazon at Santarém, Brazil, where the tidal range is about 20 cm. The photo is a low-season composite (probably taken in December), and islands and sediment bars will be underwater by about March. The Amazon controls the level of the tributary Tapajós River, which forms a natural reservoir for about 100 km upstream from the confluence. The Santarém region hosted many indigenous settlements, and dark anthropogenic soils generated by indigenous cultivation are common. Context provided by Myrtle Shock. Maps data: Google, Maxar Technologies CNES/Airbus Landsat/Copernicus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e8cc15e1-5f30-4b47-8e25-a16b1b6c49e3/9.6+Ancestral+NAmerican+Rivers.jpg Martin Gibling - Make it stand out Stages in the evolution of North American rivers. Northwestward Cretaceous drainage from the Appalachian Mountains was progressively replaced by eastward drainage from the rising Cordillera from the Paleocene onwards, with an increasing influx to the Gulf of Mexico. Modified from Blum, M. and Pecha, M. (2014), Geology 42, 607 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/679872d3-59a7-4f38-9596-6e304b3d5c1b/9.3+GrandCanyon2.jpg Martin Gibling - Make it stand out The Grand Canyon in Arizona, where the Colorado River has cut through flat-lying Mesozoic and Paleozoic strata. The Great Unconformity between Cambrian strata and underlying dark Precambrian metamorphic rocks is visible low in the canyon. Much of the canyon was cut within the past six million years. Becky Flowers discussed the Grand Canyon and the Great Unconformity in a Geology Bites episode about the thermal history of rocks. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f5885fb4-e084-4f9f-ade8-168530e00674/9.7+GulfofMexicoRiverEvolution.jpg Martin Gibling Stages in the evolution of rivers draining into the Gulf of Mexico from the Paleocene onwards. Tectonic and volcanic activity in the Cordillera, rejuvenation of the Appalachians, and the southward advance of the Laurentide Ice Sheet caused individual rivers to vary in importance. Modified from Galloway, W.E. et al. (2011), Geosphere 7, 938 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/efe46013-c97c-492d-9ce4-a73ecd50e997/11.3+YukonRiver.jpg Martin Gibling - Make it stand out Changes in drainage associated with the last Ice Age. The Yukon River initially flowed to the Pacific but later reversed its drainage to the Bering Strait. The Mackenzie River follows a meltwater valley along the mountain front to the Arctic Ocean, cutting through the former Bell River drainage, and may be as little as 12,000 years old. Modified from Duk-Rodkin, A. et al. (2001), Quaternary International 82, 5 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4fbd9d18-31e2-493a-9759-cbd54e08ff1e/12.1%28A%29+DryFalls.jpg Martin Gibling - Make it stand out Dry Falls cut into basalts of the Channeled Scablands, Washington State. In the podcast, Martin Gibling talks about the catastrophic floods that are inferred to have shaped this landscape. This is discussed in more depth in the episode on megafloods with Vic Baker. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bd9a0e59-7940-4345-b306-40bff13663e8/12.2+ScablandGoogleImage_Modified.jpg Martin Gibling - Make it stand out Part of the Channeled Scablands of Washington State, incised through a blanket of loess (wind-blown deposit) into bedrock of the Columbia Basalt Plateau. Maps data: Google, Landsat/Copernicus https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5de2c933-1f0b-4dd2-a294-919698c2f00c/12.3+ScablandsLakesFloods.jpg Martin Gibling Channeled Scablands and glacial lakes bordering the Cordilleran Ice Sheet. The outburst floods were caused by collapse of an ice dam from a lobe of the Cordilleran Ice Sheet, which held back Glacial Lake Missoula. Modified from Waitt, R.B. et al. (2019), Northwest Science 92, 318 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/edfd7c87-d80b-4511-b406-626f1afb2bdb/13.7+ChannelRiver.jpg Martin Gibling - Make it stand out Channel River, which united many of the rivers of Western Europe before its lower course was drowned by post-glacial sea-level rise, leaving its tributaries as disconnected modern rivers. Modified from Gibbard, P.L. (2007), Nature 448, 259 and Bridgland, D.R. (2003), Proceedings of the Geologists’ Association 114, 23 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/355a80a4-fe0a-4ce6-8284-5950669407ee/13.6+Subsea+English+Channel.PNG Martin Gibling - Make it stand out Subsea topography of the English Channel, showing the former Channel River. The river formed largely by great floods after the Weald-Artois ridge was breached in the Dover Strait when the ridge was overspilled by a glacial lake in the southern North Sea. After Gupta, S. et al. (2007), Nature 448, 342 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2275ff51-f4ad-476b-82db-c5ae6a5ea5ba/14.2+AnthroModificationChart.jpg Martin Gibling - Make it stand out Timeline and stages for anthropogenic modification of river systems, based largely on information from the Near East, North Africa, Northwestern Indian Subcontinent, China, and parts of Europe. The timing and intensity of anthropogenic influence vary greatly regionally, with some stages bypassed completely. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b69d5e3d-95ad-46d0-8f2b-485bc928b30e/14.5+AnthroInfluencesIllustration.jpg Martin Gibling - Make it stand out Schematic diagram showing the range of anthropogenic influences on river systems, especially from about 10,000 to 4,000 calendar years BP (Before Present). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6c53d393-c479-4434-90ff-7203a57e445c/14.7+TerracesNepal.jpg Martin Gibling Terraces in the Himalayan Foothills, Nepal, with harvesting of barley. Terrace systems were generated in the Middle East at least 6,000 years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aee15de4-45b7-4b04-aee4-7f13ee8ed021/18.4+GlenCanyonDam.jpg Martin Gibling - Make it stand out Glen Canyon Dam on the Colorado River in Arizona, completed in 1963. The dam holds back Reservoir Powell, which stretches for 300 km through the canyon country. https://www.geologybites.com/john-cottle daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f2d3f58-40a8-4a16-b66d-cb0e3f05b1e2/IMG_9068-2.jpg John Cottle John Cottle leads the team at the University of California, Santa Barbara, that launched a revolution in the field of igneous and metamorphic rock studies. As he explains in the podcast, the method his team developed involves splitting a stream of particles ablated from a rock or mineral sample by a laser beam. Each stream is ionized and enters its own mass spectrometer. One of them measures a radiometric age, and the other simultaneously measures the abundances of certain trace elements or isotopes. He describes how the split-stream method enabled his team to tease out the metamorphic histories of the Greater Himalayan Sequence and parts of Antarctica and New Zealand. The photo shows him in the Miller Range, Antarctica. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1e6342f1-242f-4341-8e30-75913b1ff374/Instrument+Setup+-+LASSICP+paper.PNG John Cottle Instrumentation setup for laser-ablation split-stream petrochronology. The laser is directed towards the sample being analyzed and causes fine particles of the sample to be ablated. The “sample out” stream is then split into two. One stream passes into a multi-collector inductively-coupled plasma (MC-ICP) mass spectrometer, and the other passes into a single-collector inductively-coupled plasma mass spectrometer (SC-ICP). The former instrument has superior isotopic ratio measurement capabilities and measures the uranium-thorium-lead ratios to obtain an age. The latter instrument is capable of rapid measurement over a large mass range and obtains the trace-element abundances. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2f77ce33-1812-4802-8c0c-a1a3992db80d/Instrument+Setup+slide.png John Cottle Details of the instrumental setup for LASS-ICP-MS at UC Santa Barbara. At top left, the laser beam is directed onto the sample in a helium atmosphere. The ablated particles are flushed with argon gas, split into two streams, and passed into two different mass spectrometers. Upon entering a mass spectrometer, the particles are heated by inductive coupling to about 11,000°K when they become ionized and form a plasma (ICP). The Nu Plasma HR machine is a multi-collector MS and is used to measure U-Th-PB isotopes to obtain a radiometric age. The Agilent 7700x Quadruple machine is a single-collector MS and is used to determine trace-element abundances. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7938dae6-6842-494a-9595-86093f188a26/Spot+Size.PNG John Cottle - Make it stand out Photomicrograph of monazite crystals indicating 10-micron-diameter laser spot sizes. This resolution enables multiple analyses to be performed across a single crystal. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/62f823d4-74f8-4786-ab28-b5ad3eacb58f/Multi-domain+ages+in+crystal.PNG John Cottle Images of a monazite crystal showing (R) the location where spot analyses were performed. The LASS analysis revealed that the crystal has several domains, each having a different age (L). The image at right was obtained using electron-probe microanalysis and shows the abundance of the trace elements yttrium and lanthanum (R). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8f2b5372-cc26-4241-8496-e8cbb66ef5b6/trace+elements+in+crystal.PNG John Cottle https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5d820431-8dea-411d-90a0-d941eb7d3830/Monograph+Fig.+4.8.PNG John Cottle Two-dimensional maps and trace-element variation diagrams of a zoned zircon crystal made using the split-stream laser-ablation technique. At top left is a reference cathodoluminescence (CL) image of the crystal showing an oscillatory zoned core (C1 and C2) surrounded by a mantle, which is in turn enveloped by a younger rim (dark). The crystal was analysed by directing the laser at the array of spots shown at top center. The top right map shows the results of the age determinations and reveals a ~ 2.8-billion-year-old igneous core with oscillatory zoning that was partially resorbed and overgrown in the late Archean and early Paleoproterozoic. The outer rim grew around 2.1 billion years ago. The remaining maps show the measured abundances of the trace elements uranium, thorium-uranium ratio, yttrium, dysprosium, gadolinium, and titanium. These reveal that the trace-element concentrations vary considerably across the crystal, even over regions that have crystallized at the same time. Such microstructure would have been invisible to the prior single or small-number spot analyses. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9809df63-78d1-48d0-b0d3-2b0bb9c03bce/Monograph+Fig.+4.8+graphs.PNG John Cottle - Make it stand out Plots of trace-element concentrations and ratios colored by U-Pb date for the zircon crystal shown in the maps above. The plots show that, for a given age, there is no correlation between the Gd/Yb and Th/U ratios, with the former being essentially constant, and the latter varying over about three orders of magnitude. In contrast, for given age domains, there is a marked positive correlation between U and Y. Correlations among these element concentrations and ratios can provide useful information about the changing nature of the source region from which the zircon crystallized over time. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92f96b9d-71e2-498c-b5d8-5c748bb90774/4.9+3D+crystal+map.PNG John Cottle By performing successive measurements while drilling down into a crystal with the laser, it is possible to create three-dimensional maps of the age and trace-element concentration within a single crystal. The example shown here is a zoned Himalayan monazite crystal. (a) Diagram showing the position of each spot analysis. The resulting maps consist of 14,526 individual laser pulses. (b) Three-dimensional isotopic date and trace-element concentration/ratio maps and cross sections. (c) Representation of different age domains identified within the monazite crystal. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7c40d868-665e-404d-a8d9-82285a75d766/4.9+b.PNG John Cottle - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00b3ddb9-236a-4141-b9c3-38b29365132a/4.9+c-cut.PNG John Cottle - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7ae38814-ac50-44bc-bd85-f7b51c4781cf/P-T-t.png John Cottle - Make it stand out The diagram shows how the metamorphic history of a rock has been determined using the methods described in the podcast. The graph, called a pseudosection, is a pressure-temperature phase diagram generated specifically for the modal abundances of elements present in the rock. The shaded areas show the pressure-temperature loci at which the various mineral combinations are stable. These are determined from a series of experiments, phase diagrams, and thermodynamic data over a range of pressure and temperature for a given bulk composition. By obtaining a date for each domain in a rock that exhibits a particular mineral combination, we can obtain a pressure-temperature trajectory over time, as shown by the heavy black arrow. The results indicate that 40 million years ago, the rock was at a pressure of about 7 kbar (corresponding to a depth of about 25 km) at a temperature of 600°C. It was then heated to a temperature of about 630°C, after which, about 33 million years ago, it began to cool during exhumation (dropping pressure). and=andalusite, bt=biotite, chl=chlorite, cor=corundum, crd=cordierite, gnt=garnet, ilm=ilmenite, ky=kyanite, pl=plagioclase, qtz=quartz, ru=rutile, sill=sillimanite, and st=staurolite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/876277d8-6318-448b-bb40-49ece402964e/IMG_7471.JPG John Cottle - Make it stand out LASS instruments in the UC Santa Barbara petrochronology lab. The instrument in the foreground is a multi-collector inductively-coupled plasma mass spectrometer. The six vertical periscope-looking black boxes are the ion detectors. This instrument is able to measure very precise U-Th-Pb or Sr, Nd, Hf isotopic compositions and is used for the age determinations. The instrument at far left with the orange logo and window is the laser-ablation system. The very thin tube exiting the gold-colored box of the ablation system contains argon and carries the ablated particles into both mass spectrometers. Directly behind the laser (barely visible) is a single-collector inductively-coupled plasma mass spectrometer, which measures trace-element concentrations and/or U-Th-Pb isotopes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8e47f809-242c-40d2-9ce0-600e1890512c/Campaign_style_U_Pb_titanite_petrochronology+2018+Himalaya.jpg John Cottle - Make it stand out Geological map of the Himalaya showing regions where a “campaign-style” study of the Greater Himalayan Sequence was conducted using the split-stream method to obtain U-Pb dates from the mineral titanite. The study used 47 different samples collected by 18 different geologists from various structural levels along over 2,000 km of the Greater Himalayan Sequence from northwest India to central Bhutan. The colors indicate the main geological formations. TSS=Tethyan Sedimentary Sequence; GHS=Greater Himalayan Sequence; LHS=Less Himalayan Sequence. The sample locations are shown by dots that are color-coded according to age, as shown in the map legend. The yellow labels are the names of the analyzed samples. The close-up maps show the regions from which samples were obtained and the ages obtained. a. Sutlej valley. b. Western Nepal. c. Annapurna area. d. Langtang. e. Mt. Everest. f. Eastern Nepal. g. Sikkim. h. Western Bhutan. i. Central Bhutan. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6c30d281-219d-462a-8b41-a676ac7341a5/Mottram+Fig.+11.PNG John Cottle - Make it stand out Conceptual model derived from the petrochronological study described above showing multiple slices in the Greater Himalayan Sequence (GHS) in both western (a) and eastern (b) Nepal. MFT=Main Frontal Thrust, MBT=Main Boundary Thrust, MCT=Main Central Thrust, and MHT=Main Himalayan Thrust. Mottram, C.M., et al. (2019), Geoscience Frontiers 10, 827 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02b12a96-7f9a-4d6d-9e91-79272d570e02/Hagen+Fig+1.PNG John Cottle In the podcast, John Cottle describes the application of the new petrochronological methods to a >3,000 km-long belt of deformed and metamorphosed sedimentary rocks in the Ross orogen of Antarctica. The map shows the rock units exposed in the Transantarctic Mountains. All Antarctica figures from Hagen-Peter, G. et al. (2016), Journal of Metamorphic Geology 34, 293 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c04019b9-07ae-47bb-ac10-8108546f4bfe/Hagen+Fig+4.PNG John Cottle - Make it stand out Field photographs of some of the sampled rocks. (a) Large-scale folds in interlayered marble, calc-silicate, and schist. (b) Sketch interpretation of the outcrop in (a). (c) Multiply-folded marble, which makes up most of the rocks in the study area. (d) Deformed and migmatitic paragneiss hosts intrusions of granite. (e) Migmatitic paragneiss with boudinaged leucosomes. (f) Garnet-tourmaline schist in contact with amphibolite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e1b5e95c-36f0-42b5-bf13-082fa49bc1ae/Hagen+Fig+11.PNG John Cottle Timeline summarizing the geochronology of metamorphic and igneous rocks spanning over 1,500 km along the Ross orogen. Using the techniques described in the podcast, John Cottle and his team identified a longer span of metamorphic events than had previously been seen. This provided evidence for the sequence events shown in the tectonic model of the Ross orogen shown below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9789bcbe-e91c-4c3d-a169-de06c28f3e56/Hagen+Fig+17.PNG John Cottle Simplified tectonic model for the evolution of the Ross orogen that explains the petrochronological observations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1dd76902-37cb-4310-bfa3-d370829a8701/Briggs+Fig+1+NZ.PNG John Cottle - Make it stand out John Cottle applied the split-stream laser-ablation methods to unravel the metamorphic history of Zelandia as it separated from Gondwana during the Cretaceous. (A) Map of the study region in New Zealand’s South Island showing the locations from which samples were obtained. The dotted lines show the metamorphic isograds that bound the regions containing the indicated metamorphically-generated minerals. Grt=garnet, Mnz=monazite, Zrn=zircon, and Kspar=K-feldspar. (B) Schematic cross section across South Island along the transect shown in the top left inset in A. The diagram is derived from the metamorphic history obtained from the combined geochronology and trace-element geochemistry of the samples obtained along the fault. Briggs et al. (2018), Lithosphere, 11, 169 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/de96e58a-fde9-49fa-b73b-2bc6fdd03a37/Briggs+Fig+2+NZ.PNG John Cottle Outcrop photographs of the granitic pegmatites from which the samples for the study referred to above were drawn. (A) Pegmatite sills within the Alpine Schist of New Zealand’s South Island. (B) Isoclinally folded pegmatite dike from which one of the samples was taken. (C) Quartz veins cutting the pegmatite parallel to sill margins. (D) An example of a graded, irregular sill margin. (E) Boudinaged pegmatite sill. (F) Pinching and swelling of a pegmatite. (G) The gneissic host rock surrounding the pegmatites. Briggs et al. (2018), Lithosphere, 11, 169 https://www.geologybites.com/john-cottle-transcript daily 0.75 2023-02-09 https://www.geologybites.com/martin-gibling-part-1-transcript daily 0.75 2023-02-09 https://www.geologybites.com/martin-gibling-part-2-transcript daily 0.75 2023-02-09 https://www.geologybites.com/anna-fleming-transcript daily 0.75 2023-02-09 https://www.geologybites.com/nadja-drabon daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7477d178-983a-49f5-8e83-29b7ac6f5f31/ND+closeup.png Nadja Drabon Nadja Drabon’s research aims to unravel the processes that formed the Earth’s earliest crust. She does this by studying extremely ancient zircons. These are few and far between, so the discovery of a new source of such zircons in the Barberton Greenstone Belt of South Africa was exciting to early Earth researchers. In the podcast, she describes how she and her team used these zircons to discern a significant change in crustal processes about 3.8 billion years ago when much more fresh crust began to form. Nadja Drabon is Assistant Professor of Earth and Planetary Sciences at Harvard University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0f348e0d-2c04-429c-980b-6466622afcca/Timescasle+Precambrian+BGS+copyright+UKRI.jpg Nadja Drabon Geological timeline showing the division of the Precambrian into the Hadean, Archean, and Proterozoic eons. In the podcast, Nadja Drabon discusses zircon crystals that were formed in the Hadean or early Archean. The zircons are detrital, their parent rocks having disappeared. Courtesy of BGS and UKRI https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e0433e5d-53dc-4b02-b369-47be0e34f1f0/Hadean+to+present.PNG Nadja Drabon - Make it stand out The Hadean Earth is thought to have been covered by an ocean of magma before it started forming its first solid crust. Early Earth researchers aim to discover what the Earth was like following the formation of the first crust and before the modern Earth developed, with its thick continents and thin, subducting seafloor. Courtesy of Alec Brenner and NASA Earth Observatory https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/026896f7-9d38-41c1-8d24-6397d0bcb8cf/locations+of+Hadean+zircons.PNG Nadja Drabon Hadean zircon locations. The vast majority known to date have been found in the Jack Hills in Western Australia. Nadja Drabon and her colleagues discovered Hadean zircons in the Green Sandstone Belt of the Barberton Greenstone Belt (BGB) in South Africa. This provides us with an opportunity to test how representative the Jack Hills zircons are of the Hadean Earth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5b61fef1-c022-49f3-bc6f-92dfb0b8867a/comparison+between+GSB+and+Jack+Hills.PNG Nadja Drabon - Make it stand out Comparison between the Green Sandstone Bed (GSB) and the Jack Hills. The ages given above are for the ages of the host sandstones that contain the Hadean zircons. The GSB is better preserved than the Jack Hills since it has been subject to less extreme metamorphism (greenschist vs. amphibolite facies). Furthermore, the GSB was silicified early in its history, enabling structures down to micron scale to be preserved., which allows for studies of the rock’s microstructure. Jack Hills photo courtesy of Bruce Watson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/88e6529d-e6d2-4542-8dd3-68df1adca917/pic+of+Green+Sandstone+Belt.PNG Nadja Drabon Field location of the Green Sandstone Belt, where the rocks appear in scattered outcrops. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b61b987e-b1e8-4145-a8bb-19b99d8b1f2b/Zircon+age+statistics.PNG Nadja Drabon Age distribution of the detrital zircons found in the Green Sandstone Bed. The inset shows the age distribution of the zircons older than 3.6 billion years (Ga). Only 0.5% of the zircons are Hadean, i.e., have ages greater than 4 Ga. This contrasts with the Jack Hills, where 3-12% of the zircons are Hadean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7212e303-986f-43a1-a6fa-e8578c38fc95/zircon+zoning.PNG Nadja Drabon Photomicrographs of ancient zircons using cathodoluminescense to reveal various domains formed during different phases of the zircon’s history. Since each domain may have a different age and different isotope and trace-element composition, it is crucial to position the laser beam that ablates the particles for the U-Pb dating in precisely the same location as the laser beam generating the particles for the trace-element and isotope abundance measurements. This “registration” problem was overcome by the split-stream laser-ablation method described by John Cottle in the previous podcast episode. As she explains in the podcast, Nadja Drabon did not use the split-stream method as it would not have provided sufficient mass-spectrum resolution to distinguish the trace elements and rare-earth elements that she analyzed. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/edc48f28-d940-42fe-baf0-e2f3b15a70c0/Hafnium+principles.PNG Nadja Drabon - Using Hafnium to probe crust-mantle differentiation The method is based on the beta decay of 176 lutetium to 176 hafnium, which has a half life of 37 Ga. The graph plots a measure of the ratio of hafnium 176 to hafnium 177 (which is constant) relative to the chondritic uniform reservoir (CHUR) over time. CHUR is the mean chemical composition of the part of the Solar Nebula from which the Earth formed. Since lutetium preferentially stays in the mantle as compared to hafnium, the rate of hafnium 176 production is greater in the mantle than in the crust. This is shown by the upward sloping line for depleted mantle (DM, i.e., the mantle after removal of crustal material). Juvenile crust is freshly formed from the mantle, and thus contains the Hf ratio similar to that of the mantle and plots closer to the line labeled DM. Rocks formed out of old crust (blue dots) reflect the signature of the mantle when it was originally extracted, with only a slight increase from decay of the small amount of 176 Lu that enters the crust. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9fceebef-5091-466a-8dc8-a9dd94050e4b/hafnium+data+with+superposed+ideals.PNG Nadja Drabon - Make it stand out Results of the hafnium isotope analysis for the GSB zircons. Before about 3.8 Ga, most of the zircons plot well below the CHUR line, suggesting that they formed out of old crust. These zircons fall on a range of eHf vs. time, which suggests that it was the same old crust that was extracted in the Hadean and subsequently repeatedly melted and recrystallized. After 3.8 Ga, the distribution of zircons spans a larger range of 176Hf/177Hf, including values that lie above the green arrow and the CHUR line, suggesting that they formed out of magmas generated from mixed juvenile and old crust. The plot above the hafnium graph shows the age distributions of zircons found in the bottom and top layers of the Green Sandstone Bed. The inset is a detailed enlargement of the older zircon populations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/679920da-4356-479f-98ca-dde317fcf8c6/sagduction.jpg Nadja Drabon In the podcast, Nadja Drabon describes a possible process by which Hadean and Archean crust might be exposed to and interact with fluids before the onset of modern plate tectonics. The diagram compares the subduction zone of modern plate tectonics with a theorized “sagduction” of a hot crust in the Hadean and early Archean. Stern, R.J. (2013), GSA Geoscience Blog https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4d42a0ce-a029-457a-8a51-1b0eec17ed05/Trace+elements+Fig.+3+in+2022+paper.jpg Nadja Drabon - Make it stand out Nadja Drabon and her colleagues measured the abundances of certain trace elements within the ancient zircons of the GSB. By plotting various ratios of these trace elements on graphs, it is possible to compare the distribution of the GSB zircons with those of zircons known to have formed in one of the modern settings in which magma is generated and then cools to form igneous rocks (tectono-magmatic settings). The colored fields represent a global compilation of zircons from different Phanerozoic (i.e., post 539 Ma) tectono-magmatic settings. The dots on the graphs are color-coded by age and reveal that the zircons older than 3.8 Ga overlap with relatively undepleted mantle, but that zircons younger than 3.8 Ga overlap with volcanic arc settings as well as undepleted mantle. Since modern volcanic arcs are characterized by melting in the presence of water, this suggests that water, maybe even an ocean, was present after 3.8 Ga. Grimes, C.B. et al. (2015), Contributions to Mineralogy and Petrology, 170(5), 1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f1b7b6fa-2189-476b-8564-73e528a2147a/oxygen+isotope+geochemistry.jpg Nadja Drabon - Make it stand out In the third type of zircon analysis described in the podcast, Nadja Drabon measured the abundance of oxygen isotopes. The ratio of 18O to 16O in a zircon is a sensitive temperature-dependent tracer of fluid and solid interactions in the crust. This ratio is determined by the thermodynamic equilibrium between the melt out of which the zircon formed and the material around it. Zircons with low values of 18O to 16O are consistent with melts derived from the mantle. Zircons that formed in melts that formed from or assimilated crust altered at low-temperature show higher values (> 6.5 ‰), and zircons that assimilated crust altered at high temperature show lower values than the mantle. VSMOW = Vienna Standard Mean Ocean Water, which is an isotopic standard for pure water with no salt or other chemicals found in the oceans. It is the water molecules that are taken from the ocean. The delta notation (symbol: δ) expresses the variation of the isotopic ratio of 18O/16O) relative to the isotopic ratio of VSMOW. Roberts, N.M.W. et al. (2014), Continent Formation Through Time, Geol. Soc. London Special Pub., 389 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e8de0f93-7036-47ea-8f39-a3892f3cc6c7/GSB+oxygen+plot.png Nadja Drabon - Oxygen isotope results for the Green Sandstone Bed The GSB contains zircons that show elevated δ18O values in the Hadean, which supports the notion that a hydrosphere was present even at that very early time. The plot above the oxygen isotope graph shows the age distributions of zircons found in the bottom and top layers of the Green Sandstone Bed. The inset is a detailed enlargement of the older zircon populations. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3316d1b4-0af3-4ec9-861f-d0db83aea673/global+comparison+of+Hf+ratios.png Nadja Drabon - Make it stand out Plots of hafnium isotope ratios in zircons taken from Archean rocks in various parts of the world with the GSB zircons superposed (black dots). As described for the hafnium isotope plots above, zircons older than 3.8 Ga predominantly plot below CHUR and over a broad range, suggesting reworking of older crust. New crustal additions, which plot above the arrows, only became common after 3.8 Ga. The results are broadly consistent with a global change between 3.8 and 3.6 Ga, when the Earth’s outer layer may have transitioned from a stagnant old crust (stagnant lid) to mobile lid tectonics. Bauer, A. et al. (2020), Geochem. Perspect. Lett. 14, 1-6 https://www.geologybites.com/geoff-abers-transcript daily 0.75 2023-02-09 https://www.geologybites.com/new-page-2 daily 0.75 2022-12-31 https://www.geologybites.com/martin-gibling-part-1-glossary daily 0.75 2023-01-27 https://www.geologybites.com/martin-gibling-part-2-glossary daily 0.75 2023-01-27 https://www.geologybites.com/anna-fleming-glossary daily 0.75 2023-01-27 https://www.geologybites.com/dan-rothman daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/07d5b874-f318-4240-95f3-6914c9e2d5d1/DR+portrait+Hayes.jpg Dan Rothman Dan Rothman’s current research aims to understand the dynamics of the Earth’s carbon cycle. As he discusses in the podcast, he thinks there is strong evidence in the sedimentary record that major disruptions in the carbon cycle throughout the Phanerozoic reflect a characteristic flux of carbon into the system. This characteristic flux holds over two orders of magnitude of variation in the duration of the observed disruptions. By interpreting this flux as an upper bound of a critical rate set by the intrinsic dynamics of the Earth’s carbon cycle, he derives a critical mass of carbon that, when injected into the system, causes a disruption. A disruption in the carbon cycle is coincident with each of the major extinctions. He shows that the mass of anthropogenic carbon emissions forecast by the end of the century is about the same as the mass of carbon dioxide outgassed by the massive volcanism that generated the portion of the Deccan Traps deposited just before the end-Cretaceous extinction. Dan Rothman is Professor of Geophysics at the Massachusetts Institute of Technology. Photo courtesy of John Hayes https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ab63d14b-63ac-4b98-8c3b-6652a055c786/carbon+cycle.PNG Dan Rothman - Make it stand out Key fluxes in the carbon cycle. Fueled by solar energy, plankton and plants use photosynthesis to convert carbon dioxide to organic carbon in the form of carbohydrates. Further up the food chain, other organisms use organic carbon as an energy source, converting it back to inorganic CO₂ via the process of respiration. The diagram shows the partitioning into organic (green) and inorganic (black) reservoirs of carbon. Since photosynthesis favors the lighter isotope of carbon (¹²C), the amount of the heavier isotope (¹³C) is depleted in organic carbon with respect to the planetary average. The amount of depletion is expressed as a measure of how much the ratio of the two isotopes departs from the planetary average in parts per thousand (δ¹³C). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c85a659d-7902-4d13-a06e-ada2d342d964/Ridgwell+and+Zeebe+Carbon+cycle-1.jpg Dan Rothman - The global biogeochemical cycling of calcium carbonate. (a) Modes of calcium carbonate transformation and recycling within the surface system and loss to the geological reservoir. 1. Precipitation of calcite by coccolithophores and foraminifera. 2. Carbonate reaching deep-sea sediments dissolves if the bottom water under-saturated and/or the organic matter flux to the sediments is sufficiently high. 3. Precipitation of calcium carbonate by corals and shelly animals. 4. Precipitation of calcium carbonate results in higher CO₂ at the surface, driving a net transfer of CO₂ from the ocean to the atmosphere. (b) Modes of calcium carbonate transformation and recycling with the geological reservoirs and return to the surface system. 5. Calcium carbonate laid down in shallow seas as platform and reef carbonates and chalks can be uplifted and exposed to erosion through rifting and mountain-building episodes. Calcium carbonate can then be directly recycled through combination with water and carbon dioxide to calcium and bicarbonate ions. 6. Thermal breakdown of carbonates subducted into the mantle or deeply buried. The decarbonation reaction is essentially the reverse of silicate weathering, and results in the creation of calcium silicates and the release of CO₂. 7. Weathering of silicate rocks in which calcium silicate combines with water and CO₂ to produce calcium and bicarbonate ions and silica. 8. Emission to the atmosphere of CO₂ produced through decarbonation. This closes the carbon cycle on the very longest tmie-scales. Ridgwell, R.E. et al. (2005), Earth and Planetary Science Letters 234, 299 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6f6737fc-d377-4ee4-864d-c54a0bf91349/PETM+C+isotope+plot.PNG Dan Rothman In the podcast, Dan Rothman describes the disruptions in the carbon cycle recorded in the ratios of stable carbon isotopes in carbonate rocks. He catalogued 31 such disruptions over the course of the Phanerozoic. The plot shows one of these events when ¹³C was depleted with respect to ¹²C during the Paleocene-Eocene Thermal Maximum (PETM), which occurred about 55.8 million years ago. The inset shows the abrupt onset and subsequent decay of the event in detail. The timescales of the events were obtained from deep-sea cores in the South Atlantic and in the Weddell Sea. The magnitude of the isotopic excursion (2.7 ± 1.1‰) was obtained from analyses of PETM carbonates formed from the skeletons of foraminifera. Note that the δ¹³C scale is inverted, with δ¹³C values being increasingly negative along the positive y direction. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/462163ed-13ed-48e0-a680-0cd7764dbed0/Extinction+rates.PNG Dan Rothman Extinction rates for marine animals during the Phanerozoic. The “Big Five” extinctions are labeled: end-Ordovician (Ord), Frasnian-Famennian (FF), end-Permian (PT), end-Triassic (TJ), and end-Cretaceous (KT). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/873017a4-595f-4523-8635-bcc42a629e3f/Size+of+disruption+vs.+diration.PNG Dan Rothman This is the key plot discussed by Dan Rothman in the podcast. It shows the relative sizes (m = mass of carbon) versus the durations of 31 disruptions of the carbon cycle during the Phanerozoic. The red dots mark the disruptions corresponding to the five major mass extinctions (see figure above), while the blue dots represent disruptions that were not associated with unusually high rates of extinction. The straight line denotes a characteristic rate of change of the carbon in the Earth system. Most of the events fall near the line (gray region), while four of the five events corresponding to the major mass extinctions fall above the line. The fifth mass extinction, in the late Devonian at the Frasnian-Famennian boundary, is clearly different, lying in the slow region below the line. Some researchers have suggested that the Frasnian-Famennian event is not an extinction event but instead represents a decrease in the rate at which new species originate. Rothman, D.H. (2017), Science Advances, 3:e1700906 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ed5ce251-cf78-4824-8c94-eebd3317f65e/Critical+mass+and+rate.PNG Dan Rothman (a) Thresholds for mass extinction expressed in terms of a critical mass Mc of carbon at timescales short compared to the principal damping timescale τ (left side of plot) and at timescales longer than the damping timescale (right side of plot). At longer timescales, the Earth system damps an injection of carbon, and so the amount of carbon that can be absorbed before the system becomes critical is proportional to the duration of the carbon-injection event. At short timescales, the carbon injection is akin to an impulse, or delta function, and the Earth system undergoes an excursion when more than a constant critical mass is injected. (b) In this plot, the critical mass is converted into a critical rate of change of carbon. For short timescales, the rate is proportional to 1/T, whereas for long timescales, the rate is constant and corresponds to the straight line in the figure above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/41111899-726b-46a6-8bf3-e7ed22b6933a/Anthro+and+KT.PNG Dan Rothman Comparison of perturbations of the modern and end-Cretaceous (KT) carbon cycles with Dan Rothman’s hypothesis for the upper bound of the threshold for excitation of the Earth’s carbon cycle (left part of figure (b) above). The dots correspond to four different estimates for the amount of anthropogenic emissions over the present century. The size of the end-Cretaceous carbon injection is an estimate of the amount of CO₂ emitted by massive volcanism over a few tens of thousands of years just before the extinction occurred. Since the excitation threshold scales with the inverse of the event duration, both the modern and ancient perturbations are equivalently near it, even though the end-Cretaceous carbon injection was 100 times larger than the modern one. Rothman, D.H. (2019), PNAS 116, 14813 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/becd8c82-9e2c-4143-a93b-25247b0d4895/Map+of+Deccan+Traps.jpg Dan Rothman The Deccan traps are extensive thick sequences of lava that were erupted at the close of the Cretaceous. While the Chixclub meteor impact is widely thought to be the direct cause of the extinction, some researchers, including Dan Rothman, hypothesize that the disruption of the carbon cycle caused by the outgassing of CO₂ during this prolific series of eruptions contributed to the environmental change associated with the end-Cretaceous mass extinction. Courtesy of Courtney Sprain https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a1c83e3-5570-4b6b-a04f-ea98d00a962c/Western-Ghats-Matheran+-hr.jpg Dan Rothman Eroded hills of the northern Western Ghats in Maharashtra, India, composed of end-Cretaceous basaltic lavas. Periods of massive volcanism generate flood basalts which form today’s large igneous provinces. Courtesy of Nichalp https://www.geologybites.com/nadja-drabon-transcript daily 0.75 2023-02-09 https://www.geologybites.com/nadja-drabon-glossary daily 0.75 2023-02-09 https://www.geologybites.com/maria-mcnamara-transcript daily 0.75 2023-02-09 https://www.geologybites.com/maria-mcnamara-glossary daily 0.75 2023-02-09 https://www.geologybites.com/romain-jolivet daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/52d817f2-b9b6-4c1d-aa32-e0093cac7746/magueule.jpg Romain Jolivet Romain Jolivet studies active faults and the relative motion of tectonic plates. His research focuses on the relationship between slow, aseismic slip that occurs “silently” between earthquakes and the rapid slip accompanying earthquakes. As he describes in the podcast, he uses interferometric synthetic aperture radar (InSAR) images from radar satellites to examine surface deformation over wide areas at meter-scale resolution. InSAR images of the 2023 Turkey-Syria earthquakes reveal complicated slip patterns occurring on well-recognized plate boundary faults as well as on hitherto ignored faults. Romain Jolivet is a Professor of Geoscience at the École normale supérieure in Paris. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7b7be3dd-ab57-48d5-81b7-e2a3e1ead1c1/Barbot+et+al+context.jpg Romain Jolivet - Make it stand out Tectonic setting of the Anatolian plate. The Mediterranean Basin, including Anatolia and the Aegean Sea. Red lines mark the major faults that accommodate the westward movement of Anatolia. The barbed black lines show subduction zones, the yellow circles show earthquakes of magnitude 3 and above, and the red triangles show volcanoes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/957ade6a-8933-4676-bb5b-4661cdcdfca2/Barbot+E+Med+context+w+rectangle.jpg Romain Jolivet - Make it stand out Close-up view of the Eastern Mediterranean region. Westward movement of Anatolia (light brown region) results from the collision between Africa, Arabia, and Eurasia as well as the Hellenic subduction zone to the south and rollback (i.e., retreat) of the subducting African plate. The Aegean Sea (turquoise region) is undergoing rapid extension, thought to be driven by slab rollback. Slab rollback is discussed in the previous podcast with Laurent Jolivet, and animated visualizations appear on that episode’s web page. The main movement of the February 2023 earthquakes occurred along the East Anatolian Fault (EAF) and the North Anatolian Fault (NAF). The Hellenic volcanic arc is colored purple. Black arrows indicate the local velocity relative to Eurasia. The black lines indicate subduction zones. The rectangle indicates the region covered by the map of the East Anatolian Fault segments shown below. BZS, Bitlis-Zagros Suture; CAFZ, Central Anatolian Fault Zone; DSTF, Dead Sea Transform Fault; EFZ, Ezinepazarı Fault Zone; KTF, Kefalonia Transform Fault; MAF, Movri-Amaliada Fault; MOF, Malatya-Ovactık Fault; NAT, North Anatolian Trough; TIP, Turkish–Iranian Plateau. Barbot, S. & Weiss, J.R. (2021), Geophysical Journal International, 226, 422 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/527b3fce-e72e-4b67-8f07-c87db6acf8b4/Guvercin+et+al+map+w+stars.jpg Romain Jolivet - Make it stand out Segments of the East Anatolian Fault derived from the historical earthquakes and geology along the fault. The pink and orange stars indicate the locations of the February 6, 2023, magnitude 7.8 and 7.5 earthquake epicenters respectively. The magnitude 7.8 earthquake ruptured the East Anatolian Fault , while the magnitude 7.5 earthquake occurred along the Sürgü fault, which branches to the west from the East Anatolian Fault. The red braces indicate the extent of slip along the named historical earthquakes. Note that in the map, north is to the top right. FC: Fault Complex; RB: Releasing Bend; RtB: Restraining Bend; DRrB: Double Restraining Bend; PB: Paired Bend; Ulv: Uluova; NAF: North Anatolian Fault. Guvercin, S.E., et al. (2022), Geophysical Journal International 230, 50 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fc3c2951-5ae2-4944-9d73-0d9db007d1c1/earthquake+sequence.jpg Romain Jolivet The history of major earthquakes along the North Anatolian Fault (colored purple and yellow) showing how the earthquakes have migrated to the west. The color shading shows surface movement, with blue representing east-to-west movement and red west-to-east. Hussain, E., et al. (2018), Nature Communications 9, 1392 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6abb8c15-8e07-410e-8500-4957d4eebac6/INSAR+concept.png Romain Jolivet InSAR images are interferograms obtained by subtracting a synthetic aperture radar image of the Earth’s surface from a second such image captured during a subsequent orbit of a radar satellite. The images are colored to represent the phase difference between the two images. The closer the fringes, the greater the deformation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b87502f0-2d6a-42a3-b850-9eb4082070b7/INSAR+subtraction.JPG Romain Jolivet https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dfe9c704-6ca2-4c2c-ae63-634962dc13b7/Sentinel+1.png Romain Jolivet - Make it stand out The InSAR image of the earthquake region described by Romain Jolivet in the podcast. It is an Interferogram of the earthquake region generated by subtracting radar images captured on successive passes of the Sentinel 1 satellite on January 29 and February 10, 2023. The earthquakes occurred on February 6. The satellite captures a 250-km-wide swath of the Earth’s surface and revisits the same location every 12 days. The image is centered on the East Anatolian Fault. The interferogram fringes appear to converge on the fault at points about 300 km apart, indicating the approximate length of the surface rupture. As explained in the podcast, deformations cannot be observed near the fault where the deformation was large and coherence was lost. The rate at which the deformation decreases (indicated by fringe spacing increases) is a measure of the extent of the slip at depth, with slip extending to greater depths causing deformation to extend farther away from the fault. The circles indicate the location of earthquakes, the largest two white ones being the magnitude 7.8 and 7.5 earthquakes of February 6. Sentinel 1 (ESA/Copernicus) InSAR processing by ISCE https://www.geologybites.com/romain-jolivet-glossary daily 0.75 2023-03-02 https://www.geologybites.com/romain-jolivet-transcript daily 0.75 2023-03-08 https://www.geologybites.com/patrick-fulton daily 0.75 2023-11-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d7c541fd-f80d-40a5-8804-a8878f2a8b74/Patrick+Fulton-welcmoe+Cornell.jpg Patrick Fulton Patrick Fulton uses observation, quantitative analysis, and numerical modeling to study heat and fluid in fault zones. He applies his research to the physics of earthquakes, tectonic processes, and the transport of subsurface heat and fluids. In the podcast, he describes how he and his team installed a borehole “temperature observatory” below 7 km of ocean. The observatory detected the remnants of frictional heating generated by the slip that caused the 2011 Tōhoku Earthquake and the devastating tsunami that led to the Fukushima nuclear disaster. Patrick Fulton is an Assistant Professor in the Department of Earth and Atmospheric Sciences at Cornell University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/49697fb3-a08f-49dc-94b4-36ee18932316/Google+Earth+map.JPG Patrick Fulton Google Earth image of Japan and a portion of the western Pacific. The Pacific plate is subducting at the Japan trench, which is the dark feature extending from top right to the bottom of the image. The earthquake epicenter was about 45 miles off the eastern coast of Honshu, Japan’s largest island. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ac9f4462-cac0-42c0-bbd5-fa4e7620b56a/map.png Patrick Fulton Map of the 2011 Tōhoku earthquake region, with the red star showing the earthquake’s epicenter. The Japanese island of Honshu sits on the small Okhotsk plate. The Pacific plate is subducting under the Okhotsk plate at the Japan trench, and is moving to the west northwest towards the trench, as indicated by the large black arrow. The shaded regions bounded by the solid contours indicate the amount of seafloor movement during the earthquake. The site of the borehole observatory discussed in the podcast is shown by the red dot labeled JFAST Site C0019. The other red dots show other sites where core samples were drilled and used for comparison with those from the JFAST borehole. The dotted line shows the extent of seafloor slip accompanying a tsunami-generating earthquake that occurred in 1896. Chester, F.M. et al. (2013), Science 342, 1208 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e385a583-80ba-4d19-887a-c46de229a797/Chester+et+al+3+in+1.jpg Patrick Fulton Seismic profile through the borehole site. The profile is annotated to show the accretionary prism (grey), ocean sediments (yellow), and oceanic igneous crust (green). The inferred location of the boundary fault between the Pacific Plate and faults in the overlying sediments is marked as black lines. The location of the borehole (C0019) discussed in the podcast is shown in red, and the black lines at right show locations of other boreholes. Chester, F.M. et al. (2013), Science 342, 1208 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a84861b-15ef-4f94-8b0b-4f987677c204/Sesimic+profile+detail.JPG Patrick Fulton Detail of the region marked by the rectangle shown in the seismic profile shown above. The pattern of lines indicates the various surfaces from which seismic reflections were received. The most significant feature is a faint but continuous reflecting boundary, which is interpreted as the plate-boundary fault. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/031ab8e2-5c28-4026-8423-87380d38b9cb/friction+principle+slides+6ff.JPG Patrick Fulton A main goal of the JFAST project was to measure the increase in temperature at the fault rupture and use that to infer the shear stress. The weight of the overlying rocks provides an estimate of the normal stress. Plugging these numbers into the formula gives the coefficient of friction along the slip surfaces. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/872a11a6-ee52-49a5-98a2-46281b76b15f/slide+22+drill+ship+used+April+1+2022.jpg Patrick Fulton The Chikyu deep-sea drilling vessel used to drill the JFAST borehole operated near its limit to install a borehole below nearly 7 km of ocean. JAMSTEC/IODP https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e05fff07-806a-49c7-aa77-1782ab068012/slide+20+sensor+string+map.png Patrick Fulton The JFAST borehole was located on the seafloor below 6,925 m of ocean. The hole extended 850 m into the sub-seafloor rocks, crossing the plate-boundary fault at about 818 m below the seafloor (mbsf). The JFAST team inserted a string of 55 temperature-sensing data loggers attached to a rope installed within a 4.5-inch steel casing. The spacing of the sensors varied, as shown in the figure, so as to maximize the spatial resolution in the temperature-profile measurement near the fault, while still obtaining sufficient measurements along the full length of the borehole to determine steady heat flow and the thermal effects of fluid flows. Fulton, P.M. et al. (2013), Science 342, 1214 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a8b57630-3304-4e87-a0f3-a9458593b6b1/slide+21+sensors.jpg Patrick Fulton The 55 temperature-sensing data loggers were encased in titanium to withstand the intense pressure. The loggers were then attached to a 830-m-long string with the varying spacing indicated above before insertion into the 4.5-inch steel casing shown below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fc27f440-5671-40b5-9a2d-fbc296edf0c4/slide+48.png Patrick Fulton Lengths of the 8.5-in drill pipe stacked up aboard the Chikyu. The sensor string with wrapped temperature sensors is strung up in front. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4d266ad0-915b-471a-a720-21d6111bccf4/slide+47.png Patrick Fulton - Make it stand out Wrapping protective tape around the temperature sensors before inserting the sensor string into the steel casing. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf106731-0a2b-492d-95c1-22ae0d82adb8/slide+46.png Patrick Fulton - Make it stand out The assembled temperature observatory (4.5-in steel casing and sensor string) was lowered into the drilled borehole on the seafloor at the end of the drill pipe. The yellow-flanged connector (top center) connects the bottom of the drill pipe (off the top of the picture) to the wellhead assembly fixed to the top of the observatory (center), with the observatory’s steel casing disappearing through the deck into the ocean (lower center). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/da3c419b-9922-417f-a111-5bf347678a7a/slide+28+core+samples.jpg Patrick Fulton Core samples extracted from the borehole were analyzed to help determine the location of the fault that slipped during the earthquake. In one technique, the cores were passed through a gamma ray detector to determine the level of naturally occurring gamma rays emitted by the rock. Shales usually emit more gamma rays than other sedimentary rocks due to the high radioactive potassium content of the clay they contain, as well as their high uranium and thorium content. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a9b0bb33-0a30-431f-a021-ab721fb2c33e/slide+32-part.png Patrick Fulton Left: A one-meter-long section of the core sample extracted from the borehole at a depth of 820 m below the seafloor at the inferred location of the plate-boundary fault. Right: Profile of the gamma rays emitted by the core sample. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/22123f7f-123c-4602-aa84-a25b7c9d8c0c/slide+35+core+sample.jpg Patrick Fulton Closeup of an 8.4-cm length of the borehole core at the plate-boundary fault zone. The image shows many small slip surfaces, including one between the red-brown (top) and dark brown (bottom) scaly clays. Chester, F.M. et al. (2013), Science 342, 1208 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/da444dc5-512f-4114-821e-650f7995a1c3/slide+42+figure+of+drill+ship+and+hole.JPG Patrick Fulton Diagram of the drill vessel drilling the borehole and installing the temperature-sensor string, with the ocean depth, borehole depth, and plate boundary fault (red) roughly to scale. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a5ade5cf-9428-4e31-a801-b86a7030a8e4/slide+44+detection+of+borehole+cover.jpg Patrick Fulton - Make it stand out The driller’s “dog house” aboard the Chikyu drill ship. The view from the underwater TV camera shown at right is output on the monitors. In the podcast, Patrick Fulton describes how the long drill pipe behaved like a wet spaghetti noodle. This made it very challenging to maneuver the bottom of the drill pipe and reenter the borehole with the 8.5-in drill bit, and then again with the observatory assembly. When the borehole casing was spotted by the ROV video camera, the captain moved the ship slowly until the hole could be reentered. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8ce02ed5-f058-4936-acc1-ab1510100b00/slide+43+-+TV+camera.png Patrick Fulton - Make it stand out After the drilling of the borehole was completed, the video camera shown here was lowered along the drill pipe to provide imagery to guide the crew while attempting to reenter the borehole to insert the observatory assembly. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c079ba8c-344f-47c6-8899-c981f270d84d/slide+52+ROV+image+of+sensor+string.JPG Patrick Fulton Video frame from the underwater camera shown above as the observatory, i.e., the 4.5-inch steel casing containing the sensor string, was inserted into the borehole. The steel casing was closed at the bottom but open at the top. Water filled the inside of the casing from the top. The relatively small inner diameter of the casing prevented convection cells from forming. Once inserted, surrounding rocks and sediments collapsed down along the side of the casing, providing good thermal contact with the surroundings. The huge mass of the rock and its enormous thermal capacity overwhelm any influence of heat conduction along the steel casing on the variation of temperature with depth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e7c84edc-5643-4a77-a10c-41ba1279d63a/slide+75+JFAST+team.jpg Patrick Fulton - Make it stand out The JFAST team aboard the Chikyu deep-sea scientific drilling ship after successful completion of the drilling and emplacement of the temperature observatory. JAMSTEC/IODP https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4674218f-a869-42dc-a167-f5fb058570e9/slide+42+return+with+ROV.JPG Patrick Fulton Nine months after installation, the sensor string is retrieved using a deep-water remotely operated vessel (ROV, blue). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2f4818d8-17fa-496f-add5-29a49dfd7d9c/slide+56+removing+ROV.jpg Patrick Fulton The Kaiko II deep-sea ROV was used to locate and retrieve the temperature sensors from the borehole. It was equipped with a video camera and robot arm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3532a0f9-e04b-42fd-8354-e23f6bbee93e/slide+58+view+of+hole+from+ROV.png Patrick Fulton - Make it stand out ROV camera image from the seafloor with the ROV robot arm approaching the borehole casing wellhead. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7eaaf713-a5a2-4d19-8143-9c1455238732/slide+61+pulling+up+sensors.jpg Patrick Fulton - Make it stand out Hauling the sensor string onto the deck of the R/V Karei. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a63f8f22-c0e4-4443-b16d-2dba63f843d4/slide+62+sensors+on+board.jpg Patrick Fulton - Make it stand out The full length of the sensor string was laid out on deck following completion of the recovery. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/77b92860-402e-4e90-8273-d7a5e9145978/slide+80+residual+temperature.png Patrick Fulton Time-space map of the sub-seafloor residual temperature field. The residual temperature is the difference between the measured temperature and the background geotherm, i.e., the steady-state temperature profile of the rocks. The yellow dots at left show sensor positions, and each row represents the corresponding sensor’s data. The blue region at left shows the low temperatures relative to the background geotherm reflecting the effects of water circulation caused by drilling and installation of the sensors. A magnitude 7.3 local earthquake occurred on December 7, 2012 (dashed line), and is thought to have affected the flow of fluids, causing the observed cooling and heating in the high-permeability zones at 784 meters below seafloor (mbsf) and 763 mbsf respectively. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/31c149d0-e5e3-4240-8b3b-07cc0d32a668/slide+74+residual+temp.png Patrick Fulton - Make it stand out A. Magnified view of of the residual temperature near the plate boundary. B. Simulated residual temperature from a model in which the fault is placed at the peak in the observed temperature anomaly, i.e., 819.8 mbsf. The fault location inferred from the temperature data is at the same stratigraphic level as the plate-boundary fault found in the neighboring coring and logging holes. As discussed in the podcast, these temperature measurements enabled Patrick Fulton and his team to determine a coefficient of dynamic friction on the fault surface of 0.08. This is about an order of magnitude lower than for most rock surfaces, and may help explain the large slip at shallow depths of the fault that contributed to the devastating tsunami. Fulton, P.M. et al. (2013), Science 342, 1214 https://www.geologybites.com/patrick-fulton-transcript daily 0.75 2023-03-13 https://www.geologybites.com/patrick-fulton-glossary daily 0.75 2023-03-13 https://www.geologybites.com/tony-watts-transcript daily 0.75 2023-03-24 https://www.geologybites.com/sujoy-mukhopadhyay daily 0.75 2023-12-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d674b623-8c26-4952-a274-0d550a4a3277/Sujoy_Lab+w+red+box+highlighting+crusher.JPG Sujoy Mukhopadhyay Sujoy Mukhopadhyay’s research group has developed new techniques for measuring the trace abundances of noble gases in Earth materials. Noble gases are powerful probes into the very early Earth because their inert nature makes them immune to chemical processes that tend to erase signatures of the early Earth. In the podcast, Sujoy Mukhopadhyay describes how he measures noble gases within two kinds of basalt — ocean island basalt and mid-ocean ridge basalt. It turns out that the two basalts have quite different amounts of an isotope of xenon. He then argues that this points to a source reservoir in the deep mantle that retains a distinct identity forged in the first 100 million years of Earth history. Sujoy Mukhopadhyay is Professor of Geochemistry at the University of California, Davis. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f53e5ba8-0ad8-4a2d-bb41-048b535eb324/Artist+rendering.jpg Sujoy Mukhopadhyay Artist impression of the early Earth showing solidification of a magma ocean and outgassing of the mantle. When the Earth formed, noble gases were trapped in the mantle. During subsequent partial or complete melting, noble gases preferentially enter the liquid phase. If the liquid approaches the surface, they preferentially enter bubbles of gases (mainly composed of carbon dioxide and water) that form as the pressure drops. When the melt reaches the surface, the bubbles can escape into the atmosphere. Courtesy of Don Dixon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a8f5c20e-3bd5-481f-b18c-5305eba7f6c4/La_Palma_lava_flows_into_the_sea_%2851564701938%29.jpg Sujoy Mukhopadhyay - Make it stand out Lavas erupting on ocean islands are thought to originate from the deepest parts of the mantle. The eruption shown here occurred in 2021 on La Palma in the Canary Islands. Copernicus Sentinel-2 satellite, ESA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c4497723-15e1-4f1f-9a5c-be75744deec1/Nur05028_-_pile_of_pillow_lava.jpg Sujoy Mukhopadhyay - Make it stand out Lavas erupting from mid-ocean ridges, where new seafloor is created, are thought to originate from relatively shallow parts of the mantle. The pillow lava shown above erupted from the Juan de Fuca Ridge about 150 miles off the coast of Oregon. NOAA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd7f192c-a212-4806-93eb-8efc79cc549f/glass.jpg Sujoy Mukhopadhyay - Make it stand out When magma erupts under water, it cools rapidly, forming a glass of basaltic composition. The glass contains tiny bubbles of volatile materials that emerge as the rising mantle source decompresses and melts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/42cfa2d7-dde9-4f64-820b-f2dbaabe022f/glass+showing+trapped+bubbles.png Sujoy Mukhopadhyay - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00bf6463-4abe-41b2-ab68-6d4c2bb685df/mixing+graph+with+data.JPG Sujoy Mukhopadhyay Plots of noble gas isotope measurements using the technique of progressively crushing a basalt, as described in the podcast. The blue points represent results from a mid-ocean basalt, and the orange and red points represent results from ocean-island-type basalts. The two types of basalt plot along separate lines, which can only be explained if the ocean-island-type basalt source reservoir contains less 129Xe than the mid-ocean ridge basalt source. Since 129Xe production is essentially complete by 100 million years after Earth formation (i.e., after about 6 half-lives of the 129 iodine decay process), the ocean island reservoir must have differentiated from the mid-ocean ridge reservoir during the first 100 million years of Earth history, i.e., over 4.5 billion years ago. Mukhopadhyay, S., & Parai R. (2019), Annual Review of Earth and Planetary Sciences 47, 389 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/119657f8-caba-4eb0-9a00-b87ee426b656/graph+mixing+with+summary.JPG Sujoy Mukhopadhyay Plot showing the expected correlation of the ratio of xenon isotopes with the helium 3 to xenon ratio for source materials with two different noble gas compositions. The 129Xe is only produced by radioactive decay of 129 iodine with a half-life of 16 million years. The other isotopes (130Xe and 3He) are primordial. The plot shows the effect of a varying amount of mixing of noble gases from the mantle sources with noble gases from the atmosphere. The more mixing (indicated by the air subduction arrows), the closer the noble gas ratios become to those of air. In the podcast, Sujoy Mukhopadhyay describes how progressive crushing of basalt samples leads to progressive release of gas from bubbles containing purer, i.e., less contaminated by air, mantle-derived noble gas. If the two mantle sources had the same noble gas isotope ratios, the measurements would all fall on a single mixing line. The green arrow indicates the effect of decay of 129 iodine during the first ~100 million years of Earth's history. Mukhopadhyay, S., & Parai R. (2019), Annual Review of Earth and Planetary Sciences 47, 389 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fe7a0fb8-e455-4672-88de-d6a32330520e/LLSVPs.jpg Sujoy Mukhopadhyay - Make it stand out Map of the seismic-shear-wave velocity of the mantle at a depth of 2,800 km, just above the core-mantle boundary. The orange and red regions show large regions of low shear-wave velocity (LLSVP), which could be caused either by a higher temperature or an increased density as compared to the surroundings. The results discussed in the podcast suggest that denser material formed in the very early Earth has not homogenized with the rest of the mantle. Torsvik, T.H. et al. (2010), Nature 466, 352 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/15671801-4a6a-40af-8e8c-b9cb51ad6898/LLSVPs+section.jpg Sujoy Mukhopadhyay - Make it stand out Cross section of the Earth’s mantle derived from high and low seismic shear wave velocity variations (blue and red, respectively). Since LLSVPs roughly coincide with the locations of plumes, it is hypothesized that they could be the source reservoirs of plumes. Some researchers have suggested that the LLSVPs are composed of subducted slab material (cooler, blue in the diagram). But the noble gas abundances demonstrate that the LLSVPs cannot be entirely composed of subducted slabs, and that they must have formed by 4.5 billion years ago, long before plate tectonics started. Numerical modeling of mantle flow shows how colder subducting oceanic slab material can pool separately from the LLSVPs near the core-mantle boundary. Allen McNamara discussed such models in his podcast. Garnero E.J. & McNamara, A.K. (2008), Science 320, 626 https://www.geologybites.com/sujoy-mukhopadhyay-transcript daily 0.75 2023-04-21 https://www.geologybites.com/bob-hazen-transcript daily 0.75 2023-06-07 https://www.geologybites.com/brian-upton-transcript daily 0.75 2023-06-07 https://www.geologybites.com/bruce-levell daily 0.75 2023-06-28 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/36984ca5-b514-415a-9f39-8299f1307925/IMG_3923.jpg Bruce Levell How can we tell if the sedimentary record is good enough to make solid inferences about the geological past? Bruce Levell tackles this question by combining fieldwork with systematic analysis based on what we know about contemporary deposition and erosion. Armed with an understanding of preservational bias, he questions the confidence with which some widely held interpretations of the sedimentary record have been made. For example, by analyzing sequences of glacially-deposited rocks in southwest Scotland, he has shown with others that, contrary to the “Hard Snowball Earth” hypothesis, parts of the Earth probably experienced a persistently active hydrological cycle and were not simply fully-frozen, at least during the earlier of the two postulated snowball glaciations. Bruce Levell is a Visiting professor in the Department of Earth Sciences at the University of Oxford. Previously, he was Chief Scientist for Geology at Royal Dutch Shell. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/700becc7-e34a-4936-ba78-512a43813df7/Siccar+Point.JPG Bruce Levell - Siccar Point, Berwickshire, Scotland, UK The unconformity that James Hutton recognized as a gap in the geological record in 1788. The person is standing on shallowly-dipping Devonian sandstones that rest unconformably on steeply-dipping marine Silurian greywacke sandstones. Across the unconformity, about 80 million years of Earth history are missing from the record. Gaps in the record are rarely so easy to discern. Photo: Colin MacFadyen/NatureScot https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1316faa3-c43f-43aa-952e-68bf98450928/Capture.JPG Bruce Levell - How Accumulation of Sedimentation Varies with Time Interval In the podcast, Bruce Levell describes this plot, which shows the decrease in the accumulation rate of sediments with increasing duration of the time over which the rate is measured. He explains how this relationship shows us that there are increasing gaps in the record caused by removal of sediment by a “preservation filter” of progressively increasing severity with time. Thus, for example, on the timescale of a day, we might have a flood deposit from a river in spate, but if we average over a year (1a), the period includes times when the flood deposit is partially or fully eroded, or when there is no deposition. The graph also shows that the filter operates from timescales of minutes to hundreds of millions of years. The color-coded bar below the graph shows durations of the various sedimentary and stratigraphic processes that affect the record. Sadler, P.M, & Jerolmack, D.J (2014), Geol. Soc. London Special Publication 401(1) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/34092d6c-0ecb-4edf-b478-5ce463fda88a/density+current+deposits.png Bruce Levell The diagram shows how the broad family of underwater density current deposits is formed. It varies from turbidity currents at bottom (forming high-density turbidites HDT and low-density turbidites LDT) to debris flows (top). The image below shows a section of a sandstone formed by turbidity currents. These currents accompany underwater “landslides” and are common in deep marine environments on the edge of continental shelves but can also occur in lakes and coastal environments. Peter Haughton https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/39420ce2-598b-4742-9c77-262d53ff7245/Event+Beds.jpg Bruce Levell - Make it stand out Part of a sandstone cliff in Cornwall, UK, that was deposited by turbidity currents on the seafloor at the edge of a continental shelf. Counting from the bottom, there are two sets of five beds, each successively thinning (i.e., containing finer grains) upwards. It is tempting to relate these sets of beds to either a single event with pulsatory but declining flows or a series of very closely-related events during which the sediment volumes delivered to this point successively decreased accompanied by a reduction in current speed. One could interpret this deterministically under the assumption that thickness is related to volume as decreasing volumes of sediment liberated by successive underwater slumps retreating away from this point, or as overflowing of a levee system by successively weaker pulses of turbidity currents flowing along a channel. But successions of five successively thinner beds might also happen by chance. Determining which of these and other plausible hypotheses are true depends largely on the wider context. The image shows about 60 cm of the section from top to bottom. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e336d4f0-578e-4895-943e-2459d67952ff/Trubi+edited.jpg Bruce Levell - Make it stand out A. Cliffs on the south coast of Sicily consisting of limestones and marls (which are richer in clay). The regular banding in the cliffs corresponds to the proportions of carbonate and clay in the beds, with lighter colors being carbonate-rich limestones, and grey and beige being clay-rich marls. The entire section was deposited in deep water with abundant planktonic foraminifera. Four beds are labeled by their assigned number (36, 42, 56, and 69), and ages of two of the beds are indicated in millions of years (Ma). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cbd0f516-e355-43db-b0e5-8be2627e65d1/Trubi+B+edited.JPG Bruce Levell B. Graphs with age varying from 4.8 million years ago (Ma) at the bottom to 3.6 Ma at the top. The scale of the sedimentary log at left shows thickness (m) from the bottom of the cliff. The percentage carbonate in the rock is shown, increasing left to right from 50% to 75%. The precession and eccentricity curves show the time-synchronized variations in orbital parameters of the Earth. The ~5-meter-thick cyclic variations of the carbonate content are correlated to the 400,000-year eccentricity cycles. This variation is partly visible in the stepped profile of the cliff, with carbonate-rich limestone beds being more erosion-resistant than clay-rich marls and therefore forming protruding steps. The smaller-scale cyclical alterations of marls between grey, white and beige, and white are correlated to the 20,000-year precession cycles. The color changes reflect the variations in the amount of carbonate from plankton skeletons that accumulated on the seafloor. This is thought to have depended on the response of the plankton population to changes in water temperature and/or seasonality resulting from the precession. Langerei,s C.G & Hilgren, F.J. (1991), Earth & Planetary Science Letters 104, 211 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c4b44e0c-640f-4bb6-aa51-c80cfb721165/Lyme+Regis.png Bruce Levell A: Coastal cliff at Lyme Regis, Dorset, UK. The cliff consists of early Jurassic limestones, marls, and mudstones that were deposited in a shallow tropical sea with very little input of sediment washed out from nearby shores. It was home to a thriving variety of marine life, including ammonites, ichthyosaurs, echinoids, molluscs and crustaceans. The cliff exposes a rhythmically bedded succession without obvious breaks . B. A plot of the thicknesses of two successions (Lyme Regis and St. Audries Bay and Quantock’s Head, Somerset) covering the same period of geological time. The various points on the graph were obtained by correlating fossils between the two successions. The changing slopes of the graph reveal that the thinner Lyme Regis succession has several breaks in deposition (horizontal slopes) and that depositional rates differ between the two sections. There are no obvious indications of this in the rock composition or fossil content. The “Angulata” zone is about 700,000 years in duration and was tied to the absolute time scale indirectly via correlation with dated volcanic rocks in Peru. Diagram from Weedon, G. P. et al. (2018), Geological Magazine, 156, 1469 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/24ec8aca-c010-4116-8e40-36ddf52b2785/preservation+of+particular+river+flood+deposit.png Bruce Levell These X-ray images of small-scale core samples of the Eel River shelf, California, illustrate how preservation of a particular river flood deposit in shallow marine settings can depend simply on what happened next. The colors are false color representations of X-ray “density,” which reflects grain size. Panels A-C document the destruction of a 3 cm-thick bed (green) deposited in January 1997 (A) over the ensuing 10 (B) and 15 (C) months. Burrowing animals rendered the bed unrecognizable by mixing up the sedimentary layer with background shallow marine muds, hence the swirls and thin streaks seen in B and especially in C. By contrast, panels D-F show the persistence of a 5 cm-thick bed shown in D (green) formed in January 1995 over the ensuing 14 (E) and 55 (F) months. In E and F, the bed (lowest green and red layers) was buried to a depth of about 14 cm by a 14 cm-thick layer deposited on top of it by the March 1995 flood. This placed it below the depth inhabited by burrowing animals and also protected it from subsequent erosion. Scale bar at left = 2 cm. Horizontal and vertical scales are the same. Wheatcroft, R.A. & Drake, D.E (2003), Marine Geology 199, 123 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fff54f64-f53c-4617-aaf0-d7b2a743c855/frozen+accident.png Bruce Levell An example of a faithful preservation of a few minutes or hours of activity. The surface shows 1 billion-year-old wave ripples formed by waves in shallow water. On their flanks are little terraces (white arrows) that record lower water levels in the troughs between the ripples when the ripple crests emerged from the water. Survival of these delicate features depended on what happened next. In this case, it was deposition of a millimetres-thick mud drape that shielded the little terraces from immediate erosion, and then the chance avoidance of a whole host of potentially erosional subsequent events. Cailleach Head, Western Scotland, UK. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d54f31c5-6325-4fde-b693-1e990666a827/Scotland+A+capture.JPG Bruce Levell - Make it stand out A. Sand-filled polygonal cracks on the top surface of a glacial tillite bed. The cracks were probably formed by frost wedges expanding and contracting. B. Pebbles on top of a poorly sorted deposit showing a frost-cracked stone whose two parts still lie next to each other. Both of these features imply exposure of the surface to the fluctuating temperatures of the atmosphere during the period ascribed to the global Sturtian glaciation (c. 717 to 660 Ma). The excellent preservation also suggests little or no re-working by water after deposition in a cold but arid setting. These observations are inconsistent with a world completely covered by thick ice. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2dc2c127-4f3b-4056-abdf-ca9dedf9dd4c/Scotland+B.jpg Bruce Levell - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/bruce-levell-transcript daily 0.75 2023-06-24 https://www.geologybites.com/bruce-levell-glossary daily 0.75 2023-06-24 https://www.geologybites.com/john-wakabayashi daily 0.75 2023-12-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a4598075-23d4-4089-875f-c6617f781905/John+W3-1.jpg John Wakabayashi The Franciscan Complex contains a great variety of rock types, from metamorphosed seafloor basalts to layers of shales and mudstones. While the metamorphic minerals in certain rocks attest to burial up to a depth of 70 km before emerging on the present-day surface, others appear to have made a smooth passage from a subduction zone trench into the Franciscan Complex. John Wakabayashi is a Professor in the Department of Earth and Environmental Sciences at California State University, Fresno. He has devoted much of his 40-year research career to the Franciscan Complex. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/336f8837-dac1-4f44-a4c7-827712b4c245/Plate+context+from+USGS.png John Wakabayashi - Present-Day Tectonic Context As its name suggests, the Franciscan Complex is a strip of disrupted rocks along the coast of California stretching about 200 km north and south of San Francisco as indicated by the black rectangle in the image. It testifies to the presence of a former subduction zone. Today, subduction has ceased, with the Pacific plate moving transversely with respect to the North American plate. This motion is accommodated by strike-slip faults, of which the San Andreas Fault is the largest. Map from USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a1b5ee0f-bd54-4b5d-b63a-a6345d210cfa/OU+Fig.+6.png John Wakabayashi - Geological Map of Western California The map shows the three belts (Coastal, Central, and Eastern) that make up the Franciscan Complex. In general, the Coastal Belt is only weakly deformed, the Central Belt is chaotic, and the Eastern Belt is highly deformed. The metamorphic grade, i.e., the temperatures and pressures to which the rocks have been subjected, increases from the Coastal Belt to the Eastern Belt. The respective metamorphic facies are mainly zeolite, prehnite-pumpellyite (with blueschist blocks), and blueschist (with eclogite blocks). Metamorphic facies are described in the next figure. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7ac69b36-29a9-4c6d-b27e-0428d31cded6/Fig.+6.7+metamorphic+facies.JPG John Wakabayashi - Diagram Illustrating the division of pressure-temperature (P-T) space into metamorphic facies Each colored field in the P-T space is defined by a distinctive assemblage of minerals that grow in the the rocks when they are subjected to the corresponding P-T conditions. The hatched area shows the low-temperature, high-pressure range of conditions commonly encountered in accretionary prisms and deeper levels of subduction zones. These conditions arise because the subducting slab remains cooler than the surrounding mantle rocks as it subducts and pressures rise. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2140cd40-683b-4d4f-a1fe-a1d8be6709eb/OU+Fig.+5.1.JPG John Wakabayashi Cartoons illustrating successive stages in the development of an accretionary prism. (a) illustrates how stacked-up fault-bounded sections (an imbricate stack) develop at the toe of the prism. (b) shows how sediment may be successively underplated to the bottom of the prism. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/91498bd6-1049-4404-a07e-444d72b0f3bb/corner+flow.png John Wakabayashi Corner flow model. Motion is induced by the drag of the subducting plate on the bottom of the wedge. The model assumes the upper crustal sediments in the wedge are not consolidated. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3cb05774-095b-433f-95ec-c17c0936e163/channel+flow.png John Wakabayashi Channel flow model, in which sediment is off-scraped, underplated, or resubducted within a pattern of return flow. Corner flow and channel flow are each broadly consistent with ranges of computer models having different parameters. Note, the vertical scale is exaggerated in these diagrams. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec5f9a80-7936-4423-9ffc-3edd6f185ebd/OU+Fig.+5.3.JPG John Wakabayashi - Make it stand out (a) Folded sediments from an accretionary prism on Santa Catalina Island, California. The veins cutting across the fold structure show that there were fluids circulating in the prism. (b) Mélange from Anglesey, Wales, UK, with blocks in a highly deformed, fine-grained matrix. (c) Schematic cross-section of an accretionary prism showing a variety of deformation mechanisms within the prism. Many of these processes could contribute to the formation of mélanges. Courtesy of the Open University, © Open University 2013 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b6ce1aea-94db-4157-ac49-a90659459be1/Fig+6+Wakabayash+2017.JPG John Wakabayashi - Make it stand out One of the many detailed geological maps of the Franciscan Complex prepared by John Wakabayashi. This one is a projection along the angle of dip of the units of the geology of the Marin Headlands region. It illustrates the imbricate fault repetitions of sandstones, shales, and basalt, as shown in the cartoon diagram above. Wakabayashi, J. (2017), Progress in Earth and Planetary Science (2017) 4:18 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/23dd7f5b-32c5-42dd-a722-0e218f76562a/1920MarinH_BsChAtOverlookCR.jpg John Wakabayashi Roadcut at the Marin Headlands north of the Golden Gate Bridge. The red-brown blocks are chert, and the olive-brown rocks are basalt. Multiple faults have placed basalt over chert, but the chert overlies basalt on depositional, i.e., the original contacts. Chert is a hard, fine-grained rock composed of silica. It was deposited onto the basaltic oceanic plate and consists of the petrified remains of microorganism skeletons, especially those of radiolaria. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/271e6141-7f50-4db4-8fbd-0403c1664fee/1695OhlHipntViewE.jpg John Wakabayashi View of part of the northern Diablo Range, showing the typical geomorphology associated with mélange of the Franciscan Complex. The foreground is underlain by mélange with gentle slopes and isolated outcrops of blocks, including some big ones (two peaks at center right). By contrast, the more distant ridge slopes more steeply as it is probably underlain by more coherent Franciscan rocks. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e5c76888-a622-4528-a584-a6d7de8c81a8/Platt+1986+Fig+6+on+Franciscan+Complex+extension.JPG John Wakabayashi - Make it stand out In the podcast, John Wakabayashi mentions the influential 1986 paper by John Platt, which was the first to describe how the rocks of an accretionary prism can be in a state of extension despite being wedged between converging plates. This figure from that paper shows a model of the tectonic evolution of the Franciscan Complex. In the lower diagram (B), he shows how underplating and resultant extension have stretched the prism. The diagram shows approximate ages of sediment in different parts of the complex in millions of years. The pressures at various depths in are given in kilobars (kb) and the depth in km is shown on the scale on the right. The metamorphic grades are indicated by the presence of metamorphic minerals: gl = glaucophane, jd = jadeite, law = lawsonite. Platt, J.P. (1986), Geological Society of America Bulletin, v. 97, 1037-1053 https://www.geologybites.com/john-wakabayashi-transcript daily 0.75 2023-07-14 https://www.geologybites.com/john-wakabayashi-glossary daily 0.75 2023-07-14 https://www.geologybites.com/kathryn-goodenough-transcript daily 0.75 2023-07-14 https://www.geologybites.com/phil-renforth-transcript daily 0.75 2023-07-16 https://www.geologybites.com/rob-butler daily 0.75 2023-08-17 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aec558fd-f48d-435a-902d-1e5236b985d3/RWHB+_1.jpg Rob Butler The Alps are the most intensively studied of all mountain chains, being readily accessed from the geological research centers of Europe. But despite this, there remains considerable uncertainty as to how they formed, especially in the Eocene (about 40 million years ago) when the events that led directly to Alpine mountain-building started. In the podcast, Rob Butler explains how much of this uncertainty stems from our fragmentary knowledge of the locations and structures of sedimentary basins and small continental blocks that lay between Europe and Africa at that time. In his research, he combines detailed studies of the sedimentary rocks flanking the Alps with the large body of structural and petrological knowledge amassed over the past two centuries to try to unravel the sequence of events leading up to the formation of the Alps. Rob Butler is Professor of Tectonics at the University of Aberdeen, Scotland, UK. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b7778644-76a2-4cd0-952e-327a362dabf9/Alpenrelief_01.jpg Rob Butler - Relief Map of the Alps The modern Alps form an arc about a thousand km long stretching from the French Riviera on the Mediterranean coast, through southern France, Switzerland, northern Italy, southwestern Germany, Austria, and the Balkans. Digital elevation data from the Shuttle Radar Topography Mission, NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2335232c-3045-4b0e-b2ba-e50d94fbbcd9/Paelogeog+for+late+Cretaceous.jpg Rob Butler A reconstruction of the paleogeography at the southern margin of Europe for the Santonian age (about 85 million years ago) of the late Cretaceous. Both this reconstruction and the one below show the presence of numerous blocks between Africa and what was to become Europe. The thick purple lines indicate subduction zones with the subducting slab dipping in the direction pointed to by the red triangles. Green/grey bands indicate rift zones. The white labels (e.g., Neotethys) indicate oceans and basins, and the small black legends refer to continental blocks (e.g., Br for Briançonnais), rock formations (e.g., Db for Dent Blanche), rifts (e.g., Sd for the Srednogorie rift-arc), and other geological units. Stampfli, G.M., et al. (2002), Journal of the Virtual Explorer 8:77 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a3152104-041c-4143-893e-fcef84ce5c34/Stamfli+oligocene-Eocene.JPG Rob Butler - Make it stand out Reconstructions of Alpine and Pyrenees area for the middle Eocene (c. 40 million years ago) and late Oligocene (c. 28 million years ago). As Rob Butler mentions in the podcast, there is an uncertainty of at least 100 km in the positions of the various units. This uncertainty presents a challenge to those seeking to reconstruct the subsequent phases of Alpine evolution. Stampfli, G.M., et al. (2002), Journal of the Virtual Explorer 8:77 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21d307c1-e160-4941-a91b-e19d9e498d42/slide+1+combined.JPG Rob Butler - Make it stand out Two different sections through the Jura belt, the top one dating from 1916. Both show how the rocks became detached from the basement of Mesozoic rocks colored grey (top) and orange (bottom). In the outer Alps towards the west (left in the sections), there are few pre-existing faults, so the movement occurs along a weak layer of Triassic evaporites (salt) lying at the top of the basement. This results in thin-skinned or decollement tectonics. Note, in various geological maps, the thrust sheets, e.g., Penninic and Helvetic, are called nappes. Top section by Butler, R.W.H. after Buxtorf, A., 1916 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fe312423-7010-4d33-9d23-5d8ca1001393/tectonic+overview.JPG Rob Butler - Make it stand out Tectonic map of Switzerland. The map shows the major thrust sheets (nappes), some of which have been folded and thrust tens of km to the northwest. The upper portion of these sheets has been eroded away, so that, in some cases, parts of the nappes are left as detached islands (klippes), such as those of the Penninic nappes along the northwest margin of the Helvetic nappes. Baumberger, R., et al. (2019), Ch. 24, 2019 Synopsis of Current Three-Dimensional Geological Mapping and Modelling in Geological Survey Organizations, AER/AGS Special Report 112, p. 249 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d0c9c07e-c200-40f1-aa2c-d369795ff110/slide+2.JPG Rob Butler - Make it stand out Panorama and sections of the external Alps, which correspond to an area that was only weakly rifted and faulted before the Alps were formed. The view at top is of the Dauphine area of southeastern France. It corresponds to the central part of the two crustal sections shown below it. The sections run east-west through the Ecrin region of southeastern France. The top section shows the present-day, shortened crust, with the ellipses (squashed circles) representing distributed strain in the crust. In the bottom section, 55 km of crustal shortening has been unwound, while maintaining a constant cross-sectional area. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5de350ad-9b0e-4cf5-9c61-c3b1c5cbcc3e/slide+7+Jura.jpg Rob Butler Looking onto the Jura of France. The geology determines the landforms here, with the ridges corresponding to anticlines. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fa681145-b2a3-4867-8002-922ac61b90d2/slide+8a.jpg Rob Butler Large-scale folding of platform carbonates in the Jura mountains. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1e6ad2b0-8675-46df-a3bc-43798ee2ab12/slide+8b.jpg Rob Butler Metamorphosed limestones that were deformed in a channel of a subduction zone. The rocks show small-scale (meter-scale or less) folding and deformation within the layers. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1ee400f8-9371-4548-b69f-bb0ed88689d4/slide+10.jpg Rob Butler The Mont-Blanc range. Here, the crust was only weakly thinned during Mesozoic rifting (Cretaceous or earlier) on the margins of the Tethys Ocean. The crust then began to shorten and thicken at the beginning of the Miocene as the Alps were forming. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/79f23476-7d79-43db-bbd2-32cef52fee68/Glarus+Thrust.JPG Rob Butler The famous Glarus thrust (red line) in the Tschingelhörner in eastern Switzerland. Permian sandstone (Verrucano) has been thrust over the younger Jurassic limestone. In the podcast, Rob Butler suggests that while such striking features have attracted a great deal of attention during the long history of Alpine geological research, it may be the more elusive distributed deformation throughout the crust that actually accounts for most of the crustal shortening accompanying the formation of the Alps. Courtesy of IG Tektonik Arena Sardona: Ruedi Homberger https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ac082c9c-05f3-477a-992f-9c3b8f081075/slide+9.jpg Rob Butler The vestigial Mer de Glace glacier, Mont Blanc range. In the podcast, Rob Butler makes the counter-intuitive point that as the mountains erode, their peaks get higher. Glacial erosion of deep valleys takes load (mass) off the lithosphere, causing the what remains to rise as a result of isostatic compensation. Thus, if the peaks themselves haven’t eroded, they rise and topographic relief is enhanced, even though average topographic elevation decreases. In the long term, however, the peaks crumble and jagged peaks turn into smooth hills, such as the Appalachians or Urals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5fcac8b1-150d-4670-87c3-76eac2e74c08/Arnot+Sandstone+at+its+type+locality.jpeg Rob Butler - Make it stand out The Annot Sandstone is a latest Eocene-early Oligocene turbidite in southeast France. The type locality is pictured above. Rob Butler is currently studying these rocks to pin down the timing of uplift at the southern edge of the Western Alps. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e1219e4-1bf3-4f6d-b5fd-d9ec712ecaf8/Arnot+Sandstone+%28turbidite+succession%29+down-system+in+the+Aiguilles+d%27Arves.jpeg Rob Butler - Make it stand out The Aiguilles d’Arves display a portion of the Annot Sandstone that was deposited earlier than the type locality units shown at left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/deca2fca-e61c-4020-a7e5-0c0cc0457959/Marnosa+Aren+1.JPG Rob Butler - Make it stand out The Marnosa Arenacea (above and right) are Miocene turbidites in the northern Apennines. These are the deposits formed by detritus eroded from the ancestral Western Alps. In the podcast, Rob Butler discusses his current interest in these rocks as potential clues to the spatial sequencing of topographic uplift at the start of Alpine mountain-building. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4190dfd1-2070-48da-91fa-d748d0bb102f/Marnosa+Aren+2.JPG Rob Butler - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/rob-butler-transcript daily 0.75 2023-08-17 https://www.geologybites.com/mike-searle-ophiolite-transcript daily 0.75 2023-09-09 https://www.geologybites.com/ana-ferreira-transcript daily 0.75 2023-09-09 https://www.geologybites.com/martin-van-kranendonk daily 0.75 2025-10-31 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c89b1a24-7317-4660-be8e-c04f683db90c/MVK+lecturing+in+field+processed-1.jpg Martin Van Kranendonk - To find evidence for very ancient life, we need to look at rocks that have been largely undisturbed over billions of years of Earth history. Such rocks have been found in the Pilbara region of northwest Australia. As Martin Van Kranendonk explains in the podcast, the 3.48-billion-year-old (Ga) rocks of the Dresser Formation there contain exceptionally well-preserved features that show unmistakable physical and chemical signatures of life. While older 3.7 Ga rocks in west Greenland may also prove to have harbored life, the Dresser Formation rocks represent the oldest widely accepted evidence for life on Earth. Martin Van Kranendonk is a Professor in the School of Biological, Earth, & Environmental Sciences at the University of New South Wales in Sydney. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f7e1a436-6aee-4a48-99e7-a61a1b2f5c05/map+of+Pilbara.JPG Martin Van Kranendonk Map of the Pilbara region of Western Australia. DevelopmentWA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e91c4f0-f63c-4dcd-ab9c-5e50619d859c/20210505_113637.jpg Martin Van Kranendonk - Make it stand out Pilbara landscape. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/46371e29-5c32-42bb-b190-c87396ba307f/geological+map.jpg Martin Van Kranendonk - Make it stand out Geological map showing the geological context of the 3.5-billion-year-old Dresser Formation (sky blue) in the Pilbara Craton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f10a7407-5711-4696-9ea4-f95f981fab89/coniform+types+slide+4.jpg Martin Van Kranendonk - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d4680c22-7bb1-4118-9fdd-ed001f5ebb7b/Dresser+mat1_cropped.jpg Martin Van Kranendonk - Make it stand out Above: highly weathered outcrop of wrinkly laminated stromatolites (below knife) and domed stromatolites (background). Left: tops of cone-like stromatolites. Below: well-preserved ripples suggest a shallow water environment. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4144256f-59a6-4c90-8f9e-a1fc4109777c/well+preserve+ripples+slide+4.jpg Martin Van Kranendonk - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e272914d-c70b-4e07-b25b-e1e8d10eb1e4/sediment+onlap+slide+4.jpg Martin Van Kranendonk - Make it stand out Yellow and green lines indicate sediment onlapping onto the side of a stromatolite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5d595146-601b-4355-99f1-390c5637534a/slide+5.JPG Martin Van Kranendonk - Make it stand out Dresser formation outcrop annotated to distinguish biogenic structures from those produced by purely inorganic processes. The white arrow indicates a 3.5-billion-year-old stromatolite with wrinkly lamination. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5ce5f7a8-6951-4bf6-86ef-9266ba1b2a60/Drilling+rig.jpg Martin Van Kranendonk Drilling into the Dresser Formation in 2019 when the exceptionally well-preserved 3.48 Ga stromatolites were found about 90 meters below the surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6f9ee2b1-566e-4d8e-b969-9242d007b746/20190508_170613.jpg Martin Van Kranendonk - Make it stand out In the podcast, Martin Van Kranendonk describes the team’s excitement upon first seeing this sample of the drill core with four small domal stromatolites with wrinkly laminations in yellow, growing up from a flat-lying bed below. The core is about 7 cm across, and the stromatolites are about 1 cm high. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dea0969d-5d36-42f4-93b1-0692c6aaae77/slide+9+current+and+columns.JPG Martin Van Kranendonk In this section, the distribution of iron (Fe) is mapped. The yellow lines delineate planar bedding, and the red arrows and lines show stromatolite columns surrounded by asymmetrical ripples, which suggests a water current was flowing from left to right. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eff2e56c-1e32-4bf9-8878-baaeda70a811/Fig+1A-1.jpg Martin Van Kranendonk Photomicrograph of stromatolites in the Dresser Formation in the Pilbara, Western Australia. The stromatolite textures range from upward-broadening and/or upward-branching finger-like structures (white arrows), to wavy and wrinkly laminae that are sometimes arranged in a columnar fashion. The inset shows a schematic drawing for stromatolite lamination. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b3ea3ff5-bb46-4c33-99f5-a2d253fcc183/slide+14.JPG Martin Van Kranendonk - Make it stand out Much of the organic matter found in the Dresser Formation stromatolites occurs in tiny pores within pyrite. Top right: scanning electron microscope image of the porous pyrite. Bottom right: infrared spectrum showing peaks in the D and G bands indicating the presence of carbon. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21865a60-6261-42e4-8cd9-62ee56997582/Fig+2D-1.jpg Martin Van Kranendonk Textures in the pyrite in the Dresser Formation showing finger-like stromatolites, with the black arrows indicating the putative growth orientation of vertical, locally upward-branching or broadening patterns. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/47ecd86c-e9dc-445d-b58a-602a40ade35e/Fig+4.JPG Martin Van Kranendonk Organic matter strands and filaments in pyrite of the Dresser Formation. (A) Electron microscope image of a branched organic matter strand that is embedded in porous pyrite (red arrow). (B, C) Organic matter strands cross pyrite grain boundaries (red arrows in B). (D) Twisted filament bundle (red arrow) containing barite (barium sulfate, Brt). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b903d398-fd9e-4cee-bf88-672871b19fd1/Fig+13.JPG Martin Van Kranendonk - Make it stand out Element distribution maps of Dresser Formation Stromatolites. As discussed in the podcast, elements such as nickel, zinc, and arsenic are produced as a by-product of certain microbial metabolisms. Left: color-coded distribution maps of nickel, arsenic, and zinc. The white arrows show the wavy laminae with central enrichment of nickel. Right: closeup distribution map of nickel and zinc. The images are high-resolution, X-Ray fluorescence maps made using the Australian Synchrotron in Melbourne. Baumgartner, R.J., et al. (2020) Precambrian Research 337 (2020) 105534 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c6b00cb-6c44-4335-8f77-8489253160f6/Picture+003.jpg Martin Van Kranendonk - Make it stand out Stromatolites are mats of sediment created by microbial communities living on their surface. Images from Shark Bay except the one below from Lake Clifton, just south of Perth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9d3a57b4-1538-4bb6-a039-2d7cab276cff/Home+soon.jpg Martin Van Kranendonk - Make it stand out Courtesy of Bernd Nicolaisen https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d497ff4d-d3b4-42e3-8345-f967914ca0a6/Lake+Clifton_Richard+Murphy_2022.jpg Martin Van Kranendonk - Make it stand out Courtesy of Richard Murphy https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/11540d27-4136-4523-8516-2d85948fada9/PIC_0042.JPG Martin Van Kranendonk - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/martin-van-kranendonk-transcript daily 0.75 2023-10-06 https://www.geologybites.com/catherine-mottram daily 0.75 2023-10-21 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3c0ead12-11d0-4f54-9601-0be3a0c1164b/CM+with+cores+in+BC+Triumph+Gold-1.jpg Catherine Mottram Catherine Mottram’s research focuses on dating methods that do not rely on zircon. She has successfully developed radiometric methods based on calcite, monazite, and other minerals that enable processes occurring at relatively low temperatures and pressures to be dated. Using these methods, she has helped unravel the deformation history of rocks as far afield as the far north of the Yukon in Canada and cast light on how minerals such as gold can collect along large-scale faults. The image shows Mottram inspecting drill cores from her research area in the Yukon, Canada. Mottram is an Associate Professor of Geology at the University of Portsmouth. Courtesy of the University of Portsmouth and Sam Shaw https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fadd134a-92e1-4c90-981f-6f579b5e59eb/Closure+temperature.jpg Catherine Mottram - Make it stand out As Catherine Mottram explains in the podcast, various geological clocks record the timing of geological processes from temperatures above 800°C to temperatures as low as 100°C. Geochronometers such as uranium-lead (U-Pb) in zircon and monazite record high-temperature igneous and metamorphic processes. Mid-temperature (500-700°C) crustal metamorphic, hydrothermal, and deformation processes are recorded by methods such as U-Pb in apatite and radioactive decay of argon and rubidium in muscovite. Using U-Pb in carbonates (e.g., calcite) is a relatively novel method for dating low-temperature fluid-flow processes. Adapted from Chew, D.M., et al. (2015) Elements 11.3: 189 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e3b604fb-5659-4df9-b312-142cfc00b4da/calcite+U-Pb+geochron+edited.jpg Catherine Mottram - Make it stand out Carbonate is ubiquitous in the upper crust and crystallizes during a range of geological processes, some of which are shown in this diagram together with an indication as to where each process occurs. In the podcast, Catherine Mottram discusses her work in the Yukon in Canada, in which the main processes involving calcite crystallization are fractures and fluid flow and ore mineralization. She also talks about calcite dating of a fossil turtle on the Isle of Wight, formed by a diagenetic process, and dating of faults in Turkey and the Eastern Mediterranean, which involved calcite dating of slickenfibres in the North Anatolian fault. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2b4c2e88-9d96-4b1f-8c54-12799e516dca/System+figure-new.jpg Catherine Mottram Schematic diagram of the magmatic and hydrothermal processes involved in the establishment of a porphyry deposit. In recent years, the demand for critical minerals, such as copper and molybdenite, has increased due to the crucial role in the green-energy transition. These metals precipitate with gold, silver, and other metals in porphyry deposits, where magmatic and hydrothermal fluid circulation deposits metal above granite intrusions in a volcanic setting. U-Pb zircon dating can provide timing of the short duration, high temperature of magmatic processes (dark pink granite and red dikes in the figure), but it has previously been challenging to date the lower-temperature fluid flow processes that can be critical for concentrating metal. In the podcast, Catherine Mottram explains how she applied the U-Pb carbonate geochronometer to reconstruct a more than 50-million-year record of carbonate precipitation within a strike-slip fault-controlled porphyry deposit in Yukon, Canada, revealing the previously untold longevity of fault-controlled fluid flow in ore deposits. The diagram also shows the volcanic pipe feeding the original volcano (diatreme) and faults with their associated highly fractured breccia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/27564263-d3ea-43fc-9d20-c21556dee6c7/turtle+edited-1.jpg Catherine Mottram - Make it stand out The partial fossilized skeleton of the ca. 127-million-year-old Isle of Wight turtle for which Catherine Mottram and her team obtained a radiometric date from the fossil’s calcite. Top left: shell rear view; top right: front body rear view; bottom left: shell front (neck cavity) view; bottom right: front body front (neck cavity) view. Courtesy of Megan Jacobs, Jacobs et al., 2023) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e8f81225-85f3-49e3-a55f-618f217efa7e/Zanskar+Valley-3.jpg Catherine Mottram The Zanskar River cuts through intensely folded sediments of the former northern margin of India. Photos: Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a59a1a46-b330-44c3-b495-e79d821ee06d/Zanskar+Valley-9.jpg Catherine Mottram - Make it stand out Calcite veins filling tension gashes created during the folding are sampled by Ian Cawood. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2d519e10-6e7c-46f3-abbf-5a61dcbbeabe/Zanskar+Valley-7.jpg Catherine Mottram - Make it stand out The large white veins are calcite that cross-cut the folding and therefore post-date the folding. Successful dating of the calcite in both types of vein would enable time constraints to be placed on the age of the folding and address the question as to whether it occurred prior to the collision of the Indian continent with Asia or following it. In this case, Catherine Mottram was unable to date the calcite as it had too little uranium and too much non-radiogenic lead. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/96e83af8-4cfa-484e-a5f5-69ec077ea095/Triumph+Gold+mining+camp.JPG Catherine Mottram - Make it stand out Mining camp in the Yukon near the research area Catherine Mottram studied using drill cores such as those shown in the first picture on this page. Almost no rocks are visible on the surface as the area is largely covered by boreal forest. Courtesy of Triumph Gold Corp. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/baa86bca-e23c-4073-88a9-9ea24cdcbf73/Triumph+Gold.jpg Catherine Mottram The site of Triumph Gold's Revenue camp in the central Dawson Range near Carmacks, Canada. Though boreal forest and vegetation covers almost all of the porphyry deposit, Triumph Gold Corporation, an exploration company, has revealed the mineralization in the subsurface through extensive drilling. Catherine Mottram has conducted most of her work on longevity of hydrothermal processes in porphyry deposits here. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec62c898-793e-495e-8397-0f437bc1a5e5/BC.jpg Catherine Mottram - Make it stand out Mottram spent the summer of 2023 in northern British Columbia, close to the small gold rush town of Atlin, working with Core Assets Corporation, a small mineral exploration company. Their 'Blue Property' is located high above the Juneau Icefield on the border with Alaska. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/98d02eae-74d1-4b5c-84a8-00683e0e21f8/IMG_20230717_131038090.jpg Catherine Mottram - Make it stand out Sarah Bowie, a University of Portsmouth PhD student (back), examining plutonic rocks near Atlin, northern British Columbia, with Dawn Kellett (front), a research scientist at the Geological Survey of Canada. The igneous rocks, faults, and mineralization are wonderfully exposed in glacially polished surfaces in the high mountains. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c65dc61b-905c-49d5-bab1-0d44ca16aabe/IMG_20230721_182905776.jpg Catherine Mottram - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/catherine-mottram-transcript daily 0.75 2023-10-22 https://www.geologybites.com/catherine-mottram-glossary daily 0.75 2023-10-26 https://www.geologybites.com/clark-johnson-2 daily 0.75 2023-11-11 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d2f0d02c-fa8d-49c2-b0ab-e4ba10218e0e/Clark+in+SA-1.jpg Clark Johnson Banded Iron Formations (BIFs) are a visually striking group of sedimentary rocks that are iron rich and almost exclusively deposited in the Precambrian. Their existence points to a major marine iron cycle that does not operate today. Several theories have been proposed to explain how the BIFs formed. While they all involve the precipitation of ferric (Fe3+) iron hydroxides from the seawater via oxidation of dissolved ferrous (Fe2+) iron that was abundant when the oceans contained very low levels of free oxygen, they disagree as to how this oxidation occurred. In the podcast, Clark Johnson describes how oxidation could have occurred without the presence of abundant free oxygen in the oceans. This would have produced abundant organic carbon. To explain the absence of this carbon today, he suggests that anaerobic bacteria “respired” the carbon via anoxygenic photosynthesis, in the process oxidizing it to carbon dioxide. Johnson is a Professor in the Department of Geoscience at the University of Wisconsin-Madison. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6351500f-3cc0-4964-acb7-0b1c7bb8ffd7/Fig_1_Brockman_BIF.jpg Clark Johnson 2.5-billion-year-old (Ga) Brockman Iron Formation, Karijini National park, Western Australia. Exposed in the walls of canyons carved by rivers in the Western Australian outback, the Brockman Iron Formation is representative of the largest BIFs in the world, with layering and banding that varies on scales from sub-mm to meters. Their red color is the result of recent surface weathering of iron oxides. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d76da9d1-1c3f-4936-89c0-06fa43bd7afb/Fig_2_Brockman_BIF_Detail.jpg Clark Johnson Detail of a fresh outcrop of the 2.5 Ga Brockman Iron Formation. Here, the major iron mineral is magnetite, and most of the remaining rock is chert (quartz). The sub-mm and mm-scale layering might represent annual deposition (analogous to varves). The cm-scale layering contains dewatering structures formed when the initial iron-silica gels were deposited on the seafloor and compacted during initial lithification. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/61ccc1cb-792c-4c91-98ec-e55d94bfb0e4/Fig_3_Kuruman_Mineralogy.jpg Clark Johnson Detail of a fresh core of the 2.5 Ga Kuruman BIF, South Africa. The core is about 2 cm across. This unit was probably deposited in the same continental margin basin system as the Brockman BIF. In this core, the layers consist of primary hematite, magnetite, and siderite (Fe carbonate), plus chert. Such fresh samples show that BIF mineralogy consists of both oxidized (Fe3+) and reduced (Fe2+) iron. The earliest iron mineral is hematite, indicating the first stage of BIF mineral formation is an oxidative one, where seawater Fe2+ is oxidized to Fe3+. The Fe2+-bearing minerals, magnetite and siderite, indicate a later reductive stage on the seafloor during early diagenesis. This second stage is needed to explain the observation that, on average, BIFs of this age contain about 60% Fe2+ (i.e., reduced iron). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/71e6af59-74ec-49b5-a07f-4484483666f0/Fig_4_Compare_Mable_Bar-Kuruman_IF.jpg Clark Johnson - Make it stand out Changes in iron mineralogy through time. In unmetamorphosed iron-rich rocks, including BIFs and related lithologies such as japerlites (hematite+chert) of Archean age, such as the 3.5 Ga Marble Bar Chert (above left), the dominant iron oxide is hematite (Fe3+). By contrast, in rocks of Proterozoic age, such as the ~2.5 Ga Kuruman Iron Formation (above right), magnetite and siderite (both Fe2+) predominate. In both cases, Fe3+ oxides were precipitated initially, which implies that the younger BIFs additionally record a later reductive process to produce the Fe2+ minerals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9293ec11-9801-423d-a5cc-7a4422a943ef/Fig_5_BIF-Crust-Time.jpg Clark Johnson Temporal changes in atmospheric oxygen and BIF deposition (top graph) and estimates for growth of the continental crust (100% equals modern volume, bottom graph). In the graphs, time advances from old at right to young at left. BIFs older than 2.7 Ga are very small; one of the oldest BIFs, the 3.7 Ga rocks at Isua Greenland, do not even plot on the presented scale. The very large BIFs deposited at the end of the Archean and early Paleoproterozoic, ~2.7-2.4 Ga age, include the Brockman and Kuruman BIFs, which were deposited before the "Great Oxidation Event" at ~2.3 to 2.4 Ga. We also know that the photic zone of the oceans started to become oxidized as early as 3.2 Ga. Thus, oxidation of seawater Fe2+ as part of the deposition of the very large ~2.7-2.4 Ga BIFs could have occurred either by oxygenic photosynthesis or by an anoxygenic photosynthetic pathway or some combination. Meanwhile, although the rate of continental crust formation over time is uncertain, all models suggest an increase in continental crust over time. As explained in the podcast, continental shelves provide the environments for BIF deposition and preserve them from subduction. They may also reflect a driver for a biological role through increased nutrient supply via continental weathering. Graphic by Clark Johnson. Data sources: Belousova et al. (2010) Lithos. 119:457-466; Dhuime et al. (2012) Science. 335:1334-1336; Konhauser et al. (2017) Earth-Science Rev. 172:140-177. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a6ddf52f-eae5-44c0-b6e4-5702ebca02d2/Fig_6_C-O_Relations_Siderite.jpg Clark Johnson <CAPTION TO BE EDITED> Carbon and oxygen isotope relations for BIF carbonates (siderite and other iron-rich carbonates) for ~2.5 Ga BIFs (colored fields) and 2.9 Ga BIFs (Symbols). Black curve is trend for microbial Fe3+ reduction (Dissimilatory Iron Reduction; "DIR"), run to completion (requiring a mixture of organic carbon and seawater carbonate) and grey arrow is trend for incomplete DIR (minimal seawater carbonate contribution). In all cases, none of the C and O isotope compositions are in equilibrium with seawater, and this is confirmed by Sr isotope studies. These relations provide powerful evidence that microbial iron reduction is responsible for producing the iron carbonates in BIFs. Figure from Johnson et al. (2020) Iron Geochemistry: An Isotopic Perspective, Springer, 360 p. Detailed notes: The reactions for microbial dissimilatory iron reduction can be written in several ways, depending upon the relative contributions of organic C and seawater carbonate to the C isotope composition of siderite. Complete reduction, which requires seawater carbonate, can be written as: 4Fe(OH)3 + CH2O + 3HCO3- ➔ 4FeCO3 + 3OH- + 7H2O https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5b489507-c589-4541-94c2-686d126f22fe/Fig_7_Fe_Relations_Magnetite-Hematite-Siderite.jpg Clark Johnson CAPTION TO BE EDITED Iron isotope relations among coexisting magnetite, hematite, and siderite in BIFs, as measured at various scales, from g- and mg-size samples to in situ measurements. If these minerals were in Fe isotope equilibrium, as might be expected if they co-precipitated abiologically on the seafloor, all of the data should scatter about the red lines, and clearly this is not the case. On the other hand, if magnetite and siderite formed by Dissimilatory Iron Reduction (DIR) of hematite, they should scatter about the 1:1 grey lines. Many data plot between the DIR and equilibrium lines, indicating variable contributions of Fe from a microbial process and a seawater component. Figure from Johnson et al. (2020) Iron Geochemistry: An Isotopic Perspective, Springer, 360 p. Superimposed on these relations is a correlation between the absolute δ56Fe values and Nd isotope compositions, where the initial Fe3+ precipitates had different Fe2+ sources prior to the initial oxidation in the photic zone: High δ56Fe values have positive εNd values indicating a hydrothermal source, whereas low δ56Fe values have negative εNd values indicating a microbial Fe2+ source from the continents (DIR shuttle). In summary, therefore, the Fe isotope composition of the initial Fe3+ hydroxides (converted to hematite during dewatering) is established by the source of Fe2+ in the oceans (continental versus hydrothermal), whereas the Fe isotope relations among coexisting magnetite, hematite, and siderite reflects, in part, a microbial component during diagenesis. https://www.geologybites.com/test-page daily 0.75 2023-11-11 https://www.geologybites.com/clark-johnson1 daily 0.75 2023-11-17 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/717e7ae8-599c-44a0-8fa9-12157d12eb16/Clark+in+SA-1.jpg Clark Johnson-1 Banded Iron Formations (BIFs) are a visually striking group of sedimentary rocks that are iron rich and almost exclusively deposited in the Precambrian. Their existence points to a major marine iron cycle that does not operate today. Several theories have been proposed to explain how the BIFs formed. While they all involve the precipitation of ferric (Fe3+) iron hydroxides from the seawater via oxidation of dissolved ferrous (Fe2+) iron that was abundant when the oceans contained very low levels of free oxygen, they disagree as to how this oxidation occurred. In the podcast, Clark Johnson describes how oxidation could have occurred without the presence of abundant free oxygen in the oceans. If oxidation occurred via biological processes, this would have produced abundant organic carbon. To explain the absence of this carbon today, he suggests that iron-reducing bacteria “respired” the carbon via anoxygenic photosynthesis, in the process oxidizing it to carbon dioxide or a carbonate mineral such as siderite. Johnson is a Professor Emeritus in the Department of Geoscience at the University of Wisconsin-Madison. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/15a3a98e-84d6-4d3d-bfbb-843af93e5969/Fig_1_Brockman_BIF.jpg Clark Johnson-1 2.5-billion-year-old (Ga) Brockman Iron Formation, Karijini National Park, Western Australia. Exposed in the walls of canyons carved by rivers in the Western Australian outback, the Brockman Iron Formation is representative of the largest BIFs in the world, with layering and banding that varies on scales from sub-mm to meters. Their red color is the result of recent surface weathering of iron oxides. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2f1405b-f18f-4b1e-81bd-55dd5aba4e5f/Fig_2_Brockman_BIF_Detail.jpg Clark Johnson-1 Detail of a fresh outcrop of the 2.5-Ga Brockman Iron Formation. Here, the major iron mineral is magnetite, and most of the remaining rock is chert (quartz). The sub-mm and mm-scale layering might represent annual deposition (analogous to varves). The cm-scale layering contains dewatering structures formed when the initial iron-silica gels were deposited on the seafloor and compacted during initial lithification. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d2fc0f82-4a49-4b87-bab6-6a573eea180f/Fig_3_Kuruman_Mineralogy.jpg Clark Johnson-1 Detail of a fresh core of the 2.5-Ga Kuruman BIF, South Africa. The core is about 2 cm across. This unit was probably deposited in the same continental margin basin system as the Brockman BIF. In this core, the layers consist of primary hematite, magnetite, and siderite (Fe carbonate), plus chert. Such fresh samples show that BIF mineralogy consists of both oxidized (Fe3+) and reduced (Fe2+) iron. The earliest iron mineral is hematite, indicating the first stage of BIF mineral formation is an oxidative one, where seawater Fe2+ is oxidized to Fe3+. The Fe2+-bearing minerals, magnetite and siderite, indicate a later reductive stage on the seafloor during early diagenesis. This second stage is needed to explain the observation that, on average, BIFs of this age contain about 60% Fe2+ (i.e., reduced iron). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/16e89a67-2329-4baf-a9b0-54a77e6c4751/Fig_4_Compare_Mable_Bar-Kuruman_IF.jpg Clark Johnson-1 Changes in iron mineralogy through time. In unmetamorphosed iron-rich rocks, including BIFs and related lithologies such as japerlites (hematite+chert) of Archean age, such as the 3.5-Ga Marble Bar Chert (above left), the dominant iron oxide is hematite (Fe3+). By contrast, in rocks of Proterozoic age, such as the ~2.5-Ga Kuruman Iron Formation (above right), magnetite and siderite (both Fe2+) predominate. In both cases, Fe3+ oxides were precipitated initially, which implies that the younger BIFs additionally record a later reductive process to produce the Fe2+ minerals. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/16775b63-7bda-4035-9be5-33a4ec3278b6/Fig_5_BIF-Crust-Time.jpg Clark Johnson-1 Temporal changes in atmospheric oxygen and BIF deposition (top graph) and estimates for growth of the continental crust (100% equals modern volume, bottom graph). In the graphs, time advances from old at right to young at left. BIFs older than 2.7 Ga are very small; one of the oldest BIFs, the 3.7-Ga rocks at Isua Greenland, do not even plot on the presented scale. The very large BIFs deposited at the end of the Archean and early Paleoproterozoic, ~2.7-2.4-Ga age, include the Brockman and Kuruman BIFs, which were deposited before the "Great Oxidation Event" at ~2.3 to 2.4 Ga. We also know that the photic zone of the oceans started to become oxidized as early as 3.2 Ga. Thus, oxidation of seawater Fe2+ as part of the deposition of the very large ~2.7-2.4-Ga BIFs could have occurred either by oxygenic photosynthesis or by an anoxygenic photosynthetic pathway or some combination. Meanwhile, although the rate of continental crust formation over time is uncertain, all models suggest an increase in continental crust over time. As explained in the podcast, continental shelves provide the environments for BIF deposition and preserve them from subduction. They may also reflect a driver for a biological role through increased nutrient supply via continental weathering. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4380c946-caf7-4959-8aa5-5a1df2d99dd8/Fig_6_C-O_Relations_Siderite_UPDATED.jpg Clark Johnson-1 The ratios of carbon (C) and oxygen (O) isotopes in the BIF carbonates (siderite and other iron-rich carbonates) depend on how they were formed. The figure shows the range of these ratios measured in the 2.5-Ga Kuruman Iron Formation (blue field) and the ~2.9 Ga-Witwatersrand-Pongola Iron Formation (orange field). The black box in upper right indicates the C and O isotope compositions corresponding to equilibrium with seawater, which is what would be expected in the carbonates if there was no microbial respiration component. The green field shows the range of C and O isotope compositions expected for carbonates that were solely formed by respiration of organic carbon and Fe3+ oxide. As the plot shows, neither of the BIF formation carbonates have C and O isotope compositions that are in equilibrium with seawater, and nor are their carbonates entirely made from respired iron oxide and organic carbon. This provides powerful evidence that microbial iron reduction was a major process in producing the iron carbonates in BIFs. Figure adapted from Johnson, C.M. et al. (2020), Iron Geochemistry: An Isotopic Perspective, Springer, 360 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6e434dea-7356-41d9-8660-e3150cdc1c0d/Marandoo+Tom+Price+-+RTZ.jpg Clark Johnson-1 The Marandoo open-pit mine in the Hamersley Group of the Marra Mamba Iron Formation in the Pilbara region of Western Australia. The mine produces 15 million tons of iron ore a year, which is crushed and screened to remove magnetite and other impurities, producing haematite as an end product. This is transported by rail and road to the ports at Dampier and Port Hedland for export to steel manufacturers in China and other Far Eastern countries. BIFs such as these are the main source of iron in today's society. Thus, the isotopic studies shown in the figure above suggest that about half of all the iron we use today was respired by bacteria about 2.5 billion years ago! Courtesy of Rio Tinto https://www.geologybites.com/clark-johnson-transcript daily 0.75 2023-11-17 https://www.geologybites.com/clark-johnson-glossary daily 0.75 2023-11-17 https://www.geologybites.com/susan-brantley daily 0.75 2024-03-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e347e141-dcac-4b1b-a985-206150ad5b99/Brantley-LAB-0004-2.jpg Susan Brantley At the core of Earth’s geological thermostat is the dissolution of silicate minerals in the presence of atmospheric carbon dioxide and liquid water. But at large scales, the effectiveness and temperature sensitivity of this reaction depends on geomorphological, climatic, and tectonic factors that vary greatly from place to place. As described in the podcast, to predict watershed-scale or global temperature sensitivity, Susan Brantley characterizes these factors using the standard formula for the temperature dependence of chemical reaction rates using an empirically-determined activation energy for each process. Overall, her results suggest a doubling of the weathering rate for each 10-degree rise in temperature, but this value changes with the spatial scale of the analysis. Susan Brantley is a Professor in the Department of Geosciences at Pennsylvania State University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c6b01ab2-b1e5-4dc8-814e-b8e6588c0396/basalt+weathering+in+Hawaii%E2%80%A6shows+the+side+of+a+canyon-2.jpg Susan Brantley The weathering process depends on minerals contained within each rock type. Here, a basalt canyon wall in Hawaii has been heavily weathered. The principal minerals involved are olivine, pyroxene, and plagioclase feldspar. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7d26547c-27c3-4510-9d16-07a7d73e4677/granitic+rock+puerto+rico+january+2006+057-2.jpg Susan Brantley A heavily weathered quartz diorite (a form of granitic rock) in Puerto Rico. The unweathered granite contains potassium feldspar, plagioclase, and smaller amounts of biotite, hornblende, and muscovite, which weather in the presence of water to form clays and dissolved positively-charged ions such as Na+, K+, Ca++, and Mg++. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3bca10e1-a1aa-4db8-a088-bbff004bb810/Science+Paper+Fig.+1.JPG Susan Brantley - Make it stand out Models for soils and watersheds on silicate rocks in the humid half of Earth’s land surface. The reaction fronts (gray hatched layers) indicate where the most CO2 is dissolved during silicate weathering. For a bedrock mineral such as CaSiO3, the weathering reaction 2CO2 + H2O + CaSiO3 —> Ca2+ + 2HCO3- + SiO2 produces dissolved inorganic carbon (derived from the atmosphere) that is transported, precipitated, and partially sequestered as buried carbonate minerals at the seafloor. In the podcast, Susan Brantley describes two simplified weathering regimes: kinetic-limited (KL) regimes and erosive-transport-limited (ETL) regimes. In the former, illustrated in (A), kinetic limitation of silicate weathering is indicated by soil profiles or catchment areas where the silicate minerals and weathering reaction surfaces are exposed everywhere at the land surface. In ETL, illustrated in (B), weathering of soil and watersheds is characterized by buried reaction fronts, and concentrations of weathering products increase until they cause dissolution to stop. The weathering rate from such watersheds is determined by the erosion rate of the soil. (C) shows how in watersheds of increasing size (shown as white teardrop shapes), the dominance of long flow paths drive the weathering rate towards the ETL regime. As watersheds become larger, they show a transition regime (TR) behavior between KL and ETL landscapes. Brantley, S.L. et al. (2023), Science 379, 382 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e71913e8-994e-45cd-b827-69479a509e21/Science+Paper+Fig.+3.JPG Susan Brantley - Make it stand out Scaling the weathering reaction to larger spatial scales. Graph (A) shows how the effective activation energy (Ea), which is a measure of temperature sensitivity, increases for kinetic-limited weathering as the spatial scale increases from lab up to watersheds. This reflects the additional temperature-dependent weathering mechanisms that come into play as the scale increases from 100-micron mineral grains to 10-cm rock fragments to 1-m soils to 100-100,000-m drainage basins. (B) shows the fractional land areas of weathering regimes. The global-scale activation energy was based on the fractional contributions of the weathering fluxes shown in (C). First, a temperature response of 11.7% per degree K was estimated using the relative proportions of global carbon dioxide consumption fluxes from the two main rock types, granite (74%) and basalt (26%). This was then used to upscale the activation energy to the globe based on the proportions from each weathering regime (C), assuming the contribution of runoff-limited watersheds to be negligible. Brantley, S.L. et sl. (2023), Science 379, 382 https://www.geologybites.com/susan-brantley-transcript daily 0.75 2023-12-31 https://www.geologybites.com/susan-brantley-glossary daily 0.75 2023-12-10 https://www.geologybites.com/mahesh-anand daily 0.75 2023-12-24 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/95efea97-1680-4484-94a7-0b3423958cfd/Professor+Anand+on+the+Crichton+Campus+in+Dumfries.jpg Mahesh Anand We have learned a great deal about the geology of the Moon from remote sensing instruments aboard lunar orbiters, from robot landers, from the Apollo landings, and from samples returned to the Earth by Apollo and robot landings. But in 2025, when NASA plans to land humans on the Moon for the first time since 1972, a new phase of lunar exploration is expected to begin. What will this mean for our understanding of the origin, evolution, and present structure of the Moon? A lot, according to Mahesh Anand. For example, as he explains in the podcast, satellite imagery suggests that volcanism continued for much longer than was previously thought, perhaps until as recently as 100 million years ago. In-situ inspection and sample return should help us explain this surprising finding. Mahesh Anand is Professor of Planetary Science and Exploration at the Open University, UK. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/86268464-13d4-4c3a-bdc1-8845464ad81a/crss+section+jpg.JPG Mahesh Anand Schematic cross-section of the Moon. Like the Earth, the Moon has a core with an inner solid part and a liquid outer part, a mantle, and a crust. The lunar core is relatively smaller (radius of 20% of the whole) compared to that of the Earth (45%). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9c4ff1fe-45b7-4340-b677-77463fcac026/slide+3.png Mahesh Anand - Make it stand out Landing-site selection for the Apollo missions was mainly governed by practical considerations to ensure safety upon landing and return to Earth. But it turned out that the selected landing sites were geologically atypical, most of them being rich in potassium, rare-earth elements, and phosphorous (KREEP). The Artemis mission landing planned for 2025 will be near the lunar South Pole, which exposes some of the Moon’s oldest surface, estimated to be at least 3.85 billion years old. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/39b9920a-3136-4151-88f7-0cdae47cf9a7/slide+5.jpg Mahesh Anand Sites of successful Moon landings. China has also landed one unmanned craft on the far side of the Moon. Source NASA, BBC https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4815a0e9-fcb8-4e7f-8095-11baba230071/slide+7.jpg Mahesh Anand The image shows the Apollo 17 landing site where a number of scientific measurements were made. The flag marks the site of a geophone, one of four installed to measure seismic waves generated by detonation of an explosive. This yielded a seismic profile down to a depth of 3 km. The mission included a lunar rover, which is visible in the distance. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f4707d02-1abc-4436-9566-def9348dbde5/slide+9.png Mahesh Anand Apollo 17 astronaut Jack Schmitt collecting lunar samples. In the image, he is shaking soil out of a rake after making a pass through the surface soil. A variety of tools were used to collect samples on the Moon’s surface, including drills, hammers, rakes, tongs, and core tubes. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f534493-3cdc-410d-84f3-8c0b2932f805/slide+10.JPG Mahesh Anand In the podcast, Anand recounts how Jack Schmitt noticed and collected material that looked unusual. This turned out be volcanic glass that contained the first water discovered on the Moon. The rock was found in the Shorty Crater within the orange soil at bottom-right in the photograph at right. The photomicrograph of the soil at left shows orange and black glass spheres having sizes of 25 to 45 microns. In his journal, Schmitt wrote: “It was volcanic material, but it was volcanic glass that had been spewed out of some fire-fountain-like eruptions 3.5 billion years ago that somehow had been protected from mixing with anything else, even though it was now at the surface. It had almost certainly been covered almost immediately by a lava flow, so that it was protected from meteor disruption and stirring. And then, when Shorty formed, somehow the pyroclastic ended up in the rim and a few other places in nearly pure form.” Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/449c7253-8011-44c7-aac0-aff9f45f6f9f/cratering+curve.JPG Mahesh Anand As mentioned in the podcast, in 2022, the Chang'e 5 mission returned a sample of lunar basalt to Earth, where a radiometric age of 2 billion years was obtained. This is much younger than previously dated samples, indicating that volcanism persisted much longer on the Moon than was previously thought. The result also provided a valuable anchoring point (red dot) for calibrating the middle portion of the cratering curve, which plots the number of craters per unit area on the Moon against the age of the surface. This improves the accuracy of the crater-counting method of dating surfaces of the Moon as well as other inner Solar System bodies such as Mars. Chen, Y. et al. (2023), Innovation Geoscience 1(1): 100014 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/62d1ffef-576c-41cd-8cbe-0da3a4694353/slide+16.JPG Mahesh Anand The presence of water on the Moon was confirmed in 2009 by NASA’s LCROSS spacecraft (illustrated at left). A section of the rocket that was used to launch the spacecraft accompanied the spacecraft in its journey to the moon and was crashed into the lunar surface into a crater near the South Pole. The debris cloud released by the impact was analyzed as the spacecraft passed through the debris. The LCROSS spacecraft was then itself crashed into the Moon, releasing another plume of surface material, which in turn was analyzed by another spacecraft, NASA’s Lunar Reconnaissance Orbiter. The results showed that crater floors in permanent shadow contained frozen water, perhaps as much as hundreds of millions of tons. The likely distribution of such water around the lunar South Pole is indicated by the blue shading. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/17de5b3e-1cbe-46f8-8593-e12dbeed9863/Artist+impression+of+prospecting+for+water.jpg Mahesh Anand Artist’s concept of astronauts prospecting for water ice near the lunar south pole. Courtesy of NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c95e1a34-81a2-49bc-937e-4ca558e00b47/Shackleton.jpg Mahesh Anand Image captured from lunar orbit of the sunlit rim of the Shackleton crater. Twenty kilometers across, this crater is deep enough to have an interior that is in permanent shadow where a substantial amount of water ice is thought to have accumulated. Courtesy of NASA, GSFC, and Arizona State University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e8784544-beca-4caa-911b-eef583a4e3fd/LoTM_Habitat.jpg Mahesh Anand A virtual reality model of a lunar colony prepared for an exhibition at the 2019 Royal Society Summer Science Exhibition. https://www.geologybites.com/claire-corkhill daily 0.75 2024-01-07 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6da7e2ce-3086-46f0-b808-acb2b85f2e6f/Claire+inside+a+radioactive+hot+cell-2.jpg Claire Corkhill Storing radioactive waste safely over timescales of millennia to hundreds of millennia raises many questions, both technical and human. In the podcast, Claire Corkhill discusses the geology such storage sites require, some new materials that can confine radioactive isotopes over extremely long timescales, and the kind of hazards, including human, we need to guard against. She appears in the photo in a new, not yet radioactive “hot cell” for remotely manipulating spent fuel. Claire Corkhill is Professor of Mineralogy and Radioactive Waste Management in the School of Earth Sciences at the University of Bristol. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/35dcbc64-fbf2-48d9-9e11-4d0cf8215091/Nuclear+fuel+rods-1.jpg Claire Corkhill Loading a fuel assembly for nuclear power station. Nuclear fuel rods contain the uranium dioxide fuel whose fission products create the high-level radioactive waste that needs to be disposed of safely over very long timescales. Each individual fuel rod has several tens of uranium dioxide fuel pellets stacked up directly on top of each other. Depending on the type of reactor, 8 - 20 fuel rods are arranged in an assembly. In the picture, newly prepared fuel rods are being loaded into a fuel assembly surrounded by a graphite sleeve, which acts as a moderator. A number of assemblies are loaded into the reactor core in a series of vertical channels that are surrounded by some means of cooling the fuel, such as CO2 gas or pressurized water. Courtesy of the Nuclear Decommissioning Authority https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f2f37115-721e-44a8-a610-cf362cda07a7/High+level+waste+glass+containers-11.jpg Claire Corkhill Stainless steel canisters used to store high-level radioactive waste that has been vitrified, i.e., combined with borosilicate glass. As explained in the podcast, having no long-range order in the arrangement of their atoms, glasses are less vulnerable to radiation damage that can disrupt crystalline material. The molten glass is poured directly into the containers, and it is left to cool down naturally. The steel has some resistance to radiation damage, but it is expected that it will completely corrode in a geological facility before radiation severely damages it. The corrosion (by groundwater) will likely take around 1,000 to 2,000 years. Courtesy of Sellafield, Ltd. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7d0f4489-0f1f-4b9f-a40c-aacb738ef5c1/cartoon+of+a+GDF-13.jpg Claire Corkhill A cartoon illustrating Claire Corkhill’s research. The process starts with problematic radioactive materials from fuel reprocessing and nuclear decommissioning (top left). The research attempts to work out how best to turn these materials into a glass or ceramic waste material (bottom left, yellow container), using natural glasses and minerals (magnifying glass) as a template. Corkhill and her team then research the glass structure to understand how it will behave over long time scales once it has been buried in a geological disposal facility (right). Drawing by Alys Mordecai https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3d22f629-0fab-45af-9a0f-fea499b197bc/High+level+waste+tunnel+at+Onkalo-4.jpg Claire Corkhill Radioactive waste disposal vault 475 meters underground at the Finnish geological disposal facility at Onkalo. The site will store 3,250 of the radioactive waste containers shown at left below. One of the disposal holes that will house one of the waste containers is just visible on the floor behind the fence. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8c7679ad-2641-419b-8eb0-ae0ad1ed40f1/LIfe+size+spent+fuel+container+Finland-5.jpg Claire Corkhill Spent fuel container for the Onkalo geological disposal facility. The individual fuel rods are placed in the array of channels in a strong boron-steel insert (right), which is inserted into a copper tube (left) and provides stability to the radioactive waste package. The copper tubes are 5m long, 1m in diameter, and 5cm thick. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/001c2a66-bb9a-407e-86e5-df35acc18fe0/Mock+up+of+spent+fuel+container+disposal+at+Onkalo-6.jpg Claire Corkhill Mockup of the disposal system for Onkalo. The copper containing the array of spent fuel rods is deposited in a vertical borehole and surrounded by rings of bentonite clay. The bentonite protects the containers and the spent fuel from groundwater. It has a layered crystalline structure, which can take water into its interlayers. As such, when it gets wet it swells, forming a tight seal around the container, thus preventing radioactive elements from escaping. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e239d498-2f4b-4899-9167-aae347cf79ee/Intermediate+level+waste+test+vault+at+Bure-10.jpg Claire Corkhill Underground rock laboratory at Bure, France, where researchers are testing methods of constructing a geological disposal facility in the Callo-oxfordian clay. This type of tunnel is designed for intermediate-level waste (not heat-generating), which will be placed in large boxes and stacked on top of one another. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/43853c41-4c7f-433f-ace2-ee87fb4ee689/crystal+structure+of+zirconolite-14.jpg Claire Corkhill Crystal structures of zirconolite, a very durable naturally-occurring mineral. As Corkhill explains in the podcast, this mineral can accommodate uranium (U) and thorium (Th) within its crystal lattice where they replace either calcium (Ca) or zirconium (Zr) atoms in the lattice, thus trapping them over a period of hundreds of millions of years, even as the crystal is damaged by radiation. The two different structures are different forms (polytypes) of the same mineral – the 3T (on the left) is generally understood to be more resistant to radiation damage than the 2M (on the right). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4640b604-668c-4a3e-b32a-b210c5c0447b/SEM+images+of+1+Ga+titanite+mineral-15.jpg Claire Corkhill Photograph (left) and scanning electron microscope (bottom right) images of a one-billion-year-old titanite mineral containing uranium and exhibiting hydrothermal alteration. In the podcast, Corkhill discusses this ancient sample, which comes from the MacArthur River province in Canada. The area highlighted in the red square includes a U- and Th-rich titanate mineral together with a zircon crystal, which has been used to provide an age of around 1 billion years. The electron microscope image shows a series of veins running through the titanate mineral (large paler region), which were caused by hydrothermal alteration. Despite the fact that radiation has made the mineral completely amorphous (it is metamict), and it has been leached by hot fluids, it still contains most of its original U content. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/16c2eb7d-8122-4909-8356-aecd15fe418a/graph+of+radioactive+decay+of+high+level+waste+glass-16.jpg Claire Corkhill Graph showing the radioactive decay of spent nuclear fuel. Since there are many different isotopes with different half-lives depicted in this curve with some of the daughter isotopes having higher radioactivity than the parent isotopes (e.g., radium is more radioactive than its parent, U), the curve is not a simple decaying exponential. It will take 10,000 years for the radioactivity to return to the same level as that of the naturally occuring uranium ore from which the fuel originated. This is still fairly radioactive, so it is desirable to let the waste decay for two more orders of magnitude, or one million years. For reference, homo sapiens first walked the Earth around 300,000 years ago. https://www.geologybites.com/david-kohlstedt daily 0.75 2024-02-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f447d6a-f642-4ac4-9bb0-a306962c73c9/DK+cropped.jpg David Kohlstedt David Kohlstedt studies the behavior of samples containing olivine and other minerals under high pressures and temperatures in order to shed light on how they behave within the lithospheric and asthenospheric mantle. A capsule such as the one shown in the image below is inserted into the black cylindrical pressure vessel, which contains a heating element. High pressures in the sample are achieved using argon gas raised to high pressure using a series of pumps. Torque is applied to the sample via a piston that is loaded into the pressure vessel from the top. The rod seen extending out of the top of the vessel is the electrical supply connection rod for the torsion driver and external torque cell. David Kohlstedt is Professor Emeritus at the School of Earth and Environmental Science at the University of Minnesota. Courtesy of Rich Ryan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/069d3973-7762-4d43-8b51-aedc4e9a505e/DSC03069.JPG David Kohlstedt Sample assembly without the jacket enclosing the pistons and the sample. The sample is in the center, followed by alumina spacers (pistons), followed by alumina tapered pistons, followed by low-thermal-conductivity zirconia pistons. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/03210ab8-7d11-4798-9da7-755aa82de0ce/Fig.+7+-+torsion+sample.jpg David Kohlstedt - Make it stand out Left: A sample of olivine and 4% mid-ocean ridge basalt (MORB) deformed in torsion to a full 360-degree rotation. An iron jacket encapsulates the sample and adjoining pistons. A crease in the jacket acts as a marker of the torsional strain, i.e., twisting, undergone by the sample. David Kohlstedt and his team chose to make the pistons out of alumina because they are stronger than the samples at high temperature (~1,300oC). Above 1,300oC, olivine reacts with alumina, so other materials such as molybdenum and thoriated tungsten are used. Right: Melt segregated into melt-rich bands containing ~25% melt leaving melt-poor regions with ~1% MORB behind. The melt-rich bands are inclined at ~15 degrees to the shear plane, antithetic to the shear direction. Modified from King, D.S. et al. (2010), J. Petrol. 52:21-42, https://doi.org/10.1093/petrology/egp062 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec31c638-262b-47e7-a5a2-d6a4b2f4075a/torsion_assembly-MEZ+v2.jpg David Kohlstedt - Make it stand out Exploded schematic view of a typical sample assembly for a torsion deformation experiment. The sample is inserted into a nickel sleeve and capped by alumina discs. Alumina and zirconia pistons complete the sample assembly, which is slipped into an iron jacket that seals against o-rings on the top and bottom steel pistons. The splines on the bottom steel piston slip into a cell for measuring torque inside the pressure vessel, while the dog teeth on the top steel piston mate with those in the torque driver/external torque cell. This complete sample assembly is loaded into the pressure vessel, which houses a wire-wound tubular furnace. Courtesy of Mark Zimmerman https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f935b52e-7c7a-4fca-8632-64c198f6f280/Fig.+6a+-+Treatise+adjusted.jpg David Kohlstedt - Make it stand out Backscattered scanning electron micrograph at the scale of individual mineral crystals showing the distribution of melt in an undeformed, partially molten rock composed of olivine plus basalt. Melt is present in all triple (three-grain) junctions and along some grain boundaries (two-grain junctions) but has no preferred orientation. The sample was formed by pressing a mixture of olivine and 5% basalt powders in a nickel capsule at a temperature of 1,200oC and a pressure of 300 MPa for 3 hours to form a coherent, fully dense sample. This is the starting material for a deformation experiment. Kohlstedt, D.L. (2007), Properties of rocks and minerals – constitutive equations, rheological behavior, and viscosity of rocks, in Treatise on Geophysics, ed. G. Schubert, vol. 2.14, pp. 389-417 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2400596b-28d5-4e9c-873e-eebcad68a513/Fig.+6b+-++MSA_9.jpg David Kohlstedt - Make it stand out Reflected-light optical micrograph of a sample of olivine + 3% basalt deformed by a stress of 170 MPa to a shear strain greater than 2 at a temperature of 1,200oC and a pressure of 300 MPa. The image reveals a strong melt preferred orientation that developed at ~25 degrees to the shear plane and opposite to the shear direction. In this sample, the melt remained distributed on the grain scale and has not yet segregated into melt-rich bands. Olivine grains are light gray, and basalt is black. Modified from Kohlstedt, D.L. (2002), Partial melting and deformation, in Plastic Deformation in Minerals and Rocks, eds. S.I. Karato, H.R. Wenk, Reviews in Mineralogy and Geochemistry, Mineralogical Society of America, vol. 51, pp. 105-125 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f90b8408-6caa-40ba-a617-88e02bed3438/Sheared+sample.jpg David Kohlstedt - Make it stand out Optical microscopy image of two orthogonal planes of a sheared sample. Images such as this one formed the basis of the sketches shown below. The sample contains melt-depleted lenses (outlined with dashes) that are generally longer in the direction normal to shear (y) than parallel to shear (x). This sample was deformed in simple shear rather than in torsion at T = 1250oC, P = 300 MPa at a shear stress of 116 MPa to a shear strain of 3.4. Melt-rich bands form under both types of loading conditions. Holtzman, B.K. et al. (2007), J. Petrol. 48:2379-2406 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a6fbe17-63e8-4288-aa42-c75ff8bf8070/Fig.+8+-+Holtzman+-+Science+sketch.jpg David Kohlstedt Sketch of the distribution of melt and the way strain is partitioned in experimentally deformed samples of olivine plus basalt. (a) Melt-rich bands (yellow) form forking and rejoining networks with larger bands at higher angles relative to the shear plane (flat red arrow) connected by smaller bands at lower angles. In three dimensions, the melt-rich layers connect and surround melt-depleted lenses (green). (b) Partition of strain between forking bands and lenses between the bands. David Kohlstedt’s experiments were the first to observe such structures form. The flat arrows indicate the total shear and the component concentrated in the bands. The narrow black half-arrows indicate the alignment of the olivine crystals normal to the shear direction in the lenses. The black lines mark the orientation of the shear plane in the lenses, back-rotated relative to the sample shear plane as a result of the way the strain is partitioned between the melt-rich bands and the lenses. Artwork by Benjamin K. Holtzman. Modified from Holtzman, B.K. et al. (2003), Science 301:1227-1230 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8ec37a9d-0897-4571-bdda-d62a5f10332b/Fig.+9+-+Hirschmann-Kohlstedt+AGU+2012.jpg David Kohlstedt - Determining the Water Content of a Sample As he explains in the podcast, David Kohlstedt ran experiments in which the amount of water present in a sample was varied by controlling the pressure at a fixed temperature so as to determine the dependence of rock strength on water content. In fact, it is the hydrogen ion H+ derived from the dissociation of water into H+ and OH- ions that weakens the minerals, not water. The hydrogen ions, being tiny, diffuse very rapidly from the water introduced into the sample assembly into the sample. Once inside the sample, the hydrogen combines with oxygen ions that are part of the olivine structure to form OH- ions. It is the infrared absorption spectrum of these OH- ions that are used to indicate the effective amount of water within the sample. The figure shows infrared spectra taken from five olivine crystals, each heated to 1,100 degrees C while subjected to different pressures and thus subject to different water fugacities. Notice that the water fugacity (fH2O) changes by 7 orders of magnitude in response to a change in pressure of only about 2 orders of magnitude. The increase in water solubility/concentration is in response to the increase in water fugacity. The sharp peaks correspond to OH-stretching bands. The concentration of hydrogen is obtained by integrating the area under each absorption spectrum. Hirschmann et al. (2012), Adapted from Kohlstedt, D.L. et al. (1996), Contrib. Mineral. Petrol. 123:345-357 https://www.geologybites.com/damian-nance daily 0.75 2024-04-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/86b718b1-e699-4d56-8865-ef21f2771f54/DN-2.jpg Damian Nance Damian Nance draws on a wide range of geological evidence to formulate theories about the large-scale dynamics of the lithosphere and mantle spanning a period going back to the Archean. A major focus of his research is the supercontinent cycle. As he discusses in the podcast, our newly acquired knowledge of the deep mantle casts the supercontinent cycle into a whole new light — as a mantle-lithosphere phenomenon rather than a purely tectonic one playing out on and just below the Earth’s surface. Nance is Distinguished Professor Emeritus of Geological Sciences at Ohio University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/959260ff-d840-47ef-a474-cb56d6be825e/Supercontinent+Timeline.JPG Damian Nance - Make it stand out This timeline was proposed by David Evans (a 2021 Geology Bites guest). The timeline indicates the possible existence of Pannotia as well as of Kenorland, a Paleoproterozoic supercontinent that preceded Nuna. Black lines represent rift zones associated with supercontinental breakup. Red stars in the Superia supercraton (lower right inset) indicate possible mantle plume focal points of radiating swarms of mafic dykes. Evans, D.A.D., et al. (2016), Geol. Soc., London, Special Publications, 424, 1-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d1148047-872d-4670-a147-34b36de9516f/Pannotia+Hasui+2010+slide+5.jpg Damian Nance - Pannotia Pannotia, if it existed, lasted from about 630 million years ago to 530 million years ago. In the podcast, Damian Nance explains why its existence is controversial, but that even if it was only a close gathering of continents, it might have been enough to reverse the pattern of flow in the mantle. Orange regions are ancient continental blocks (cratons), and the yellow areas indicate presumed other continental material. Hasui, Y.A. (2010), Geociências. v. 29. n. 2. P. 141 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a480d92b-dfd0-46d9-8e9d-c1733c9db9d6/Rodinia+Li+et+al+2012.png Damian Nance - Rodinia Rodinia existed during the Mesoproterozoic and Neoproterozoic between about 900 million years ago and 750 million years ago. The cratons are shown in light green, other continental material is shown in dark green, and the orange band indicates Grenville-age (1.3-0.9 Ma) orogens along which the supercontinent was assembled. Li, J. et al. (2012), Precambrian Research 309, 181 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/09daff70-3d1d-456e-b2e3-bed4ba54f27a/Nuna+Zhang+et+al+2012.PNG Damian Nance - Nuna Nuna, also sometimes called Columbia, existed from about 1.7 billion years ago to 1.5 billion years ago. Cratons older than 2,300 Ma are shown in pale grey, mountain ranges aged 1,660 to 1,500 Ma are shown in dark grey, the entire light area with a green border indicates the extent of Nuna at 1,590 Ma, and the red lines indicate presumptive subduction. Zhang, S. et al. (2012), Earth and Planetary Science Letters, 353-354, 145 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d6b295fd-5aff-4adf-9e44-3505fac21102/Degree+1+and+2+annotated.jpg Damian Nance - Make it stand out Computer modeling of the evolution of mantle flow patterns discussed in the podcast, with supercontinent assembly occurring above downwelling regions (blue), and supercontinent breakup fostered by mantle plumes in upwelling regions (yellow). The modelling suggests a random mantle circulation when the continents are scattered (a). Mantle convection then tends to evolve to a degree-1 structure with antipodal areas of upwelling and downwelling, and the downwelling leading to the formation of a supercontinent above it (b—>c). Once the supercontinent is formed, subduction of the closing oceans stops, and subduction jumps to the edges of the supercontinent, forming a subduction girdle around it (d). The subduction girdle influences mantle dynamics in such a way as to convert the downwelling beneath the supercontinent into an upwelling, thereby producing a mantle with a degree-2 structure, i.e., one with two antipodal areas of upwelling bisected by a downwelling girdle (d). The dynamical process of true polar wander (TPW) causes the supercontinents, being a region of excess mass, to move towards the equator (d—>e). The upwelling beneath the supercontinent causes it to break up (e), scatter the continents, and eventually return the mantle flow to a degree-1 structure (e—>b). Li, Z.-X., et al. (2009), Physics of Earth and Planetary Interiors 176, 143 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a025a4b-966d-4aff-bf1b-ac97be1f58e2/LLSVPs.PNG Damian Nance Seismic shear wave velocity map at the core-mantle boundary (CMB) showing the present-day distribution of large low-shear velocity provinces (LLSVPs) (red shaded areas). Stars represent 12 active hot-spot volcanoes generated by plumes that rise from the CMB. The green circles indicate the locations on the CMB of sources that erupted large igneous provinces (LIPs) over the past 300 million years. The concentration of the sources of both LIPs and hot-spot volcanoes on the edges of the LLSVPs is striking. Burke, K. (2011), Annual Reviews of Earth and Planetary Science 39:1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7872f9cd-b7eb-4678-ab31-1fccf1f9ce3e/slide+30.JPG Damian Nance - Without Pannotia Without Pannotia, the cycle has shown fairly steady post-Archean repetition at an interval of about 650 million years. With this interval, the next supercontinent would assemble about 350 million years from now. Nance, D. et al. (2022), Earth-Science Reviews, 232, 104128 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3610716a-002f-4206-b240-79f639c6e60c/slide+29.JPG Damian Nance - With Pannotia With Pannotia, the cycle would appear to be accelerating toward an interval of about 350 million years, a trend that is enhanced with inclusion of Kenorland. In this case, the next supercontinent would assemble about 75 million years from now. Nance, D. et al. (2022), Earth-Science Reviews, 232, 104128 https://www.geologybites.com/richard-ernst daily 0.75 2024-04-10 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/76c766d3-e665-47cd-ba80-99c8078ce3e8/Justin+Tang+Conversation+w+book+cropped.jpg Richard Ernst Richard Ernst studies the huge volcanic events called Large Igneous Provinces (LIPs) — their structure, distribution, and origin as well as their connection with mineral, metal, and hydrocarbon resources; supercontinent breakup; and mass extinctions. He has also been studying LIP planetary analogues, especially on Venus and Mars. He has written the definitive textbook on the subject. Ernst is Scientist in Residence in the Department of Earth Sciences, Carleton University, Ottawa, Canada, and Professor in the Faculty of Geology and Geography at Tomsk State University, Tomsk, Russia. Courtesy of Justin Tang and Carleton University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6c723b1d-eb48-40f9-af0e-a2f4b6c7580a/Figure+1a+Global+LIPs+maps++AGU+book+2019+Oct+4++REV.jpg Richard Ernst - Make it stand out Global map showing the distribution of Large Igneous Provinces (LIPs) over the past 500 million years (Ma). Continental LIPs are outlined in black, oceanic LIPs are blue, and silica-rich LIPs are orange. CAMP = Central Atlantic Magmatic Province; HALIP = High Arctic Large Igneous Province; NAIP = North Atlantic Igneous Province. After Ernst, R. E. et al. (2021), Chapter 1 in AGU Geophysical Monograph 255 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/84570bb6-cb75-42fe-8eb2-0b790051354a/LIPs+500-1000+Ma.PNG Richard Ernst - Make it stand out Global map showing the distribution of LIPs and silica-rich LIPs during the period 500 - 1000 Ma. As Ernst mentions in the podcast, the Franklin and Thule LIPs, emplaced at 716 Ma, coincide with the onset of the Sturtian glaciation, the first “Snowball Earth” glaciation, and are thought to have played a role in triggering the glaciation. After Ernst, R. E. et al. (2021), Chapter 1 in AGU Geophysical Monograph 255 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/90f4b5c3-10e7-4fa7-8e36-1bd69ed0f7c8/Mackenzie_Large_Igneous_Province+By+Black+Tusk+-+Own+work+based+on+MLIP+map+information+from+%5B1%5D%2C+CC+BY+3.0%2C+httpscommons.wikimedia.orgwindex.phpcuri Richard Ernst - Make it stand out Map of the Mackenzie large igneous province and its sub-features. The blue star marks the approximate focal point for the 1,270-million-year-old magmatic activity. Credit: Black Tusk https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/911e9a1d-5611-4e55-a10f-0eccd9865766/McKenzie+dike+swarm+photo.jpg Richard Ernst - Make it stand out In the podcast, Richard Ernst mentions the deeply eroded Mackenzie event in Canada, the remains of which include the 2,000-km-long Mackenzie dyke swarm and the Coppermine volcanics. The star marks the focal point of the swarm. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5b1a5e3d-0957-4dc4-8d13-b1acd0f7687d/CAMP_Magmatism_in_the_context_of_Pangea.jpg Richard Ernst - Make it stand out Map showing the location of large residual elements of the Central Atlantic Magmatic Province that erupted about 201 million years ago, covering an area of 11 million square kilometers. Courtesy of Williamborg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0518a1e2-c6f6-48b3-b23a-f88ad5366a55/Morocco+CAMP.jpg Richard Ernst - Make it stand out Lava flows of the Central Atlantic Magmatic Province in the High Atlas mountains of Morocco. Courtesy of Marzoli https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5e591478-2d69-40e1-8705-d371b806781f/Siberian+Traps+map.jpg Richard Ernst - Make it stand out The Siberian traps form vast ranges of volcanic hills in Siberia between the Ural Mountains and Lake Baikal. They are mainly composed of basalt and tuff from lava and ash expelled 252-251 million years ago at the Permian-Triassic boundary and coincident with Earth’s most severe mass extinction. Athena Review https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d26e3707-82ac-41a4-9c4c-f4d2e69ba1c4/Siberian+Traps+Layered+igneous+rock+of+the+Siberian+Traps+on+the+Putorana+Plateau.jpg Richard Ernst - Make it stand out A striking example of the multiple successive lava flows of the Siberian Traps in the Putorana Plateau in northern Siberia. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6cae4cb9-66b4-4a02-b3dc-6c6320c5bc0a/Sahara+2012.jpg Richard Ernst Dyke swarms can be indications of the former presence of a LIP that has been eroded away. Such swarms supplied the large quantities of lava that formed the LIP. In the image, Richard Ernst is collecting samples from a dolerite dyke in the Sahara desert that may have fed a Proterozoic LIP. The dyke forms a ridge of darker material that runs from bottom left to the right peak. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c02f100d-a4f4-43c8-9078-876f6fbd9248/Lu+et+al+fig+1B+Sturtian+age+comparisons.PNG Richard Ernst Graph showing the close temporal relationship between the emplacement of large igneous provinces and the onset of the Sturtian “Snowball Earth” glaciation around 720 million years ago. From top to bottom, the graph shows the Hubei–Shaanxi Magmatic Province in South China, the Irkutsk LIP in Siberia, and the Franklin LIP in Laurentia. The insert provides the most precise dates (white stars) on these magmatic provinces. Lu, K. et al. (2022), Earth and Planetary Science Letters 594, 117736 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4a4786b0-4aaf-4561-aacf-08b3f45f198f/Flood+basaltyanimation.gif Richard Ernst Cartoon of the formation of a flood basalt. In the podcast, Ernst discusses models of LIP emplacement that invoke the arrival of a plume of hot material originating from the deep mantle. As the plume rises, the head widens, uplifting a wide region of the lithosphere and supplying melt through a swarm of radiating dykes that form along fractures associated with the uplift. Courtesy of Bob White and Lindsey Smith https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c4f1f114-8ca0-4986-a48f-8eb27e613585/Great+Dyke+Fig+1+REV.jpg Richard Ernst - Make it stand out In the podcast, Richard Ernst describes the nearly 4,000-km-long Great Dyke of Atla Regio (GDAR) (purple). The image also shows other dykes (orange lines) belonging to the giant radiating swarm of Ozza Mons, Atla Regio plume centre, Venus. Within the region delimited by the blue circle, the dykes radiate out from a posited mantle plume head. Beyond the circle, the dykes change direction in response to the influence of the regional stress field associated with the 10,000-km-long Parga Chasmata (rift system). Owing to the absence of erosion on Venus, long, laterally-emplaced dykes stand out on the surface of Venus as graben. After El Bilali, H. et al. (2024), Nature Communications, 15:1759 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6a4db2f7-e5dc-4059-b9a5-fb140f411ba6/Tharsis+region.jpg Richard Ernst - Make it stand out Shaded relief map of the Tharsis volcanic province on Mars from the Mars Orbiter Laser Altimeter. The thin black lines indicate grabens; thin grey lines indicate wrinkle ridges.; thick black lines indicate ridges having an elevation of about 3 km. Mège, D, et al. (2001), Geological Society of America Special Paper 352 https://www.geologybites.com/scott-bolton daily 0.75 2024-05-27 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00b1b535-8a92-45a0-83be-e4e92d0f9201/scott-bolton-juno-d019345-0953.JPG Scott Bolton Juno is the latest space probe to visit Jupiter. Since its arrival in 2017, its orbit around the giant planet has progressively shifted to take it close to Jupiter’s moons and rings. In December 2023 and February 2024, it flew by the innermost Galilean Moon, Io, approaching within a distance of only 1,500 km. This enabled it to capture high-resolution imagery of Io’s constantly changing surface, including hitherto unseen regions near its poles. As discussed in the podcast, Juno is equipped with a microwave instrument that enables it to look slightly below the moon’s surface into its lava lakes, as well as a suite of magnetometers to study Jupiter’s giant magnetosphere and its interaction with Io. Scott Bolton’s research focuses on Jupiter and Saturn and the formation and evolution of the solar system. He has led a number of science investigations on the Cassini, Galileo, Voyager, and Magellan missions and is the Principal Investigator of the Juno Mission. He is Director of the Space Sciences Department at Southwest Research Institute in San Antonio, Texas. Courtesy of Southwest Research Institute https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5315512f-47c9-4ea0-ba3f-03d7fba313fa/The_Galilean_satellites_the_four_largest_moons_of_Jupiter.jpg Scott Bolton - Make it stand out The Galilean moons Io, Europa, Ganymede, and Callisto (left to right) to relative scale and in order of increasing distance from Jupiter. Jupiter has a total of 95 recognized moons, the latest discovered in 2017. There are four moons with orbits interior to Io, and the rest lie beyond Callisto. NASA/JPL/DLR https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ac828bdf-35a9-48ca-80e8-10351a6526ef/Where_Juno%27s_instruments_are_attached_2_%28crop%29.jpg Scott Bolton - Make it stand out Diagram showing the location of Juno’s instruments. In the podcast, Bolton discusses the imagery captured by the visible-light camera (JunoCam), the particle and magnetic field measurements with the energetic-particle detector (JEDI), the plasma waves instrument (Waves), and the fluxgate magnetometer (FGM), as well as the novel use of the microwave radiometer (MWR) to look at Io’s surface and perhaps below the surface of its lava lakes as well. NASA/JPL https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7b8306e2-dd13-42e8-b719-1bc4f1e32996/extended+mission+orbit.PNG Scott Bolton As mentioned in the podcast, without the need for any thrusting from Juno’s rocket engines, asymmetry in Jupiter’s gravitational field rotates and shortens Juno’s orbit, moving it inwards to successively approach each of the Galilean moons. The orbit has given us our first-ever views of the moons’ polar regions. Each of the orbits is labeled PJ for perijove, the point of closest approach to the planet. NASA/JPL-Caltech/SwRI https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c54a762f-575e-47ca-b992-3d59b9443cae/whole+Io.PNG Scott Bolton Color-enhanced image of Io taken by Juno on February 3, 2024. As discussed in the podcast, constant volcanic activity produces lava flows and lakes that change between successive fly-bys, which at this stage of Juno’s mission are 35 days apart. The entire surface is continually replaced by volcanism every few thousand years. NASA/JPL-Caltech/SwRI/MSSS/Thomas Thomopoulos https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/324f1f62-f70a-4c5b-95ab-b12c609b49c2/highest+res+from+PJ+58.PNG Scott Bolton - Make it stand out Io's leading hemisphere taken on February 3, 2024, from Juno’s closest approach, 1,500 km from Io’s surface. In this image, the surface is lit by light reflected off Jupiter’s surface. At top center, which is near Io's equator, is the large volcano Shamshu Patera with a patchwork of lava flows. Shamshu Patera is surrounded by several non-volcanic mountains. At center right is a feature that is thought to be a lava lake. Pixel scale is 1 km/pixel; Io’s diameter is 3,643 km. NASA/SwRI/JPL/MSSS/Jason Perry https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/757c94b4-e5e2-44ac-b9d6-b561087998ca/Io+S+Pole+Apr+9+2024.PNG Scott Bolton The first-ever image of Io’s south polar region, captured from a distance of 10,250 miles during Juno's 60th fly-by of Jupiter on April 9, 2024. NASA/JPL-Caltech/SwRI/MSSS. Image processing: Gerald Eichstädt/Thomas Thomopoulos (CC BY) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eed3fabc-ab41-49ae-9be3-f731e7652be1/NASA++JPL-Caltech++SwRI++MSSS++Bj%C3%B6rn+J%C3%B3nsson+CC+NC+SA.PNG Scott Bolton A comparison of Io's appearance on December 30, 2023, and February 3, 2024. The later image shows strong specular reflections from several features that appear dark in the earlier image. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c324e5b3-5f61-4683-b4ba-7d4f311efe5a/loki-iceland.PNG Scott Bolton Superposition of Loki Patera onto Iceland. With a width of 230 km, Loki Patera is the largest lava sea in the solar system. Jesper Sandberg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/43581ce4-0be2-4f1f-901f-89e4ea08d2f2/mountains.PNG Scott Bolton The image shows mountains on Io’s surface, some much taller than Mount Everest. They appear to be tilted and fractured slabs of crust formed tectonically rather than by volcanism. NASA / SwRI/ MSSS / Andrew R Brown https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/23b792b4-04d0-42f8-9e74-d3273651697d/Io+in+IR+and+visible.jpg Scott Bolton These composite views depicting volcanic activity on Io were generated using both visible light and infrared data collected by Juno during fly-bys on Dec. 14, 2022, (left), and March 1, 2023. NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ee4df940-a633-4d44-b07e-5f7ad5b6d54c/Models+of+Io.PNG Scott Bolton Juno’s infrared and visible-light mapping of the entire surface of Io, as well as the gravity studies, will help distinguish the various models that have been proposed for Io’s interior. In the podcast, Bolton discusses the difference between a magma ocean model (top right) and other models in which there are just pockets of magma below the surface. Johns Hopkins University APL, University of Arizona, Mike Yakovlev, SciTechDaily https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dc0f3e2a-5ac7-4fc6-abba-eabba9a1bffb/PIA01627_Ringe.jpg Scott Bolton Schema of Jupiter’s rings, which lie close to Jupiter, well within the orbit of Io. The main and halo rings mainly consist of dust ejected from the moons Metis, Adrastea. NASA/JPL/Cornell University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/651536bf-99af-4256-b829-054842cf0ca1/dust+ring.jpg Scott Bolton Jupiter’s main dust ring captured by Juno from within the ring as Juno made its first data-collecting orbit around Jupiter in August 2016. The ring lies about 55,000 km from Jupiter’s surface, is 6,500 km wide, and 30-300 km thick. In the podcast, Bolton mentioned that Juno may fly through the rings even though the dust they contain is hazardous for the space probe. Jupiter’s rings are much fainter than those of Saturn and were only discovered by the Voyager 1 space probe in 1979. NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c4bf3ea5-705b-46b0-a408-927a02f7431f/aurora+spot+rendering.PNG Scott Bolton In the podcast, Bolton discusses Jupiter’s huge magnetosphere, part of which is filled with charge particles emitted by the volcanoes on Io. These spiral along magnetic field lines toward Jupiter’s poles, where they create a zone of intense aural emission, which appears as a bright spot in the aurora. In this artist’s rendering, Io is shown as the star-like object at right so as to indicate the high flux of largely invisible charged particles it emits. RIKEN https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bc7055cb-e44d-47a4-9f99-219e1260e1f4/aurora.jpg Scott Bolton UV image from the Hubble Space Telescope showing the glowing aurora on Jupiter’s north pole. The aurora is generated, as on Earth, by charged particles moving and accelerating rapidly in the planet’s magnetic field. The various spots in the aurora result from the channeling of charged particles emitted by Io’s volcanoes, as well as by the impact of Jupiter’s rapidly rotating and intense magnetosphere on the surfaces of Ganymede and Europa, as Bolton mentions in the podcast. ASA/ESA, John Clarke (University of Michigan) https://www.geologybites.com/bob-white daily 0.75 2024-05-07 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/850311a9-6dbe-40f3-b12d-fd497dd032d1/Bob+White+processed-1.jpg Bob White Bob White and his research group use highly sensitive seismometers to measure seismic waves from controlled sources and earthquakes. He uses this data to learn about the structure and behavior of the lithosphere. In the podcast, White describes how he obtained an unprecedentedly detailed real-time view of the lateral movement of melt about 6 km below the surface of Iceland just before it erupted. White is Emeritus Professor of Geophysics in the Department of Earth Sciences at the University of Cambridge. In the image, he is connecting a battery for a broadband seismometer in the Highlands of north Iceland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/acc81518-be35-465c-8f1f-34c5a1a5d545/Bardabunga+Study+Area.PNG Bob White Map of the area White and his team studied leading up to the 2014 eruption just before the laterally flowing melt reached the Holuhraun volcano. Each of the main segments (S1 to S4) became seismically quiet once a new segment had intruded beyond it, producing the step-like propagation of seismicity. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/42d9d858-6b0b-4a86-a6fd-0b3352069b84/Augustdottir+206+Fig+2a.PNG Bob White - Make it stand out Propagation of seismicity through time is revealed in this plot of the earthquake locations measured in distance along the dike versus time. The phases where the melt propagated are shaded grey, the eruption periods are shown in peach, and the fissure location is orange. The plot shows the stop-start propagation of the dike as well as the way that seismicity ceases once an underground channel has been opened up. Ágústsdóttir, T., et al. (2016), Geophys. Res. Lett., 43, doi:10.1002/2015GL067423 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9b808dc3-6ac6-4923-be8f-71d3e6924467/Fig+8.PNG Bob White - Make it stand out Diagrammatic cross-section through the Bárðarbunga volcano caldera and the dike along which the melt flowed before erupting. The detected earthquakes are colored by depth, from shallowest (yellow) to deepest (purple). Ágústsdóttir, T., et al. (2019), Journal of Geophysical Research, Solid Earth, 124, 8331 https://www.geologybites.com/paul-smith daily 0.75 2024-06-09 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8af8e583-1876-4d7e-ab1d-66ad5f2200e9/PS+edited+dirty.jpg Paul Smith As he explains in the podcast, Paul Smith believes that we need to bring diverse research disciplines to bear on the question of life’s explosive proliferation between 541 and 530 million years ago during the Cambrian period. These disciplines include paleobiology, sedimentology, and geochemistry. He suggests that only when sufficiently evolved genetics and conducive environmental conditions coincided could complex feedback loops begin to operate and drive explosive growth in the abundance and diversity of life. Smith is Director of the Oxford University Museum of Natural History and Professor of Natural History at the University of Oxford. The photo was taken after a day of excavating at Sirius Passet in northern Greenland. Courtesy of Jan Audun Rasmussen https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/19d3da51-1aa1-4117-b20f-19fe5634ba57/Time+Scale.PNG Paul Smith Geological timescale of animal origins. In the two major Snowball Earth glaciations in the Cryogenian period, life survived in limited areas of unfrozen ocean and melt-water ponds on the surface of the ice that covered nearly all the planet. As discussed by Paul Hoffman in his episode of Geology Bites, all modern life is thought to be descended from these organisms. In this episode, Paul Smith talks about the emergence of much more complex life about 100 million years later in the Ediacaran and Cambrian. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d3ff4406-5353-4989-b50d-432efc85b4ef/Picture2.png Paul Smith The major diversification of marine taxa between 635 and 443 million years ago. The red box indicates the time interval discussed in the podcast. EB: Ediacaran biota. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/00cc75e6-8dee-44f7-bd57-a52764696654/Tree+of+Life+exhibit.jpg Paul Smith - Make it stand out Tree of Life exhibit at the Oxford University Museum of Natural History. Today’s living species are shown at the outermost reaches of the tree. Moving back in time towards the center of the tree, the branching points show the last common ancestor between species. The diversification of the Cambrian explosion appears about halfway to the center (not to scale) just after the divergence of the chordates, molluscs, and arthropods. The tree was constructed using a combination of genetic information, which, as Smith explains in the podcast, provides the scaffolding or framework of the tree, and morphological data from fossils that informs the morphological evolution of groups in their early history. To learn about the evolution of body plans of animal groups that populate the tree of life, we must rely on a combination of genetics and paleobiology. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4261b47c-a6de-4c0e-bb02-4592a74713cf/Nature+-+interconnected+causes+Smith+%26+Harper+2013.jpg Paul Smith In the podcast, Smith suggests that no single process is responsible for the Cambrian explosion. Tectonic and geological, developmental, and ecological processes have been hypothesized as isolated, singular causes. Instead, many of these processes are parts of connected feedback loops that together generated the Cambrian explosion. Each box corresponds broadly to a stand-alone hypothesis or suite of related hypotheses (red, geological; blue, geochemical; green, biological). The red arrows connect the explosion in animal diversity to five proximal causes. The figure represents the interval of time at the beginning of the Cambrian, 541 million to 521 million years ago. Smith, M.P., et al. (2013), Science 341, 1355 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/01e894c1-7681-4179-8f22-15108c58c010/Lagerstatten+23.jpg Paul Smith The configuration of the continents following the breakup of the Rodinia supercontinent about 750 million years ago. The locations of the sites where exceptionally well-preserved beds (Lagerstätten) of Cambrian fossils have been found are marked. Today, the Burgess Shale is in the Canadian Rockies, Sirius Passet is in the far north of Greenland, and Chengjiang is in southern China. cpgeosystems.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/24993208-18eb-4426-bf74-1fcf12e8bfb8/WalcottQuarry080509.jpg Paul Smith - Make it stand out The most famous of the Burgess Shale Formation members at the Walcott Quarry. It dates from 508 million years ago, about 10 million years younger than the Sirius Passet locality. Outcropping at an elevation of 7,500 ft. in the Canadian Rockies, it was discovered by paleontologist Charles Walcott in 1909. Photo: Mark A. Wilson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9d3935fa-ff40-4996-87e9-b18d5c41ab66/Burgess+Shale+art+51.jpg Paul Smith Artist’s impression of the deep-water shelf environment where the Burgess Shale biota lived. Courtesy of D.W. Miller https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/25e91af3-a1a4-4508-91af-e797642ee613/Satellite+view+SP+25.PNG Paul Smith Satellite view of North America and Greenland showing the location of Sirius Passet. This location is one of the few known Cambrian Lagerstätten. Their fossils contain preserved soft-tissue structures that provide an important window to the evolution of animals at the time of the Cambrian explosion. NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b6e5fb42-990f-4000-a63a-d8b48e518199/SP+53.JPG Paul Smith - Make it stand out Geology of the Sirius Passet locality. The fossils lie in the laminated mudstones and muddy siltstones of the Cambrian formation at left. These are bounded at right by a fault where they are in contact with older white carbonate rocks of the uppermost Ediacaran. The fossil quarry site is marked by the red rectangle. At the left end of the rectangle, members of Smith’s team can just be seen. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f7b4a578-3eb0-4744-ad83-4d3d0b09e09e/37a.jpg Paul Smith - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f178a464-4c52-49c6-9cc5-0901c0089955/37d.jpg Paul Smith - Make it stand out Left: searching for fossils in the mudstone scree. Above: preparing the samples for the flight south. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8fc23364-5936-4ee5-8b39-ffa4bfa3e161/Harper+et+al+slide+38.PNG Paul Smith - Make it stand out Some of the fauna from the Sirius Passet locality (scale bar = 1 cm). The fauna are dominated by arthropods, some of which lived on the microbial mat surfaces (e.g., a and b left) together with sponges (j) and others in the water column above (e.g., f left, a right). Rarer elements of the fauna include loriciferans (h), palaeoscolecid worms (i), vetulicolians (b right) and polychaete worms (c right). Harper, D.A.T., et al. (2019), Journal of the Geological Society 176, 1023 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/579fbefe-6ceb-4416-9311-b74514fe9952/59.JPG Paul Smith As described in the podcast, all the sites of exceptional preservation in the Cambrian appear to have been located at the deep end of a continental shelf where light and nutrients were limited, but where the substrate was stable and free from disturbance by the action of waves and tides. The depositional location of the Sirius Passet Lagerstätte is indicated by a red star. Harper, D.A.T., et al. (2019), Journal of the Geological Society 176, 1023 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d42b4170-b27b-4ed1-a928-32a936c5e00f/Vinther+et+al+2011+-+Vetulicolians.jpg Paul Smith https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/69223b73-acd1-4285-9510-886a184dba36/KC_Vet_Eretesia_Signed.jpg Paul Smith - Make it stand out Left: Vetulicolians from Sirius Passet. The scale bar is 5 cm. Vinther, J. et al. (2011), Paleontology, 54, 711 Above: artist’s impression of a vetulicolian colony. In the podcast, Smith describes these creatures as having a tail at one end and an open crisp (potato chip) packet at the other. Courtesy of Katherine Child https://www.geologybites.com/alex-copley daily 0.75 2024-07-15 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/555898bf-1bc4-4692-953b-a3d21f1f4ded/AC+with+dog.jpg Alex Copley In the podcast, Alex Copley describes the sharply contrasting nature of the very strong and dry regions of continental plates called cratons, and the much weaker regions where the rocks contain some water. The weaker regions form zones of deformation thousands of kilometers long where the behavior of the lithosphere is far from rigid. In his research, Copley tries to understand how this differentiation comes about, why it appears to have persisted as far back in time as the Archean, and how it affects the present-day topography and seismic behavior of mountain belts. Copley is Professor of Tectonics in the Department of Earth Sciences at the University of Cambridge. Photo: Helen Williams https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c1a1c9c6-e65f-4267-9239-7e4004c76992/Fig+1+Copley+and+Weller+2024+global+map.jpg Alex Copley - Make it stand out Global topography and earthquakes. The shaded regions indicate the locations of Archean cratons, which are the anhydrous, strong parts of continental plates. The dots indicate magnitude ≥ 5.5 earthquakes from 1964 to 2020. Where numerous earthquakes occur on continents, they reveal the regions of pervasive deformation discussed in the podcast. In the hemisphere shown, these are the Alpine-Himalayan belt and the East African rift region. Copley, A., et al. (2024), Precambrian Research 403, 107324, after Engdahl, e. et al. (1998) Bull. Seismol. Soc. Amer. 88, 722–743 and International Seismological Centre (2023), ISC-EHB dataset https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a5422f4f-b16b-424c-a433-ee6323b38a10/network+of+active+faults.JPG Alex Copley This simplified tectonic map of a ~1,200-km-wide region shows a network of active faults in a continental region of pervasive deformation on the southeast margin of the Tibetan Plateau. Copley, A. (2008), Geophys. J. Int. 174, 1081 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c84eab93-8120-4cb7-be87-8d350d0acc71/viscosity.JPG Alex Copley Plot of viscosities of various minerals as a function of temperature and water content. The viscosity of a mineral, which affects the strength of a rock containing that mineral, is much lower when it is wet than when it is dry. Copley, A., et al. (2024), Precambrian Research 403, 107324 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8ec1ab1c-e209-4e6f-b446-c6107487a482/max+supportable+crust.JPG Alex Copley - Make it stand out In the podcast, Copley describes how continental deformation and topography evolved since the Archean. (a) The crust is hydrous, hot and weak, and can support only minor topography. Melting in thicker crust begins to generate a residue of strong blocks. (b) The crust is hot, and weak and also contains localized rigid blocks, which can support significant topography. Large melt fractions in thick crust generate granitic rocks and leave a strong, anhydrous residue. (c) The crust contains extensive rigid blocks produced by high-grade metamorphism and the extraction of melt. There are plentiful, thick mountain belts supported and underthrust by rigid blocks. The rate of production of strong crust by melt extraction slows. Copley, A., et al. (2024), Precambrian Research 403, 107324 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a7a831e-6c7d-480a-a1cc-eb2569d16c5f/graph+of+supportable+crust+over+time.JPG Alex Copley Graph showing the increase of the maximum supportable crust thickness, i.e., topography, over time (green curve). As explained in the podcast, this increase is thought to result from overall cooling of the crust over time as radiogenic heating diminishes (red curve), and from the production of strong blocks that form the anhydrous residue left from partial melting. Evidence for this partial melting appears in the geological record as early granitic-composition rocks, specifically, tonalites, trondhjemites, and granodiorites (TTG. blue curve), which often occur together in geological records, indicating similar petrogenetic processes. Copley, A., et al. (2024), Precambrian Research 403, 107324 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/885ac2f0-4613-4a6e-b957-5a64d6a932d4/Canada.JPG Alex Copley - Make it stand out In the podcast, Copley mentioned a study of a region in Canada where rocks containing hydrous minerals were thrust on top of a dry cratonic basement. By dating the events and the rocks involved, Copley and his collaborators were able to determine the rate of diffusion of water into a dry cratonic rock. It was very slow — the water penetrated only 3 km into the basement over a period of about 30 million years. This helps explain the longevity of the cratonic cores of continents. (A) Geological map of the Ungava Peninsula in northern Quebec, Canada. The labeled line shows locations of the cross section in (B). The overthrust “wet” rocks are the rocks of the Cape Smith thrust fold belt and the Narsajuac arc, and the dry basement rocks belong to the Superior craton. Whyte, A.J., et al. (2021), Geochemistry, Geophysics, Geosystems, 22, e2021GC009988, modified from St-Onge, M. R., et al. (2000), Canadian Mineralogist, 38(2), 379 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f6882fc1-7d35-4cc0-ab50-9f76d7376223/water+diffusion.png Alex Copley A vertically exaggerated drawing illustrating processes operating in the ancient thrust belt shown above. Blue arrows indicate areas of water diffusion from the dehydrating overriding wedge into the anhydrous craton below. Thermal diffusion (white arrows) operates along thermal gradients from warmer (lightly shaded) to cooler (dark shaded) portions of the lithosphere. The brittle-ductile transition is shown as a green dashed line. Whyte, A.J., et al. (2021), Geochemistry, Geophysics, Geosystems, 22, e2021GC009988 https://www.geologybites.com/shanan-peters daily 0.75 2024-07-01 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/66f50d11-178f-4c33-9f68-14dd6f2f3d05/IMG_8031.jpg Shanan Peters Shanan Peters believes we need to assemble a global record of sedimentary rock coverage over geological time. As he explains in the podcast, such a record enables us to disentangle real changes in the long-term evolution of the Earth-life system from biases introduced by the unevenness and incompleteness of the sedimentary record. To this end, he and his team have established Macrostrat, a platform for the aggregation and distribution of our knowledge about the spatial and temporal distribution of sedimentary rocks. In the podcast, he describes some important findings made possible by Macrostrat. One of them is that gaps in the record are often as revealing about the underlying processes involved as the rocks preserved above and below the gaps. Peters is a Professor in the Department of Geoscience at the University of Wisconsin-Madison. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9bc26073-cbe9-4c23-89d3-17aa43f35099/slide+1.jpg Shanan Peters - Make it stand out Peters and his team have created Macrostrat., a platform for the aggregation and distribution of geological data relevant to the spatial and temporal distribution of sedimentary, igneous, and metamorphic rocks, as well as data extracted from them. As of June 2024, it contains 35,481 stratigraphic rock units from 1,534 regions, which are delineated on the map on land as the shaded regions and as green dots on the sea floor. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a29f28ce-e91b-4284-9262-367024434124/slide+2.png Shanan Peters - Make it stand out At https://macrostrat.org/map, clicking on a location brings up a window with information about the lithostratigraphic unit of that location. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/307fab4a-e39d-41ca-bf4c-4a87f0fd0e0c/slide+3.JPG Shanan Peters - Make it stand out Macrostrat enables users to link a column to a geological or topographical map. Column view by Daven Quinn https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6420cb70-8b60-4376-b9a8-78b7ea044ae0/slide+4.png Shanan Peters - Make it stand out As discussed in the podcast, Macrostrat enabled Peters to compile a record of the proportion of the globe covered by sedimentary rocks. The record shows a dramatic increase at the start of the Phanerozoic. Parc: Paleoarchean; Marc: Mesoarchean; Narc: Neoarchean; Pptz: Paleoproterozoic; Mptz: Mesoproterozoic; Nptz: Neoproterozoic; Pz: Paleozoic; Mz: Mesozoic; Cz: Cenozoic. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/471012fa-cfca-41f1-99bc-37a804cb0e7b/slide+7.JPG Shanan Peters - Make it stand out This diagram compares the proportion of Macrostrat columns covered by marine sediment in North America (black line with grey error bars) with the global proportion of continental shelves that are flooded (blue line). The disposition of the continents during the Cambrian (C), Permian (P), end-Jurassic (J), and Paleogene (Pg) are shown. The covariation of the sedimentary rock cover and continental shelf flooding is apparent. Both decline significantly between the Permian and Triassic (Tr) during the assembly of the supercontinent Pangea. Cm: Cambrian; O: Ordovician; S: Silurian; D: Devonian; C: Carboniferous; K: Cretaceous; Ng: Neogene; Q: Quaternary. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fdc90922-8bca-477b-b620-9bd9fa002a78/slide+8.JPG Shanan Peters - Make it stand out Reconstruction of sea level during the late Cambrian (right) shows extensive flooding of the North American continental shelf, which corresponds to peaks in the plot of the global proportion of continental shelves that are flooded shown in the previous figure. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f74673c3-11b4-4e6f-9571-0872df730763/slide+9.JPG Shanan Peters - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2f920c1c-db62-47c2-8890-c1f666515a22/slide+10.JPG Shanan Peters - Make it stand out Outcrops of the Great Unconformity in Colorado (top) and Wisconsin (bottom) superposed on the Macrostratigraphy time series of proportional coverage of North America by sedimentary rocks with the period when the Great Unconformity was buried highlighted in green. The Great Unconformity juxtaposes Cambrian sedimentary rocks on top of very much older Proterozoic metamorphic and igneous rocks. It is very prominent in North America, and famously so in the Grand Canyon, but also in other locations around the world. Peters describes the Great Unconformity as identified by Macrostrat as the most important transition in the entire rock record. https://www.geologybites.com/roberta-rudnick daily 0.75 2024-08-01 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fbdc81de-cd5c-47c5-8961-0b6797acd718/me+and+murph%2C+Whidbey+Island.jpeg Roberta Rudnick The average composition of continental crust approximates that of an intermediate rock such as andesite. But mantle-derived magmas are basaltic in composition, with less silica and more magnesium and iron. Roberta Rudnick was one of the first to recognize this discrepancy. In the podcast, she describes the measurements that led us to identify what has come to be known as the continental crustal composition paradox. She then explains the various theories that purport to resolve the paradox. While some are more speculative than others, she thinks all of them probably play a role in resolving the paradox. Rudnick is a Distinguished Professor in the Department of Earth Science at the University of California Santa Barbara. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1fc651e7-4800-46ec-b74a-ce4dba6d6638/slide+7.JPG Roberta Rudnick - Continental Crust Continental crust is conventionally divided into three layers — upper, middle, and lower. The layers are defined by the variation of seismic wave speed (Vp) with depth, as indicated in the figure. The divisions are somewhat arbitrary, as the seismic wave speed varies continuously, albeit non-linearly, with depth. Rudnick, R. L. & Fountain, D.M. (1995), Reviews of Geophysics, 33, 3 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/86393bd6-5f9f-423b-8dc2-0e19432ab1d1/Grid+Sampling+Thunder+Bay.JPG Roberta Rudnick - Measuring the Composition of the Upper Crust As Rudnick describes in the podcast, one way of determining the average composition of the upper crust is simply to measure the composition at many locations. In one study, 14,000 grid samples were analyzed from the Canadian Shield for major and a few trace elements. Such studies show that major elements may vary by a factor of two, but trace elements vary by orders of magnitude. Space shuttle view of Thunder Bay, Ontario Grid measurements by Eade et al. (1973), grid for illustrative purposes only https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/65ec95ce-4dd5-4092-8ff9-3b6429d74e2d/slide+9.png Roberta Rudnick - Analyzing Shales In the podcast, Rudnick says that fine-grained sedimentary rocks, such as the shales pictured here (at top), have trace-element compositions that are reflective of the upper crust as a whole, but only for the insoluble elements. The soluble elements, such as magnesium, calcium, and sodium, have been weathered out and transported to the oceans. Mancos Shale, Utah; photo: J. St. John https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8dc43469-2f30-4ba1-ba9b-4623a65f5a16/slide+11.png Roberta Rudnick - Granulite Terranes Granulites are highly metamorphosed rocks that come from the lower crust. They are brought to the surface through uplift, erosion, and tectonic transport along faults. The image shows granulites that, before metamorphosis, were fine-grained, clay-rich sedimentary rocks. Mauricio Mazzuchelli, Ivrea Zone, Italy https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fc0a6853-558f-4ab9-a4c0-6f3e3ed8bb4d/slide+12-1.jpg Roberta Rudnick - Make it stand out Professor Shukrani Manya, University of Dar es Salaam, Tanzania https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d2149645-9ea5-4fc5-8cb4-9e3b119faa71/sldie+12-2.jpg Roberta Rudnick - Make it stand out Bill McDonough, Queensland, Australia https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5cab3bc7-8358-436d-bfbc-583f420754c8/slide+12-3.jpg Roberta Rudnick - Make it stand out Professors Gao and Wu, Shanxi, China https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/919940fe-ac99-4d9d-8f77-8998b98c145a/slide+13.png Roberta Rudnick - Seismic Wave Velocities As she explains in the podcast, seismic wave velocities provide a way of studying the lower continental crust remotely. In this plot, the velocity of seismic p-waves is plotted against the silica content of rocks that characterize the upper crust (blue), the middle crust (red), and the lower crust (green). The speeds increase with depth by an amount that cannot be explained just by the effects of metamorphosing surface rocks but requires a change in the major element composition of the rocks. Huang, Y. et al. (2013), Geochemistry, Geophysics, Geosystems 14(6): 2003, doi: 10.1002/ggge.20129 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1b529690-0062-4391-82c8-4b11dcd61136/slide+15.JPG Roberta Rudnick - Composition of Continental Crust Quite remarkably, the measurements of continental crust composition made by F.W.Clarke over 100 years ago agree quite well with modern estimates. Rudnick et al. (2003), pub. Elsevier Ltd.,Treatise on Geochemistry, vol. 3, pp. 1-64 Clarke, F. W. (1889), Phil. Soc. Washington Bull. Vol. XI pp. 131-142 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bd7beb64-e84e-4d05-bc85-126ced8c2566/slide+18.JPG Roberta Rudnick - Trace-Element Composition of Continental Crust The plot shows the average abundances of rare earth elements and other selected trace elements in average continental crust. The abundances are normalized to the corresponding abundances in the primitive mantle. The data show a relative depletion of Nb (niobium) and a relative enrichment of Pb (lead). This signature matches that of lavas generated by the magmatism above subduction zones that creates island arc volcanoes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/adb94f8c-fb54-4d3f-8991-ec533af96ab6/Fig+3.2+OU+S339.JPG Roberta Rudnick - Trace-Element Composition of Basalts Trace-element abundances in basalts normalized to the primitive mantle abundances. The abundances in island arc basalts (IAB) show a relative depletion of Nb and a relative enrichment of Pb, which is similar to what we see in the continental crust, as shown in the plot above. By contrast, basalts produced at ocean islands above mantle plumes, such as Hawaii (OIB), and at mid-ocean ridges (MORB) do not show this signature. As Rudnick says in the podcast, this strongly suggests that continental crust is formed in island arc volcanoes that erupt above subduction zones. Courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2d4259bf-c41c-4109-bcdb-57575e88ccbe/OU+subduction+zone.JPG Roberta Rudnick Illustration of a volcanic arc and its relationship to a subduction zone. Courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/48673bdc-7837-4a84-a084-788e99efdf83/Aleutians.png Roberta Rudnick Example of island arc volcanoes above a subduction zone: the Aleutian islands above the Aleutian subduction zone. Photo: John Lyons/USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/067a6fb5-814c-4e00-811a-32a716bfed88/foundering.JPG Roberta Rudnick - I: Lower Crustal Removal — Density Foundering One way to convert material with a basaltic composition into an andesitic (intermediate) composition, which is what we measure for continental crust taken as a whole, is to remove a mafic component. In the podcast, Rudnick describes how a dense continental rock could break off and sink into the mantle. This idea was also discussed by Peter Molnar in his episode as a possible contributor to the extreme elevation of present-day Tibet. continental crust = pale green; orange = lithospheric mantle; blue = eclogite; dark green = asthenospheric mantle. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7f787073-4ce1-4b89-91dc-8db89744360c/relamination+2.JPG Roberta Rudnick - I: Lower Crustal Removal — ‘Relamination’ Relamination posits that when continental plates subduct, the downgoing plate partially melts and separates into more felsic material that is buoyant and more mafic material that is denser. The former rises and is incorporated into the base of the continental crust, thereby making the crust more silica-rich overall. The denser material sinks into the mantle. In the figure, the downgoing plate should be labeled as a continental plate rather than as an oceanic plate. Relamination has been suggested for other tectonic settings as well, such as when sediment accumulated on an oceanic plate is subducted, when an island arc is subducted, or when a fore-arc or accretionary prism is subducted. Hacker, B.R. et al. (2015), Annual Review of Earth and Planetary Science 43:167–205 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/504e2d1d-ea87-4f90-836a-693ab7536fa3/Weathering.JPG Roberta Rudnick - III: Chemical Weathering Chemical Weathering The about of Mg in continental crust can be reduced by chemical weathering. Water dissolves the soluble elements, which include Mg. These wash into the sea, where they are absorbed by oceanic crust, which eventually subducts. The denser Mg sinks with the subducting slab into the mantle while less dense material, including Na and possibly Ca return to the crust via magmatism at volcanic island arcs. https://www.geologybites.com/evan-smith daily 0.75 2024-08-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5b5563b0-da59-4a59-a5de-56bd4bc424e7/evan-smith-636x358.jpg Evan Smith Evan Smith was one of the first to recognize that among the rare diamonds that come from the very deep mantle, a highly prized few belong to a distinct class. These so-called CLIPPIR diamonds contain inclusions that give us a new source of knowledge about the mantle. And, as Smith explains in the podcast, analysis of the inclusions suggests a direct link to subducted oceanic lithosphere. According to the hypothesis Smith favors, when the subducting slab reaches the lower mantle transition zone at a depth of about 650 km, carbon in the form of diamond, and other light elements separate out from the slab and rise to the base of the lithosphere as buoyant diapirs. They then reside there until violently brought to the surface along kimberlite pipes. Evan Smith is a Senior Research Scientist at the Gemological Institute of America, New York. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9e8e80df-63da-483b-b443-4f7515fde8d1/Rough_cullinan_diamond.jpg Evan Smith - Cullinan Diamond The Cullinan Diamond (left) is the largest gem-quality rough diamond ever found. Weighing in at 3,106 carats (621 g) it gives its name to the new class of deep-mantle gem-quality diamonds discussed in the podcast: Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed (CLIPPIR). The largest cut clear-cut diamond in the world is the 530-carat (106 g) Cullinan I, taken from the Cullinan Diamond. It is mounted in the head of the Sovereign’s Sceptre of the Crown Jewels of the United Kingdom (right). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f005748-c126-43b5-b3ce-918a9cca21b2/220px-Sovereign%27s_Sceptre_with_Cross.png Evan Smith - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f248260a-7878-4eb1-8d05-59209e6f6547/Fig.+2+Shirey+et+al+2024.jpg Evan Smith - Make it stand out A variety of diamonds that formed below the lithosphere. The examples shown in b and f are CLIPPIR diamonds. In the latter, the inclusions appear as black spots. Shirey, S.B. et al. (2024), Annual Review of Earth and Planetary Sciences 52, 249. From a to f, courtesy of Janina Czas, EPL; Gem Diamonds Ltd., Robert Weldon; Bulanova G. P. et al (2010), Control. Min. Petrol. 160: 489; Regier M.E. et al. (2023), Earth Planet. Sci. Lett. 602: 117923; Janina Czas, EPL; Smith E.M. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/57856a9b-ea27-4d73-a346-0ca1094df643/Metal+inclusion-OC2.jpg Evan Smith - Metal inclusion In this magnified view, a metallic inclusion is a reflective silver in appearance and is surrounded by a black, graphite-bearing decompression crack. The image is 2.5 mm across. Photo: Evan Smith https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2c6be075-74a6-418d-a019-ca9886c4f651/Karowe+mine+in+Botswana_Credit+Evan+Smith.jpg Evan Smith - Make it stand out Karowe mine in Botswana, which is an important producer of CLIPPIR diamonds. The 1,109-carat Lesedi La Rona diamond (right), the fifth largest diamond ever found, was found at the Karowe mine. Diamond photo courtesy of Lucara Diamond https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a4ef0550-0e85-47bb-b5f6-92a4d5890afe/Karowe_AK6_diamond.jpg Evan Smith - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6731fc60-a3b7-464b-a401-28cf70188272/Experimental+mantle+mineralogy+-from+Shirey+et+al+2024.jpg Evan Smith Mantle mineralogy diagrams for two major rock types in the mantle — peridotite (left) and basaltic ocean crust (right). These are the rock types of which the convecting mantle and the subducting oceanic lithosphere are made. The diagrams show what minerals make up these rocks as a function of depth in the Earth. As you go deeper, the constituent minerals change. Majoritic garnet, which is one of the tell-tale high-pressure phases present in CLIPPIR diamonds, is shown in purple. Rock names are shown in the gray columns at right, with lherzolite and harzburgite being forms of peridotite, the main rock type of the mantle. The other rock names are new ones proposed by Shirey, S.B. et al. (2024) based on their mineral assemblages. cf = calcium ferrite; cpx = clinopyroxene; NAL = new aluminous phase. After Shirey, S.B. et al. (2024), Annual Review of Earth and Planetary Sciences 52, 249 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c999b740-ffe6-43f0-8d15-bca0fc4032bb/Figure+5_cartoon+model.jpg Evan Smith Cartoon model showing a cross-section of the Earth with a thickened ancient continental lithosphere, which is where most mined diamonds come from. The 660-km-depth line marks the top of the lower mantle and a transition zone where the seismic velocity changes, indicating changes in the mineral phases across the transition zone. The cartoon shows a subducting slab releasing hydrous (blue) and carbonatitic (red) fluids that contribute to the growth of sublithospheric diamonds. As Smith discusses in the podcast, these fluids also contribute to the evolution of metallic liquid from which the CLIPPIR diamonds grow. Smith, E.M. et al. (2021), in Marquardt, H. et al. (eds.), Mantle Convection and Surface Expressions, American Geophysical Union, 179 https://www.geologybites.com/sara-seager daily 0.75 2024-09-01 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/69e65272-6658-48d5-bdcc-6b4299173410/IOA__Sara-Seager-SUB.jpg Sara Seager During the past couple of decades, we have discovered that stars with planetary systems are not rare, exceptional cases, as we once assumed, but actually quite commonplace. However, because exoplanets are like fireflies next to blinding searchlights, they are incredibly difficult to study. Yet, as Sara Seager explains, we are making astonishing progress. Various ingenious methods and the use of powerful space telescopes enable us to learn about exoplanet atmospheres and even, in some cases, what their surfaces consist of. Sara Seager’s research concentrates on the detection and analysis of exoplanet atmospheres, and she has just won the prestigious Kavli Prize for this work. She has had leadership roles in space missions designed to discover new exoplanets and find Earth analogs orbiting a sun-like star. She is a Professor of Aeronautics and Astronautics, Professor of Planetary Science, and Professor of Physics at the Massachusetts Institute of Technology. Photo courtesy of Justin Knight & Harper Collins https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/84d19a26-efa5-4b4e-950f-7bb710f36846/5K_Exo_Info_FINAL.png Sara Seager - Make it stand out In May, 2022 the count of confirmed exoplanets passed the 5,000 mark. As the infographic shows, larger planets make up the bulk of these, but this probably reflects the biases of our detection methods, rather than the true population distribution. Sara Seager describes new detection methods, such as gravitational lensing, that are not subject to the same biases. NASA/JPL-Caltech https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6c2afb10-c194-4d8d-9ea7-210640641ea6/transit+fig+from++NASA+Ames.jpg Sara Seager When a planet moves in front of its star, it blocks out some of the star’s light. The plot at bottom illustrates the light curve that characterizes such a transit. NASA Ames https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6d72f956-501f-4895-b133-c9a8b8c2f1f6/slide+2.jpg Sara Seager - Make it stand out Light-curve measurement of an ultra-hot gas-giant exoplanet, WASP-18b. It orbits its star, WASP-18, every 23 hours, is 400 light-years from Earth, and is 10 times more massive than Jupiter. The bottom curve shows the light curve for one of the 29 transits shown in the top plot. NASA/TESS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4387a4fa-b177-47a6-ae9f-5babe3d7250f/ESA+radial+velocity.jpg Sara Seager As Seager explains in the podcast, exoplanets can be detected by measuring tiny periodic variations in a star’s radial velocity. This motion makes the light from the star appear slightly bluer when it is moving toward the observer, and slightly redder when moving away. Since no transit is needed, the radial velocity (as well as the plane-of-the-sky movement, or astrometry method; see below) can detect planets whose orbits are not fortuitously aligned with the star along our line of sight. ESA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/54a2b46d-6a6a-4491-84f8-989d96ca8abf/slide+7.png Sara Seager Radial velocity measurement of an exoplanet named 51 Pegasi b, located about 50 light years away. It is the prototype of the “hot Jupiter” class of planets. ELODIE Spectrograph https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/966d7339-e6c9-4b6d-bde1-73a4352cb9dc/slide+9.jpg Sara Seager The “wobble” in a star's motion caused by the gravitational pull of a planet (Gliese 876b) as the planet and star orbit around a common center of mass can reveal the presence of an exoplanet. NASA/ESA, Feild (STScl) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/217e0a84-04cc-4826-b21c-a166c969d318/slide+3.jpg Sara Seager During transit, we can look for signs of a planetary atmosphere by detecting a change in the light from the star caused by a contribution from light transmitted through the planetary atmosphere. The gases in the atmosphere impose a transmission spectrum on the light; characteristic features of such a spectrum reveal the atmosphere’s composition. NASA/ESA/CSA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cc6a68b9-6abd-4632-9707-a27147775c34/slide+4.jpg Sara Seager At the beginning and end of an exoplanet transit, its atmosphere blocks some light from the star just before and just after the exoplanet disk respectively, causing a slope at the edges of the transit light curve. The light curve shown was captured over 6.5 hours of observation of the gas-giant planet WASP-96b 1,1150 light years from Earth, by the James Webb Space Telescope. The atmosphere’s transmission spectrum indicates the presence of sodium in the atmosphere. NASA, ESA, CSA, STScl https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d25aa515-e0cc-48e7-82dd-f00f63f376f3/Picture6.gif Sara Seager The graph cycles through measurements of a transit light curve over a range of wavelengths shown at top right (in microns). This shows an increased planet size around 4.3 microns, indicating the presence of a strongly absorbing gas active at this wavelength. This turns out to be CO2, which, while not the dominant form of carbon in the WASP 39b atmosphere, is a strongly absorbing component. Data from the JWST Transiting Exoplanet Community Early Release Science Team. Animation by Pat Wachiraphan, William Waalkes, and Zach Berta-Thompson. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/41c1a5cc-1cfc-4cc3-b4b7-f1e3cf624e08/K2-18b+from+JWST.jpg Sara Seager The figure shows the transmission spectrum of K2-18b’s atmosphere obtained with the Webb telescope. In the podcast, Seager says that this exoplanet provides her favorite example of the detection of an exoplanet atmosphere and of what it can tell us about an exoplanet surface. She points out that the presence of methane but surprising absence of ammonia suggests that ammonia, being much more soluble than methane, has dissolved out into a liquid covering the planet’s surface. That liquid could be a water ocean or liquid magma and there is an ongoing debate as to whether or not the hydrogen, water, and methane atmospheres of K2-18b and its ilk overly a massive rocky planet with a deep magma ocean. K2-18b, 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a8c9f424-d2c9-4c23-8921-93f2bd58b67d/Grav+lens+credit+NASA%2C+ESA%2C+and+Sahu+%28STScl%29.jpg Sara Seager - Make it stand out As Seager says in the podcast, gravitational lensing is a good way to obtain exoplanet statistics, as a great many stars can be monitored in parallel. Such studies suggest that the Milky Way contains at least 100 billion planets, which corresponds to at least one planet for every star on average. This would imply that there are about 1,500 exoplanets with just 50 light years from Earth. NASA, ESA, and K. Sahu (STScI) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ee1d800f-4a39-44d1-8597-b357a7d33224/ROMANNewModelV8RomanStill00049.png Sara Seager - Nancy Grace Roman Space Telescope The Roman Space Telescope is designed with a wide field of view so as to monitor a large number of stars for gravitational-lensing events. It is scheduled to launch in 2027, when it is expected to dramatically increase the number of detected exoplanets. It is also equipped with a small field-of-view camera and a spectrometer with a coronagraphic instrument to block out starlight and directly image exoplanets. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a6c14d3b-cc77-4a8b-a2a9-687fe7c2c9e2/Hu+et+al+model+spectra.jpg Sara Seager The surface of a rocky exoplanet is expected to show an emission spectrum that has weak absorption features imposed on it. The absorption features are specific to each rock type, which gives us a means of determining what rock type(s) dominate an exoplanetary surface. The plot at right shows a spectrum for exoplanet Kepler-20f modeled by Seager and her colleagues under various assumptions for the dominant surface rock type. The modeled depth of the dip in brightness of the star+planet system (y-axis) is plotted as a function of wavelength (x-axis) when the planet transits behind the star. Hu, R., et al. (2012), The Astrophysical Journal 752, 7 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a0fc23b3-786d-4b9a-b31c-27162138473a/thermal+phase+curve+from+webbtelescope.org.jpg Sara Seager - Make it stand out The diagram explains what causes us to see a thermal phase curve in a star/exoplanet system where the exoplanet is tidally locked to the star, i.e., always has the same side facing the star. The principle is similar to that of the phases of our Moon, except we see the phases in the thermal infrared rather than in visible light. At top, the figure shows the phases of the exoplanet as it orbits its star. The middle diagram illustrates the overall brightness (line position) and overall thermal brightness (color) of the star and planet as the planet traces out its orbit. When the planet is on the far side of the star, the hot side of the planet, i.e., the one facing the star, is fully visible to us, and we see the maximum amount of thermal infrared from its surface. Conversely, when it is on the near side of the star, we see only the dark, cold side, and the thermal infrared is at a minimum. If there is no atmosphere on the planet, we expect the thermal infrared phase to be exactly synchronized with the orbital phase. But, as Seager explains in the podcast, if there is an atmosphere, the heat on the illuminated side will be partially smeared out by strong winds, and we may see a lag between the orbital phase curve and the thermal phase curve. NASA, ESA, CSA, Dani Player (STScI) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/324f90bb-6eb4-409f-b5e9-1393b15d7329/visiblity+of+heated+side+for+WASP+43+b.png Sara Seager Another illustration showing how the visibility of the heated face of the exoplanet varies around its orbit, producing a variation in the thermal emission we can see, i.e., a thermal phase curve. The temperature scale is shown for the hot gas exoplanet WASP-43 b. NASA, ESA, CSA, Ralf Crawford (STScI) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c590b0e3-c539-49c9-997b-d02ab15de322/therma+phase+curves+wasp-planets.net.png Sara Seager - Make it stand out The thermal phase curve of WASP-43 b observed by the James Webb Space Telescope is the shallow variation on which the primary (front) and secondary (back) transits are superimposed. NASA, ESA, CSA, Ralf Crawford (STScI) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2c3fe172-577e-47bf-8d0e-dacf514f4207/bare+rock+evidence+Kreidberg+2019+Nature.jpg Sara Seager - Evidence for Lack of Atmosphere This thermal phase curve of an Earth-like exoplanet is symmetric and has a large amplitude that implies a dayside temperature of over 700C and a nightside temperature consistent with -273C (zero kelvin). The data are well fitted by a bare-rock model with no atmosphere (red line). Kreidberg, L., et al. (2019), Nature 573, 87 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2889cbe0-eb0c-41ae-adf3-6095d62a79e1/WASP-121+b+atmosphere.jpg Sara Seager - Evidence for the Presence of an Atmosphere Thermal phase curves from observations of the hot-Jupiter exoplanet WASP-121 b by the Hubble Space Telescope. The differences between the phase curves in different years are thought to be caused by variability in the planet’s atmosphere. NASA, ESA, Changeat, Q., et al. (2024) https://doi.org/10.48550/arXiv.2401.01465 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/461cf33a-a6a8-44d2-97a1-b51c246f7502/Lag+in+phase+curve.jpg Sara Seager Asymmetrical phase curve showing an offset in the thermal emission peak from the orbital phase (0.5 on the x axis) when the planet is on the other side of the star and showing its full hot side to us. As Seager says in the podcast, this could be explained by the presence of atmospheric winds that transport heat across the surface. Credit https://wasp-planets.net/tag/phase-curve/ https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f84fb785-7b1b-4424-b3ed-a3be29a7d229/starshot+concept+Breakthrough+initiatives.jpg Sara Seager In the podcast, Seager mentions the idea, very much only in concept phase now, of sending a fleet of space ships to our nearest neighbor star, Alpha Centauri. They would be propelled by Earth-based laser beams to 20 percent of the speed of light and take 20 years to reach the star. As they shoot past, they would capture closeup images of its planets and transmit them back to Earth. Breakthrough Initiatives https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1e4a7a50-258f-49aa-b10e-4f0bcf48ace5/Rocket+Lab+1.png Sara Seager - Make it stand out Artist’s concept of the Rocket Lab probe approaching the dense atmosphere of Venus. The probe, which is only 40 cm in diameter, will search for organic chemicals in the cloud particles and explore the habitability of the clouds. It does this by shining a laser into the clouds and looking for polarization of light scattered by particles and fluorescence from organic molecules. French, R., et al. (2022), Aerospace 9(8), 445 https://doi.org/10.3390/aerospace9080445 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d4e7986e-62fb-41f2-ad4b-d72969dffc06/Rocket+Lab+2.png Sara Seager - Make it stand out During a period of only about six minutes as it descends through the atmosphere, the probe collects data from the cloud layer between 60 and 45 km above the surface. https://www.geologybites.com/rufus-catchings daily 0.75 2024-09-23 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aa29aeeb-99c9-43b6-a823-9b2d841f3669/Building-Turkiye.jpg Rufus Catchings California is riddled with faults. Although some of the most active faults are revealed by surface features, the majority are invisible unless probed by geophysical methods. Fortunately, faults affect the speed and amplitude of seismic waves. As Rufus Catchings explains in the podcast, we can detect such speed and amplitude changes when seismic waves propagate through the ground. Using an array of seismometers to measure seismic wave speeds, we can then generate an image of subsurface seismic speeds and see exactly where the faults lie. Rufus Catchings is a Research Geophysicist at the US Geological Survey (USGS). Over the past 40 years, he has studied many dozens of faults in California and elsewhere to pin down their precise locations and help assess the risks they pose. In the image, Catchings is installing a seismometer on the roof of a building in Turkey near the devastating 6 February 2023 Mw 7.8 Turkey Earthquake. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7cfcb6e0-9254-4e5d-90ee-ee715a33ba51/MS_054-2018-Faulting-in-California-Educators.jpg Rufus Catchings - Make it stand out Map of the major faults in California. The thick red trace marks the San Andreas Fault. In the podcast, Catchings discusses faults in the vicinity of San Francisco and Los Angeles, as well as others elsewhere in the US and internationally. Courtesy of the California Department of Conservation, California Geological Survey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4040a279-144e-4c8d-82de-e898c138aaaf/Seismic+Survey+SF+Bay+2.jpg Rufus Catchings Placing a linear array of seismometers on the water’s edge of the San Francisco Bay. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f09602e3-6b5c-4434-a697-e24fe4e07242/Urban+Weight+Drop-+Napa+Area.jpg Rufus Catchings Conducting a seismic survey in the City of Vallejo, near Napa, California. A 500-lb accelerated weight drop is used as the seismic energy source, and seismic sensors (under the cones) record the resulting seismic energy. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bba7538e-5eb9-4994-8e28-05daa8b19f1c/Urban+SF+Peninsula+Weight+Drop2.jpg Rufus Catchings Conducting a seismic survey across the Serra Fault in the City of San Carlos on the San Francisco Peninsula. A 1100-lb weight (attached to the skid steer) is used to generate the seismic energy source, and the seismic energy is recorded with a long array of seismometers, one of which is below the cone. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d23eb93a-40bd-4d3f-a50a-b045bdd9b422/SAF-Explosive+Holes.jpg Rufus Catchings Preparing for a seismic survey across the San Andreas Fault in Central California. The third person from the camera is standing on the active main trace of the San Andreas Fault at the base of the hill. The white devices are seismometers that are placed in the boreholes. Boreholes with red flags show locations of deeper holes in which explosives are detonated to generate seismic energy. The seismic profile extends to the next hill so that all nearby traces of the San Andreas Fault can be imaged. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f37009d-284b-4309-9705-9b35d49a65e8/Seisgun+Source+-+Catchings.png Rufus Catchings - Seismic gun source (Catchings) Catchings uses a seisgun to generate seismic energy used to image the San Andreas Fault in Central California. A seisgun shoots 400-grain black-powder shotgun blanks into the ground surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e67add3a-5dd0-4310-94a1-f9a1aca07672/Surface+Nodal+Seismometer-+Turkiye.jpg Rufus Catchings USGS and Turkish scientists deploying a linear array of seismometers in the city of Gaziantep, near the epicenter of the 6 February 2023 Mw 7.8 Turkish earthquake epicenter. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/558a1f46-7915-4bc1-ada0-aa2e4724e3e1/reverse-normal-and-strike-slip-faults.png Rufus Catchings - Make it stand out The San Andreas Fault, which defines the boundary between the North American Plate and the Pacific Plate, is a strike-slip fault. As Catchings says in the podcast though, movement along reverse faults can often produce the most violent shaking for a given size earthquake. Trista L. Thornberry-Ehrlich (Colorado State University) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1726467f-b165-4059-9b9f-3fd1669d25aa/Guided+Waves+concept.jpg Rufus Catchings Fault zones can act as waveguides and trap seismic waves. Although the fault zone is a region where seismic waves travel more slowly, the wave-guiding effect causes the amplitude of seismic waves to increase. In the podcast, Catchings describes studies in which he used the peak seismic wave amplitudes, measured as peak ground velocity, i.e., shaking movement, to indicate the surface trace of a fault. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f5bed3ab-f209-4098-93dd-30609d3d8817/Guided+waves+-+fault+geometry.jpg Rufus Catchings Guided waves are transmitted only along continuously connected faults. In the diagrams at right, seismic energy enters a fault zone from the bottom. The dark lines mark the surface, and seismic traces are plotted above the dark line. In the top row, the effects of various subsurface-connected fault configurations on the amplitude of guided waves are shown. In the bottom row in the left example, the faults are only slightly connected at the edge, and some guided wave energy is transmitted. In the other two bottom-row examples, the faults are not connected, and the seismic traces show that no guided waves are transmitted. After Li, Y. G. & Vidale, J. E. (1996), Bulletin of the Seismological Society of America, 86, 371 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/063de3d5-51ab-4a38-b7e7-95468db4f5a2/guided+waves+PGV.jpg Rufus Catchings This example illustrates the use of peak ground velocity (PGV) to locate the surface trace of a fault. The plot at top shows the peak ground velocity, i.e., amplitude of a seismic wave, along a line from west to east. The peak is located where the fault intersects the surface. Seismic wave speeds are indicated — 3 km/s outside the fault zone and 2 km/s within the fault zone. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/06abe0d2-b8e8-4917-83ac-1454fdcebfe9/SAF+guided+wave+example.jpg Rufus Catchings - Make it stand out Left: Near San Francisco, the San Andreas Fault runs through San Andreas Lake. The San Andreas Fault was named after this lake following the 1906 San Francisco earthquake. Center: Catchings and his colleagues generated an explosion on the active trace of the San Andreas Fault (red blot at top) and measured seismic wave speeds and ground velocity amplitudes along the seismic profile line marked on the map. The red lines show where the surface ruptured in the 1906 earthquake (mapped by Schussler, 1906), and the red arrows indicate where the rupture lines intersect the profile. The results of the study are shown below. Right: Google Earth image showing the San Francisco Peninsula and Bay. The white box shows the location of the study area along the San Francisco Peninsula. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f7820aa7-c265-4cc5-a59b-c048c0ee10ea/SAF+2020+results.jpg Rufus Catchings - Fault Locations from Peak Ground Velocities and S-Wave Velocities Top: Peak seismic wave amplitudes of guided S waves along the profile shown in the previous figure. The known traces of the San Andreas Fault correspond to high peak ground velocities, confirming the technique as a way to identify surface fault locations. Bottom: Tomographic image of S-wave velocities along the seismic profile. A low-velocity region marks two of the 1906 rupture traces. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e23010f3-1c57-4d05-bb76-8b9680a16de7/Napa+map+from+ppt.jpg Rufus Catchings Google Earth image of the northeastern San Francisco Bay area showing the 2014 M 6.0 Napa earthquake surface rupture (thick red line); other thin red lines show historically active faults and yellow lines show Quaternary (not historical) faults. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/30d2029c-eab4-43b5-b934-1140cd36a87d/Napa+2014+results.jpg Rufus Catchings As described in the podcast, Catchings and his team were able to infer that faults to the south (e.g., Franklin Fault) and north of the 2014 surface rupture of the West Napa Fault were connected because seismic guided-wave energy from aftershocks propagated to these faults. The thick red line marks part of the single inferred fault. This increased the inferred fault length tenfold, suggesting that a much larger earthquake is possible on the fault system. The maximum magnitude of an earthquake on a given fault is proportional to the length of the fault. The longer fault also extends to the Maacama Fault to the north and to the Calaveras Fault to the south, suggesting the possibility of an even longer fault system. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0fc3b47e-72d9-4ebf-a939-1bdf29c84677/SoCal_fault_lines.jpg Rufus Catchings The map shows some of the more significant faults in southern California. The San Andreas Fault Zone runs diagonally across the middle of the map. The Hollywood fault, which was one of the faults studied by Catchings and discussed in the podcast, runs roughly east-west to the northeast of the dot marking Los Angeles. Miracosta College https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/35c8f45c-980c-40bf-bb06-6a3d52796493/N+LA+Map.jpg Rufus Catchings - Make it stand out In the podcast, Catchings describes imaging the Hollywood Fault by using repetitive artificial impacts to allow subtraction of the “cultural noise” of a dense urban neighborhood. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/81fc9668-9a3c-483a-a58a-2e887ea22676/Hollywood-Night+5.JPG Rufus Catchings - Make it stand out Line of seismic sensors used to image the Hollywood Fault. The seismic survey was conducted at night to minimize cultural noise. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ba5c8dd8-1edb-4c38-9792-74abf25dc96e/night+planning.jpg Rufus Catchings - Make it stand out Seismic-imaging crew planning a night seismic survey in Hollywood, California. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5243af3d-7e06-486e-9bc2-54c8830465d4/night+cones.jpg Rufus Catchings - Make it stand out Seismic array recording guided waves at night in Hollywood. Seismometers are white-colored devices between the cones. Guided waves are being generated several blocks away. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0546c7ee-92be-4092-a160-8d4f3b1a0c82/Hollywood+Fig+2.jpg Rufus Catchings - Make it stand out Google Earth image of one of the areas studied by Catchings, showing the locations of traces of the Hollywood Fault (yellow lines) and other faults (green lines). The small red stars mark “shot points,” where an accelerated weight or a hammer was used to strike a steel plate on the ground and input seismic energy into the ground. The right blue line (HW1) marks the plane of the seismic wave speed sections shown below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bbe1ac8d-b06c-4478-913d-e9a8fe707454/Hollywood+fig+7.jpg Rufus Catchings Tomographic P-wave velocity model along the section HW1, showing the location of nearby streets. Slightly south of the surface trace of the Hollywood Fault, there is a zone of high velocities, especially for velocities above about 1,500 m/s. As mentioned in the podcast, faults can act as groundwater barriers, and the figure is consistent with this interpretation since it suggests that the depth of the top of the water table (1,500 m/s contour) is higher to the south of the fault than to the north of the fault. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9cdb0fcd-ba5f-4035-995c-04e13fb6d44b/Hollywood+Fig+13.jpg Rufus Catchings As Catchings mentions in the podcast, a high ratio of P-wave to S-wave speeds (Vp/Vs) often provides the clearest indication of the presence of a fault as the broken-up nature of the rocks in a fault zone slows both P- and S-waves down, but the presence of water can mitigate or reverse this effect for P-waves. The profile at right shows a zone of high Vp/Vs near the surface trace of the Hollywood Fault (dashed lines). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58e521cc-3a36-432c-b208-3700ced7e8c2/Hollywood+paper+fi+11.jpg Rufus Catchings S-wave velocities (Vs) along the same section as above, showing a zone of low Vs to a depth of at least 40m. This is consistent with a near-vertical fault. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f3075640-d0e0-4e65-89a7-c7e3cf4cc7b0/new-madrid-seismic-zone-map-lg.jpg Rufus Catchings The New Madrid Seismic Zone lies near the middle of the North American plate. In 1999, Catchings and his colleagues performed a study of the crustal seismic wave speeds in this region. The results revealed the presence of a thick, dense lower crust, covered by sediment-filled basins. These features are consistent with continental rifting in which the New Madrid Seismic Zone is the failed third arm of the continental rifting whose rifted arms resulted in the Gulf of Mexico. The map shows earthquakes greater than magnitude 2.5. Red circles: post-1972 earthquakes; blue circles: pre-1973 earthquakes. geology.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cb0b2c37-3010-4e1a-bdd3-a6d1268ff9a9/Koyna+maps.jpg Rufus Catchings In the podcast, Catchings described a case of induced seismicity when the increased pore pressure and weight from a reservoir caused a damaging M 6.3 earthquake in 1967 in India. Top: Map showing the location of the Koyna and Warna reservoirs. Bottom: Map with the interpretative fault system. Such faults, often called step-over faults, connect two main faults that are displaced from each other. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/997281b5-1b11-43e7-b6b2-42b5961141ac/Koyna+tomo.jpg Rufus Catchings Tomographic images of the fault system near the Koyna and Warna reservoirs, India. Catchings’ studies showed that the main faults correspond to zones of low seismic wave velocities. https://www.geologybites.com/adam-simon daily 0.75 2024-10-25 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aca1217a-e5d5-430b-827e-06315659ca68/10.+Adam+fieldwork+in+Alaska.jpeg Adam Simon In the podcast, Simon concentrates on the three metals — nickel, cobalt, and manganese — that form part of a lithium-ion battery’s cathode. He explains how they facilitate transfer of lithium ions into and out of the cathode and improve battery characteristics, such as energy density, charging and discharging capacity, and battery lifetime. But his favorite metal is copper, since it is fundamental to the energy transition in so many ways and because we will need such prodigious amounts of it. He describes his current efforts to help locate new copper deposits from the chemical and isotopic fingerprints they leave in ground water. Simon is Professor of Economic Geology at the University of Michigan. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a03a6e5e-94b4-4191-a0cb-010072a63128/The-principle-of-the-lithium-ion-battery-LiB-showing-the-intercalation-of-lithium-ions.png Adam Simon The principle of the lithium-ion battery showing the intercalation of lithium ions (yellow spheres) into the anode and cathode matrices upon charge and discharge, respectively. The anode is lined with a copper sheet to collect the current, and the cathode is made of graphite with varying amounts of the metals discussed in the podcast — nickel, cobalt, and manganese. The metals facilitate the transfer of charge to and from the lithium ions within the cathode. Ghiji, M., et al (2020), Energies 13, 5117 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ab547c57-9c1f-4ce1-a04f-358c089dafb0/Li%2C+Cu+table.jpg Adam Simon - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58024bba-28bc-424d-abe6-c8d1da8a02d5/Ni%2C+Co%2C+Mn+table.jpg Adam Simon - Make it stand out In the podcast, Simon talked about the geological origin of the economically important deposit types highlighted in red. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d08c3c0d-bcb3-44e1-ba3e-11bcddb39c41/2.+LIthium+global+map.jpg Adam Simon - Make it stand out Map showing sites of major lithium pegmatite and lithium brine deposits. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/458d5ed4-3732-4499-a1fc-28e5aebcf23e/8.+formation+of+lithium+pegmatites.jpg Adam Simon As Simon explains in the podcast, in the final phases of the emplacement of a granite, highly evolved, silica-rich melt can crystallize into pegmatites, which can have giant meter-scale crystals of the lithium-bearing mineral spodumene. MPa: megapascals. David Silva https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c10b2e84-de25-4996-a0f3-5de0dc5addb1/a5ae0a_594df9e54ac846afb7986c8c716ca28f.png Adam Simon Greenbushes lithium pegmatite mine in Australia, where the lithium mineral spodumene occurs in pegmatite veins associated with a granite intrusion. Talison Lithium Pty Ltd. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e384a6e5-5508-4294-8c54-022600b4745a/Spodumene-usa59abg.jpg Adam Simon Sample of spodumene, the lithium mineral that occurs in economically important quantities in pegmatites associated with granite. It is a pyroxene consisting of lithium aluminum inosilicate, LiAl(SiO3)2. This sample is about 14-cm long. Rob Lavinsky, iRocks.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/171238cd-ebb5-44b7-b583-3bfea06fad49/4.+lithium+brine+formation+cartoon.png Adam Simon The diagram shows how ground waters rich in lithium accumulate in salars and are then concentrated by evaporation. Bradley Cave https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02bb433e-2814-4991-b480-83fa1bcd3439/20170617_AMM932_.png Adam Simon - Brines As Simon says in the podcast, the largest lithium brine sources occur in a triangle spanning Chile, Bolivia, and Argentina. The Salar de Uyini, the world’s largest lithium deposit, occurs in western Bolivia. Economist https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bfae8dc4-b08d-44bf-a39e-9b7acfd7033e/SQMsan-pedro-de-atacama-atacama-salar-the-worlds-largest-lithium-deposit-evaporation-ponds-of-the-sociedad-quimica-mineral-de-chile-lithium-minechile-antofagasta-region.jpg Adam Simon Lithium brine evaporation ponds in the Atacama desert. Brine is pumped out of a nearby lake into a series of evaporation ponds. Over a period of 12-18 months, the water evaporates and salts precipitate, including lithium in the form of lithium carbonate. Photo: Sociedad Quimica Mineral de Chile https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d097729e-0f8b-4592-a4a4-e178e367f01b/Lithium_Brine.jpg Adam Simon Schematic of direct lithium extraction from lithium-rich ground water. This process does not result in the depletion of ground water, which is important, especially in desert regions. LazerRocDoc https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8c3fd624-390f-4cc6-895a-e391a4e7049e/9.+copper+deposits+global+map.jpg Adam Simon - Make it stand out Location of major copper deposits. Not all deposits shown have been mined. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1c84ffb3-d972-47e7-a75f-9eda6459668f/subvolcanic_porphyry.gif Adam Simon - Formation of Copper Porphyry Deposits In the podcast, Simon describes how, in magmatically active environments such as above subduction zones, water exsolves from a rising, decompressing granitic melt to form bubbles. These accumulate at the top of a magma chamber. The copper present in the magma preferentially partitions out of the magma into the bubbles. Then, as the bubbles rise toward the surface, cooling and further decompressing, copper minerals precipitate out to form veins in the groundmass of the porphyritic rock that forms. In the figure, the copper-bearing veins are shown diagrammatically in red. Porphyritic deposits supply 60 percent of global copper. W.J. McMillan for the B.C. & Yukon Chamber of Mines https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8bea4807-7b1a-47ae-8a26-b7ca2db32371/11.+Bingham+canyon+copper+mine.jpg Adam Simon Bingham Canyon open cast porphyry copper mine, Utah, U.S. Eric Prado https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4626ed42-acf2-4ddb-b699-40b19dbb6cd8/12.+copper+rich+ore+from+the+Golpu+porphyry.jpg Adam Simon Sample of copper-sulfide-rich ore from the Golpu porphyry copper deposit, Papua New Guinea. This ore is 2.15 percent copper by weight and also contains 2.23g of gold per ton. GeoInsite https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9d413d13-3498-41f0-a0c5-433d71fa3d2d/Copper+electrode.jpg Adam Simon Copper sheets produced at the Ruashi copper-cobalt mine in the Democratic Republic of Congo. The sheets are sent to battery manufacturers who machine it to size. Left to right: Brandon Finn, Pascal Mambwe, and Adam Simon. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8f30a14a-6416-443c-b14d-3df07de5af77/13.+Nickel+deposits+map+global.jpg Adam Simon - Make it stand out Location of laterite and magmatic nickel deposits and of sedimentary cobalt deposits. Most of these deposits contain cobalt, as indicated on the map. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6a368148-f2cf-4b89-805d-ab0f44c44a65/14.+Nickel+laterite+mine.jpg Adam Simon Open cast laterite nickel deposit, New Caledonia. New Caledonia contains over 7 million tons of nickel, or about 10 percent of the world’s nickel reserves. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/843dea01-b14c-4f43-b5cf-ac59631e3447/15.+Garnierite+nickel+rich+ore+from+laterite.jpg Adam Simon Garnierite nickel ore sample from Camps Des Sapins mine, New Caledonia. Garnierite is a complex nickel silicate mineral that precipitates out at the base of a weathered zone of ultramafic rocks from the breakdown of olivine. Didier Descouens https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c032de33-bd01-4a66-a77f-4534303b6b85/16.+Cobalt+deposits+world+map.png Adam Simon - Make it stand out World map showing the distribution of major cobalt-bearing mineral deposits, which contain at least 500,000 tons of cobalt, and selected smaller deposits that represent minor types. The sizes of the symbols for terrestrial deposits reflect the amounts of cobalt they contain. USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b0ca511c-14a5-4d1b-af9b-720313e2a769/17.+Ruashi+cobalt+copper+mine+DRC.jpeg Adam Simon - Make it stand out The Ruashi sediment-hosted copper-cobalt mine in the Democratic Republic of the Congo. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9654018f-59e8-485f-af23-dc55826d0010/cobalt-copper+ore+DRC.jpeg Adam Simon Cobalt and copper ore from the Democratic Republic of Congo. The black mineral is a cobalt oxy-hydroxide mineral called heterogenite, and the green mineral is the common hydrous copper phyllosilicate mineral called chrysocolla. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/74250920-f75d-4141-8756-8b75dc95411a/Mn+map.jpg Adam Simon - Make it stand out World map showing distribution of terrestrial sedimentary and supergene manganese deposits and manganese nodule concentrations in the oceans. Supergene ore deposits are those that are formed by rain-water circulation and concomitant oxidation and chemical weathering of manganese-bearing rocks near the Earth’s surface. The manganese is present in the rocks as oxides, hydroxides, silicates, and carbonates. The term “supergene” in ore deposit geology refers to processes or enrichments that occur relatively near the surface as opposed to deep hypogene processes. Adam Simon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a6f4dc9-79d7-40d2-bf59-b7ced281e91a/20.+Manganese+mine+Australia.png Adam Simon - Make it stand out The Groote Eylandt manganese mine in Northern Territory, Australia. The ore is mined by shallow open-cut mining methods and is transported by road to a nearby port. Northern Territory government https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/50dff27e-438b-4538-a12c-e4a59581ac62/Mn+or++pyrolusite+%28manganese+dioxide%29+is+one+of+the+most+common+manganese+minerals+Credit+Shutterstock.jpg Adam Simon The manganese dioxide mineral pyrolusite is one of the most common manganese minerals. Shutterstock https://www.geologybites.com/joe-macgregor daily 0.75 2024-11-14 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a0032ea1-5806-47a4-8eb1-e08d5b369077/headshot_new_small.jpg Joe MacGregor A thick ice sheet covers 80 percent of Greenland. Until recently, our best geological maps of the island were based on the exposed periphery, with the subglacial geology inferred by extrapolating from the edges and using educated guesswork. In April 2024, Joe MacGregor and his colleagues assembled new data about the rocks below Greenland’s ice from seismic, gravity, magnetic, and topographic surveys. The result is a new geological map that, for the first time, features several geological provinces that bear no relation to those exposed on Greenland’s ice-free periphery. His team also uncovered networks of long and straight subglacial valleys. MacGregor is a Research Physical Scientist at NASA’s Goddard Space Flight Center. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b855fb7c-d29d-4b89-b7ef-74473dc7fa78/Dawes+2009+map.jpg Joe MacGregor - Make it stand out The best geological map of Greenland prior to the new map discussed in the podcast. The map relied on extrapolating the geology of the ice-free exposures of rock around Greenland’s periphery and correlating rocks from one coast to another, as well as information from drill sites, nunataks (mountains and ridges that protrude from the ice cap), glacial erratics, provenance studies of detritus in sedimentary rocks, and, to a very limited extent, geophysical data. Dawes, P.R. (2009), Geological Survey of Denmark and Greenland Bulletin 17, 57 https://doi.org/10.34194/geusb.v17.5014 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/286174e2-2d76-4789-9c5b-f2c9f5d2f2c9/Orion+P3.jpg Joe MacGregor - Make it stand out Much of airborne geophysical survey work used to prepare the new geological map of Greenland was performed using the Lockheed P-3 Orion aircraft. A special feature is the tail boom housing a magnetometer designed to capture magnetic anomalies in the Earth’s magnetic field caused by submarines. Jeremy Harbeck, NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cfc00aea-ab93-48a6-905c-3f88fdf8df76/Annotated+aricraft.jpg Joe MacGregor - Make it stand out Annotated diagram of the P-3 Orion, showing the location of the instruments used to capture the geophysical data discussed in the podcast. NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4e06db37-56d5-4f05-a39a-8a00bb2f7543/Arctic_flight_trajectories_2009-2019_20191203.jpg Joe MacGregor - Make it stand out Arctic survey flights conducted as part of NASA’s Operation IceBridge. Since 1993, NASA has flown over a million kilometers over the Arctic to conduct geophysical surveys. NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e4291a89-0a8e-4520-b3ba-5425d63b00cd/2023gl107357-sup-0001-supporting+information+si-s01.jpg Joe MacGregor - Make it stand out In the podcast, MacGregor describes a new method of visualizing the surface of the ice sheet in which the simulated illumination of a digital elevation model varies according to the direction of surface ice flow. (A) Map of Greenland’s surface shaded using flow-aware hillshade, in which the artificial illumination direction (and corresponding shadows) at each pixel is 90 degrees counterclockwise to the ice-flow direction. The resulting shading emphasizes small-scale variability in the ice-sheet surface slope, which is primarily related to variability in the topography under the ice. The change in shading from the middle of the ice sheet to the periphery reflects the smaller slopes in the interior and the smaller surface bumps induced by subglacial topography, because as the ice thickness decreases, the surface becomes more sensitive to what is going on below. The map is based on the laser altimetry data. (B) The green lines are manual tracings of linear features in the map. GrIMP: Greenland Ice Mapping Project. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a2e7d9ba-384e-45d1-b6db-c28b7ee2fd4b/Fig+2.jpg Joe MacGregor - Make it stand out Results from each of the individual geophysical data types surveyed with hand-drawn boundaries. (A, B) Depth to the Moho discontinuity and shear-wave speed anomaly at 10 km depth respectively from seismic tomography. As mentioned in the podcast, the shallower depths and lower shear-wave velocities are pronounced near the central east coast. (C) Gravity anomaly. (D) Earth Magnetic Anomaly Grid. (E) Topography assuming ice‐free conditions and rebounded to adjust for isostatic sinking of surface under the ice-sheet weight. The map is based on the radar sounding measurements discussed in the podcast. (F) Ice surface with flow-aware hillshade with geological provinces on the ice-free surface. (G) Superposition of all the traced boundaries from each of the geophysical surveys. Credits for individual surveys appear in MacGregor, J. A. et al. (2024) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0d38d719-2ca6-4daa-b102-f222ece1d444/Fig+3.jpg Joe MacGregor - Make it stand out (A) This is the new geological map. It is based on the set of geophysical surveys whose results are summarized in the maps in the previous figure. The geological provinces are colored by age. Three newly identified provinces (unshaded Regions A, B, and C) do not correspond to known provinces of the exposed periphery of Greenland. (B) Map showing the major ice flows and newly discovered network of long straight valleys (purple lines labeled as surface linations in the legend) discussed in the podcast. The dotted line shows the hypothesized track of the hotspot currently under Iceland (see next figure). (C, D) Zoom-ins on the Petermann Glacier and the Northeast Greenland Ice Stream (NEGIS). These originate close to the boundaries of the newly identified geological provinces. See below for images of these glaciers. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a6b3cedd-df4f-4082-bece-ac188c9cef55/Hotspot+track+Martos+et+al.png Joe MacGregor - Make it stand out Suggested track of the Iceland hot spot based on variations in the Earth’s magnetic field. This serves as an indicator of the amount of heat being supplied to base of the Greenland Ice Sheet from the Earth’s interior. A band of warmer-than-expected rock stretching from northwest to southeast Greenland, together with models of the lithosphere derived from gravity data, is interpreted to be the scar left as the Greenland tectonic plate moved over the hot spot. Martos, M. M. et al. (2018) Geophysical Research Letters 45, 8214 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/83ad7d68-7bf9-43ad-8952-1c6ad54c8bb6/Zacharaias.jpg Joe MacGregor An iceberg near the calving front of Zachariæ Isstrøm. As mentioned in the podcast, this glacier flows into the sea at the northeast end of the the Northeast Greenland Ice Stream that starts at a point near the boundary of one of the newly discovered inland geological provinces. NASA, Jeremy Harbeck https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a4055720-500d-4cb2-9a5d-081e4a3b5c2e/Petermann.jpg Joe MacGregor - Make it stand out One of the largest in Greenland, the Petermann glacier flows into the sea at the northwest end of an expanding zone of fast-flowing ice. Copernicus Sentinel-2 satellite, 2022 https://www.geologybites.com/mike-searle-central-asia daily 0.75 2024-12-21 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/79fd3910-9c36-4ccc-ba6d-7562b0be1e0b/mike+filming+copy.jpg Mike Searle Central Asia The Karakoram, Hindu Kush, and Pamir are among the major Central Asian mountain ranges that contain some of the highest peaks in the world. In the podcast, Mike Searle describes the origin and geology of six Central Asian ranges and how they relate to the Himalaya and the collision of the Indian plate with Asia. India continues to plow into Asia to this day. How is this movement accomodated? Searle explains the extrusion and crustal shortening models that have been proposed and describes the detailed mapping in the field in northern India he and his colleagues conducted that showed that both mechanisms are operating. Searle is Emeritus Professor of Earth Sciences at the University of Oxford https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b02408ad-ce65-440a-afa0-86fa666dc480/High_Asia_Mountain_Ranges.jpg Mike Searle Central Asia - Make it stand out Satellite image labeled with five of the mountain ranges Searle discusses in the podcast — the Karakoram, the Hindu Kush, the Pamir, the Kunlun Shan, and the Tien Shan. The Gangdese, also discussed, is to the east of the region covered by the image along the southern margin of Tibet. NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bd1f1a6e-bd22-4638-bea9-7b00097347d2/Jolivet+%2CM.2015.png Mike Searle Central Asia Main continental blocks and terranes of Asia and position of the suture zones, several of which are mentioned in the podcast. The mountain ranges that are the topic of the podcast lie between India and the Central Asian Orogenic Belt. BH, Bayan Har; Hel, Helmand; HK, Hindu Kush; Ind. Indochina; Kh, Kohistan; Ku, Kudi; NQi, North Qiangtang; P, Pamir; Qi, Qilian Shan; SG, Songpan–Garzeˆ; Sib., Sibumasu; SQi, South Qiangtang; WB, West Burma. Suture zones: 1, Indus–Yarlung–Zangbo; 2, Bangong Nujiang; 3, Yushu–Batang; 4, Jinsha; 5, Longmu Co–Shanghu; 6, Panjao; 7, Solonker; 8, Jilin; 9, Mongol–Okhotsk; 10, Kunlun–Anyemaqen. Jolivet, M. (2015), Geological Society, London, Special Publications, 427, http://doi.org/10.1144/SP427.2 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e4c61ed-1f8b-452e-ba77-0bb5e41422ef/Mike+on+Yak%2C+Karakoram.jpg Mike Searle Central Asia Many parts of the central Asian mountain ranges are not accessible by road. Therefore, in the 1980s, Searle and his colleagues organized major Himalayan mountaineering expeditions to do geological field work, especially for terrain at higher elevations. The image shows Searle and a porter riding a yak across the North Braldu river in the Karakoram near the Pakistan-China border. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5b9825aa-cf89-4da7-adc4-268769e609be/Geology+of+N+Pakistan.jpg Mike Searle Central Asia - Make it stand out Geological map of northern Pakistan spanning the Karakoram and Hindu Kush. The map shows the main granitic-type rocks that were formed both before and after the India-Asia collision and that occur in the Asian plate, north of the suture zone (SSZ) between the Indian and the Asian plates. The massive Baltoro granite is shown in black. Hildebrand, P.R. et al. (1998), Geology 26, 871 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7a44b317-bf7f-4eb8-9789-e386cacaf16e/Metamorphic+facies+OU.jpg Mike Searle Central Asia In the podcast, Searle discusses the Barrovian regional metamorphism that accompanied the India-Asian collision and the metamorphic facies corresponding to the peak temperature and pressure experienced by the rocks. The pressure-temperature (PT) zones corresponding to the various facies are shown in the diagram. In the Karakoram, the lower-grade rocks are greenschist facies, with chlorite, biote, and garnet as the incoming metamorphic minerals with increasing PT. The higher-grade rocks are amphibolite facies with staurolite, kyanite, and sillimanite as the incoming metamorphic minerals. Courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7398847d-bdf9-4624-a5c1-75b1c77676e9/Trango+Towers.png Mike Searle Central Asia The Trango Towers are granite cliffs that rise about 3,000 meters above the Baltoro glacier in the far northeast of Pakistan. In the podcast, Searle explains that the Baltoro granite, which is what is exposed in the Trango Towers, is a giant, continuous batholith that was emplaced 13-20 million years ago during the intense regional metamorphism accompanying the India-Asia collision. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f0ad1362-4f40-481c-8de1-09f8f0efe46b/Karakoram+geology.jpg Mike Searle Central Asia - Make it stand out Landsat image showing the Baltoro glacier, center. NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3a5af8d8-571b-4e5d-895d-8ea42b173d6a/Karakoram+geology.jpg Mike Searle Central Asia - Make it stand out Annotated photographs of mountains that lie within the region imaged by Landsat above. (b) Layla peak, the sharply pointed summit at left, consists of orthogneissses (formed by metamorphosing igneous rocks) with a granite intrusion (K7 granite) dated at 21.7 Ma. (c) Taken from the rock-strewn surface of the Baltoro glacier, the photograph shows the northern margin of the Baltoro batholith. The heat from the intruding Baltoro granite metamorphosed the adjacent Carboniferous black shales to sillimanite, cordierite, and andalusite hornfels. (d) Another image showing the northern margin of the Baltoro batholith, here consisting of the Baltoro granite of the Lobsang Spire (foreground at right with a climber near the bottom for scale). The rest of the image shows the pre-collision orthogneisses of the Cretaceous Muztagh Tower (top left). (e) South face of the Uli Biaho Tower (6,427 m) showing homogeneous granite. (f) Another homogeneous granite tower, here with 1,800-m-high cliffs (Shipton Spire, 5,885 m). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/567e0bde-4347-4d11-8cfd-4a9757ca853b/Baltoro+Age+constraints.jpg Mike Searle Central Asia Cliff profile in the Hushe Valley, Pakistan, shows gneisses formed before the India-Asia collision. They are intruded by Baltoro granite (K7 granite), and later cut by a thin lamprophyre dyke. In the podcast, Searle explains that lamprophyre dykes have a geochemical signature that tells us they originate from the mantle. The presence of these dykes suggests that hot material from the mantle may have been the source of the extra heat needed to melt the huge volume of crustal rock that then cooled and formed the giant Baltoro granite batholith. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0c4857a0-9eba-495b-ab13-22f4ed1682e2/Peng.%2C+C-C.+et+al+HK+deep+sesimic+zone.jpg Mike Searle Central Asia In the podcast, Searle describes the seismic zone in the Hindu Kush where exceptionally deep earthquakes are occurring. The map shows that the deep earthquakes define a narrow region, which reveals where the old, cold slabs of lithosphere are subducting — a deep one from the Hindu Kush dipping toward the north and a shallower one from the Pamir dipping toward the south. The abbreviations label faults, thrust systems, and a suture zone (SSZ). Peng, C.-C., et al. (2020) Earth Planet. Sci. Lett. 530, 115905 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f8a5fa6-41c1-4788-9d56-b7235d246eff/Searle+et+al+model+of+deep+SZ.jpg Mike Searle Central Asia - Make it stand out Model of the Hindu Kush seismic zone with an interpretation of possible ultra-high-pressure (UHP) metamorphic rocks formed by subduction of continental rocks to depths of over 200 km. Continental UHP rocks are known from over 20 world-wide occurrences ranging from Cambrian to Pliocene. These rocks include eclogites, some with a high-pressure polymorph of quartz called coesite, and others bearing diamonds. In the podcast, Searle suggests that two converging continental subduction zones, the deep Hindu Kush zone and the shallower Pamir zone, are elevating the Pamir plateau. Searle, M., et al. (2001), Journal of Geology, 109, 143 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0fbe6efb-799e-465f-bcd2-4d7d60d9e024/DEM+Pamir+etc+.jpg Mike Searle Central Asia - Make it stand out Digital elevation model for the Pamir plateau and adjacent ranges. The Pamir forms an extended region of high elevation running from the Karakoram-Hindu Kush in the south to the Tien Shan in the north. US Geological Survey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7ba6bef5-1036-410b-a18e-f57525b3e4f3/Pamir-Karakoram+knot+from+space.jpg Mike Searle Central Asia - Make it stand out Photograph of the Pamir and Karakoram looking east, taken from the International Space Station. Photo: Tim Peake and NASA; geological interpretation: Searle, M. P., et al. (2018), Geol. Soc. London Special Publication 483 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b3d5de9a-4a34-4879-ab24-e1498d0d5074/Pamir+terranes+Searle+%26+Hacker++2018.jpg Mike Searle Central Asia - Make it stand out Simplified geological map of the Pamir-Karakoram-western Tibet region showing the major terranes, suture zones, and faults. The region covered by the map is shown in the inset at top left. The Shyok suture marks the border between the Indian plate and the Asian plate. In the podcast, Searle discusses the two syntaxes at each end of the Himalaya that may affect the continental subduction mode — ultra-deep to the east in the Hindu Kush and shallow to the west along the Karakoram and the Himalaya. The 8,126-m peak Nanga Parbat (NP) is located at the western syntaxis. The map also shows the prominent strike-slip faults — the Karakoram fault and the Altyn Tagh fault — along which the extrusion of Tibetan crust is thought to occur (see below). Searle, M. P., et al. (2018), Geol. Soc. London Special Publication 483 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/303fc805-9161-4827-b32d-2050726925a8/Simple+underthrusting+model+Fig+2.jpg Mike Searle Central Asia - Make it stand out Conceptual diagram of the underthrusting of lower Indian crust and shortening of the upper Indian crust. (a) Simplified pre-collision disposition of India and Asia separated by the Tethyan Ocean. (b) The model originally proposed by Argand in 1924 with about 1,000 km of underthrusting of Indian crust beneath the Asian crust, resulting in the double-thickness crust of Tibet. (c) The updated Argand-type model described in the podcast in which the upper Indian crust has been scraped off to form the Himalaya, and the Precambrian lower Indian crust has underthrust north under Tibet. In this model, about 500 km of crustal shortening across the Neoproterozoic-Phanerozoic rocks of the Himalaya is balanced by 500 km of northward underthrusting of the still older Archaean-Mesoproterozoic Indian lower crust. Searle, M. et al. (2011) Journal of the Geological Society 168, 633 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/efe7ab6f-1473-4189-93c4-b9a8064ff1cf/Tibet+Extrusion.png Mike Searle Central Asia In the alternative model as to how India’s northward movement is being accommodated, a rigid block of Tibetan crust is extruded to the east between large strike-slip faults—the Altyn Tagh fault on the northern side and the Karakoram fault on the southern side. Reconstructions of SE Asia according to the extrusion model are shown here: (a) at c. 32 Ma and (b) at 16 Ma. (c) Experiments with plasticene (non-hardening modeling clay) showing deformation by a rigid Indian plate of a layered plasticene block with a free boundary on the eastern side. “Faults” develop and blocks extrude to the east. (a), (b) Leloup et al. (2001) and Replumaz et al. (2003); (c) Tapponnier et al. (1982) and Peltzer et al. (1988) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c803be71-5207-476f-81ca-f59d315a792d/Tibet+GPS+Gan+et+al+%282007%29.png Mike Searle Central Asia Horizontal velocities measured by GPS satellites across Tibet relative to a stable Eurasia, which supports the model of Tibetan crust extruding to the east. In the podcast, Searle explains that detailed mapping across the Karakoram strike-slip fault indicates a maximum of 300 km of slip. So, while extrusion can accommodate some of India’s northward movement, other mechanisms, such as upper-crustal shortening and lower-crustal under-thrusting, must also be playing a role. Gan et al. (2007) https://www.geologybites.com/rob-strachan daily 0.75 2024-12-11 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d49fb399-f0d5-4666-af6d-496ebf9eb5eb/3.+Rob+B.png Rob Strachan The Caledonian orogeny took place during a multiphase collision of crustal blocks in the early stages of the assembly of Pangea between about 490 million years ago and 390 million years ago. In the process, Himalayan-scale mountains were formed. While these mountains have been worn down today, we still see plenty of evidence for their existence in locations straddling the Atlantic and the Norwegian Sea. In the podcast, Rob Strachan describes the tectonic movements that led to the orogen and explains how we can reconstruct the sequence of events that occurred and what we can learn about today’s mountain-forming processes by studying the exhumed rocks of ancient orogens. Strachan has studied the rocks of the Caledonian orogen for over 40 years, focusing on unraveling the history of the orogen in what is Scotland today. He is Emeritus Professor of Geology at the University of Portsmouth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/50fa3d1e-53a2-412e-b986-b04de7511a16/Supercontinent+Timeline.JPG Rob Strachan - Make it stand out Supercontinent timeline. The Caledonian orogeny took place after the breakup of Rodinia at about 750 million years ago (Ma) when three of the continental blocks that would ultimately form part of Pangea assembled. These blocks were (i) Laurentia, which corresponds to present-day North America, Greenland, and Scotland; (ii) Baltica, corresponding to present day-Scandinavia; and (iii) Avalonia, corresponding to southern Britain and parts of mainland northern Europe. Evans, D. A. D., et al. (2016), Geol. Soc. London, Special Pub. 424, 1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2e1ec844-29fe-4dee-ba49-c3e051c26e28/Rodinia.jpg Rob Strachan Reconstruction of Rodinia about 1,000 million years ago before it broke up and oceans, such as the Iapetus formed between the dispersing continental blocks. Au: Australia; Am: Amazonia; Ba: Baltica; La: Laurentia; RP: Rio de la Plata; Si: Siberia; Wa: West Africa. S: Scotland; EG: East Greenland; Sv: Svalbard; P Pearya; red lines: areas affected by a prior orogeny (Grenville-Sveconorwegian) about one billion years ago. After Cawood, P.A, et al. (2016), Earth and Planetary Science Letters 449, 118 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c220c7a5-b775-47f9-849a-604e65b290f8/6.+Ediacaran+to+Devonian+reconstructions+%28from+Geology+of+Scotland%2C+referenced+to+Holdsworth+et+al.+2012%29.png Rob Strachan - Make it stand out Reconstruction of continental positions from the Ediacaran to the Devonian. (a) Laurentia drifts away from Gondwana (part of the supercontinent Rodinia) as the Iapetus Ocean grows from a mid-ocean spreading ridge. (b) A south-dipping subduction zone develops within the Iapetus Ocean and starts to consume the Iapetus oceanic crust. Avalonia rifts away from Gondwana. (c) The Iapetus is almost entirely swallowed up by subduction zones, and Avalonia collides with Baltica and then with Laurentia. (d) Baltica and Avalonia have joined Laurentia to form Larussia, and the Caledonian orogeny comes to an end. Woodcock, N.H, et al. (2012) Geological History of Britain and Ireland (second edition), Wiley-Blackwell https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fce09f66-7f0f-4e18-9f7f-fee786cd6ea9/7.+Oceanic+lithosphere+cross-section+%28from+Furnes+%26+Dilek+2014%29.jpg Rob Strachan In the podcast, Strachan explains that some oceanic crust is thrust onto the margins of Laurentia and Avalonia during the final phases of the closure of the Iapetus Ocean to form ophiolites. The remains of the Caledonian ophiolites are often missing some of the full sequence of oceanic lithosphere as represented in the cross-section shown here. In the Shetlands, for example, only the mantle and lower crustal rocks are present, and the pillow lavas and deep-sea sediments are absent. Furnes & Dilek 2014 (need cite) https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/495fd088-c90f-4629-9a0f-0c92df640541/8.+Interlayered+ultramafic+rocks%2C+Unst+ophiolite%2C+Shetland.JPG Rob Strachan Layered ultramafic rocks in the Unst ophiolite of Shetland. These correspond to the light-blue layer just below the Moho shown in the cross-section above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a81ab74f-4486-4c3a-ae8b-14043933dc4d/9.+Lake+District+Ordovician+volcanics+and+interbedded+volcaniclastic+rocks.png Rob Strachan - Make it stand out Lake District Ordovician volcanics and interbedded volcaniclastic rocks. In the podcast, Strachan describes the igneous rocks that are associated with the convergence and ultimate closure of oceans. These are formed by melting of mantle rocks above a subduction zone. The volcanic rocks seen in the Lake District in Northwest England comprise thick successions of volcanic rocks that were erupted above a subduction zone, which is thought to have dipped southwards underneath Avalonia during the closure of the Iapetus Ocean. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/558c2858-6766-4b5a-bafa-a4ec7344f114/10.+Newer+Granites.png Rob Strachan - Make it stand out Toward the end of the Caledonian orogeny, the metamorphosed rocks adjacent to the suture zone between Laurentia and Avalonia were intruded by huge granite plutons, which were probably formed as a result of the melting of mantle and crustal material above the subduction zone that was dipping underneath Laurentia. Top and bottom right: granite in the Cairngorm mountains of Scotland; bottom left: Shap granite, Lake District, England. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4dc0c0cd-c908-49db-a1e6-01cdf5869b5c/11.+Caledonian+tectonic+model+from+Searle+2021.png Rob Strachan - Make it stand out Caledonian tectonic model. (a) Rifted margin of Laurentia approaching an intra-oceanic subduction zone above which has developed the juvenile Midland Valley arc (volcano at right). (b) Large-scale folding of Dalradian and Moine strata on Laurentia following its collision with the Midland Valley arc, and the switch in the direction of subduction zone dip so that oceanic lithosphere is now being subducted under Laurentia (note the developing accretionary prism that is now exposed in the Southern Uplands) (c) Final collision of Avalonia and Baltica with different sectors of the Laurentian margin during the final closure of Iapetus (note also the development of the main strike-slip/lateral faults). (GGF = Great Glen Fault; HBF = Highland Boundary Fault; SUF = Southern Uplands Fault). Searle, M. P. (2021), Geological Magazine https://doi.org/10.1017/S0016756821000947 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/82b7a83f-0408-49e5-a366-368aa90fd767/13.+Siccar+Point+unconformity+between+Silurian+greywackes+underneath+and+Upper+Devonian+sandstone+above.jpg Rob Strachan - Make it stand out Siccar Point, one of the most famous of the sites where Hutton and Lyell first understood the magnitude of geological time, is an unconformity between Silurian greywackes underneath and Upper Devonian sandstone above. The Silurian greywackes are part of the accretionary prism that was uplifted and then eroded during the final closure of Iapetus and the collision of Avalonia with Laurentia. A long period of non-deposition then followed before the Upper Devonian sandstones were laid down unconformably on the older strata. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/034b657d-9583-47a0-9107-b117d7ecfe21/14.+Dalradian-equivalent+sediments+of+the+Eleonore+Bay+Supergroup+%28late+Neoproterozoic%29+in+the+Stauning+Alps%2C+East+Greenland+Caledonides.jpg Rob Strachan - Make it stand out Neoproterozoic to Cambrian sedimentary rocks of the Eleonore Bay Supergroup that were laid down on the edge of Laurentia as the Iapetus Ocean widened. This succession is broadly time-equivalent to the Dalradian Supergroup in Scotland; they were thrust many 10s of km westwards during the Caledonian orogeny. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f6fa7027-5aed-4b91-b170-204097c9c46b/15.+Probable+Caledonian+folds+in+basement+gneisses%2C+East+Greenland.jpg Rob Strachan - Make it stand out The folded rocks here are Paleoproterozoic basement gneisses in East Greenland, and the huge fold that can be seen probably formed during the Caledonian orogeny. The image is viewed to the north, so the sense of overturning of the fold is to the left, consistent with thrusting and overfolding toward the foreland in the west. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ba5bd268-5f9f-4d5e-9920-216d411ef02d/16.+Reconstruction+of+extended+Baltica+continental+margin+prior+to+collision.png Rob Strachan - Make it stand out This hypothetical cross-section restores the sedimentary strata that are now stacked up in Norway as a series of thrust nappes into what is thought to have been their original location on the Baltica passive margin during the Silurian just as it is about to enter the Iapetus subduction zone that was dipping west under Laurentia (East Greenland). Jamtveit, B., et al. (2018), Nature Scientific Reports, 8, 17011. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02b6128c-b6fd-40a7-8659-ff4c31c88612/17.+Areas+of+ultra-high+pressure+%28UHP%29+rocks+in+the+Western+Gneiss+Region.png Rob Strachan - Make it stand out During the collision of Laurentia and Baltica, continental rocks of the Baltican margin were subducted to depths of about 100 km where they underwent high-pressure metamorphism. They then returned to the surface where we see them today as the ultra-high pressure (UHP) rocks in the Western Gneiss Region of Norway. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d923c450-6f80-4e9a-afa6-53c5d66e8403/18.+Eclogite+in+Western+Gneiss+Region+%28from+Haakon+Fossen+Structural+Geology+blog%29.png Rob Strachan - Make it stand out Eclogite in Western Gneiss Region. Eclogite is a rock formed at high temperatures and pressures by metamorphosing a rock of basaltic composition Minerals: garnet (red); omphacite, a sodium-rich pyroxene (geen); quartz (colorless, glassy). The garnets are about 10 mm across. Courtesy of Haaken Fossen https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c97f40d-9c3e-4ae8-b198-99c76ca9e7d4/19-1.+Caledonian+thrusting+and+exhumation+of+WGR+in+Norway.png Rob Strachan - Make it stand out Scandian collision and east-directed nappe stacking (left) followed by slab detachment, uplift, extension, and exhumation of Western Gneiss Region (right) Brueckner, H.K. et al. (2013), Lithosphere, doi: 10.1130/L256.1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/38432070-4676-44b4-a257-bfb14168484d/19-2.+Caledonian+thrusting+and+exhumation+of+WGR+in+Norway.png Rob Strachan - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ff8476f0-59db-4c23-9854-ef6a8262aefe/21.+Britain+and+Ireland+terrane+map+%28from+Open+University+2003%29-map+part.jpg Rob Strachan The main terranes in the British Isles and the names of the main faults. The terranes north of the Highland Boundary Fault (HBF) are thought to have always been part of Laurentia; those south of the Iapetus Suture are thought to have always been part of Gondwana (Avalonia). Between the Iapetus Suture and the Highland Boundary Fault are two terranes (the ‘intermediate terranes’) that are thought to have evolved within the Iapetus Ocean. OIT: Outer Isles Thrust; MTZ: Moine Thrust Zone; GGF: Great Glen Fault; SUF: Southern Uplands Fault; MSF: Menai Straits Fault; WBF: Welsh Borderlands Fault. Courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cb26f8f0-812d-40c6-83cb-3658af839343/22.+Moine+Thrust+at+Knockan+Crag.jpg Rob Strachan - Make it stand out Moine Thrust at Knockan Crag, a Geopark in Scotland where the Moine Thrust forms a sharp boundary. Mylonitic Moine rocks lie above buff-colored Cambro-Ordovician carbonates, viewed east. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b5efc090-8350-4fc4-abf4-92548c4ee954/24.+Newer+Granite+Suite+%28from+Woodcock+et+al.+2016%29.jpg Rob Strachan - Make it stand out Map showing location of granites intruded in the late stages of the Caledonian orogeny. As discussed in the podcast, these rocks were formed from the melting of mantle and crustal material above the subduction zones that consumed the Iapetus. Miles, A.J. et al. (2016), Gondwana Research, 39, 250 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7534e5e4-b579-4980-b88d-21754f60d15b/25.+Tectonic+reconstruction+of+the+Midland+Valley+and+the+Southern+Uplands+during+Silurian+times+%28from+Open+University+2003%29..jpg Rob Strachan - Make it stand out This shows the tectonic framework on the northwest margin of the Iapetus Ocean during the Silurian. Laurentian crust north of the Highland Boundary Fault is out of view to the left (northwest). The top diagram shows Iapetan oceanic lithosphere being subducted northwestwards, resulting in a) construction of the Southern Uplands accretionary prism made up of oceanic sediments that were progressively scraped off the subducting oceanic plate, and b) magmatism in the Midland Valley due to melting of the mantle wedge above the subduction zone. Sedimentary rocks also accumulated in the Midland Valley between the main plutonic/volcanic centers. The bottom diagram shows the complexity of the Southern Uplands accretionary prism, which is typical of modern examples. Thrust faults (in red) separate different packages of oceanic sediment that have been progressively scraped off the downgoing plate; hence these packages get younger from 1 to 6. Within each package, the order of the strata is still more or less right-way-up as shown by the inverted Y sign. Courtesy of the Open University https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b00d4eca-0795-4076-bd21-66bfc88bebd7/27.+The+Northern+Scottish+Highlands+as+a+displaced+segment+of+the+East+Greenland-Norway+Scandian+collision+%28after+Open+University+2003%29.jpg Rob Strachan Reconstruction of the end of the Caledonian following ~700-500 km of movement along the Great Glen Fault. In the podcast, Strachan discusses a model in which the Northern Scottish Highlands were further north during Caledonian times, collided with Baltica, and then were displaced to the south by ~700-500 km along the Great Glen Fault. (Dewey & Strachan 2003). Open University 2003 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a5111ddc-c62d-44ff-8d93-f9c08ea48e1c/20.+Linkage+of+terranes+across+to+Maritime+Canada+%28from+Waldron+et+al.+2022%29.png Rob Strachan - Make it stand out This very simplified reconstruction represents the point at which Pangaea had assembled by approximately 330 million years ago (Ma). In Scotland, the light blue represents the deformed margin of Laurentia (the Northern Highland and Grampian terranes), and the dark green the terranes that developed just outboard of Laurentia within the Iapetus Ocean (the Midland Valley and Southern Uplands terranes). The corresponding units are shown to the west in Maritime Canada and the Appalachians, to the north in East Greenland, and on the Baltica side, an area of green represents Laurentian arcs that were thrust onto Baltica crust during the final continental collision. On the far left, a key includes five different units, one of which is Avalonia. This reflects the very complex geology of the various pieces of crust that collided with Laurentia. The simplified view adopted in the podcast is that all the crust south of the Iapetus Suture in Britain and Ireland can be referred to loosely as ‘Avalonia’ with the proviso that it may in fact be rather more complex. Waldron, J. W. F. et al. (2022), Earth Science Reviews, 233, 104163 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/508c0a74-f141-49a0-b5dd-89026a335941/1.+Introductory+slide+of+Caledonides.jpg Rob Strachan Reconstruction of the continental blocks before the opening of the northern Atlantic about 54 million years ago. The green shading shows the areas that were caught up in the Caledonian orogeny, which at the time of the orogeny formed the margins of Laurentia, Baltica, and Avalonia. Today, these areas run from the Appalachian mountains and Newfoundland in North America through the northern British Isles to eastern Greenland and western Norway. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/028c5c9c-cf0a-41ab-a42e-8d0cf716f26c/28-1.+Dispersal+of+the+North+Atlantic+Caledonides+since+140+Ma.png Rob Strachan - Make it stand out Dispersal of different parts of the Caledonides during the opening of the North Atlantic Ocean, which did not start until 54 Ma, about 350 million years after the end of the Caledonian orogeny. Gasser, D. 2014, Geological Society of London Special Publication 390, 93 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f247a69-8abc-47b4-a7de-9e1fde1d9a86/28-2.+Dispersal+of+the+North+Atlantic+Caledonides+since+140+Ma.png Rob Strachan - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/mike-searle-central-asia-glossary daily 0.75 2024-12-17 https://www.geologybites.com/test-for-subscribing daily 0.75 2025-01-02 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a6692477-3428-4b5c-8e9d-9c9880b664e0/Apple+Podcasts.png Test for subscribing - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/18c78e8c-2885-408e-9f0e-ac15e7854095/Spotify.png Test for subscribing - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dcb94c2a-4f55-4a86-ab09-73ba7bc03843/Amazon+Music.png Test for subscribing - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/richard-fortey-deep-time daily 0.75 2025-03-08 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/88d9ffc3-770f-48ca-82ac-4f94884dec92/Fortey+Guardian.png Richard Fortey deep time Richard Fortey has devoted his long and prolific research career at the Natural History Museum in London to the study of fossils, especially the long-extinct marine arthropods called trilobites. In an earlier episode of Geology Bites, he talked about measuring time with trilobites. In this episode, he describes how it was the fossils in the geological record that gave us the first markers along the runway of deep time, providing the structure and language within which our modern conception of deep time emerged. Fortey was head of arthropod paleontology at the Natural History Museum in London and is the author of popular science books on a range of subjects including geology, palaeontology, evolution and natural history. Photo: Eamonn McCabe/The Guardian https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/50fc5e9b-b6f7-4a4d-9dd4-8a6faf7f4dc5/ChronostratChart2024-12.png Richard Fortey deep time - Make it stand out The modern geological timescale (December 2024 version). Many of the names we have given to the various periods were derived from locations where the rocks of that age were first studied. The temporal boundaries of the periods were usually defined by the first appearance of certain fossils in sedimentary rocks. With the advent of radiometric dating of minerals, especially in igneous rocks adjacent to or intercalated with fossil-bearing sedimentary rocks, absolute ages have been assigned to boundaries between the periods. International Commission on Stratigraphy https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ad984914-1210-4d39-8961-85f456db8d3c/James_Ussher_by_Sir_Peter_Lely.jpg Richard Fortey deep time Bishop Usher (1591-1656) calculated the date of Creation to have been nightfall on 22 October, 4004 BC. He determined this from a literal reading of the Old Testament. Right: title page of Usher’s Annals of the World Painting by Sir Peter Lely https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a9d1ee2d-b41b-4c00-a50c-0dc91bb543ac/Annals_of_the_World_-_title_page.jpg Richard Fortey deep time - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3878c3c0-6298-4f97-a9d2-10df2e38cd71/Buffon_1707-1788.jpg Richard Fortey deep time Count Buffon (1707-1788) calculated the age of the Earth by estimating its rate of cooling. He experimented with a small globe having a composition resembling that of the Earth. This led him to estimate that the Earth was at least 75,000 years old. One key reason his figure was much lower than the actual age was the omission of radioactive heating of the Earth by the decay of isotopes, particularly those of potassium, uranium, and thorium. Painting by François-Hubert Drouais https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/04a9cee8-6b93-4d6c-a0a8-a52ad0b34061/13.+Siccar+Point+unconformity+between+Silurian+greywackes+underneath+and+Upper+Devonian+sandstone+above.jpg Richard Fortey deep time - Make it stand out The major angular unconformity at Siccar Point on the east coast of Scotland. Here the more gently sloping Devonian sandstones (c.375 Ma) overlay the near vertical Silurian greywackes (c.440 Ma). Viewed by James Hutton while on a boat trip in 1788, this was one of the sites that solidified Hutton and Lyell's new concepts of Earth's geology: that it was formed by slow continuous processes similar to those still occurring today operating over vast periods of time. Photo: Rob Strachan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/452dc2ed-9c8a-4e4c-add9-7e218d1a8888/Sir_Henry_Raeburn_-_James_Hutton%2C_1726_-_1797._Geologist_-_PG_2686_-_National_Galleries_of_Scotland.jpg Richard Fortey deep time - Make it stand out Portrait of James Hutton (1726-1797), often referred to as the “Father of Modern Geology.” Here is the final paragraph of this 1788 paper Theory of the Earth. WE have now got to the end of our reasoning; we have no data further to conclude immediately from that which actually is: But we have got enough; we have the satisfaction to find, that in nature there is wisdom, system, and consistency. For having, in the natural history of this earth, seen a succession of worlds, we may from this conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions. But if the succession of worlds is established in the system of nature, it is in vain to look for any thing higher in the origin of the earth. The result, therefore, of our present enquiry is, that we find no vestige of a beginning,--no prospect of an end. Hutton, J. (1788), Transactions of the Royal Society of Edinburgh, vol. I, Part II, 209 Painting by Sir Henry Raeburn https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/499e458b-ca4c-4d03-97b6-45e544b429da/Lyell_1840.jpg Richard Fortey deep time Portrait of Charles Lyell (1797-1875) who, in his multi-volume Principles of Geology, proposed that the Earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. This view was termed uniformitarianism, as opposed to catastrophism, which posited that the Earth was largely shaped by sudden, short-lived, violent events. Painting by Alexander Craig https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ff41e44f-937d-48f8-9e44-fa74ee98cb7c/Geological_map_Britain_William_Smith_1815.jpg Richard Fortey deep time - Make it stand out The first geological map of Britain, created by William Smith in 1815. In the podcast, Fortey explains that Smith used fossils as markers of the different geological units, without necessarily believing in the theory of evolution. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/18d1185d-54b8-448a-acb4-6075e7a65374/IMG_3122+%281%29.jpg Richard Fortey deep time - Clock of the Long Now The clock is intended to make us rethink our perception of time and engage in truly long-term thinking. The prototype pictured here was activated on the final day of the last millennium and is on display at the Science Museum, London. The clock is designed to keep time for 10,000 years. The final version of the clock is intended to be a monument-scale version of this prototype — a vast mechanism big enough for visitors to walk through. Manufacture and site construction of a full-scale prototype is taking place in the Sierra Diablo mountains in Texas. The clock uses a torsional pendulum that rotates slowly, making the clock tick once every 30 seconds. This prototype is driven by falling weights (right), but the full-size clock would be powered by the energy from footfalls of visitors or by changes in temperature. Any drift in the clock’s rate will be corrected by a mechanism sensing the sun passing overhead at noon. Clock of the Long Now https://www.geologybites.com/home-2 daily 0.75 2025-01-08 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3eed1046-49a4-4779-8c9f-fd7ff4645f14/Richard+Fortey.jpeg Home-2 The Earth is about 4.5 billion years old. How can we begin to grasp what this vast period of time really means, given that it is so far beyond the time scale of a human life, indeed of human civilization? In the podcast, Richard Fortey talks about how we came to a realization of deep time, how we have attempted to tame it, and how it has changed our conception of the primacy of humankind in Earth history. https://www.geologybites.com/early-earth daily 0.75 2025-01-09 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a1597afe-262e-4714-8cbe-e1e437fdd28b/RR+2015.jpg Early earth - Roberta Rudnick on the Continental Crustal Composition Paradox Continental crust is derived from magmas that come from the mantle. So, naively, one might expect it to mirror the composition of those magmas. But our measurements indicate that it does not. Continental crust contains significantly more silica and less magnesium and iron than mantle-derived magmas. How can we be sure this discrepancy is real, and what do we think explains it? In the podcast, Roberta Rudnick presents our current thinking about these questions. Surprisingly, more than 30 years after she and others first identified the so-called continental crustal composition paradox, there is still no consensus among geologists as to which of the many proposed hypotheses most convincingly solves the paradox. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21dcd95f-2c79-4eb8-abab-3831f04dead3/Clark_DSC-0728_Field_Portrait_cropped.jpg Early earth - Clark Johnson on the Banded Iron Formations In the early Proterozoic, about 2.5 billion years ago, enormous thicknesses of iron-rich rocks were deposited on continental shelves. Striking cliffs of these rocks form the walls of many canyons in Western Australia and South Africa. They are called the banded iron formations (BIFs) because they show vivid banding between the reddest, most iron-rich layers and ochre-colored layers containing siliceous material such as chert. What is the origin of the BIFs? For many years, the prevailing theory was that large amounts of dissolved iron were present in the early oceans, and it was the oxygen from the first oxygen-producing life forms in the water that oxidized this iron into an insoluble form, which then precipitated out of the oceans to form the BIFs. In the podcast, Clark Johnson explains how biological processes may have been responsible for oxidation of iron in seawater under oxic or anoxic conditions, as well as later reduction as the BIF sediments compacted on the seafloor. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d10eb267-e59b-4265-9ad9-72f90c5f5776/MVK+cropped-1.jpg Early earth - Martin Van Kranendonk on the Earliest Life on Earth Stromatolites are the layered structures left behind by microbial communities. They are the fossil evidence for far and away the earliest life on Earth. But the interpretation of the very earliest stromatolite-like structures as being biogenic in origin is controversial. Martin Van Kranendonk tells the story of the discovery of almost pristine stromatolites in 3.48-billion-year rocks of the Pilbara of Western Australia. By meticulous study of their structure, relationship to their geological environment, and chemical and isotopic composition, he establishes a convincing case for life on Earth going back at least as far as the age of these Pilbara rocks. In the image, Martin Van Kranendonk is on one of the main stromatolite outcrops in the Pilbara , looking down on the tops of multiple cone-shaped stromatolites of the 3.4 Ga Strelley Pool Formation, only slightly younger than the 3.48 Ga Dresser Formation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/865777cc-74f4-4319-8f3a-35304be3e8b6/Sujoy_MassSpecFix.JPG Early earth - Sujoy Mukhopadhyay on Probing the Hadean World with Noble Gases In a recent episode, Nadja Drabon spoke about newly discovered zircon crystals from the late Hadean and early Archean. The zircons revealed information about processes occurring in the Earth’s nascent crust, casting light on when and how modern-day plate tectonics may have started. In this episode, we talk about a very different source of information about the early Earth, namely the abundances of noble gases occurring within present-day basalts. It turns out that these can probe the Earth’s mantle and atmosphere even further back in time – to the first 100 million years of Earth history. Sujoy Mukhopadhyay leads a team of researchers who have developed new techniques for measuring the abundances of noble gas isotopes in a variety of Earth materials. He used his results to identify mantle reservoirs that formed during the first 100 million years of Earth history and, amazingly, survive to the present day. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/14dafb73-4272-40c0-8022-443513b99ba4/ND+Cropped.jpg Early earth - Nadja Drabon on a New Lens into the Hadean Eon Vanishingly few traces of the early Earth are known, so when a new source of zircon crystals of Hadean age is discovered, it makes a big difference to what we can infer about that eon. In the podcast, Nadja Drabon describes how she analyzed the new zircons she and her colleagues discovered and what they reveal about the Earth’s crust between about 4 and 3.6 billion years ago. Nadja Drabon in the Green Sandstone Bed in South Africa https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a3c03dfa-2f25-46c1-9674-34b5bd33fea1/MG+in+Iceland.jpg Early earth - Martin Gibling on Rivers in the Geological Record Rivers can seem very ephemeral, often changing course or drying up entirely. Yet some rivers have persisted for tens or even hundreds of millions of years, even testifying to the breakup of Pangea, the most recent supercontinent, about 200 million years ago. In the podcast, Martin Gibling talks about rivers old and new, and how they are affected by tectonic processes over tens of millions of years, as well as by human activities over a few thousand years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6d762726-0034-4721-b91d-57886492fc1c/YouTube+talk.JPG Early earth - Bob Hazen on the Evolution of Minerals During the course of Earth history, new types of rock have appeared on the scene as the Earth cooled and plates formed and started to move and interact in accordance with plate tectonics. The different rock types reflect the particular assemblage that composed them, and each tectonic environment favors the formation of a particular rock type, such as granite or basalt. But what about the minerals themselves? Have they been present since the Earth formed, or did they, too, only appear when certain conditions were met? In the podcast, Bob Hazen discusses mineral evolution, which turns out to be fertile ground for probing the deep history of Earth. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c7bc249-0cec-4785-9c2f-a31f7ac5c93a/FB+pic.jpg Early earth - Rick Carlson on Probing the Early Solar System Almost all the evidence about the nascent solar system has been erased by processes accompanying the formation of the Sun and the bodies that formed out of the circumsolar disk about 4.6 billion years ago. But some meteorites and the tiny dust grains contained within them have anomalous compositions that can be understood only by invoking a history going back to the giant molecular cloud progenitor of the solar system, and to the stars that ejected the material that formed the cloud. Rick Carlson is an isotope geochemist who measures such anomalies and uses them as clues to the birth of the solar system. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1635005983198-ULIRJ8OPJBYML20P69J3/thumbnail_Peter+Cawood+5443m+%281%29.jpg Early earth - Peter Cawood on When Plate Tectonics Started We know that the Earth was formed as a ball of molten material and quickly differentiated into a metallic core and a rocky mantle. We also know that at some point, the Earth’s surface formed itself into the rigid blocks we call plates, and that these plates started moving and interacting as part of a global process we call plate tectonics. But when was this point reached? Peter Cawood explains how five quite different types of evidence preserved in the geological record all point to the same answer. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1621997195912-VZ91LHKB0T3N9K0KAXUQ/CJ+close+crop.jpg Early earth - Claude Jaupart on Whether the Earth is Cooling Down The Earth is losing heat. Claude Jaupart wants to know how much, and so he has measured the heat flowing up through the top layers of the crust by making measurements down hundreds of boreholes. But the Earth continues to generate heat through radioactive decay of elements such as potassium, uranium and thorium. He calculates that for the past two billion years at least, the radioactive heat generation has not kept up with heat loss, and that the Earth is therefore cooling down - though at the extremely slow rate of 100 °C over a billion years. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1618882775696-MMULJBZF8YIVNL5WYJSP/102209_Compression_141.jpg Early earth - Sarah Stewart on a New Scenario For How the Moon Formed Sarah Stewart uses computer-based dynamical simulations and lab experiments to create scenarios for the collision of a massive body with the Earth that can reproduce the composition, orbits, and spins of the Earth and Moon today. She believes a new kind of object called a synestia formed in the immediate aftermath of such a collision. Here she is in her lab with an instrument that can generate very high temperatures and pressures in a target to simulate conditions after the impact. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1616613115290-YSMWS8CUWI1BIQPA1JJG/DE+in+VT.jpg Early earth - David Evans on Supercontinents David Evans is a tectonic jigsaw puzzle-master. Using a wide diversity of geological clues, he reconstructs the supercontinents into which almost all of the Earth’s landmasses were joined at various points in Earth history. His own observational work focuses on magnetism imprinted in ancient rocks, which can tell us the latitude at which these rocks formed. To measure these magnetic signals, he has a specialized paleomagnetism lab at Yale. Courtesy of Saran Morgan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600442430600-9LFL6JLCCUNYZQJ8OXMD/JV+with+the+SIMS.jpg Early earth John Valley using the ion microprobe at the University of Wisconsin in Madison to date a zircon crystal, with Takayuki Ushikubo and Noriko Kita. Photo courtesy of John Valley https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1600456890390-2K5Z62GRZ1W770B41DVR/Sara+Russell+cropped.jpg Early earth - Sara Russell on What the Asteroids Can Tell Us About the Earth The asteroid belt is a region lying between the orbits of Mars and Jupiter that contains billions of asteroids, ranging from some as small as pebbles to as large as nearly 1000 km across. Sara Russell explains how we can use asteroids to help us unravel how the solar system formed and to cast light on questions such as how the Earth got its water and organic materials. Photo courtesy of Tammana Begum https://www.geologybites.com/home-2-1 daily 0.75 2025-01-09 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3eed1046-49a4-4779-8c9f-fd7ff4645f14/Richard+Fortey.jpeg Home-2 (Copy) The Earth is about 4.5 billion years old. How can we begin to grasp what this vast period of time really means, given that it is so far beyond the time scale of a human life, indeed of human civilization? In the podcast, Richard Fortey talks about how we came to a realization of deep time, how we have attempted to tame it, and how it has changed our conception of the primacy of humankind in Earth history. https://www.geologybites.com/home-3 daily 0.75 2025-01-09 https://www.geologybites.com/isabel-montanez daily 0.75 2025-03-08 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7c502c01-2b69-42d4-8c6b-3d03797eb2f0/IMG_6188.jpeg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5ca96e15-8f25-4b49-a57b-0c7423a85389/Slide+1+overview+of+paleo+CO2+proxies.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f4b9335f-d581-406c-8a33-73b3135ad681/Slide+2+-+stomata+explanatory.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21cfda2c-28a6-432e-997d-96352b12d19c/Slide+4+-+seawater+density+and+temp+modeled.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0582a70e-15b5-49b9-bf30-3167c57333a4/Slide+4+-+modeled+sea+ice+for+low+and+high+CO2+levels.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/526192e5-dbcb-46eb-bcd9-11a40f84363b/Slide+7+-+measured+CO2+levels.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ea199e7a-e70b-4e59-b4ee-180c0ffd4bf1/SLide+6+-+time+since+water+contact+with+surface.png https://www.geologybites.com/ruth-siddall daily 0.75 2025-02-19 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd6910a9-ffd7-4c72-96b7-999a139b8a43/RS.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fd7b1acd-2c52-46ae-a0ec-d7a917895da8/The+Monument+1.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e94f83fd-d606-4785-b872-8669f461d497/Jura+Limestone+fossils+1+Plantation+Place.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6b413f51-00d6-4ba9-9f87-14db47905a62/Jura+Limestone+fossils+3+Plantation+Place.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d71d4ffc-cbdb-4ddc-b0f3-9f3164c7a876/The+Monument+Portland+Stone.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0819d7d3-0378-44fc-948e-3856252fea8d/Jura+Limestone+fossils+2+Plantation+Place.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0dca48f3-0880-4d1a-9d53-fd08ec7fa0e2/Malta+Memorial+Fossils.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6bf6336d-a412-4955-bfa9-0b5187a2b317/MinsterCt.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3198a542-c12a-49c7-adc9-25b27191f296/MinsterCt-detail.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dae5c63a-de30-4cfe-96ac-f84f80226ab6/St+Paul%27s+Cathedral.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/36e9498d-d163-43f0-bc63-f28a96de83ba/Firenze%2C_piazza_san_giovanni_e_piazza_del_duomo_durante_il_lockdown_%282020%29.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/37b96961-a8c0-4f97-8b08-709b510fb5e2/Jura+Limestone+fossils+4+Plantation+Place.jpg https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/71489436-c0a9-4f24-8f88-e6df50e8c833/Malta+Memorial.jpg https://www.geologybites.com/ruth-siddall-1-1 daily 0.75 2025-04-15 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/71b282fe-4bd7-41c5-845b-7bea8dac4596/walking+tour+1.jpg Ruth Siddall 1 In the podcast, Ruth Siddall explains the kinds of geology on display in the building stone of cities and takes us on one of her favorite urban geology walks in London. She has developed nearly 50 urban geology-themed walks and built up a database of over 4,300 urban localities of geological interest. Siddall is a postdoctoral researcher at Trinity College, Dublin, studying the social history and geological provenance of stone in 18th century buildings in Britain and Ireland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bb292a50-217e-4bb9-aaee-b4a6e49a5203/St+Paul%27s+Cathedral.jpg Ruth Siddall 1 St. Paul’s cathedral in London, completed in 1710, was built with Portland Stone. There is a rich archive documenting architect Christopher Wren’s ordering of Portland Stone from the quarries. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/06e694dc-58f4-4f11-8b3d-bfb04edf2b71/Firenze%2C_piazza_san_giovanni_e_piazza_del_duomo_durante_il_lockdown_%282020%29.jpg Ruth Siddall 1 Santa Maria del Fiore Cathedral and Baptistry. Brunelleschi kept good accounts of the sourcing of the Pietra Serena sandstone used to build the dome. Decorative white marble was sourced from Carrara and Pisa, pink limestone came from Verona and other locations in Tuscany, and green serpentinite came from Prato. Photo: Sailko https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7e3f386b-a4bb-47d4-b318-1be7e774e58a/Florence+Duomo.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f9e185f8-8eea-43b2-b791-8ad1b772e529/The+Monument+1.jpg Ruth Siddall 1 - Make it stand out Monument commemorating the Great Fire of London of 1666, which started close to this site and raged across the City for the next three days. The main building material is Portland Stone, the stone chosen by Christopher Wren and his fellow architects to rebuild London in a monumental style. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9c5cc2cc-2081-4630-bc90-3347f936b462/The+Monument+Portland+Stone.jpg Ruth Siddall 1 - Make it stand out Portland Stone has a long history of quarrying, but only came into mainstream use following the Great Fire. It is quarried from the Isle of Portland on the Dorset Coast from the uppermost strata of the Jurassic succession. There are a number of varieties of Portland Stone, but this is the most frequently used, called Whitbed. It is a pale grey limestone with scattered fossils, mainly the oyster-shell species Liostrea. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/39698abe-b54d-4d07-ab32-5eb98ab7b434/Jura+Limestone+fossils+1+Plantation+Place.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3dd7e064-f504-4ea8-a65d-92e6171aff59/Jura+Limestone+fossils+2+Plantation+Place.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9d4156da-4731-416e-af04-404eb86d56e7/Jura+Limestone+fossils+3+Plantation+Place.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/76b2e8ef-a501-4b43-9940-e91226b5891e/Jura+Limestone+fossils+4+Plantation+Place.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/241c282c-13a0-4735-9bb5-8c006fc2bc06/10-Minster-Court-2013-01-30-2000x1333.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eb056332-f264-43ee-8fc4-cd79e04b0511/MinsterCt-detail.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02791379-3f8e-4971-ad1a-83045ba9ce1f/24+Gt+Tower+St.jpg Ruth Siddall 1 - Make it stand out The igneous plutonic rocks at 24 Great Tower Street. Left: Dark Shap Granite 9 (field of view 12 cm), with its distinctive, brick-shaped, pink, K-feldspar phenocrysts is from Shap Fell in Cumbria and is just under 400 million years old. The groundmass is made up of orange K-feldspar, grey quartz, plagioclase, and biotite. Center: Bon Accord Red (field of view 12 cm ), quarried near Uthammar on the Kalmar Coast of Sweden, is composed of large crystals of brick-red K-feldspar with grey quartz and black biotite. This is a variety of rapakivi granite, intruded during the same magmatic phase as the Baltic Brown Wiborgite seen at our first location. This red granite lacks the ovoids and is the variety of rapakivi granite called pyterlite. It was intruded as part of a suite of granitoids in the Baltic region, known generically as the ‘Coastal Reds’ by stone workers. This variety comes from the Figeholm Granite, intruded at ~ 1.4 Ga. The name ‘Bon Accord’ is an allusion to the fact that these granites were shipped direct from the quarry to Aberdeen where they were cut, shaped, and polished. ‘Bon Accord’ is Aberdeen’s motto. Right: Labrador Antique (field of view 8cm) anorthsite composed of 90% calcium-rich plagioclase with crystals that flash shades of peacock blues. This phenomenon, called ‘schillerescence,’ can appear in many plagioclase feldspars, but is well-developed here. Texturally the stone here most resembles a variety from Norway that is (confusingly) called Labrador Antique. It is 930 million years old and is quarried from the Rogaland Igneous Province at Sirevag near Stavanger. In addition to the schillerescence, a distinctive texture is the bimodal grain size with larger grains up to a centimeter or more across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4de298a9-8ee5-4fd0-b347-eba19fbc765a/Malta+Memorial.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4ddf0e83-53c2-4d13-90f2-685ecb6ee6e2/Malta+Memorial+Fossils.jpg Ruth Siddall 1 - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/30e7ae3d-28d1-40ad-bb6b-d30e1e116a0d/Portland+Reef.jpg Ruth Siddall 1 - Make it stand out In the podcast, Siddall mentions several different facies of Portland Stone. This less common reefal facies seen at Caxton House in Westminster is hard to view in the field but well displayed here. It consists of carbonate rocks that are formed from the skeletons of reef-building organisms and lime mud. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8d2fe519-5980-4f58-a85b-5cc6dff019bf/Park+Lane+Hilton.jpg Ruth Siddall 1 - Make it stand out A garnet porphyroblast showing top-to-the-right sense of shear is visible at the Hilton Hotel in Park Lane. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c08d6fa9-db37-4aa1-973e-c9100936af85/Tower.jpg Ruth Siddall 1 - Make it stand out The Tower of London along with some churches are the only buildings that survived the Great Fire of London in 1666. The stone used in medieval construction was mainly Kentish Ragstone, a Cretaceous hard grey limestone from Kent. 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https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4dea8535-f662-49e7-949d-bf10b826ae1c/slide+11.png https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e30956b3-1c3d-46b5-ae62-1872244e3c53/slide+14.png https://www.geologybites.com/folarin-kolawole daily 0.75 2025-06-04 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0236fd8c-3b4d-42fb-846f-1215cc84ccf9/P5170560_edit.jpg Folarin Kolawole From East Africa to southwest USA, many regions of the Earth’s continental lithosphere are rifting. We see evidence of past rifting along the passive margins of continents that were once contiguous but are now separated by wide oceans. How does something as apparently solid and durable as a continent break apart? Kolawole is especially interested in the early stages of rifting, and in his research he uses field observation, seismic imaging, and mechanical study of rocks. He is Assistant Professor of Earth and Environmental Sciences, Seismology, Geology, and Tectonophysics at the Lamont-Doherty Earth Observatory of Columbia University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/abf75839-3ff8-4c86-b166-63d26741277d/map+of+rift+locations.jpg Folarin Kolawole - Make it stand out Locations of active continental rifts with their extension velocities. In the podcast, Kolawole focuses on the East African rifting that extends from the northeast corner of the continent down to Malawi and Botswana. Kolawole explains why he thinks the rift, though only in its early phase today, will continue to stretch and eventually lead to a full continental breakup. Heckenbach, E.L. et al.(2021), Geochemistry, Geophysics, Geosystems 22, e2020GC0095777 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f60a71f8-da9f-466d-abc5-a05e8eca2012/Fig.+9+Grant+et+al..jpeg Folarin Kolawole - Make it stand out Cartoons illustrating the early phases of continental rifting described in the podcast. (a) Rift nucleation phase: diffuse faulting with faults lengthening as they exploit weaknesses in the crust. This results in the exponential distribution of fault lengths shown in the plot. Note, the plot is on a log-log scale. (b) Stretching phase, during which border faults are established and strain is distributed across the intra-rift faults and large border faults. (c) The maturation phases of rifting during which strain migrates to the rift axis. The faults become linked and lengthen. Grant, C. et al. (2024), Earth and Planetary Science Letters 646, 118957 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1064bbae-8dcd-48ec-8b04-c39581619900/slide+2.jpg Folarin Kolawole - Make it stand out Diagram of the driving forces, resisting factors, and weakening processes that accompany rifting. In the podcast, Kolawole points out the importance of pre-existing zones of weakness in a continent in determining where rifting initiates. The block diagram illustrates a preexisting shear zone (1) that can determine a rift location and also break a rift into segments (2). Faults and shear zones (3) can weaken the crust as can necking and thermal weakening (4). Shallow intrusion of melt (5) as well as alteration of the rock (6) can also cause weakening. Outside forces caused by erosion (7) and sedimentation (8) also promote long-lived faulting. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0b146fea-c560-4a20-8719-eceb48674957/Tomogram+of+plume+5g.jpg Folarin Kolawole Seismic tomography cross-section of the mantle below Africa along the plane indicated by the red line in the inset map. Red indicates slower seismic wave speeds, which is interpreted as indicating warmer material. The section suggests a wide swathe of warmer mantle that impinges on the mantle-lithosphere boundary below northeast Africa. This is suggestive of the presence of a mantle superplume, which Kolawole describes as a driver of the East-African rift system that is likely to ensure the rift continues and eventually causes the continent to split apart on either side of a newly forming ocean. Boyce, A. et al. (2023), Geochemistry, Geophysics, Geosystems 8, e2022GC010775 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a79b32af-f9c2-474b-99b2-df896b097671/Volcanism+Brune+et+al+2023.jpg Folarin Kolawole - Make it stand out East African Rift volcanic fields (shaded grey) and major volcanoes (triangles). Brune, S. et al. (2023), Nature Reviews Earth & Environment https://doi.org/10.1038/s43017-023-00391-3 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0276054d-5da9-4631-ab29-305604ae133a/Plume+visualization+Brune+et+al+2023.jpg Folarin Kolawole Schematic representation of the mantle plume location beneath East Africa on the basis of seismic tomography. Plume structure at depth is consistent with the distribution of volcanism shown at left. Brune, S. et al. (2023), Nature Reviews Earth & Environment https://doi.org/10.1038/s43017-023-00391-3 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c285412e-5d36-4e8b-8fcd-3ff019fc34a3/Rift+and+cratons.jpg Folarin Kolawole In the podcast, Kolawole explains that rifts preferentially occur along weaknesses in the lithosphere inherited from previous rifting episodes, and that rifts tend to skirt around hard, old cratonic regions. The map shows the location of recent rifting (pink) and Permo-Triassic rifting (yellow), and how they both avoid cratons, in this case the Tanzania craton and the Niassa craton. Brune, S. et al. (2023), Nature Reviews Earth & Environment https://doi.org/10.1038/s43017-023-00391-3 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/98f53fb6-000a-4450-87f9-379c8e3f076a/Nsanje+graben.jpg Folarin Kolawole East African rift in southern Malawi showing the Nsanje fault, which is at the western boundary of the graben that runs along the rift axis. Kolawole, F. et al. (2025), Extensional Tectonics: Rifting and Continental Extension, Geophysical Monograph 278, First Edition https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5f2546f1-f31e-4281-9fa3-af1fdcf66428/Afar+%28David+Ferguson%29.jpg Folarin Kolawole Widespread faulting at the rift axis in the Afar region of northern Ethiopia. David Ferguson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6eb6cac8-301d-4bb1-9086-fc56b44d3d6b/After+volcanism.jpg Folarin Kolawole - Make it stand out June 2009 volcanic eruption in the Afar region. David Ferguson https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58886756-c155-4884-9e3c-489d118501cf/crevicwe.jpg Folarin Kolawole Crevice formed in the Afar region during a sequence of large earthquakes in 2005 triggered by injection of magma into the shallow crust. Lorraine Field https://www.geologybites.com/renee-tamblyn daily 0.75 2025-07-16 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bbc137f0-b773-43a8-9396-79154e7df3df/RT+closeup.jpg Renee Tamblyn In the podcast, Renée Tamblyn explains how we think the first continental lithosphere formed. In her own research, she has focused on the critical role played by water released from hydrous minerals that formed within oceanic lithosphere on the sea floor. She is a Postdoctoral Researcher at the University of Bern. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1964c2e5-478c-4407-9410-281a3fda149f/hot+Hadean.jpg Renee Tamblyn Conventionally, researchers have believed that the Hadean was hot with magma oceans, floating “rockbergs,” and meteor bombardments. The Moon’s orbit was closer to the Earth, and there was a dense steam atmosphere. Courtesy of Chesley Bonesal https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf04b6f5-3600-419b-84c9-2dc080b56b0d/cool+Hadean.jpg Renee Tamblyn Now, some researchers think the Earth cooled rapidly in the Hadean. The image depicts liquid water oceans and a basaltic shield volcano. The first lithosphere to form was probably similar to today’s basaltic oceanic lithosphere. Silicon-rich, continental lithosphere did not appear until the Archean, hundreds of millions of years later. Courtesy of Don Dixon https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/89fb0af1-eca9-41e6-be81-adbb731cc9bb/Archean+cratons.jpg Renee Tamblyn - Make it stand out Map of the Archean cratons. In the podcast, Tamblyn explains that the earliest continental blocks that survive to the present day are the Archean cratons. While the map suggests that they make up much of the continents, most are hidden beneath sedimentary cover or ice. Hasterok, D. et al. (2022), Earth-Science Reviews 231, 104069 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5c60b054-0d48-4c2f-9b21-5d66ef70fc03/Acasta.jpg Renee Tamblyn Sample of the Acasta gneiss, the oldest known rock (4.03 billion years old). It is a deformed tonalite-granodiorite and formed as a member of the type of intrusive rock discussed in the podcast. These formed the bulk of the early continents — the tonalites, trondhjemites, and granodiorites (TTGs). Chip Clark/Smithsonian Institution National Museum of Natural History https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/033a2f5d-aae0-4be2-bf4f-8ff8984bf909/pillowed+komatiite.jpg Renee Tamblyn 3.4-billion-year-old pillowed komatiite from the Barberton Greenstone Belt, South Africa. As Tamblyn explains in the podcast, komatiites are lavas that are extremely rich in magnesium. Pillows form when lava is erupted into water as the hot lava forms blobs and nodules that are quickly quenched by the cooler water. This provides strong evidence of an ancient sea floor. The rectangular magnet is 3 cm in length. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/177b52c3-6209-49bf-9ca7-eec2819f8094/QAP.jpg Renee Tamblyn In the podcast, Tamblyn explains that the oldest preserved continental rocks comprise a suite of intrusive rocks that are rich in silica, sodium, and calcium, but poor in potassium. These are tonalites, trondhjemites, and granodiorites (TTGs). In terms of their mineral content, TTGs contain abundant quartz and plagioclase, but little alkali feldspar. Shown at right is a ternary diagram of plutonic rock types classified according to their quartz (Q), alkali feldspar (A), and plagioclase feldspar (P) content. Tonalites and granodiorites populate the right center of the triangle. Trondhjemites are a variety of tonalite in which the plagioclase is mainly in the form of sodium-rich oligoclase. The numbers along the edges indicate percentages of quartz (left and right edges) and plagioclase (bottom edge). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ab28b591-3c48-4b30-a13f-caa2ce3276b8/TTG.jpg Renee Tamblyn When rocks undergo partial melting, they separate into lighter-colored leucosomes and darker melanosomes. The leucosomes then segregate themselves from the unmelted rock and, when they cool, form rocks containing predominantly plagioclase feldspar and quartz, i.e., TTG in composition. In the migmatite shown here, these melts have been frozen during their escape of the parent rock. The parent rock was a metamorphosed basalt containing garnet and amphibole. Kendrick, J. et al. (2024), Journal of Petrology, 65, egae066 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4f1d0214-722f-4a3f-9cf7-9d1410153616/Kaapvaal+craton.jpg Renee Tamblyn - Make it stand out Kaapvaal Craton, South Africa. The hills are formed of TTGs , which dominate the geological record of the craton. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8deada39-c8ca-4005-8d6b-b2d188f8aeba/Kaapvaal+craton-2.jpg Renee Tamblyn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9fdbf9f5-93cd-475d-81ac-ff53b77235b7/draweing.jpg Renee Tamblyn Hypothetical cross section of the mantle and crust in the Archean showing eruption of komatiites in an oceanic plateau (later to become preserved as a greenstone belt) and the formation of TTGs, forming the continental crust. Blue arrows indicate the uptake and release of water from hydrous phases in the komatiites (green). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/128c5e4c-a384-4e19-9279-8bc3db582977/cont+crust+over+time.png Renee Tamblyn Graph showing the amount of continental crust over time as predicted by different crustal growth models with time advancing to the left. The models use a variety of different methodologies and approaches and differ widely in their predictions. As Tamblyn says in the podcast, the timing of continental crust formation is one of the big unsolved problems in Earth science. Korenga, J. (2018), https://doi.org/10.1098/rsta.2017.0408 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/68353b98-15c5-4bda-a155-c29e97b55f5a/Losty+City.jpg Renee Tamblyn - Make it stand out Lost City hydrothermal field on the Mid-Atlantic Ridge, at approximately 2,000 meters (6,562 feet) in depth. As Tamblyn explains in the podcast, methane-producing Archaea survive here, powered by molecular hydrogen produced by oxidation reactions in the underlying ultramafic rocks (peridotites) that make up the upper mantle. Courtesy of Schmidt Ocean Institute https://www.geologybites.com/andreas-fichtner daily 0.75 2025-07-23 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f38ca7f9-804e-47f2-9033-5afb7f12e068/Andreas+Fichtner_LOWRES_010_20230905.jpg Andreas Fichtner In the podcast, Andreas Fichtner describes the state of the art in seismic imaging. Despite enormous improvements in our capabilities over the past decades, there are still many structures and data types that remain elusive. Fichtner explains the various types of challenges faced by researchers seeking to sharpen our images of the Earth’s interior from seismic data. While some challenges appear insurmountable, others are gradually yielding to improved methods and computational power, and we can expect to see continual improvements over the next decade. Fichtner is a Professor in the Department of Earth and Planetary Sciences at the Federal Institute of Technology in Zurich. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b4be1172-3c2d-490c-ad34-9203e75e19f5/breat+-+Earth.png Andreas Fichtner As Fichtner explained in the podcast, although the absolute size of the resolvable structures is much smaller in the case of medical ultrasound, the relative resolution of seismic images is better than that of ultrasound. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8a07eda1-7244-4975-a2a4-57a9944232ad/Tohoku.jpg Andreas Fichtner - Make it stand out Seismic recording of S-waves (body waves) from the Tohoku earthquake that struck on March 11, 2011. The recording was made at the Black Forest Observatory in Germany, 83.3 degrees of latitude west of the earthquake epicenter. The body waves arrive first as they travel faster than the surface waves. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/951190fe-f8a1-47cf-893e-96e4d11a99f8/phases.png Andreas Fichtner Each wave travels along a different path through the Earth and therefore “sees” a different part of the Earth. The diagram shows a section of the Earth with the simulated earthquake at left. The illustrative P-waves are shown in red and S-waves in green. The ray-path designations describe the wave type and its journey through different layers. P = primary wave; S = secondary wave; K = P-wave that travels through the earth’s outer core; c = reflection from the core-mantle boundary. Thus, for example, an ScP designation refers to an S-wave traveling toward the center of the Earth, reflecting off the outer core, and converting to a P-wave that travels upward. For illustrative purposes, S-waves propagating from the simulated earthquake are shown in the top hemisphere, and P-waves are shown in the bottom hemisphere (though some of them are then converted into S-waves). Brian Kennett https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ba9f1634-a93e-4e03-acf6-46d7d709239b/Earthquakes.jpg Andreas Fichtner - Make it stand out Locations of the 2,366 earthquakes whose seismic waves were used in the model. The colors indicate how often an event was incorporated into an iteration, which ranges from 1 to 99. One of the factors used to determine the frequency with which an earthquake is included is how distinctive the earthquake is in relation to the others. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1c45addc-ecd9-44e6-aa9c-e9c4c202ca23/seismic+stations.jpg Andreas Fichtner - Make it stand out Locations of the 27,879 seismic stations used in the model. Colors indicate the number of earthquakes recorded by each receiver. Stations with fewer than 200 event recordings are shown as small black dots. The legend for the colored dots is shown by the bar below the map. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5fc0ae9b-dfe3-4e96-9af4-a26cd81b68a5/100+km.jpg Andreas Fichtner - Make it stand out Horizontal slice at a depth of 100 km showing relative variations in the speed of vertically polarized S-waves (Vsv). The mid-oceanic ridges in the Atlantic and South Pacific show up prominently, as do hot-spot regions with active volcanism, such as Hawaii (H), Iceland (I), the Canaries (C), and La Réunion (R). The model also shows the contrast between the old, cold cratons and hot spots in Africa. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/916a2906-4a6e-4a15-be8c-64b499633040/200+km.jpg Andreas Fichtner - Make it stand out At a depth of around 200 km, subducting slabs come into sharper focus. The figure shows several of these, including the Nazca (N), Cocos (Co), and Caribbean (C) slabs, as well as the almost-continuous subduction of the Pacific plate (PP) beneath its neighboring plates toward Asia and Oceania. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d0804751-5d85-4c64-a00b-27a0550a51b7/400+km.jpg Andreas Fichtner - Make it stand out The slice at a depth of 400 km reveals the subducting slabs that have advanced deeper into the mantle along the direction of subduction. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/273a5378-29e5-44b7-a443-f43845ac5230/2800+km.jpg Andreas Fichtner - Make it stand out Close to the core-mantle boundary at 2,800 km depth, the slice shows the large-low-shear velocity provinces. These play an important role in our understanding of mantle dynamics and heat transport and are discussed in the podcast episode with Allen McNamara. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6d0c0f32-6e91-4cbb-aa6c-a93773829379/sections.jpg Andreas Fichtner - Make it stand out Comparison of cross sections of REVEAL with two earlier global tomographic models — GLAD M25 (Lei et al., 2020) and SEMUCB WM11 (French and Romanowicz, 2014). The geographical locations of the cross sections are indicated by the lines connecting colored dots on the globe, which correspond to the colored dots at the top of each section. The comparison shows how REVEAL produces sharper images, and hence cross sections than its predecessors. This enables us to place tighter spatial and temperature constraints on mantle features such as subducted slabs, the low-velocity region below east Africa, and (below) the Iceland plume. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cf7576bd-5f72-4615-8c24-8b8eb111c2e3/iceland_REVEAL_64.4_-17.4_300.0_map+14.56.59.png Andreas Fichtner - Make it stand out REVEAL cross section of Iceland plume. The location of cross section is shown on the map above, and the section down to the core-mantle boundary is shown at right. As Fichtner pointed out in the podcast, the Iceland plume is the only such structure that appears in all the tomographic models, while we have not yet been able to consistently image other suspected plumes, such as the one below Hawaii. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9274a804-795e-41e1-bbdf-2a6ba8272e0e/iceland_REVEAL_64.4_-17.4_300.0_slice+14.56.59.png Andreas Fichtner - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0482c06b-5284-41c5-9e66-24c8aa3f0a51/Fiber+1.jpg Andreas Fichtner - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0ae90b24-a24e-4d2c-bbe7-455ee4f155f3/Fiber+2.jpg Andreas Fichtner - Make it stand out Fiber-optic cables include defects (*) that backscatter light passing along the cable. By measuring the round-trip travel time of light from the source to the defect and back using a laser interferometer, the distance to the defect can be calculated. When a seismic wave deforms the cable, there is a slight but detectable change in the travel time of the light to the defect, enabling the displacement caused by the seismic wave to be determined. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fe9a734c-c2d4-49a5-9e9b-0334e07a0f9b/volcano.jpg Andreas Fichtner - Make it stand out Fichtner and his team used a 12-km-long fiber-optic cable around and within the caldera to obtain high-resolution seismic data from Iceland’s most active volcano. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eae45da8-fdf2-4e30-99f2-b28c9960dd86/volcano-1.jpg Andreas Fichtner - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/19bd66d8-7063-48a6-a05b-0b1860a2bc7c/volcano+3.png Andreas Fichtner - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/48665bc9-b072-44d4-8006-61d4735a529e/micrquakes.png Andreas Fichtner Fiber-optic data obtained during an eruption of Grimsvöten. This revealed about 1,000 small earthquakes a week, about 100 times more than the regional seismometer network was able to detect. This enabled the dynamics of the eruption to be monitored with much higher spatial resolution than was previously possible. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ee3bec20-92d0-4af2-9dc5-a8d5cd0448e4/Greenland+ice+sheet.jpg Andreas Fichtner - Make it stand out The Northeast Greenland Ice Stream is the largest ice flow in Greenland and transports 12 percent of Greenland’s ice flow to the sea. In the first experiment of its kind, Fichtner and his team laid a 1,500-m-long fiber-optic cable down a borehole in the ice. They then made a 14-hour continuous recording of the cable deformation. This revealed the presence of over 100 microquakes in less than a second. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6da1311e-0489-47ca-86ec-6770822a87ee/ice+flow.jpg Andreas Fichtner - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/db6e2685-6145-4c17-ba62-1e3911581e58/borehole.png Andreas Fichtner - Make it stand out 1,500-m-deep borehole in the ice. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3593b664-ae03-46b6-b5a7-4860d999f333/laying+fiber.png Andreas Fichtner - Make it stand out Inserting the optic fiber into the borehole. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d7be86e8-211c-4fe0-bcce-e0115e1722ec/ice+quakes.jpg Andreas Fichtner - Make it stand out The results of Fichtner’s experiment show that hundreds of micro ice quakes occur within the space of a couple of seconds. The quakes are probably triggering each other in a kind of domino effect extending for hundreds of meters. It had previously been thought that such ice streams flowed like a viscous fluid. Instead, this experiment showed that they move in a rapid stick-slip motion. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/92bbe4e3-efcd-4448-962c-1bd7566f43bd/Fig+1.jpg Andreas Fichtner Map of the Long Valley Caldera, California study area showing the fiber-optic cables (green lines), seismic stations (blue triangles), and earthquakes (red dots). The black dashed line delineates the limit of the caldera. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dac8856d-d24e-443c-92b2-5c9a5fe189b2/Biondi+Fig+2.jpg Andreas Fichtner - Make it stand out A fiber-optic cable was used to record earthquakes and seismic signals with much higher temporal and spatial resolution than was previously possible. Here, two fiber-optic cables covering an approximately 100-km north-south transect across the Long Valley Caldera in California. The panels on the left display S-wave anomalies from the initial model derived from the seismic-station data, while the panels on the right show the S-wave velocity anomalies obtained using the fiber-optic-cable data. The depth of the slices in the top panels is 1 km. The caldera and the extent of the lakes are shown by the black dashed lines. The panels in the 2nd and 3rd rows show model cross sections along the lines AA’ and BB’ indicated in the map shown above. The fiber-optic-based model shows a clear improvement in resolution as compared to the initial model. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5bfb92a5-dff0-4955-a3c7-c9a3ded77c29/Biondi+Fig+3.jpg Andreas Fichtner - Make it stand out Sections showing the ratio of the P-wave velocities to the S-wave velocities along the sections AA’ and BB’ shown in the map above. The red dots indicate earthquakes occurring within 10 km of the cross sections. The fiber-optic-derived images highlight a definite separation between the shallow hydrothermal system and the large magma chamber located at ~12-kilometer depth. The combination of the geological evidence with these results enabled the researchers to determine the origin of the seismicity in the caldera. They concluded that fluids exsolved through second boiling provide the source of the observed uplift and seismicity. https://www.geologybites.com/cees-van-staal daily 0.75 2025-08-18 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0c614ae8-b297-43f0-878c-6347c344a933/van+Staal.jpg Cees Van Staal In the podcast, Cees Van Staal tells us about the Paleozoic tectonic events that led to the formation of the Appalachians. The events are closely related to those involved in the Caledonian orogeny and the mountains it created in what is now Ireland, Scotland, east Greenland, and Norway. However, the Appalachians that we see today are not the worn-down remnants of the Paleozoic mountains. Instead, they reflect much more a topography that was created during processes associated with rifting and magmatism that accompanied the opening of the Atlantic Ocean, as well as the effects of the ice ages as recently as about 10,000 years ago. Van Staal is Emeritus scientist at the Geological Survey of Canada and an Adjunct/Research Professor in the Department of Earth and Environmental Sciences at the University of Waterloo in Ontario. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bb67464e-85a6-4882-9a28-8d90da610858/early+cambrian+reconstruction.jpg Cees Van Staal Reconstruction of continental plate locations in the early Cambrian. The terranes that later rifted away from Gondwana and accreted to Laurentia as part of the Appalachian/Caledonian orogeny include Ganderia, Avalonia, and Meguma, which is not shown but forms part of Armorican Terrane Assemblage (AMT), which is sometimes called Cadomia in other paleogeographic reconstructions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/858b2e35-9220-42b5-89b8-1cb1c2a5e5ca/plates+at+445+Ma.jpg Cees Van Staal - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f9bb16de-c357-4010-abaf-02aff37ce632/plates+at+400+Ma.jpg Cees Van Staal - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a96a734-706e-4791-9fe7-e7fc9de9d58d/slide+1.jpg Cees Van Staal - Make it stand out Diagrammatic cross sections of the Laurentian margin and adjacent terranes in New Brunswick during the Silurian Salinic and Devonian Acadian orogenies, which followed earlier accretion of arc terranes during the Ordovician Taconic orogeny. The Taconic orogeny was the result of the collision between Laurentia and a volcanic island arc system in the Iapetus Ocean. The Salinic and the Acadian orogenies involved the collisions of Ganderia and Avalonia, respectively, with Laurentia. The work of Van Staal and others has deduced that a very similar orogenic evolution is manifest in Newfoundland. Top: Arrival of Ganderia at the Laurentian margin, creating the Salinic orogeny. When the last vestige of the Iapetus Ocean was closed, this orogeny terminated, and the north-dipping Salinic slab broke off. Stepping back from the subduction zone behind accreted Ganderia lies an oceanic strait called the Acadian seaway where a subduction zone initiates closure of the Rheic Ocean. Bottom: Avalonia is pulled under the Ganderian margin by the north- and shallowly-dipping Acadian subduction zone. SCLM=sub-continental lithospheric mantle; MCS=Matapedia cover sequence; BBF=Bamford Brook fault. Figures by Van Staal; Wilson, R.A., Van Staal, C. et al. (2017), American Journal of Science 317, 449 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2b503f58-23c0-4590-90b8-16be603889a4/image001.png Cees Van Staal - Configurations of Laurentia, Baltica, and West Gondwana prior to the opening of the Atlantic Ocean. At a high level, this shows the relationship between the Caledonian orogeny in Greenland, Scandinavia, and the northern British Isles towards to north, and the Northern and Southern Appalachians to the south. The red dots mark locations where evidence for hyperextension (discussed in the podcast) has been observed. Configurations of Laurentia, Baltica, and West Gondwana prior to the opening of the Atlantic Ocean. At a high level, this shows the relationship between the Caledonian orogeny in Greenland, Scandinavia, and the northern British Isles toward the north, and the Northern and Southern Appalachians to the south. The red dots mark locations where evidence for hyperextension (discussed in the podcast) has been observed. BVBL, Baie Verte Brompton Line; FCL, Fairhead Clew Bay Line; HBF, Highland Boundary Fault; IAS, Iapetus suture; NR, Newfoundland re-entrant; QR, Quebec re-entrant; RIL, Red Indian Line; RP, Rockall promontory; SLP, St Laurence promontory; UA, Upper Allochthon. Van Staal, C.R. & Dewey. J.F. (2023), Journal of the Geological Society, London, Special Publication vol. 531 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bceca0d0-357a-4e55-aa6d-0c640d9f4088/Fig2.jpg Cees Van Staal - Make it stand out Reconstruction of the Appalachian-Caledonian Mountain belt between Newfoundland, Ireland, and Scotland before the Mesozoic opening of the Atlantic Ocean. The colored regions indicate the elements of the Taconic-Grampian Tract. For further explanation and depth beyond the scope of the podcast, see Van Staal and Dewey (2023) cited below and in the Further Reading section. Van Staal, C.R. & Dewey. J.F. (2023), Journal of the Geological Society, London, Special Publication vol. 531 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f7639787-3af5-49a7-a6d9-8465701fc812/Betts.jpg Cees Van Staal In the podcast, Van Staal mentions the obduction of ophiolites that took place as the terranes originating from Gondwana accreted to the Laurentian margin. This image shows the gabbro of the c. 490 Ma Betts Cove ophiolite, located on the eastern shore of the Baie Verte Peninsula in northwestern Newfoundland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cbc4be23-6ba0-49b8-9e4d-6f5b5fd4e50d/ca.+560+Ma+Birchy+Complex.png Cees Van Staal Ocean-continent transition rocks of the c. 560 Ma Birchy Complex, which is located on the Baie Verte peninsula. Van Staal is fourth from left. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/59b02166-91ac-4bfa-a9c1-54ba8ce8e0e6/490+Ma+Advocate+ophiolite.JPG Cees Van Staal Van Staal studying the rocks of the highly deformed basaltic and boninitic rocks of the c. 490 Ma Advocate ophiolite on the north coast of the Baie Verte peninsula. These are part of the the Baie Verte ophiolite complexes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ca3ae999-b970-4a94-89b2-d4321fb63069/CVS+on+rock.jpg Cees Van Staal The c. 478 Ma arc gabbro and associated tonalites that intruded into older Cambrian ophiolites. They form part of a volcanic arc that developed above these old ophiolites. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b8a79062-f1de-4940-9f04-a2422420b65e/xenoliths.jpg Cees Van Staal - Make it stand out Cambrian trondhjemite (a type of tonalite, which is a granitoid), including xenoliths of older basalt, which include boninite. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c2c79e88-aa42-41c5-86f6-c5c1e953539f/dike.jpg Cees Van Staal - Make it stand out Intrusion into the trondhjemite by younger c. 478 Ma mafic dykes. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d45523af-4899-45cc-8c6c-120e6fd8bc7b/DSC_0094.JPG Cees Van Staal - Make it stand out Coastal exposures of northern Newfoundland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ed175e90-b56d-4cf8-ab97-dfbd78b862bd/IMGP0100westport.JPG Cees Van Staal - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/claudio-faccenna daily 0.75 2025-09-20 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/26e8593d-a6cd-4e1d-a33c-ca8c37aba211/IMG_7179.JPG Claudio Faccenna Subduction zones can be very long-lived, persisting for tens or even hundreds of millions of years. During that time, they rarely stay still, but instead retreat, advance, move laterally, or reverse direction. In the podcast, Claudio Faccenna discusses the processes that govern these movements. It turns out that they depend not only on the properties of the subducting slab, but also on the environment, including the proximity of other subduction zones. Faccenna has been studying how convergent margins evolve for over 30 years, concentrating particularly on the Mediterranean region. He is Head of the lithospheric dynamics section at the Helmholtz Center for Geosciences at GFZ in Potsdam in Germany and also a Professor at the Department of Science at Roma Tre University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e447bd7b-481e-4243-953c-f77c004a7c93/Figure1.new.png Claudio Faccenna - Make it stand out Geodynamics of a subduction zone showing driving and resisting forces and the typical mantle flow pattern created by the descending slab (modified after Forsyth and Uyeda, 1975; Magni et al., 2024). Pull on the slab (Fnb) caused by the negative buoyancy of the subducting lithosphere is the main driving force of plate motion and is estimated to be about an order of magnitude greater than ridge push (Frp). Fnb stems from the increasing density of the lithosphere as it thickens and cools as it moves away from the spreading ridge. Another driving force is trench suction (Fts). Resisting forces (yellow arrows) include mantle drag (Rd.o), resistance at the subduction interface (Rs-c), bending resistance (Rb), mantle resistance along the slab (Rs,), resistance force due to dynamic pressure (Ra) and mantle resistance on the ridge (Rr). Modified from Magni, V., et al. (2025), Nat Rev Earth Environ 6, 51–66 https://doi.org/10.1038/s43017-024-00612-3 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b47d8cf4-fe40-491e-9598-62733481fdfd/slide+1.jpg Claudio Faccenna - Make it stand out Top: map of subduction zone locations. Bottom: depth profiles of Pacific subduction zones. Western Pacific subduction zones, which subduct toward the west, are drawn in blue, and eastern Pacific subduction zones, which subduct toward the east, are drawn in red. Dashed lines indicate depths of 410 km and 660 km, which correspond to mantle transition zones where the seismic velocity, mineral phases, density, and viscosity change. Zero on the distance scale corresponds to proximity to the coastline. The figure shows that the shapes of the subducting slabs vary considerably. This is thought to result from the interaction of several factors, including the slab's properties, the mantle's characteristics, and forces on the plate. Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ae7d8fbc-b985-493d-b927-9b03e899c024/poverview_GAP_P4_1.png Claudio Faccenna The figure shows sections of P-wave tomography anomalies along the yellow lines on the map (Fukao & Obayashi, 2013), seismicity (orange dots on profiles; Engdahl et al., 1998), plate velocities (orange vectors; Argus et al., 2011), and volcanoes (cyan inverted triangles; Siebert & Simkin, 2023). The Western Pacific and Japan subduction zones (the two most northerly zones) do not appear to penetrate the lower mantle, unlike those of Indonesia and Kermadec (north of New Zealand). Whether a slab penetrates the lower mantle depends on factors such as the duration of subduction and the angle at which the slab reaches the 660-km discontinuity, with steeper angles favoring descent. Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf3ed979-e1c0-497f-beae-f8beb60ee497/poverview_GAP_P4_2.png Claudio Faccenna - Make it stand out Subduction zones along the west coast of the Americas. In the podcast, Faccenna describes how the slab subducting below the Andes has entered the lower mantle where its lateral movement is restricted by the higher viscosity there. The subduction zones beneath northern South America and Central America show evidence of penetration into the lower mantle, reaching depths of 1,300 km or more. By contrast, the younger Caribbean subduction zone does not. Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/63e89fa6-3547-4521-b932-df51810d4f83/Slide+5+animated.gif Claudio Faccenna - Make it stand out Three-dimensional numerical simulation of a subduction zone and the associated mantle flow (white arrows) induced by rollback (i.e., retreat) of the slab. Color indicates pressure in the lithosphere with blue and red indicating compressional and extensional pressures respectively. The simulation shows how lateral mantle flow moves away from beneath the slab and circulates around its edge in a toroidal pattern. The third dimension of the subduction zone—its length—appears to be a critical parameter. Smaller slabs are expected to retreat faster than larger ones and not penetrate into the lower mantle, thus being relatively free to migrate backward. Holt, A. F. et al. (2017), Geophysical Journal International, 209(1), 250 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/58f2376f-26cb-450a-bcf4-c8447f28fe05/slide+7.jpg Claudio Faccenna - Make it stand out Left: map showing seafloor ages in the western Pacific. The back-arc basins shown appear mainly as the red and orange regions, i.e., having the youngest ages of 0 and 30 million years. Center: more detailed seafloor-age map of the Izu-Bonin-Marianas region. Right: P-wave tomography sections along the green lines labeled A, B, and C, revealing the varying shape of the subduction zone going from north to south. The western Pacific subduction zone is characterized by back-arc extension in the overriding plate that began within the last 30 million years (left panel). Tomography and seismicity data show that along the Izu–Bonin region (section B1–B2), a double subduction system is present, resulting from subduction of both the Pacific Plate (to the east) and the Philippine Plate (to the west). Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bcdee180-a5ef-42f1-8981-5c957de4936d/slide+10.gif Claudio Faccenna - Make it stand out The Izu–Mariana subduction system is unique in that the trench is advancing toward the overriding plate (right panel). Bottom left: tomographic section along the red line on the map at right shows the two subducting slabs. Top left: numerical model of single subduction and double subduction. The double-subduction simulation replicates quite a few features appearing on the tomographic section, such as the apparent flattening out of the subducting slabs between the depths of 400 and 600 km. In a single-slab system, the trench migrates backward, whereas in a double-slab system, the rear slab drives trench advance. The simulation also reproduces the tomographic section (bottom left, section along the red line on the map at right), which clearly shows the presence of two subducting slabs. Faccenna, C. et al. (2018), Tectonophysics, 746, 229 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b6c5a5a3-61e1-4427-9f07-d41f238b8926/slide+8.gif Claudio Faccenna - Make it stand out Three-dimensional numerical simulation of a double-subduction zone with both subducting slabs dipping in the same direction. The rear trench advances while the front one rolls back. Color indicates pressure in the lithosphere with blue and red indicating compressional and extensional pressures respectively. A version of such a simulation may help us understand the double subduction zone in the Izu-Bonin-Marianas region shown in the previous figure. Holt, A. F. et al. (2017), Geophysical Journal International, 209(1), 250 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b58787d4-f33d-4054-ad63-2f0ba9864b0f/slide+16.jpg Claudio Faccenna - Make it stand out The origin of the Andes is intriguing as this major mountain belt formed without a collision between two continental plates, unlike the Alpine–Himalayan belt. Numerical simulations (left panel) of subduction dynamics, combined with tectonic reconstructions (central panel), show slab penetration into the lower mantle beneath the central Andes. In the model, rollback velocity decreases once the slab becomes anchored in the lower mantle, leading to widespread compression in the overriding plate (shown in white in the upper plate, left panel). In the Central Andes, slab rollback slows and eventually becomes slower than the westward motion of South America, causing compression in the upper plate. Faccenna, C. et al. (2017), Earth and Planetary Science Letters, 463, 189 https://www.geologybites.com/alphabetic-index daily 0.75 2026-03-26 https://www.geologybites.com/jiri-zak daily 0.75 2025-10-15 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d13c2adf-bb74-4d20-aedf-9dd1bba9fa0c/JZ.jpg Jiri Zak In the podcast, Jiří Žák describes the two main orogenies whose remnants figure prominently in central European geology: the Cadomian orogeny that lasted from the late Neoproterozoic to the early Cambrian (c. 700 Ma to c. 425 Ma) and the Variscan orogeny that occurred in the late Paleozoic (c. 380 Ma to 280 Ma). The Cadomian took place on the northern margins of Gondwana, only later to rift and travel north to form what was to become Europe. The Variscan was caused by the collision of Gondwana with Laurussia in the final stages of the assembly of the supercontinent Pangea. Both orogenies have been heavily eroded, and we see their imprint in the form of metamorphic rocks, volcanic rocks, granites, and deformation structures. These are scattered across Europe, from southern Britain to eastern Europe. Žák has been studying the geology of central Europe for over 25 years using methods ranging from structural studies in the field to detrital zircon geochronology. He is a Professor in the Institute of Geology and Paleontology at Charles University in Prague. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/310a6abc-bb2b-47a4-9bea-68f8d5021ad3/orogen+types.jpg Jiri Zak In the podcast, Jiří Žák talks about the Cadomian and the Variscan orogenies. The former was an accretionary orogen, in which material accumulates on a continental margin as oceanic plates subduct. The overriding plate incorporates island arcs, the accretionary wedge, and oceanic crust at the plate margin. Such orogens also include features such as forearcs and magmatic arcs associated with ongoing subduction. A present-day example is the western margin of South America with ongoing subduction of the Nazca plate. The Variscan was a collisional orogen, which occurs when two continental plates collide at the final stage of convergence between two plates. Buoyant continental lithosphere or other massive oceanic features such as plateaus are forced into the subduction zone. Collisional orogens result in crustal thickening, shortening, and the formation of extensive mountain ranges. The Alpine-Himalayan orogenic belt represents a prime example of a collisional orogen. Condie, K. (2014), Mineralogical Magazine 78, 623 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e5c77c1e-2e4a-4d16-abd2-d8893d0e0309/Slide+1.jpg Jiri Zak - Make it stand out Map of Europe showing the main geological units as defined by their structural origin and presumed terrane provenance. Provenance is determined from the age profile of detrital zircons (see episode with Ulf Linnemann) and from trace element signatures. As the map shows, practically all of central and southern Europe (shaded grey) was derived from Gondwana. These terranes contain Cadomian and Lower Paleozoic basement rocks. The map also shows the main suture zones. A Alps, AM Armorican massif, B Balkans, BM Bohemian massif, BV Brunovistulia, CIZ Central Iberia Zone, D Dinarides, DO Dobrogea, EC Eastern Carpathians, H Hellenides, IM Iberian massif, IST Istanbul terrane, KB Kirsehir block, MC massif Central, MGCR Mid-German Crystalline Rise, MM Menderes massif, MP Malopolska block, MU Moldanubian unit, OMZ Ossa-Morena Zone, P Pyrenees, R Rhodope, S Schwarzwald, SC Scythian platform, SM Serbo-Macedonian massif, SPZ South Portuguese Zone, SX Saxothuringian unit, TBU Teplá–Barrandian unit, V Vosges. Sen, F. (2021), International Geology Review 64, 2416 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/022b4eb9-b171-41b5-807f-089abcaf63d1/slide+3.jpg Jiri Zak Deformed sedimentary rocks from the late Neoproterozoic to early Cambrian in the central Bohemian Massif. The sediments formed as deposits of deep-marine turbidity currents on the former trench slope of a subduction zone and were then accreted as part of an accretionary wedge at the northern margin of Gondwana. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1fc9704b-3e70-4de3-a175-d6d8c9032144/slide+4.jpg Jiri Zak Pillow lava compositionally corresponding to mid-ocean ridge basalts, forming large, up to km-scale blocks mixed with the turbidites (above). These lavas formed on the ocean floor of an oceanic plate that subducted beneath the northern margin of Gondwana and were subsequently scraped off the plate surface and included within the accretionary wedge. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/02cd2d0f-0ea5-4bdf-bc6f-3dc4a49614e3/slide+5.jpg Jiri Zak The hammer marks the Cadomian unconformity in the Bohemian Massif where deformed and weakly metamorphosed slates of the Cadomian accretionary wedge of late Neoproterozoic to early Cambrian age (right of hammer) are overlain by moderately tilted and non-metamorphosed middle-to-late Cambrian strata deposited in an extensional basin (left of hammer). The former were formed during the Cadomian orogeny, while the latter were deposited as the Gondwana northern margin started to rift apart. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/54e7230d-241c-4a31-b4d3-b30905a17546/slide+6.jpg Jiri Zak - Make it stand out There is a debate as to how far the Cadomian terranes, specifically the major Teplá–Barrandian unit of the central Bohemian Massif, traveled away from Gondwana before they accreted to Baltica, eventually to become part of Europe. These figures illustrate contrasting models that have been proposed. (a) In this model there is a large separation between the Teplá–Barrandian unit and Gondwana, and the unit forms a completely detached microplate called Perunica (P). (b)-(d) In these models, there is little separation, and the Teplá–Barrandian unit remains part of the hyper-extended Gondwana shelf. Žák, J et al. (2018), International Geology Review 60, 319 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2b2c6a96-7ee1-4f95-b630-15aea69db0ff/slide+7.jpg Jiri Zak Upper Ordovician glaciomarine deposits with dropstones in the central Bohemian Massif. The presence of such deposits show that at this time the northern Gondwana margin was still far enough to the south of the equator to be within reach of continental glaciation. This suggests that the margin was part of the peri-Gondwana shelf, which favors the low-separation models illustrated in (b)-(d) above. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fe616adb-528f-40a6-aee7-33ef07f04e9d/slide+8.jpg Jiri Zak These lower Devonian limestones in Prague were deposited in warm, subtropical seas. They document the continental drift of the peri-Gondwana shelf from highly southerly latitudes toward the equator before being caught up in the Variscan orogeny when they were folded and faulted following continental collision. The memorial plaque commemorates the French paleontologist Joachim Barrande (1799-1883), who pioneered geological and paleontological research in this region. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f80640bf-005a-4031-9340-a39eb84f5e92/slide+9.jpg Jiri Zak - Make it stand out A paleogeographic model showing the break-up of the former northern Gondwanan Cadomian active margin in the late Cambrian and early Ordovician, opening of the Rheic Ocean, transition to an early Paleozoic passive margin, and, finally, the Laurussia-Gondwana collision to form the Variscan orogenic belt. The terranes discussed in the podcast form parts of Avalonia, the Saxothuringian and Ossa-Morena Zones, the Variscan Autochthon, and the Mid-Variscan Allochthon. The Saxothuringian Zone now makes up the northwestern part of the Bohemian Massif. The Ossa-Morena Zone now forms part of the Iberian Massif in Spain and Portugal. The Variscan Autochthon comprises geological units now mainly exposed in southern Europe. The Mid-Variscan Allochthon includes the Teplá-Barrandian and Moldanubian units of the present-day Bohemian Massif. Catalán, J.R et al. (2021), Earth-Science Reviews 220, 103700 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6935737b-be0d-45ae-a34d-7cbcc32c8e77/slide+10.jpg Jiri Zak - Make it stand out Geological map of the present-day Bohemian Massif. The geological structure is complex, largely as a result of the Cadmonian and Variscan orogenies. The map covers a region stretching from southern Poland in the north to northern Austria in the south. It reveals a section across the Variscan orogen from the outer foreland basins (Rhenohercynian) through low-grade Cadomian basement terranes (Saxothuringian and Teplá-Barrandian) to the exhumed high-grade orogenic core (Moldanubian). Adapted from the Geological map of the Czech Republic 1:5,000,000 published by the Czech Geological Survey, Prague, 2007 https://www.geologybites.com/tom-herring daily 0.75 2025-10-23 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b73a2f6d-bd64-404e-8113-261eea3fe2d1/TAH_SouthKorea-DamStudy.jpg Tom Herring There are three main types of geodetic measurement systems — satellite-based systems such as GPS, very long baseline interferometry (VLBI), and interferometric synthetic-aperture radar (InSAR). While each type of systems has its particular strengths, the cost of satellite-based receivers has plummeted. Millimeter-level accuracy will soon be incorporated into phones. This has broadened the kinds of geological questions we can now address with such systems. In the podcast, Tom Herring describes impressive geological applications as well as applications in civil engineering, such as dams and tall buildings, and agriculture. Herring is a pioneer in high-precision geodetic analytical methods and applications for satellite-based navigation systems to study the Earth’s surface. He is a Professor in the Earth, Atmospheric, and Planetary Sciences department at the Massachusetts Institute of Technology. The image shows Herring in front of a dam near the DMZ in South Korea where the concern was to be prepared for North Korea to breach dams on their side of the border in an attempt to flood South Korean infrastructure. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/68a4da0f-0bd8-469d-b222-e91225a62872/GPS_Positioning_geodesy_org.png Tom Herring - Make it stand out Principle of satellite-based position measurement. The distances are referred to pseudo-distances as they include errors from clock differences and atmospheric delays. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3a2776f2-9191-47d3-bac1-719d1e5a489d/signal+correlation.jpg Tom Herring - Make it stand out Four satellites are needed to estimate the 3D position and the receiver clock error. This feature allows the use of inexpensive clocks in the ground receivers. With more than four satellites (which is always the case now), atmospheric delays can be estimated. This is necessary in order to achieve mm accuracy positioning. The ionospheric delays are determined by making measurements at two (or more) frequencies. This exploits the fact that, at microwave frequencies, the refractive index of the ionosphere depends in a known way on the frequency. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ea335783-515f-45aa-bf53-804b35875375/herr04.JPG Tom Herring Atmospheric layers alter the GPS signals and can introduce significant errors. The most important effects arise as the radio waves pass through the Earth’s charged ionosphere and water-laden troposphere. As Herring describes in the podcast, when four or more satellite signals are detected, the receivers can correct for atmospheric effects. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2425e690-8f4d-4043-97a1-dfa937cae295/Inexpensive_GNSS.jpeg Tom Herring - Make it stand out Inexpensive Global Navigation Satellite System (GNSS) receiver costing $700. GNSS refers to a set of satellite-based systems such as GPS, the Russian GLONASS system, and the European Galileo system. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b0300061-3d19-4f8e-b088-6675f83cd58e/Expensive_GNSS.jpeg Tom Herring - Make it stand out Expensive GNSS receiver costing about $20,000. The white plastic covers on both antennas are for the protection of the antenna elements. The antenna elements lie below the plastic in the center and sit on a metal sheet (that can’t be seen) called the ground plane. This reduces the noise from signals reflected from the ground underneath the antenna. Ideally, the antennas would see only signals coming directly from the satellites, not reflected ones. Reflected signals are a big problem for accuracy in urban canyons. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e67c0daf-a783-47bd-9023-8bf9cf928958/ContinousGPSSite_Oman_2009.jpeg Tom Herring Permanent GNSS receiver in Oman where Herring has studied the subsidence of an oil and gas field during production. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d4824985-b70e-46d3-bd71-9feac5b86622/Testing_GPS_on_roof-GreenBuildng54MIT.jpeg Tom Herring - Make it stand out Testing a GPS system on the roof of a tower on the MIT campus. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/be740327-985c-440c-8001-882b94a0766c/NZ_SouthernAlps_2004.jpeg Tom Herring - Make it stand out GNSS receiver installed in the Southern Alps of New Zealand to measure uplift rates across the Alps. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9afa6604-24b3-4c79-9593-12bcaa8dc091/obs_vlbi_ggos_web_v2-1024x949.png Tom Herring - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/10f4a3be-9c2a-4266-ae99-a47090825686/ivsnetmapl-1024x779.png Tom Herring - Make it stand out Locations of VLBI antennas. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b50b958c-3ec9-42d1-9426-9493aa6ab32d/ONSA_JPL_timeseries.png Tom Herring - Make it stand out From top to bottom, GPS measurements of the northward, eastward, and vertical change in position of the Onsala Space Observatory, Sweden. The height uplift is 2.4 mm/yr, which is mainly caused by rebound following the melting of the Fennoscandia Ice sheet about 10,000 years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/65b73e32-5766-4908-b01a-d348fe9508df/Ridgecrest+interferogram+Fig+11.jpg Tom Herring - Make it stand out InSAR observations of the earthquake sequence (a Mw 6.4 foreshock and a Mw 7.1 mainshock), which struck Ridgecrest, southern California in 2019. The figure shows observed (a, e), modeled, and residual InSAR interferograms. (b) and (f) are modeled by the best-fitting foreshock-only and (c) and (g) are the corresponding results for the mainshock-only. The colors denote ground displacement along the line-of-sight from the spacecraft ranging from almost 6 cm (red) to -6m (blue). A color key is shown at bottom right in (h). The figures show phase measurements, which wrap through each cycle every 11.8 cm of displacement. Such measurements reveal a complex pattern of coseismic movement dominated overall by a right-lateral motion. He, L. et al. (2022), Journal of Geophysical Research: Solid Earth, 127, e2021JB022779 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3ea05c7c-4f8c-49f9-a65b-0518f768cf05/P595-NAFixed_raw.png Tom Herring - Make it stand out Position change in a North America fixed reference frame of a GPS sensor located close to the epicenter of the Ridgecrest earthquake between 2005 and 2025. Up to the time of the Ridgecrest earthquake, the site moved north at 8 mm/yr, west at 6.9 mm/yr, and sank slowly at -0.9 mm/yr. Since the total motions in height are much smaller, the noise and annual signals (probably from seasonal water changes) are more visible. This motion can be accounted for by the site’s proximity to the Pacific plate, which is moving to the northwest and exerting a drag on the North American plate. Earthquakes are marked by the dotted red lines, though only the Ridgecrest sequence is large enough to be visible at the scale shown. At the time of Ridgecrest, some of the accumulated stress is released, and the site jumps backward, i.e., in a southeasterly direction. The plots also show that the current velocity of the site is still quite different from what it was before the Ridgecrest earthquakes and averages 6.4 (N), 3.8 (W), and -3.6 (U). The motions after the earthquakes are referred to as post-seismic deformation. Postseismic deformations are thought to come from continued motion on and around the fault that ruptured (especially around the beginning and end of the fault). These motions may involve slow slipping along the fault or viscoelastic flow caused by high stresses at the ends of the rupture. Herring, T.A. et al. (2016), Reviews of Geophysics, 54 (4), 759 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dcc2ff93-94a0-4df7-aa60-4c6b6fea0bee/Al-Hamra+cover.jpg Tom Herring - Make it stand out The Al-Hamra Tower in Kuwait City is 413-m tall with 86 floors. The measurements at right show the motion of the ground and the top of the building during a Mw 7.3 earthquake that occurred in 2017 642 km from Kuwait on the Iran-Iraq border. The top of the Al-Hamra Tower moved with amplitudes of up to 160 mm, up to four time larger than the ground motion amplitudes. Tower motions detected with GPS persisted for about 12.5 minutes after the seismic S-waves arrived at the tower. Skidmore, Owings, and Merrill LLP https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8010b164-8612-418f-b2f8-fffaead923a9/SSE+Time+Series.jpg Tom Herring - Make it stand out The black trace at bottom shows the GPS time series of the common signal seen among all the sites in Northern California. The overall linear velocity has been removed, allowing the deviations from linear motion to be shown. The label PC 1 refers to the first principal component of the motion, which contains the signal most common to all sites. The top trace is the tremor count in the region of maximum slip, and the middle trace is velocity. The blue bands are spaced at 10-month intervals and are 21 days wide. They show how regular the peaks in slow-slip events are, much more so than most earthquakes. While the regular release of stress in smaller tremors suggests that large stresses leading to destructive earthquakes become less likely, these events transfer stress to other regions, possibly to shallower depths, which would enhance the likelihood of a damaging earthquake. Overall, this study shows that there is an area on the subduction zone interface that accumulates strain over about 10 months and then releases it over about 20 days. The elastic properties of the crust mean we can see the effects of this slip at depth on Earth’s surface. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bd41e927-45e3-4992-8778-495fe5560655/Zubovitch_CAsia_velocities.png Tom Herring - Make it stand out The map shows surface velocities relative to Eurasia as measured by GPS. The velocities show that half the India-Eurasia motion is accommodated across the Tien Shan in Kyrgyzstan and Kazakhstan. Herring and his MIT colleagues were instrumental in getting the GPS network installed in this region. Zubovich, A.V. et al. (2010), Tectonics, 29 TC6014 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/377f7fe2-f8de-4e1f-b23b-cf70461b5862/India-Eurasia+wider+scale.jpg Tom Herring - Make it stand out GPS velocity field with respect to the Eurasian plate. The red vectors indicate data from a network of Chinese GPS receivers, and the pink vectors are from other published results. Such results help constrain the various theories as to how the northward movement of India is accommodated. One particular controversy is the degree to which the movement is accommodated by slip along major bounding faults, such as the Karakoram fault or the Altyn Tagh fault. These results generally favor continuous crustal deformation rather than major movement along the faults. Wang, W. et al. (2017) Geophysical Journal International, 208, 1088 https://www.geologybites.com/keith-klepeis daily 0.75 2025-11-13 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/882d99a5-4e93-4f14-8b51-d88c9f29180e/edited-1.jpg Keith Klepeis Plutons are bodies of igneous rock that crystallize from magma at depth below the Earth’s surface. But even though this magma never makes it to the surface, it still has to travel many kilometers up from its source near the base of the crust to the upper crust where plutons form. In the podcast, Keith Klepeis explains how it makes that journey and describes the shape of the resulting structures. Many of his findings come from one region in particular that provides an exceptional window into the origin, evolution, and structure of plutons — the Southern Fiordland region of New Zealand’s South Island. Klepeis is a Professor in the Department of Geography and Geosciences at the University of Vermont. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/cea6f8ea-f970-4936-93a4-39fe114beaed/IMG_3250.JPG Keith Klepeis The Southern Fiordland region of New Zealand’s South Island. The region exposes a large batholith called the Median Batholith, but the only adequate exposures of rock in this rugged temperate rain forest are along the fjord coastlines and above the treeline near the peaks. In the podcast, Klepeis explains how they relied on boats and helicopters to do their fieldwork. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f00f97b8-a4c9-4f6d-80de-eb18ea36ec0e/slide+2.png Keith Klepeis - Subduction Zone Most plutons form above a subducting oceanic plate. Once it reaches a depth of about 150 km, the subducting lithosphere with its basalts and sediments undergoes dehydration reactions that liberate water. The water rises and, when it travels through the overriding mantle wedge, reduces the melting temperature to about 1,000 C, with the result that magma is created. While some magma reaches the surface and forms a Cordilleran volcanic arc, the remainder cools at depth, forming the plutons and their associated structures that Klepeis describes in the podcast. Adapted from Lillie, R.J. (2005), Parks and Plates: The Geology of our National Parks, Monuments, and Seashores https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/27382d3f-57a3-4a94-9206-6cb070a316d0/slide+3.png Keith Klepeis Diagrammatic cross section through the continental crust across a subduction zone showing a volcanic system with its underlying feeder dikes and batholith. Basaltic magmas pool at the base of the crust where they differentiate and melt crustal rocks. According to the currently favored “Mush” model, this happens without chemical interaction with the surrounding material More evolved andesitic magmas then rise to the middle crust forming granitic batholith complexes. Magmatic fluids continue to ascend through the crust and may form a shallow pre-eruptive chamber. The figure shows the mushroom-like shapes of the crustal melt/crystal mix described in the podcast. The MOHO is the boundary between the crust (pale green) and mantle lithosphere (purple). The mantle wedge is pale grey/blue region between the subducting crust and the mantle lithosphere. Plutons form as part of the batholithic complex shown in the shallow crust. Richards, J. P. (2011), Ore Geology Reviews, v. 40, 1 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c271e3f7-18ed-49f9-87e6-dd64654490d2/slide+4.jpg Keith Klepeis Schematic cross section of an active continental margin subduction zone, showing the dehydration of the subducting slab, hydration and melting of a heterogeneous mantle wedge (including enriched sub-continental lithospheric mantle), and crustal underplating of mantle-derived melts. Remelting of the underplate to produce tonalitic magmas and a possible of crustal melting are also shown. As magmas pass through the continental crust they may differentiate further and/or assimilate continental crust. Winter (2001) An Introduction to Igneous and Metamorphic Petrology, Prentice Hall https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0a931772-5f4d-4a37-94b3-e71930682ba4/slide+5.jpg Keith Klepeis - The Median Batholith Klepeis and his team focused their recent research on the Median Batholith (shaded red) in the South Fiordland region of New Zealand. Today, the batholith is offset by the Alpine Fault. The inset at bottom right shows a reconstruction of the batholith prior to 37 million years ago. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e4861f17-c48e-4735-9996-f4d2078aefb4/slide+6.jpg Keith Klepeis Geological map of Southern Fiordland. The map labels the lower, middle, and upper crustal regions that are all exposed thanks to tilting caused by compressional faulting along the Alpine Fault (black line running along the western coast). This unique geometry enabled Klepeis and his team to map the 3-dimensional structure of the crust and reveal the conduit and mushroom-like sheet structure of the intruding magma. Klepeis, K. A. et al. (2022) Tectonics, 41, e2021TC007097 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4a4d69c8-fa9e-48bd-be85-0a602a8560d2/slide+8.jpg Keith Klepeis - Make it stand out Reconstructing the crustal section of the Southern Fiordland magmatic arc. The map on the left shows Fiordland shaded by its depth during the Cretaceous. The deepest exposures are on the west side, shaded in purple and yellow. The crustal section in the center is a diagrammatic representation of the structure and is annotated at right with its composition, showing that the crust becomes Increasingly mafic with depth. The upper crust (above 30 km) is mainly granite, tonalite, and diorite forming bulbous and/or steep-sided bodies. Below 30-km depth, there are layered sheets. In the middle crust is the Western Fiordland Orthogneiss (WFO), which is a major part of the Median batholith. The Misty pluton, which Klepeis mentions in the podcast, is a part of the WFO. This section represents a major magma flare-up, covering about 2,300 sq km, of which 70 percent was emplaced in just 3 million years. Image: Klepeis, K. A. et al. (2022) Tectonics, 41, e2021TC007097 Timing of emplacement: Schwartz, J. J. et al. (2017), Lithosphere, 9(3), 343 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1ce780b7-7aaf-46df-9350-4c49d321d9e6/crustalcolumn.jpg Keith Klepeis Block diagram showing the internal components of the Misty pluton, which is one of the plutons of the Southern Fiordland batholith. A conduit rising through the lithospheric mantle feeds a sheet-like basalt structure, which in turn connects to steep-sided granitic bodies in the middle and upper crust (colored in mauve and pink). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/62c09c02-959a-4638-ad61-97a27c98e714/slide+11.jpg Keith Klepeis - Make it stand out Western coastline exposure of the deepest, lower-crustal level shows steep feeder zones and conduits where mafic, crystal-rich magma was injected into lower-crustal diorites. Most of the rocks in the feeder zone here are hornblendites, which are composed almost entirely of hornblende. The hornblendites are thought to be modified products of mantle-derived melt. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d69ee939-6ba7-4638-a3b7-32313aab31ec/slide+12.jpg Keith Klepeis - Make it stand out These rocks show the intrusion of dark mafic dike swarms into a deforming light-colored dioritic magma mush, where there is evidence of undulose margins and boudinage. The undulose margins and boudinage (the pulling apart of the igneous layers into fragments as the magmas deform) indicate that the mafic and dioritic magma were mingling and intruding together prior to their full crystallization at the base of the lower crust (depths of ~40 km). Granite dikes and veins that cut across the mafic and dioritic layers. This tells us that the granites arrived after the mafic and dioritic magmas had intruded and mingled and supports the idea that the intrusion of mafic magma helped release and mobilize granitic melts that were essentially trapped inside the dioritic mush. Textures such as these have led to the idea that cyclic intrusions help mobilize and move granite melts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1cad7e97-b20b-45a8-8464-c8763a69dd33/slide+13.jpg Keith Klepeis - Make it stand out This outcrop shows mobilized granitic melts and mafic layers that have been pulled apart during deformation. Prior to the deformation, the dark material formed discrete layers, like those shown in the previous photo. The deformation shows that the different magma types were moving together as interacting mushes within the lower crust. Even more clearly than in the previous image, the granite cuts across both the mafic and dioritic units, further indicating that the granites were mobilized after the mafic dykes intruded the dioritic mush. As with the previous image, this supports the idea that sequences of mafic and dioritic intrusions help mobilize and move granite melts. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/48921aec-dfe9-4560-82a5-9673a2e556fa/slide+15.jpg Keith Klepeis - Make it stand out The curved, tightly folded white intrusion to the right of the geologist's hand in the photo shows that these rocks have been heavily deformed (pure shear). Structures such as these allowed the researchers to map a zone of compaction at the base of the crust. Evidence of compaction also appears in the photo on the right, where dark colored-layers are distorted and pulled apart. Left photo courtesy of Joshua Schwartz https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2883e14b-3bb8-4494-af1b-fe2d44224e1a/slide+16.jpg Keith Klepeis - Make it stand out Outcrop of fully-fledged dikes and thick pegmatites that occur away from the base of the Misty pluton. The coherent structure of the intrusion suggests the magma was emplaced into a fairly well-crystallized host capable of exhibiting brittle-like breaking. A crystal-rich host results from fractional crystallization and the progressive removal of the remaining melt. The horizontal alignment of the crystals suggests that the host mush has been compacted and enough melt has been removed to enable the crystals to align. At the same time, the undulose margins of the dike and the exchange of the dark hornblende crystals across its margin indicate that, although crystal-rich, the host was not fully crystallized and could still exhibit ductile behavior. This supports the general picture that as the host mush becomes increasingly crystal-rich as melts are gradually extracted, the dikes that move magma through the crystallizing mush become more organized and regular in shape. The dyke here is about 30 cm across. https://www.geologybites.com/anat-shahar daily 0.75 2025-12-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/65acab9c-e1c5-4eeb-a55a-8847b52dea07/Headshot.jpg Anat Shahar Since all forms of life on Earth require liquid water, at least at some stage in their life cycle, it is natural to suppose that in order to be habitable, an exoplanet should also have liquid water. While much of the public discussion has focused on constraining the so-called Goldilocks zone, i.e., not too hot nor too cold for liquid water to exist, an equally key issue is how a planet would get its water in the first place. In the podcast, Anat Shahar explains how her modeling and experiments predict that plenty of water would form as a result of chemical reactions between the hydrogen atmospheres observed on many exoplanets and the magma ocean with which planets initially form. Shahar is a Staff Scientist and Deputy for Research Advancement at the Earth and Planets Laboratory at the Carnegie Institution for Science in Washington, DC. Photo: Badro Lab at IPGP, Paris https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/813b7f28-2f0e-4074-8365-55a547c0bf00/Diagram_of_different_habitable_zone_regions_by_Chester_Harman.jpg Anat Shahar - Make it stand out Diagram showing the boundaries of the habitable zone for stars of different surface temperatures. The habitable zone is defined as the zone in which liquid water can exist. The models on which these results are based include the effects of greenhouse gases in the atmosphere, tidal locking, and other effects, some of which involve complex feedback mechanisms. These effects mean that at any given level of starlight incident on the planet, the habitable zone boundaries depend upon the temperature of the star, which is why the habitable zone boundaries are curved in the diagram. Various planets within our solar system are shown, along with selected exoplanets. Kasting, J.F., et al. (2013), PNAS 111 (35) 12641 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2ee7f00f-1769-4099-a85b-8812dfaa5510/Embryo+Earth+Illustration.jpg Anat Shahar - Make it stand out Stages in the evolution of Earth. Left: planetary embryo that is too small to retain an atmosphere. Center: the protoplanet grows to a size at which it can accrete a hydrogen atmosphere and differentiate into a metallic core and molten silicate mantle. It is in this stage that the water-producing chemical reactions between the atmosphere and magma ocean described in the podcast take place. Right: modern Earth with a metallic core, oxidized mantle, and water in the mantle, lithosphere (not shown), and atmosphere. The core density is 10 percent lighter than it would be if it was pure iron, implying that there are some light elements in the core. Illustration by Edward Young/UCLA and Katherine Cain/Carnegie Institution for Science https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/880c314c-7963-4ef1-9b31-4f785bb240ba/slide+1.jpg Anat Shahar Diagram of the diamond anvil compressor used in Shahar’s high-pressure experiments that simulate conditions on large planets. The inset (right) of the diamond assembly is about 5 mm across. The entire diamond anvil compressor is 6 cm high and 3 cm across. The diamonds compress the sample up to a pressure between 16 and 60 GPa. Lasers above and below are directed onto the sample, heating it to temperatures of 4,000 K and above. Courtesy of Francesca Miozzi https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b943467d-510c-48c7-ab82-f9ceb069c6e1/diamondanvilcell_side.jpg Anat Shahar Photomicrograph of the diamond anvil used in Shahar’s high-pressure experiments. Between the diamond tips is a gasket that holds a silicate magma ocean-like sample prepared in the lab and the hydrogen. The diamonds are between 1/2 to 1 carat in size with the tip facing the sample being about 300 microns across. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bfad7ffe-e681-41fa-ab8e-99d3a7e89e42/slide+2.jpg Anat Shahar - Make it stand out Left: photomicrograph showing the sample of simulated mantle material in the inner region surrounded by the gasket. Center: sample after heating. The colorful part is the melt. Right: sample following removal from the diamond anvil compressor with resin added to keep the sample intact and extractable for subsequent analysis. Courtesy of Francesca Miozzi https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9727e673-4ceb-43e9-9b58-2cd8dc7a461e/Exp_11_Metal%2Bcavity_annotated.png Anat Shahar - Make it stand out Electron microscope image of a sample after it was subjected to high temperature and pressure in the presence of hydrogen. The residual cavity is where water was created. The iron-rich bleb was formed when the iron oxide (FeO) was reduced by the hydrogen during the water-forming process, as shown in the next figure at left. Courtesy of Francesca Miozzi https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/fb666b5f-ddbf-4696-80e4-04a4a1b38e50/slide+7a.jpg Anat Shahar - Make it stand out Interaction of a hydrogen-rich gas with a magma ocean. Left: hydrogen dissolves in the magma ocean and water is produced in the magma through the reduction of iron oxide. Right: on a small body that is not fully molten, water may be produced only where molten magma (red) is present. The other colors represent the rest of the differentiated planetesimal. Courtesy of Francesca Miozzi https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e4acf53f-042d-40d1-b42f-061e6aab8a8a/Slide+7b.jpg Anat Shahar - Make it stand out Conceptual illustration of three possible scenarios for interior–atmosphere interaction in big planetary bodies, often referred to as sub-Neptunes (between 1 and 17 Earth masses). Left: free fluid water and Fe-enriched blebs are entrained in the magma ocean. Centre: water is outgassed to create a steam atmosphere while the Fe-enriched blebs sink toward the centre. Right: extreme scenario in which all phases are miscible. Courtesy of Francesca Miozzi https://www.geologybites.com/carina-hoorn daily 0.75 2025-12-27 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e0bc1571-1199-4aa1-87fa-c1aa8c5d7109/CH-additional+edited-1.jpg Carina Hoorn The Amazon Basin is the most biodiverse region on Earth, being the home of one in five of all bird species, one in five of all fish species, and over 40,000 plant species. In the podcast, Carina Hoorn explains how the rise of the Andes and marine incursions drove an increase in biodiversity in the Early Miocene. This involved the arrival of fresh river-borne sediments from the eroding mountains and the diversification of aqueous environments caused by influxes of salt water during the marine incursions. Hoorn is an Associate Professor in the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam and Research Associate at the Negaunee Integrative Research Center, Earth Science Section, Field Museum of Natural History, Chicago. Photo: Daniel Winitsky https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ddf70ba3-be46-4cd1-a0da-12a12ef8e5ff/Fig+13%2C+Wessling.jpg Carina Hoorn In the podcast, Hoorn describes the various aqueous environments that prevailed in the Pebas Wetlands System. Lacustrine: freshwater lake environment; fluvio-lacustrine: part lake and part stream waters; estuarine: raised salinity in a lacustrine system; mangrove: shallow saline environments where mangrove trees line the shore. While the Pebas system has no close modern analogue, the Brazilian Pantanal and the Florida Everglades are probably the closest. FBZ: Foreland Basin Zone; PCZ: Pericratonic Zone. Wesselingh, F.P. et al. (2001), Cainozoic Research, 1(1-2) 35 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dcbe7654-dddc-4eda-87aa-2e2d46692b53/slide+2-2.png Carina Hoorn - Make it stand out Map showing present-day average number of vertebrate species per square km. Antonelli, A. et al. (2018), Nature Geoscience 11, 718 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6ea05ea1-fa9d-4049-9b4e-9f1e084d2096/amazon_201167.jpg Carina Hoorn - Make it stand out Amazonian blackwater lake (left), rainforest, and whitewater river. The whitewater river is laden with sediments from erosion of the Andes. Photo Rhett A. Butler for Mongabay https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e1228465-2b54-4ec9-8f0f-54cc0e9c2dd0/scale.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3e3873c3-d765-48fb-b400-3b186514471f/slide+4.jpg Carina Hoorn - Make it stand out In the podcast, Hoorn attributes some of the rise of the Andes and subsidence of the Amazon basin to the flat slab subduction of the Nazca plate under the west coast of South America. The flexural and dynamic effects of the subduction have been modeled and support the idea that the subduction could have driven the topographic and sedimentary evolution of the western Amazon since the Miocene, eventually shaping the present-day landscape. Left: map of the topography calculated by models of the flexural and dynamic effects of the subduction. Turquoise arrows represent drainage directions. The thin dotted line represents the approximate location of the cartoon cross section shown at right. Right: modeled cross section with gray dotted regions indicate sedimentary infill, with region 1 indicating the oldest deposits and 3 the youngest. The letters I and P on the cross sections mark the estimated locations of the Iquitos and Purus Arches. Eakin, C. M. et al. (2014), 404, 250 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b4632923-12da-495a-9ab9-1ce2d5bc6588/Pebas+map.jpg Carina Hoorn Map of northern South America during the Miocene (23 - 5.3 million years ago). It shows the reconstructed extent of the Pebas wetland system, which Hoorn discusses in the podcast. The Pebas wetland acted as a barrier to the dispersal for most mammals and plants, but was a permeable system for certain plants as well as fish, and aquatic mammal taxa. Boonstra, M. et al. (2015), Palaeogeography, Palaeoclimatology, Palaeoecology 417, 176 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d3e8dc53-7bc8-49e3-91f2-1970b4a741cb/Los+Chorros+1.jpg Carina Hoorn - Make it stand out Outcrops along the Colombia stretch of the Amazon River at Los Chorros with Miocene fossils from the Pebas wetlands. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/101d1a96-24e5-487f-a9a1-85454865d933/Los+Chorros+2.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5a6a70db-c4c6-43db-ad05-09e13f1e5b45/fossil+1.png Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2879791a-9394-478a-b28d-920fc8628fe0/fossil+3.png Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/33e5ecc0-f82a-4577-be7a-8982cf3c759d/fossil+2.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2a67fa09-9f1d-4b1a-9f30-1d84590f0d64/mangrove+fossil+2.png Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/226b6d6b-0c36-477a-ad17-564c1e808b4c/fossil+4.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/47532ba7-84fb-45ba-bdad-38a23b460973/Purussaurus.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e2da0a18-5918-4302-ae94-a1198f713f51/slide+8.png Carina Hoorn Molluscs and ostracods radiated in the Amazon wetland. This diversification accompanied the development of a freshwater wetland with episodic marine influence. The marine influence varied in nature across the wetland and included tidal features and mangroves. Wesselingh, F. P. and Ramos, M.. I. (2010), Amazonian aquatic invertebrate faunas (Mollusca, Ostracoda) and their development over the past 30 million years. In: Hoorn C., Wesselingh F.P., editors. Amazonia, Landscape and Species Evolution: a Look into the Past. Wiley-Blackwell; Oxford: 2010, 302 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ca05e6d4-ba36-4c40-ba24-9bf24c476735/slide+10.png Carina Hoorn In the Miocene, the Amazon basin had a rich diversity of reptiles. The picture is a life reconstruction of a young to sub-adult Purussaurus attacking a ground sloth Pseudoprepotherium in a swamp of proto-Amazonia. Jorge A. González https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a92d5d10-68cf-49e7-83ec-5a915ba25770/slide+13-2.png Carina Hoorn - Make it stand out Marine fish that reached the Amazon during the Miocene marine incursions settled and diversified. Fontanelle, J.. P. et al. (2021), Journal of Biogeography, 48(6), 1406 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/af20761a-9754-49df-91c1-96c47c270ee1/slide+13-1.png Carina Hoorn - Make it stand out The neotropical freshwater sting-rays are an example of a family that arrived during marine incursions that occurred during the Oligocene/Miocene. @OneEarth https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e3a50a13-9179-411b-a8d2-a5a4123539fa/pink+dolphin+2.jpg Carina Hoorn The Amazon pink dolphin Inia geoffrensis is derived from a marine species. Michel Viard https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/60331e92-b481-447c-8ea7-e1f4959fea4b/slide+16.png Carina Hoorn Map showing the number of coastal species in the region of each shaded box. These owe their existence here to the marine incursions. Bernal, R. et al. (2019), Journal of Biogeography, 46(8), 1749 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7b3ec948-2439-4d1c-8f4b-f4f7c948d8f4/slide+16-2.png Carina Hoorn Modern plants that are still distributed in the former marine incursion pathway, which is thought to have left a geochemical imprint in the soils on top of the Solimões/Pebas formation. It has been shown that the bedrock and soils of the Pebas/Amazonas are much richer due either to general chemistry or chemistry related to marine incursions. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/32ad9975-f5a8-42b2-891a-630e9936380c/TADP+slide+7.jpg Carina Hoorn TransAmazon Drilling Project site in the Acre Basin, Municipality of Rodrigues Alves (AC). The core was drilled for scientific purposes only so as to help us understand the history of the Amazon environment and biodiversity. The drilling reached a depth of 923 meters. Isaac Bezerra https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ae228279-2de2-49df-9b4c-58ff41317004/TADP+slide+10.jpg Carina Hoorn - Make it stand out Portions of the drill core comprising fluvial deposits and paleosols. The red colors and the mottling are typical for tropical soils. The context suggests the location was an abandoned river channel. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/65fbb465-d3dd-43e9-8529-c5e9874fd56a/TADP+slide+12-2.jpg Carina Hoorn - Make it stand out The red flags mark pollen samples, which are adhered to clay particles deposited in environments such as fluvial overbanks and floodplains. Hoorn’s collaborator Angelo Plata-Torres is pictured. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1e117efe-5d44-45b7-80b5-9b94d7137b75/TADP+slide+12-1.jpg Carina Hoorn - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://www.geologybites.com/michael-manga daily 0.75 2026-01-21 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/10f94887-f499-4882-b479-2a279945606e/82274E89-538E-4CD4-BAB7-173058EAA1F2.jpeg Michael Manga In the podcast, Michael Manga talks about the various ways in which the presence of water can affect eruptions, both here on Earth and elsewhere in the Solar System. Most dramatically, it can vastly amplify the explosive power of a volcanic eruption. The 2022 Hunga Tonga eruption, the most powerful eruption in a lifetime, was a good example of this. Manga is a Professor in the Earth and Planetary Science department of the University of California, Berkeley. In the photo he is sampling the Regnano mud volcano in the Apennines in Italy. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d6656b4e-f4f8-4a25-b800-aa947b0d2089/slide+8.png Michael Manga - Make it stand out Eruption of Mount St. Helens in 1980. During the eruption, the flank of the volcano collapsed. In this eruption, dissolved water within the magma formed bubbles as the magma depressurized, which drove the eruption. G. Rosenquist https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8c7bb08c-ab5d-42a1-b0b9-2525a7686c7f/slide+9.png Michael Manga Eruption of Mount Pinatubo in 1991. The ash cloud reached the stratosphere and caused about 0.5°C of cooling for several years. The Hunga Tonga eruption was comparable in explosive power to this eruption. As with the Mount St. Helens eruption, the Mount Pinatubo eruption was driven in part by bubbles formed from water dissolved in the magma. USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/53a4edd5-651e-4796-a779-efeec9d191ea/slide+11-1.png Michael Manga The Hunga Tonga eruption on 15 January, 2022, was the largest eruption in our lifetimes. The plume reached a height of 58 kilometers, and the explosion was heard in Alaska, 8,000 km away. The explosive power stemmed from the conversion of thermal energy to kinetic by the sudden conversion of a large amount of water to steam. The eruption took place at a depth of 850 meters, well above the ~2,200-meter depth below which the pressure is too great for magma to create steam. The image at right and the time-lapse videos below show the spreading of the volcanic ash in the atmosphere. Eventually that ash falls down to the surface. USGS https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/54bddd41-7c4a-4a00-8e5a-841674030e6b/Tonga_Volcano_Eruption_2022-01-15_0320Z_to_0610Z_Himawari-8_visible.gif Michael Manga - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/dc17ed34-c40a-421a-b2e2-cfc8cf66a922/tonga-eruption-jan-15-2022.gif Michael Manga - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/53cfbcd9-effb-4246-bd6c-292d338f8e86/slide+12.png Michael Manga - Make it stand out In the podcast, Manga describes the 2012 Havre eruption, which was the largest explosive eruption to date since 1650 AD. As gas vesicles formed within the submarine erupting magma, the magma cooled rapidly and formed pumice, a rock that is full of bubbles and therefore lighter than water. Following the eruption, large floating rafts of pumice drifted across the oceans for months. Martin Jutzeler, University of Tasmania https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/3f1a3820-c0af-4789-9178-d451a55cb5ea/slide+30.jpg Michael Manga - Make it stand out Pumice raft from the Havre submarine volcano seen in the Kermadec Arc in July 2012. HMNZ Canterbury and Rebecca Carey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/21409ac1-3dae-4367-920a-255ef23bfe3f/slide+12-1.jpg Michael Manga Overgrown pumice from the Havre eruption recovered eight months after the eruption took place. Rebecca Carey https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/432a5f1c-e0ee-4e95-839f-0cbcf6cb2164/slide+12-2.png Michael Manga - Make it stand out Scott Bryan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f8e59433-95b2-4fbc-92ec-52b576d51c5f/slide+19.jpg Michael Manga - Make it stand out Map of the seafloor following the Havre eruption showed an extensive area blanketed by pumice. The map was made using multibeam sonar. Individual pieces of giant pumice can be seen. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/44bd5b44-5479-4e7b-a195-b6e80bbab000/slide+75.jpg Michael Manga - Make it stand out The depth at which an eruption occurs determines the style of eruption. The Hunga Tonga eruption occurred at the relatively shallow depth of 150-200 meters below the ocean surface. The magma fragmented on its way up to the vent, creating a large surface area for contact between magma and water. This caused a very large volume of steam to be generated that greatly magnified the explosive power. The Havre eruption started at about 850 meters below the surface, where the pressure was high enough to inhibit steam formation. The erupting magma remained coherent and formed clasts of pumice as it emerged, some of which were buoyant enough to float and form rafts, while the rest fell to the seafloor as giant clasts. In its later phases, the eruption moved to depths of over 1,000 meters, and the magma emerged effusively in thick flows forming a dome on the seafloor. Manga, M. et al. (2018), Earth and Planetary Science Letters, 489, 49 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/75a5cfe4-113c-48ea-abfb-b0ee2ad52921/mud+volcano+Azerbaijan-1.png Michael Manga - Make it stand out In some mud volcanoes, the sediment comes from depths of over 1 km and is mobilized by tectonic activity. Manga and his team were interested in how fast the mud rose and how the eruptions are influenced by earthquakes. Above and right: mud volcanoes in Azerbaijan studied by Manga and his team. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87437344-26bb-4a98-b5ac-75d2e79ce6e7/mud-2.png Michael Manga - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a906650-eeb9-46fd-afcd-c7b028ece6db/20100417_4_17gigjok_gos.jpg Michael Manga In the podcast, Manga mentions the 2010 Eyjafjallajökull eruption in Iceland, which created an enormous cloud of ash that halted air traffic throughout most of Europe. The volcano erupted under ice, and the meltwater produced flowed into the volcanic vent, helping to drive the explosivity of the eruption. The water helped quench the magma to make volcanic ash, and the steam generated from that cooling helped power the eruption. Oddur Sigurðsson, Iceland Meteorological Office https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/74d6c623-63d8-4b84-b92e-ba3820ffee5a/IMG_1311.png Michael Manga - Make it stand out As basaltic lava flows cool under ice, meltwater flows around the lava, and this affects the direction of the thermal gradient. Columns appear at right angles to the steepest temperature gradient as the basalt cools and contracts. The chaotic directions of the columns in this lava flows in southern Iceland reflects this interaction between the lava, ice, and meltwater. Oliver Strimpel https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f283dac9-a195-46ac-8099-4a5387c477a5/2F7FF07F-77D3-43F9-9A19-B24CBACBD364_1_105_c.jpeg Michael Manga - Make it stand out In the podcast, Manga describes how lava flowing over ice can melt and vaporize the meltwater, which then blasts its way through the lava flow making a tiny volcano. These are called rootless cones because there is actually no magma being supplied from below. Above and right: rootless cones made of lava in Iceland. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/87fc3199-65c5-4eb9-97bc-b07f09ba5542/2D4FFCAE-77E9-448E-9442-7EADD2904022_1_105_c.jpeg Michael Manga - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/57723907-1713-412d-81c8-d6af87aae73e/Rootless_Cones.jpg Michael Manga - Make it stand out Above, rows of rootless cones in the Phlegra Dorsa region of Mars, formed by lava interacting with ice, as seen by HiRISE in 2008. Jim Secosky modified HiRISE image, NASA https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0aa1a605-ca16-4d46-9244-ef3dde3ed536/MarsCones-ESP_030192_2020.jpg Michael Manga - Make it stand out Closeup of three rootless cones in Amazonis Planitia on Mars captured by HiRISE in 2013. NASA/JPL/University of Arizona https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ef7f698a-a064-4d80-bff6-820dcf224162/Enceladus+eruptions.png Michael Manga Synthetic image of icy curtain eruptions on Enceladus. The image was compiled from imagery captured by the Cassini spacecraft. The source of the erupted water is a tidally heated liquid ocean below a ~10-km-thick ice cover. As soon as it is ejected, the water freezes and falls back onto the surface as snow, making Enceladus the whitest object in the solar system. NASA/JPL/Caltech/SSI/PSI https://www.geologybites.com/sara-pruss daily 0.75 2026-02-11 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/b97c0a01-6775-4ad9-9954-6b399a6ee69a/sara-pruss-crop.jpg.png Sara Pruss In the podcast, Sara Pruss describes the first multicellular animals to build reefs. They were sponges called archaeocyaths. Pruss explains the evidence that the rise of the archaeocyaths fostered an increase in animal diversity. But they were relatively short-lived, and when they died out in the Middle Cambrian, the diversity declined. Over geological time, reef-building organisms appear and disappear again and again until the corals we have today appeared in the Middle Triassic, about 240 million years ago. Pruss is currently trying to understand why reefs are such a persistent feature of the geological record, despite the environmental stresses imposed on them. She is a Professor of Geosciences at Smith College. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/eb94cc5c-3b5e-447d-a898-7a506c82403e/timeline.-1.jpg Sara Pruss Timeline of reef-building organisms from the Precambrian (PC) at left to the Neogene (Neo, 20.4 to 2.4 million years ago) at right. Although microbes formed reef-like structures in the Neoproterozoic (PC, far left), reefs built by multicellular animals did not appear until the early Paleozoic, of which the earliest were the archaeocyaths, a type of sponge. From then until the present, reefs diversified, underwent extinctions many times, and then diversified again. Paleozoic reefs consisted of sponges, corals, foraminifera, algae, bryozoans, and brachiopods, among others. The major extinction event at the end of the Paleozoic (Permian-Triassic, at the center of the timeline) eliminated these forms as reef constituents, and new groups (e.g., the first scleractinian (stony) corals which dominate coral reefs today) appeared in the Triassic. Lipps, J. H. & Stanley Jr, J. D. (2016), Reefs Through Time: An Evolutionary View in Coral Reefs at the Crossroads https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a9424ce4-e860-4b2d-8f21-a3e651285b74/timeline.-2.jpg Sara Pruss Primary reef builders during the Neoproterozoic (Ediacaran) and early Paleozoic (Cambrian, Ordovician, and Silurian). The Neoproterozoic is primarily dominated by microbial organisms including the stromatolites (see Geology Bites episode with Martin Van Kranendonk). The Cambrian is dominated by a variety of sponge organisms including the archaeocyaths. In the Ordovician and Silurian, coral and stromatoporoid species became the dominant reef builders. The red star denotes the approximate interval of the Mongolian reefs where some of the best-preserved archaeocyath reefs are found. Cordie, D. R. et al. (2019), Palaeogeography, Palaeoclimatology, Palaeoecology 514, 206 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/7627facf-7286-428e-8c24-467ad00b6998/tree+of+life.png Sara Pruss The archaeocyaths are a class of the phylum Porifera (Sponges), the line at the bottom of the tree shown here. As the figure shows, Sponges split diverged from all the other phyla shown very early in evolutionary history. Telford, M.J. et al. (2015), Current Biology 25(19), 876 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/22e93a41-527d-489f-952d-6b6ee358a026/7_Carrara_Archaeos_Microscope_Final.png Sara Pruss - Make it stand out a, b: Archaeocyaths from the Carrara Formation and Mule Springs Formation in the western United states. These are the last known occurrences of archaeocyaths in the western United States. c: Archaecyaths with a microbial coating that was made into the thin sections shown above right in c and d. d: the largest archaeocyath from the Carrara formation. White arrows show microbial coatings forming around archaeocyaths. All scale bars are 5 mm. Pruss, S.B. et al. (2024), Palaios 39(6): 210 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ad55ebc6-554f-4963-ad33-cfcabb007fa0/8_Carrara_Archaeos_Scans.png Sara Pruss - Make it stand out Whatever it is, the way you tell your story online can make all the difference. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf126fee-a585-4834-89fb-7d9ebcd47ad5/thin+sections.png Sara Pruss - Make it stand out Archaeocyath thin sections from the lower Poleta Formation near Gold Point, Nevada. The archaeocyath cups are 1-2 cm in diameter. Courtesy of M. Slaymaker https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/83b74c16-5ed5-47d3-94f0-ccafec0d14f1/archaeocyatha3.jpg Sara Pruss Sketch of form and structure of achaeocyaths. Archaeocyatha were sessile, filter-feeding, calcareous, sponge-like organisms, characterized by a conical, vase-shaped, or cylindrical skeleton. Their structure consisted of two porous, nested calcite cones (inner and outer walls) separated by a space called the intervallum, which contained vertical plates (septa, taeniae) or horizontal plates (tabulae). Root-like structures at the bottom (holdfast) secured them in place. https://alchetron.com/Archaeocyatha https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/718bb719-912d-45a1-b17b-fbc42d67f1de/Fig3_Lighthouse_point_counts.png Sara Pruss - Make it stand out Archaeocyath patch reefs on the southern coast of Labrador near Forteau. These are exposed along the sea cliffs, and Pruss and her team sampled the reefs and surrounding beds to determine how much skeletal mass was present within and around the reefs. TFM is the percentage of total fossil material counted in thin section, and archaeo represents the amount of skeletal material that is comprised of archaeocyaths. Notably, some beds outside the reef mounds themselves have high skeletal abundance without any archaeocyaths, for example F-LH-9-9, TFM: 9.5%, 0% Archaeo. Here, many of the animals living on and around the reefs would have been trilobites and echinoderms. Pruss, S.. B., et al. (2012), Lethaia 45(3), 401 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ec273808-cd69-4c66-87b6-9f6b4ed10fc2/figure+4+ArchaeosSEM.png Sara Pruss - Make it stand out Phosphatized internal molds of archaeocyaths from the upper Salaagol Formation in southwestern Mongolia. Pruss, S. B. et al. (2019), Palaeogeography, Palaeoclimatology, Palaeoecology 513, 166 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1a5829b5-7eaf-4b1b-8e72-4b8af7bfc362/IMG_0622.JPG Sara Pruss - Make it stand out The upper Harkless Formation and the archaeocyath reefs in southern Nevada. In the foreground is sandstone that overlies the archaeocyath reef beds. In the background, the ridges on the hills represent the archaeocyath reef horizon and overlying siliciclastic beds. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5de36ce7-46ad-4074-9953-5af02ab6129c/IMG_0599.JPG Sara Pruss - Make it stand out The gray beds in the center of the outcrop to the right of the measuring stick (2 m) are the archaeocyath reef mounds of the upper Harkless Formation. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/db29116b-6a43-43a7-bd6a-042ba13fbcf4/IMG_0584.JPG Sara Pruss - Make it stand out In this closeup of an upper Harkless Formation archaeocyath reef, the cup architecture of the archaeocyath skeleton can be seen, mostly as cross-sections of cones. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6af6881e-55a6-475a-b706-6f244f362637/Close-Up_archaeo_reef_fabrics.png Sara Pruss - Make it stand out In this portion of the reef, occasional circular cross-sections of the archaeocyath cones can be seen (white arrows), as well as the dark gray microbial fabrics surrounding them. This shows the close relationship between the archaeocyaths and the microbial fabrics that lived with them. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6c9c3587-7858-4699-94eb-9d50a7e74296/IMG_6538.jpg Sara Pruss Archaeocyath individual from the lower Harkless reef near Gold Point, Nevada, showing the cone shape, the cross-section revealing the intervallum and septae, and central cavity. (See the labeled sketch above.) Rheva Wolf and Quinnlan Steele https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4ea8cdd6-c5c1-4a1e-b91e-7f3ba184f11d/modern+sponges.png Sara Pruss - Make it stand out Modern calcareous sponges provide the closest analog to the archaeocyaths. https://www.inaturalist.org/taxa/60583-Calcarea https://www.geologybites.com/hal-levison daily 0.75 2026-03-06 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f0e33ac0-2d1e-4785-9f46-b2d5481933f4/HL+at+Briefing+NASA.jpg Hal Levison A key question about the early history of the Solar System is whether the giant planets formed roughly at the distances from the Sun they presently occupy, or, as some theories predict, much closer to the Sun. The discovery of other solar systems with radically different configurations of planets has made this question more pressing, since it appears that the configuration of the Solar System might be atypical. In the podcast, Hal Levison explains why the Trojan asteroids of Jupiter offer us the best opportunity to discriminate between the various models of Solar System evolution. And that is why a spacecraft called Lucy is now well on its way to a rendezvous with these asteroids. Hal Levison is the Principal Investigator of the Lucy mission. He studies the dynamics of astronomical objects and, in particular, the formation and long-term behavior of solar system bodies. He is one of the original proponents of the Nice model (named after the city where it was conceived), a scenario that proposes the migration of the giant planets from an initial compact configuration closer to the Sun to their present positions. He is Chief Scientist in the Department of Space Sciences at the Southwest Research Institute in Boulder, Colorado. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bdb99b39-d3d4-4ab4-872b-282056d0578a/trojans_nolabels.gif Hal Levison Animation showing the leading and trailing swarms of Trojan asteroids (green) on either side of Jupiter (yellow). The inner planets Mars (red), Earth (blue), Venus (white), and Mercury (brown) are also shown. As Levison explains in the podcast, the Trojans occupy a stable orbit where the centrifugal force and the gravitational pull of the Sun and Jupiter are balanced. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/9a418444-734d-4f8e-bb0d-e85c6e7b314e/Lucy+to+scale+w+person.png Hal Levison Lucy’s two solar panels are the largest part of the spacecraft, each measuring 7.3 m in diameter. These are needed as Lucy is going further from the Sun than any previous solar-powered mission. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf418cbf-c349-4491-a16d-9488491226ac/Instruments.png Hal Levison Instruments carried by Lucy. L’Ralph is a color-imaging camera, which will take color images of the Trojans and help determine how active they are. It also has an infrared-imaging spectrometer that will look for the absorption lines that serve as the fingerprints for silicates, ices, and organics that are expected to be present on the surface of the Trojan asteroids. L’LORRI, the LOng Range Reconnaissance Imager is a high spatial resolution visible imager covering the wavelengths 0.35-0.85 microns. This camera will provide the most detailed images of the surface of the Trojans. L’TES is a Thermal Emission Spectrometer (6-75 microns) that will allow the Lucy team to learn much more about the properties of the Trojans, such as their thermal inertia andhow well the bodies retain heat, which tells us about the composition and structure of material on the surface of the asteroids. Lucy will also use its High Gain Antenna to determine the masses of the targets using the Doppler shift of the radio signal. It will also be able to use its terminal-tracking camera (T2CAM) to take wide-field images of the asteroids to better constrain the asteroids’ shapes. The combination will allow the bulk density of these bodies to be determined. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d97a6328-28d0-492b-bc96-648e33d71952/Lucy+prelaunch.png Hal Levison Lucy atop an Atlas V 401 rocket on the launchpad. As Levison explains in the podcast, a relatively small rocket was used to save costs. This resulted in a slow initial speed relative to the Earth. Multiple Earth gravity assists were used to accelerate the spacecraft into an orbit that reaches out as far as the orbit of Jupiter and the Trojans. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bf400ec7-3d6a-447b-9eb3-26b37f9a1e37/traj_Dinkinesh.jpg Hal Levison The first body approached by Lucy in 2023 was an asteroid named Dinkinesh in the main asteroid belt. Although primarily intended as a test of Lucy’s instruments, it turned out to be an interesting object in its own right. Imagery from Lucy’s L’LORRI revealed a satellite that is itself a contact binary. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/296ada9e-c8a9-4ad3-9795-430828c0b656/Dinkinesh-FirstLook-LLORRI.png Hal Levison Dinkinesh and its satellite captured from a distance of 430 km. Dinkinesh has a diameter of 700 m. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/f7d56ebe-5952-4910-8441-d0b8592bb3be/Dinkinesh+with+satellites+contact+binary.png Hal Levison - Make it stand out Dinkinesh and its satellite Selam, showing that the satellite is a contact binary. It is the first contact binary satellite of an asteroid ever seen. Each component of Selam has a diameter of 100 m. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/30383097-85ee-4ac5-b4ca-05404ba90248/djencounter_movie_release_v2.gif Hal Levison Donaldjohanson is about 8 x 3.5 km in size. It is a fragment of a massive collision that occurred about 150 million years ago that produced the Erigone family of asteroids. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bb89d6eb-43ae-469e-9030-67fc7778cd89/Lucy_Plaque_FINAL_hires.png Hal Levison - Make it stand out Computer simulations predict that the orbit that takes Lucy to its final encounter with Patroclus in the trailing Trojan swarm is stable with an average lifetime of 2 million years. At its farthest from the Sun, it reaches the orbit of Jupiter, and at its closest to the Sun, it flies just within the orbit of the Earth. Levison and the Lucy team decided to place a plaque on Lucy intended as a message to our distant descendents. By contrast, the Pioneer and Voyager spacecraft are traveling away from the Solar System, and therefore their plaques were designed to tell aliens about our existence and civilization. https://www.geologybites.com/esther-sumner daily 0.75 2026-03-26 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/0e670c77-55f0-44b9-b646-7c16ae75ceb0/ES-2.jpg Esther Sumner Turbidity currents are massive underwater events, sometimes stretching for hundreds of kilometers and lasting for days. But since they mostly occur in the deep ocean, we have rarely observed them directly. In the podcast, Esther Sumner describes how she and her team instrumented an active submarine canyon with “smart boulders” and acoustic doppler current profilers to reveal how sediment moves across the seafloor. She also tells us about the day her team accidentally flew an underwater robot into a live turbidity current, which swept the rover down the Mendocino canyon off the California coast. She is an Associate Professor of geology and geophysics at the University of Southampton. In the image, Sumner is scanning a sediment core. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5d21105f-6a7c-43d1-8626-aebf8c8d009f/13.+Siccar+Point+unconformity+between+Silurian+greywackes+underneath+and+Upper+Devonian+sandstone+above.jpg Esther Sumner - Make it stand out The steeply-dipping rocks below Hutton’s famous unconformity at Siccar Point in Scotland are Silurian marine turbidites. They appear in the lower right half of the image around the puddle. Rob Strachan https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bbad8f91-d20c-4bc8-acea-f6aacc6aa3c7/moauntain-scale+turbidite.jpg Esther Sumner - Make it stand out Outcrop of turbidites in the Italian Apennines showing the repeated bedding draped across an entire mountainside. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/52410acc-1d67-4eda-89d0-ea0184a2bda3/Bouma+Sequence.png Esther Sumner The classic facies succession for a single-flow turbidite is called the Bouma sequence. The diagram shows the sequence first described by Arnold Bouma in 1962, with five distinct, vertical layers representing deposition from a waning turbidity current. Multiple turbidity currents (a turbidite sequence) form repeated graded sequences. Complete Bouma sequences are rare and turbidites often contain other sedimentary structures as well. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aa4384d8-e7aa-4905-adad-bec94496cf56/Outcrop4+%28Bouma%29.png Esther Sumner Turbidite outcrops showing various typical structures. Top left: two of the five Bouma divisions: planar laminated sand and ripple cross-laminated sand. Bottom left: grain-size break within a single turbidity current. Below the break is structureless sand, above the grain-size break is convolute lamination (a type of dewatering structure). As Sumner mentions in the podcast, it is quite rare to see the textbook Bouma sequence in the field. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/81a77716-3304-4a49-8462-8206a86be7f5/slide+73+TC+diagram.png Esther Sumner - Make it stand out Diagram of a turbidity current showing two main components: a fast, short-lived destructive base flow and a long-lived, dilute cloud that rides above the base flow. The base flow can sweep boulders and experimental equipment along with it. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c1808cfa-147d-444f-8102-5f88ec6e5836/3D+diagram+of+flow.jpg Esther Sumner Turbidity currents often flow down submarine canyons. Such canyons are erosional conduits that enable sediment to be transported from the terrestrial and shallow marine environment out into the deep sea. In the diagram, the vertical scale is greatly exaggerated. Encyclopaedia Britannica, Inc. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/821e243c-5999-4409-bc4c-4f6fd1e75a81/Monetery+Bay+2.png Esther Sumner The Monterey Canyon is a submarine canyon off the west coast of California. Together with the Monterey Bay Aquarium Research Institute, Sumner has been involved with several studies of turbidity currents there. In the cross sections at left, the vertical scales are greatly exaggerated but the same in both sections, showing that the Monterey Canyon is similar in scale to the Grand Canyon. Base map made with GeoMapApp (www.geomapapp.org) / CC BY https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d5f23933-b743-4616-a0ca-5f02fe56fa4d/Bengal+fan.jpg Esther Sumner When the submarine canyons reach the deep sea, the sediment they carry can be deposited as submarine fans. These are some of the largest sediment accumulations on Earth. In the podcast, Sumner explains that the Bengal fan is composed of sediments from many millions of years of erosion of the Himalayas. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/d4c9ddc3-d05a-4670-828c-b481d768d692/relative+durations.png Esther Sumner - Make it stand out Plot showing relative durations of various turbidity currents at the locations marked with red stars in the map above. The turbidity currents of the Congo Canyon are far more prolonged than any other monitored oceanic turbidity currents. In the podcast, Sumner talks about how some flows reach steady state, maintain constant velocity, and stretch out over time — and she specifically names Congo Canyon as the place where turbidity currents are being monitored for much, much longer durations, i.e., days or even in excess of weeks. Top: Base map made with GeoMapApp (www.geomapapp.org) / CC BY Bottom: Azpiroz-Zabala, M. et al. (2017), Science Advances 3: e1700200 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4ac8229e-3e2e-47ed-b353-5bc1adb7cc13/Monterey+4.png Esther Sumner Sumner and her team used acoustic doppler current profilers to measure the velocity profile of the water flow in Monterey Canyon. As indicated in the inset at bottom left, the instrument directs beams of high-frequency sound toward the seafloor and looks for the reflections coming from different depths. The use of three dispersed beacons allows for the flow direction as well as its speed to be measured. We can deduce flow velocities from the shifts in frequency of these reflections. The results, plotted at bottom right, show the velocity profile peaking at up to 8 m/s. Base map made with GeoMapApp (www.geomapapp.org) / CC BY https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/4b47c6f0-48a6-4d03-868e-7584fe602f32/smart+bouder+2.jpg Esther Sumner - Make it stand out In the podcast, Sumner describes measuring flows on the seafloor with “smart” boulders. https://www.mbari.org/technology/benthic-event-detectors/ https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/bcd65d70-6ce3-482e-b69d-a7bbf89ddc1a/smart+boulder+internals.jpg Esther Sumner - Make it stand out Smart boulders contain accelerometers and depth (pressure) sensors. They also have acoustic modems, enabling them to transmit data, even through over a meter of sediment. The data is picked up by a wave glider (right). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/2c757636-4ab7-41b7-8c6a-b7eff763b112/wave+glider.jpg Esther Sumner - Make it stand out Wave glider, serving as a mobile hotspot for the smart boulders. https://www.mbari.org/technology/wave-glider-based-communications-hotspot/ https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/080efcff-dd80-41fb-b934-718a1df85f1d/ROV+DocRicketts.jpg Esther Sumner In the podcast, Sumner describes the day when she was aboard a ship operating the remotely operated vehicle (ROV) Doc Ricketts, which is the size of a small car. Equipped with strong lights, it can descend to a depth of 4,000 meters. https://www.mbari.org/ https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/34b4e286-e538-46c5-9047-879a4f08992f/turbidity-animation.gif Esther Sumner Cartoon (not to scale) of the research vessel Western Flyer at the surface, the ROV Doc Ricketts near the seafloor, and the two types of flow that affected the ROV in Mendocino Canyon. Kim Fulton-Bennett, (c) 2015 MBARI Sumner E.J., and C.K. Paull (2014), Swept away by a turbidity current in Mendocino submarine canyon, California. Geophysical Research Letters, 41(21): 7611-7618. doi.org/10.1002/2014GL061863 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/1202b8b6-830c-420a-af5d-2a9cd4378fd5/Taiwan+1.jpg Esther Sumner Map showing the complex tectonic setting of Taiwan. The region experiences frequent large earthquakes and high uplift rates. https://commons.wikimedia.org/wiki/File:Philippine_Sea_plate.JPG https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/c56112ac-bd72-4a51-8ffc-efba9face736/Pingtung.png Esther Sumner Location of cables south of Taiwan broken by submarine flow triggered by the Pingtung earthquakes in 2006. Two epicentres are shown by black stars. Turbidity currents were triggered by the earthquake, the largest one traveling down the Gaoping canyon, progressively rupturing cables (numbered circles). As Sumner describes in the podcast, the timing of the rupture of the fiber-optic cables provides a way of measuring the movement of the turbidity currents triggered by the earthquake. Speeds of 13 m/s were inferred in the mid-canyon region and 6 m/s at the Manila trench. Talling, P. T. et al. (2012), Sedimentology 59, 1937 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/aa6a90a7-6038-42ee-8e00-2b8ad5037af1/0_What_is_a_turbidite.png Esther Sumner - Make it stand out Monterey canyon is an example of a land-attached canyon where the head is practically at the coast. In such canyons, the source of sediment that can feed turbidity currents is long-shore drift and river sediment. Base map made with GeoMapApp (www.geomapapp.org) / CC BY https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/8d8dbd31-4def-49e2-bc12-2833423ca092/Whittard.jpg Esther Sumner - Make it stand out Sumner and her team are currently working on Whittard canyon, a land-detached canyon off the UK’s southwest coast. Such canyons were assumed to be inactive at present-day sea level, but recent work shows they can have fast, destructive turbidity currents. NASA WorldWind and Mike Norton https://www.geologybites.com/steve-jacobsen daily 0.75 2026-04-03 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/a144133c-0e53-426b-8993-3a862f90664e/IMG_1780.jpg Steve Jacobsen Most of the material in the Earth and other planets exists under extremes of pressure and temperature quite unlike those we inhabit on the surface of the Earth. Steve Jacobsen is a mineral physicist who studies how rocks and minerals behave under such alien conditions. In the podcast, we discuss his experiments and what we’ve learned about three extreme environments: the core-mantle boundary, the mantle transition zone, and the surface of the Moon. Jacobsen is a Professor of Geological Sciences at the University of Colorado Boulder. The image shows him in his Raman spectroscopy lab at Northwestern University. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/39a7f413-4c1f-4b77-9bf8-810c002247a6/Section+GeologyIn.com.png Steve Jacobsen - Make it stand out Diagrammatic cross-section of the earth showing the core-mantle boundary at a depth of 2,900 km and the mantle transition zone between the seismic-wave speed discontinuities at 410-km depth and 660-km depth. Copyright GeologyIn.com https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/ccaf6917-2e6f-4662-b8ee-864579e46c85/GraphicalAbstractVER1.jpg Steve Jacobsen In order to reach the temperature and pressure conditions that prevail at the core-mantle boundary the sample is subjected to a two-stage process: an initial shock to heat the sample, followed by a subsequent shockless “ramp” compression that increases the pressure without significantly further heating. If the sample was just shocked to reach the required pressure, it would be accompanied by heating to a temperature much higher than the target 4,000K temperature. This is indicated by the dotted blue line in the graph below. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/78e3829f-82d8-4aca-8de6-e764162e6b37/fp_ramp_cartoon.jpg Steve Jacobsen Diagram showing how temperature and pressure increase with depth in the Earth. Superposed on the diagram in blue are the temperature-pressure paths taken by samples in the experiments Jacobsen describes in the podcast. The dotted line shows how the temperature and pressure increase in the sample if it is simply shocked, equivalent to being hit by a hammer. But to reproduce the conditions in the mantle, the experiments depart from the shock curve as shown by the solid blue line to follow the Earth’s geotherm, shown in green (present Earth) and blue (the hotter early Earth). https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/43c0b83c-8aab-4b27-9088-0ba7e1bd52c2/sandia-z-machine.jpg Steve Jacobsen - Make it stand out The Z Machine at Sandia National Laboratories, Albuquerque, New Mexico. In the podcast, Jacobsen describes how he uses this machine to study the properties of mantle material at the pressures and temperatures that prevail at the core-mantle boundary. The Z machine is 33 metres in diameter and is the most powerful pulsed-power facility in the world. The concentric rings of metal modules visible in the image are banks of capacitors that store huge amounts of electrical energy. When fired, all of this energy is discharged simultaneously inward along transmission lines toward the small central hub, where a tiny target sample sits. There, the 20-mega-amp pulse — lasting a few nanoseconds — generates the desired pressures and temperatures in the sample. The yellow safety railings, walkways, and blue water-cooling pipes give a sense of the machine's industrial scale, yet the science happens in a target no larger than a thimble at the very centre. Sandia National Laboratories https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/e6e00778-5019-46d1-8a36-91854f603f2c/The_Z_Machine_%288056998596%29.jpg Steve Jacobsen - Make it stand out The Z Machine during a discharge, captured in a long-exposure photograph. The impressive branching arcs and blue-white glow are produced by the intense electromagnetic fields ionising the surrounding air — essentially energy leaking from the machine during the pulse. The actual experiment is hidden from view, taking place inside a sealed target chamber at the centre. Sandia National Laboratories https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/deeb8b58-6589-424e-80c4-2a8540205d88/A1477_BenchtopPeople1.jpg Steve Jacobsen Steve Jacobsen (right) and a colleague examine a target assembly for the Z Machine at Sandia National Laboratories. The precision-machined disc carries the tiny mineral sample at its centre — the thimble-sized target where the full power of the machine's converging electrical pulse will be focused. This is the hardware that bridges the 33-metre-wide ring of capacitors seen in the above images and the millimetre-scale crystal samples shown below. Sandia National Laboratories https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/542b75d7-94e8-4ced-98f3-d4eb2b25f271/DAC-5.jpg Steve Jacobsen Diamond anvil cell. In the podcast, Jacobsen also describes using a diamond anvil cell to compress samples to core-mantle boundary pressures but maintaining the sample at room temperature. These experiments enable him and his team to use X-ray diffraction to determine the structure of the material at high pressure and also to study the sample’s optical properties. By varying the composition of https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/117addb4-a664-401b-b929-59869cb86a6c/MgFeO.jpg Steve Jacobsen Crystals of ferropericlase with varying iron content. From left to right: pure MgO (periclase), transparent and colorless; 5% iron, amber; 20% iron, nearly black; and pure FeO (wüstite), fully opaque. In the podcast, Jacobsen describes how increasing the iron content of ferropericlase simultaneously raises its density and lowers its shear-wave velocity — a combination that could explain the puzzling seismic signature of the ultra-low velocity zones at the base of the mantle, where material is both anomalously dense and anomalously slow. His experiments on the Z Machine aim to measure these properties across a range of iron contents at core–mantle boundary pressures, to see whether iron-enriched ferropericlase can match what seismologists observe. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/6801a817-8e96-4889-a235-5b4696c0b6d7/Jacobsen-wadsleyite-crystals.jpg Steve Jacobsen Wadsleyite crystals. These deep green crystals are the high-pressure form of olivine that is thought to be the dominant mineral in the mantle transition zone, between about 410 and 520 km depth. Wadsleyite is of particular interest because its crystal structure can incorporate small amounts of water as hydroxyl groups — making the transition zone a potentially vast reservoir of water within the Earth. These crystals were synthesised in the laboratory at high pressure; wadsleyite does not survive the journey to the surface intact, as it reverts to olivine when pressure drops. https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/09c54ecf-27c5-4c30-ab9c-84fc8b2e932a/BlueRingwoodite.jpg Steve Jacobsen A crystal of ringwoodite. This is the high-pressure polymorph of olivine that is stable between about 520 and 660 km depth in the mantle transition zone. In the podcast, Jacobsen points out ringwoodite's remarkably large capacity to incorporate the chemical components of water as hydrogen defects in its crystal structure. This property makes the transition zone a potentially enormous reservoir of water within the Earth. Jacobsen suggests that the transition zone may act as a kind of sponge, absorbing water and other incompatible elements from ascending melts — an idea developed by Bercovici and Karato in their "transition zone water filter" model. He goes further, speculating that a planet may need to be large enough to sustain the pressures required for ringwoodite to exist before it can hold liquid water on its surface — noting that Mars, which barely reaches these pressures, has no transition zone and no surface water. Image by Jasperox CC BY 3.0 https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/5bdf8a56-7569-496e-ac33-5f66d52a4772/ICON_ProjectOlympus-1.jpg Steve Jacobsen Artist's rendering of ICON's Project Olympus concept for 3D-printing a landing pad on the lunar surface using local regolith. In the podcast, Jacobsen describes how his group is developing the materials science behind this kind of additive manufacturing — using lasers to melt simulated lunar soil into solid building material, one layer at a time. ICON https://images.squarespace-cdn.com/content/v1/5eed6938a6185b0158bd62dc/626043f3-b7d9-4b49-81dd-7e3763b0bd74/VMX-Jacobsen-ICONinc-VER2.jpg Steve Jacobsen A cross-section through a 3D-printed brick made from lunar regolith simulant by laser powder bed fusion. The layering is clearly visible — each layer represents a single pass of the laser melting a bed of simulated lunar soil, which then solidifies before the next layer is added. In the podcast, Jacobsen describes the material as having roughly the composition of a mixture of basalt and anorthosite. The porosity and bubbles result in part from volatile elements such as sodium and potassium boiling off during melting. A key challenge Jacobsen discusses is that real lunar regolith — modified by 4.5 billion years of space weathering and coated with nanoscale iron particles — may behave quite differently from the simulants used in the lab, particularly in how it absorbs laser energy. ICON