This transcript was generated automatically and lightly edited for readability.

Oliver Strimpel: This is Geology Bites with Oliver Strimpel. Deep time is the temporal runway along which all of Earth history has unfolded. I find it quite astonishing that this runway is long enough to encompass fully one-third of the age of the universe. Put another way, when we handle a piece of Earth's most ancient rocks, the minerals in our hand were assembled when the universe was just two-thirds of its present age. I've been wanting to do an episode on this topic for some time now, but when I came across an article by Richard Fortey written for the Geological Society of London, I knew who I should talk to.

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, we talked about measuring time with trilobites. 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. Richard Fortey, welcome back to Geology Bites.

Richard Fortey: It's good to be here.

Oliver Strimpel: What time scales were thought to span Earth history before the advent of deep time?

Richard Fortey: Well, it depends on how you compute how old the Earth is. A lot of the early estimates, for example those made in France particularly, were, I would say, actually quite scientific. They were attempts to get to an answer, knowing that there must be an answer out there. The famous Count Buffon, for example, produced an estimate which would now be regarded as absurdly short. But it was based on the perfectly good scientific notion of the Earth cooling from a liquid state into a solid state, and how long that would take. Of course, it didn't factor in the enormous importance of radioactive decay and the production of heat within the system, but it was a scientific response. And you could even argue for poor old Bishop Ussher, who always seems to get a bad press. It was he who totted up the lives of the biblical characters one by one and came back to the figure of 4004 BC, the famous figure for creation. It's easy to mock, but what he thought he was doing was a perfectly rational process to get a figure, at least for humanity. So the story of deep time is really one of ever-increasing accuracy about the age, particularly of the solar system and the planet, and of dethroning human beings themselves from the centrality of that position, and eventually eliminating them from the calculations.

Oliver Strimpel: How did we discover deep time? Was there a particular pivotal moment or observation that really tipped the scales from thinking in terms of thousands of years to millions and millions?

Richard Fortey: Well, I think the classical view of this is that there was a European Enlightenment that preceded the British perspective on this, but the issues had been around long before that. And there was a point, particularly with the Scottish Enlightenment, James Hutton in Scotland, who recognized the continuity of geological processes, but he did so in a conception of seeing neither a beginning nor an end.

Oliver Strimpel: That's right. He said, "We find no vestige of a beginning, no prospect of an end."

Richard Fortey: Yes, his idea was that time was, as it were, infinite, and we couldn't know the beginning and the end. There were various attempts to actually put figures on the time that must have accumulated to allow the world to have formed, but this was initially when the rocks themselves were subdivided into formations, and those formations could be recognized widely and put in order. It was obvious that one formation underlying another formation had to be older, and you built it up like some sort of layer cake, one layer on another and another and another, and then made various calculations about how long it would take for those cake layers to add up to form a whole sedimentary pile.

And then the time scale slipped. I mean, remember 4004 BC. Even if you did very simple calculations, based on Hutton's and Lyell's principles, you would actually measure rates from things you could measure in the field now and extrapolate them back into the past. So how long would it take for all those sediments that were being mapped and recognized as one lying over another lying over another, how long would it take for them to accumulate? It was obvious even by the 19th century that we were dealing with millions. But just how many millions was the question. And that had to wait for methods of calibration, particularly from the decay of radioactive minerals.

Oliver Strimpel: Just to come back to this pivotal moment when we came to realize that the immensity of time was measured in millions, or even tens or hundreds of millions, rather than in thousands. One of the things that is often mentioned is that Hutton and his colleagues came across an unconformity at Siccar Point, a promontory on the east coast of Scotland. And somehow they managed to infer that to get something like an eroded landscape before another layer was deposited and then tipped up required orders of magnitude more time than mere thousands of years, mere millennia, could supply.

Richard Fortey: Yeah. There were other critical places, but Siccar Point is one of the holy sites in geology, in a way, because there you had to recognize from the rocks in front of you that there was a great period of earth movements, and that had to be followed by erosion. And then, in turn, eventually the sea would return and lay down some more sedimentary rocks. Just that one locality encapsulated the necessity for vast eons of time in order to accomplish the geology you could see in front of you. There were a number of what you might call critical cases where the scales might fall from people's eyes, geologically speaking.

But remember that this is also part of perception and belief. I can remember just a few years ago going down into the Grand Canyon on mule back, which is something that takes hours and hours and hours. And as you go down, you see magnificent strata laid out one after the other. I was with some very, very nice people who turned out to be creationists, and about two-thirds of the way down the Grand Canyon, they proceeded to explain to me how everything we saw had been carved out by Noah's flood. So belief systems actually control what you see, and partly it was the capacity to make objective observations that turned geology into a science and almost made deep time a necessity in order to explain what you could see in the rocks in front of you, and in the rocks as you went round Europe.

Oliver Strimpel: That's really interesting. As you say, it's partly in the eye of the beholder, but if you're taking an objective view, just coming back to Siccar Point as an example, you really would struggle to explain how all those sequences of events that, as you say, were encapsulated in a single site could have taken place in centuries or millennia, wouldn't you?

Richard Fortey: Yes, but if you are a sufficient believer in the flood, you could probably convert what you see into something that could be explained by some sort of flood. And remember, the path of this whole process was what you might call the gradualistic view of the evolution of the planet. That is, one event follows rather smoothly from another. Perhaps nervousness about things like the flood pushed the idea of catastrophes, geological catastrophes, global catastrophes, to one side for decades. Charles Lyell's principles, often called uniformitarianism, of being able to look at the processes going on right now to understand the processes recorded in the rocks that went on in the past, were such a creative way of looking at strata that they eclipsed for many years the notion that Earth history had been interrupted by catastrophes.

If you go back to 18th-century France, the idea of a succession of catastrophes was very much part of geological modeling. But you could say that for many, many years, Lyell's, or Lyellian, principles elbowed out the idea that the Earth might have been punctuated by catastrophes of the extinction-of-the-dinosaurs variety, in favor of smooth, gently evolving landscapes, using the principles of erosion and deposition that we could see today, extended into deep geological time. So even the process of discovering deep time evolved to take on board more events in Earth's history than was initially the case.

Oliver Strimpel: And it seems that, in a way, we've come full circle now, because a modern understanding of deep time does indeed have gradual change and punctuation by catastrophes.

Richard Fortey: There were millions of years, somewhere in the later Precambrian, the "boring billion," where, if you like, the Lyellian processes just quietly went on uninterrupted. But now I think our current view, of course, is much more dynamic: there were major events, particularly generated by plate collisions, that interrupted this kind of smooth, gently evolving world that Lyell perhaps might have preferred.

Oliver Strimpel: What was the reaction at the time to the realization that the history of the Earth was vastly longer than previously thought?

Richard Fortey: We tend to think of the reaction as, did society throw up its hands in horror? I think there was a kind of community of scholars across Europe who were basically freethinking. They had been dealing with extended notions of deep time for a long time before it actually percolated into what you might call public consciousness. Then perhaps there was a reaction from certain parts of the religious community, who probably felt the notion of deep time was unsettling and might even challenge the faith. That's one of the reasons why resistance was met. But among the freethinkers, I think, the notion of much longer periods of time for Earth history was quite a familiar one. These savants were used to toying with an idea that took many, many years to become part of the mainstream.

Oliver Strimpel: For many years following the resetting of the geological time scale, and even before it, as you said, the time scale was really based upon the stratigraphy: the piling up of the sequences, known about as a series of events, and how much time you need for that. And then absolute age dating, obtained from the radioactive decay of certain elements, actually put figures on it.

Richard Fortey: Those figures could be tested and retested and refined, but once you reset it, you reset everything else, and you've then got time to accommodate the subsequent discoveries, if you like, or subsequent realizations of such things as the continuous movement of plates on the surface of the Earth, which are made possible by having these great spans of time available for the reorganization of the whole planet.

Oliver Strimpel: That's interesting. I suppose if you think of history over such a short time scale as being all the time available, it does by necessity limit the number of changes that you can expect to have happened in that time. And the Earth was really essentially fixed during those few millennia.

Richard Fortey: Well, the story of 20th-century geology is really the freeing of the continents, and the realization that, for example, Gondwana and Pangaea, which had been accepted for a long time... But it was another revolution to realize, because of the time we've got available, that Pangaea itself was simply a, if you can use the word, passing phase. It went on for millions of years, but it was a phase in the history of the planet, and it was preceded by dispersed continents again. And then if you look further back into the murk of the Precambrian, perhaps those continents themselves came together in another Pangaea still further back in geological time. So you could say that what geologists had was a kind of freedom of vision, and they needed billions of years to allow it to play out on our home planet. And of course, beyond that, the astronomers made it part of the evolutionary model for our solar system. So yes, the notion of deep time has changed everything.

Oliver Strimpel: When deep time was established, it was really with respect to the stratigraphic time scale, and then all the work that you and others have done to pin down times based upon the evolution of fast-changing species such as the trilobites, which you're an expert on. That was all done really within the framework of deep time, but without the help of any absolute dating system, wasn't it?

Richard Fortey: Yes, absolutely, that's right. I think it's an important point. We always go back to our own geological saint, don't we? William Smith and his geological map. He used fossils as markers, but Smith himself, though he may have entertained private thoughts about evolution, was interested in fossils as time markers. I don't think he had any particular commitment to evolutionary theory. His subdivision of Britain's rocks, for example, was that of a practical man for practical ends, to help such things as the pushing through of the canals at the time, and his theoretical involvement was fairly minimal.

So what we had, long before figures were put on it, was a time scale domesticated by naming the periods: Cambrian, Ordovician. That's somehow much easier to grasp. I still have to remind myself what the latest absolute figures for the base and top of the Ordovician are. Human beings don't work like that, quite, do they? They like memorable names rather than 217.6 million. So the naming of the geological periods, and the Precambrian below, admittedly, was still terra incognita, was a way of domesticating time in a strange way. And then after that, when radiometric dating allowed absolute figures to be put on them, most of the work had already been done psychologically, because the geological periods had been well characterized by their fossil contents, even to the extent that popular encyclopedias were produced in the 19th century. I well remember my first Arthur Mee encyclopedia as a kid, leafing through the pages and getting to the age of the dinosaurs, the era of the trilobites. So it was pretty much a matter of domesticating what was already known to be a vast period of time, but without necessarily having to have the figures to hand.

And then a lot of the 20th century was involved with investigating the so-called Precambrian, which Darwin had looked at with a certain measure of discombobulation: what do we do about that? And the Precambrian now is, I won't say tamed, but certainly, for example, the notion that it was lifeless has been completely overturned. And the importance of that long period in the Precambrian, when organisms themselves altered the Earth's atmosphere, has now, I think, been absorbed into popular culture, but it took a very long time.

Oliver Strimpel: As a paleontologist, you have a very good handle on the tamed subdivisions of deep time from the fossil record. Did the advent of radiometric dating actually change your view of anything? Did things have to be reordered, or was it just putting a few decimal places on numbers that we already knew?

Richard Fortey: Yes, that's a good question. Of course, not all rocks are full of fossils, and vast swathes of ancient desert deposits, things like that, actually relied on the absolute dates that could be obtained from minerals, to the extent that the fossil record would be irrelevant for those sorts of deposits. And of course, I haven't even talked about igneous rocks, the timing that could be obtained for the intrusion of the vast bodies that occupy so much of our mountain belts. That's got nothing to do with the fossil record. It's got nothing to do with the relative time scale. Many of those now go straight to the radiometric clock to say what age they are. The accurate dates have been fed into mainstream geology, fossils having done their duty.

Oliver Strimpel: And yet we use the stratigraphically determined names in parallel with the so-many-millions-of-years throughout.

Richard Fortey: Yes, indeed, it gives you a language. And of course a lot of science is about developing a language which you can exchange between people, which has a certain degree of precision. And the feeding in of well-supported absolute ages to the old stratigraphic terms has changed the way you put together global pictures, because traditionally you relied on the correlation of strata between one part of the world and another, often based on fossils. Well, if you've got the right sort of rocks, you don't have to worry about that now. You go straight to the age.

Oliver Strimpel: We've already talked about the implications of deep time for fields other than geology, and in particular you mentioned evolution and astronomy. Talking about evolution, do you think that the availability of deep time, if you like, was crucial in the development of Darwin's thinking about evolution?

Richard Fortey: It's well known that Darwin had Lyell's Principles of Geology sent to him even on the Beagle. So when you say essential, absolutely it was. It fed into his mindset, it set his way of thinking, it gave him the time that he needed for descent with modification, which initially was a gradualistic idea. It's become a little more punctuated since. But it was crucial to Darwin, just as it was crucial to those who wished to interpret the early years of the solar system. The influence of just having those time scales available can't be overstated, really. But it soon became accepted, and people, including me, became very insouciant about throwing figures like 550 million years ago around without acknowledging the long and tortuous journey to get to those figures.

Oliver Strimpel: Time scales that are so far beyond our experience are really hard to grasp, and some people find them frightening. Do you think that's the reason why so many people still believe in biblical time?

Richard Fortey: I think there's something rather lonely about the whole geological time scale and the brief moment that humankind has really spent on it. And I think the notion that, even if you allow for a generous time scale, evolution has somehow been directed towards humanity is still surprisingly pervasive. Even among some academics I know, I think they would still like to view the whole evolution of the cosmos as a kind of motor that eventually produces a conscious creature that can actually appreciate the profundity of God's work. In fact, there's very little positive correlation between atheism and belief in evolution and the geological time scale.

Oliver Strimpel: You mean to say that whether or not you believe in God doesn't really determine whether or not you believe in the geological time scale.

Richard Fortey: Yeah. There are people who accept the geological time scale but still have a notion that evolution has been directed towards a being, which would have to be the human being, that is able to appreciate God's work, which is the universe. It's a metaphysical position which I've encountered several times. The rather godless unraveling of billions of years of time, leading eventually to the current world and our current prominence in it, has a kind of mechanistic basis to it, looked at in a certain way, which I think people resist. It has to be all about something. And the all-about-something is probably still human beings and their consciousness and their awareness of their own history.

Oliver Strimpel: It reminds me of the way in which this has been rationalized, if you like, through the anthropic principle, in which we argue that there could have been many different universes in which the fundamental constants of nature were different. But if the physics and these constants were different, the universe would have been so different we wouldn't be here to observe it. And so our mere existence constrains the kind of universe we find ourselves in.

Richard Fortey: Yes, I think that's right. As an atheistic skeptic, of course, I find such views very hard to grapple with.

Oliver Strimpel: The anthropic principle is not really a physical explanation of how things came to be where they are, but it might rationalize the nature of our universe without recourse to any deity.

Richard Fortey: Yes, indeed.

Oliver Strimpel: As we've described, even if we don't deny the immensity of deep time, we still need ways to come to grips with it and, as you said, to domesticate it or tame it. You mentioned the role of names and geological periods, which make them sound more familiar and allow us to place them in order. What about the role of geological maps? Does that help us, do you think?

Richard Fortey: If you've been to an area, and I have done work in areas where nobody's been before, the first thing you do is make a map. Making a map sets the reality of the whole business. I've worked in the Australian Outback, where nobody had really made maps, and there's something immensely satisfying about taking a stretch of ground that's virtually unknown and mapping it. That then tells you what rocks you should investigate first if you're looking for fossils. And indeed, in my career, I've had some extraordinary turnabouts, where I was told I was going to look at some Ordovician rocks and they turned out to be Devonian. Mapping is all part of that.

And I suppose that was William Smith's great contribution. His early map still resembles the present map, and it was a way of grasping the underlying reality of Britain in a very profound way for people. Now, as you drive through the landscape, you are driving over Smith's map, whether people acknowledge it or not. One of the reasons I wrote my book The Hidden Landscape, about the geology of Britain, was exactly that: to show how that underlying map influences everything that you still see on the surface. I think human beings probably need maps. Even the Aboriginal peoples of the Australian Outback had ways of taming the ground by having their own particular mapping system. Maybe it's very crucial to human beings. Oh, I don't know.

Oliver Strimpel: Do you think deep time is indeed one of the fundamental discoveries, as I suggested in my introduction?

Richard Fortey: Yes, I think it's changed the way we perceive so many Earth processes, and indeed changed our perception of where we human beings fit into the grand scheme of things. Before deep time, I suppose you could say our own history dominated time, and now we realize that we are just one second at the end of this vast catalog of time. So it puts human beings into proportion, and by putting human beings into proportion, of course, it contributes to, hopefully, thinking sensibly about the future of our climate and world. The story of the unraveling of deep time is really one of letting go of the centrality of human beings and our own time scale, and realizing that we are almost just an afterthought in this vast narrative. So it helps to put us in our place in the universe.

Oliver Strimpel: Richard Fortey, thank you very much.

Richard Fortey: Oh, it's been my pleasure.

Oliver Strimpel: To see pictures and illustrations that support this podcast, go to geologybites.com, where you'll also find a subject matter index of all the episodes. There you can also give me feedback, which I welcome, as well as sign up to get my emails about new episodes.