In Our Time - The Permian-Triassic Boundary

Episode Date: June 28, 2007

Melvyn Bragg and guests discuss the Permian-Triassic boundary. 250 million years ago, in the Permian period of geological time, the most ferocious predators on earth were the Gorgonopsians. Up to ten feet in length, they had dog-like heads and huge sabre-like teeth. Mammals in appearance, their eyes were set in the side of their heads like reptiles. They looked like a cross between a lion and giant monitor lizard and were so ugly that they are named after the gorgons from Greek mythology – creatures that turned everything that saw them to stone. Fortunately, you’ll never meet a gorgonopsian or any of their descendants because they went extinct at the end of the Permian period. And they weren’t alone. Up to 95% of all life died with them. It’s the greatest mass extinction the world has ever known and it marks what is called the Permian-Triassic boundary. But what caused this catastrophic juncture in life, what evidence do we have for what happened and what do events like this tell us about the pattern and process of evolution itself?With Richard Corfield, Senior Lecturer in Earth Sciences at the Open University; Mike Benton, Professor of Vertebrate Palaeontology in the Department of Earth Sciences at the University of Bristol; Jane Francis, Professor of Palaeoclimatology at the University of Leeds

This BBC podcast is supported by ads outside the UK. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio 4. I hope you enjoy the program. Hello, 250 million years ago, in the Permian period of geological time, the most ferocious predators on earth were the Gorgonopsians.

Up to 10 feet in length, they had dog-like heads and huge saber-like teeth, mammals in appearance, their eyes were set in the side of their heads like reptiles. In fact, they looked like a cross-boot in a lion and a giant monitor lizard and were so ugly that they're named after the Gorgans from Greek mythology, creatures that turned everything that saw them to stone. Fortunately, you'll never meet a Gorgonopsium or any of their descendants because they went extinct at the end of the Permian period. And they weren't alone.

Up to 96% of all life died with them. It's the greatest mass extinction the world has ever known, and it marks what's called the Permian-Triassic boundary. But what caused this catastrophe? What evidence do we have for what happened? And do events like this tell us about the pattern and process of evolution itself? With me to discuss the Permian-Toracic boundary are Mike Benton, Professor of Vertebrate Pallientology at the Department of Earth Sciences at the University of Bristol.

Jane Francis, Professor of Pallien Climatology at the University of Leeds, and Richard Caulfield, Senior Lecture in Earth Sciences at the Open University. Richard Caulfield, before we talk about the Great Dying, what do we know about the world 250 million years ago which marks this boundary between the two periods, Permian and Triassic? Well, the Permatriassic boundary actually marks the division between two major eras of Earth history.

There are three, the Paleozoic, the Mesozoic, and the Cenozoic. And the Permatriassic boundary, the Permian and the Triassic, are periods which bracket this era boundary between the Paleozoic and the Mesozoic. And era boundaries tend to be based on mass extinctions, and it was clear several decades ago

that something major happened at the Permatrassic boundary. But what the world was like was it was very alien compared to what we're used to today. Not alien in the sense that it was a world of bacteria, for example, as it would have been during the Precambrian, but because although the oceans teamed with life in the Paleozoic, which is this period of time between 560 to about 251 million years before present, that's the Permitratic Mandrae. The oceans were colonised with brachyopods,

which are superficially similar to mollusks, but quite different genetically. Trilobites, which are related to the present-day Woodlaus, that's about the only living relative of the trilobites, which were enormously abundant during the Paleozovites, during the Paleozoic in the oceans. And there were crinoids, which are sea lilies related to echinoderms. And this ocean was characterized by some of the most spectacular reef builders this planet has ever known.

If you go to Wenlock Edge, for example, in the Welsh borderland, you'll see the entirety of that hill, the Wenlock Edge, is made up of Silurian, which is a period of the Paleozoic reefs. And so you imagine a world of slumbering sea. washing against a land which has only just begun to be colonized by the land plants, where the highest form of life is a primitive fish called a cathodian or a placoderm. And that gives you a sense of what the Paleozoic was like. It's a sort of distorted mirror of the world we have today, where the ecological niches were filled in a superficially similar fashion to what we would expect today,

but the genetics behind it all was quite, quite different. In the deep ocean, off-shelf, because the organisms I've just been talking about all lived within a few hundred metres of the sea shore. In the deep ocean, you had giant colonies of floating organisms called Graptoites, so-called from the Greek to write lithos in rock. And they're called that because they look like writing in the rocks. That's the only trace left of the Graptoilites, which were an enormously important. and abundant group during the Paleozoic. Imagine then the deep ocean colonized by free-floating mats of these animals, which looked very superficially like seaweed. They were colonial, and they lived in tiny vessels on the sides of these long strips of protoplasm.

And these were the masters of the surface ocean. Graptolytes became completely extinct at the perma trachyacic boundary, as did the trilobites, as did the brachyopods pretty much. the Gogonopsiums, there's a way that we can describe it and sort of recognise it on land. Was it anything that we would recognise on land then 250 million years ago and say, oh, it's like this, like that, like the other? Well, the land plants had started colonising the land in the Silurian, which had been about 100 million years before the Permatranic boundary. And in the Devonian, which is the period which immediately follows the Silurian, the land had begun to be colonised by animals, tetrapods. And so there were things which had got as far as the amphibian stage of evolution, and in fact a bit beyond because there were mammal-like reptiles

and the beginnings of the reptile clade on land at that time. Like Benton, can you give us some idea of what was lost at that boundary, the boundary between, as has been explained, the boundary between these two eras? What was lost, how was the quantity of it and what was the quality of it? As we've heard, of course, life in the Permian was quite different from today. And there are many places around the world where you can look at how things were. And the extraordinary thing was that life had never been more diverse, had never been more varied. And if I can paint a picture of the deep oceans and then of the land immediately before the event,

that will maybe exemplify this. So in the deep oceans, or should I say in the oceans, around the fringes were coral reefs like today, more or less. in the deeper oceans or various other kinds of creatures that we've heard about. The coral reefs are known in particular, and they really show the kind of level of diversity. So in China, in other parts of the world where this has been studied, there are maybe 100 species of creatures, there are corals of various kinds, and other fixed organisms living on the seabed that make the structure of the reef. There are snail-like creatures and other things, worms and so on,

crawling in amongst them, feeding on the reef. there are fishers, sharks and others, and swimming mollusks, aminoid-like creatures swimming above. And in places where people have studied this, there are as many as 100 species in quite a complex sort of ecosystem. And that had evolved and was quite stable and was quite successful. And similarly on land, life had never been more diverse. Again, as we've heard, there were tetrapods, the land-living vertebrates.

And we've been working in Russia and have been able to reconstruct quite extensively what the ecosystems were like. You've mentioned Gorgonopsians. They are the favorite reptiles of the time. They are saber-tooths. And, of course, they're a kind of creature that indicates a complex ecosystem, meaning that they're top predators.

And they were big animals, as you described at the very start. They were feeding on giant herbophores, the size of hippopotamuses. There were these big fat reptiles called pariosaws, which were rather hideous to our eyes, although no doubt quite attractive to each other. no doubt, but they're big, wide heads with tiny teeth, they fed on plants, their skin was covered

in warty excrescences. But that illustrates the complexity of the ecosystem. The 30 or 40 species living together on land, ranging from modest-sized fish-eating creatures that lived in the shallow waters, the lakes and the rivers, through to herbivores and small carnivores on land that would be feeding on insects and other smaller creatures, right through to these. hipposized herbivores and the giant carnivores. Now you described, can you just develop the idea, can you just tell us more about where you get evidence for this? For a lot of people listening, including myself,

251 million years ago is a long time to gather the evidence of the detail which has already been described by the two of you so far. And we know that 96% of life was lost and the things changed massively. It's pointed out genetic differences and so on. So where do you get the evidence and how can you be sure enough about it? Yes. One of the interesting problems about the parametricatic mass extinction is that you can't really observe it in Western Europe or in North America terribly well.

So it hasn't been studied in great detail in the classic times of geology, you know, in Victorian times, for example. The parts of the world that you can observe it are, as has been pointed out, often quite dangerous and difficult. so that if you want to look at the marine fossils, you have to go to Iraq or Afghanistan or Pakistan or South China. Now, fortunately, with the opening up of China in the last 10 or 15 years, it's become possible for scientists from around the world to study those sections. And there are some wonderful localities with great thicknesses of these reef limestones containing millions and millions of fossil shells.

And it's been possible then to work millimeter by millimeter, through the rocks and really document in great detail what these things were doing. What's your dating system? Well, the dating in that case is quite convincing. Often it's a long, as I'm sure you're aware, it can be quite a long line of argument where you go from one rock formation with a dinosaur fossil and you have to go sideways and sideways and sideways until you eventually get something you can date.

In the case of the Chinese limestones, there are layers of volcanic ash. conveniently it seems at different layers and volcanic ashes can be dated because they are originally molten contain molten material that crystallised instantly at that time and you can date those by various direct methods

Jane Francis can you give us some idea of the evidence we can gather from plants and vegetation that was there 250 million years ago and how we can be sure of that well I think if you want to describe the Permian in terms of what was on the land in terms of vegetation, I think the word you'd use is lush. Perhaps one of the most famous flora's from Permian times is in the Southern Hemisphere, actually,

and it's a famous Glossopteris flora. So if you imagine the continents of South America, South Africa, Antarctica and Australia, that were all joined together in this gondwana landmass. In the rocks, we find a lot of leaf fossils, wood fossils, roots, all parts of this tree called Glossopteris. To you and me, it would look like a normal kind of tree with big leaves, but a type of tree that's now extinct. It went extinct at the end of the Permian.

And it's very, very common. And we think from various pieces of evidence that it was a deciduous tree and it shed these big, big waxy leaves every autumn. And they fell into wet peaty swamps where they were preserved. And they now form some of the most important cold deposits in the southern hemisphere. So if you go to say to Australia, even India, which was once tucked into all these Gondwanan continents and some of these other continents,

there are thick coal seams they're made of Glysopterus. In fact, even on Antarctica, which is where I work, there are thick coal seams there of this age, made of these Glysopteris plants, although they're not obviously economic in Antarctica, but they are there. So Glisopteris was a really important plant. And I think it was particularly well adapted

to living in these very wet, lush conditions that we have around at that time. And that was made extinct in this. Yes, that went extinct, yes. There's also something called fungal spike, which gives you a lot of evidence. Over to you, am I for a fungal spike, right? Well, a lot of the evidence for what was growing in the vegetation comes from what we call palinology, which is looking at pollen and spores that are really easily preserved within rocks. So there's a whole group of scientists that are designed.

up rocks and they pick out these tiny fossilized pollen and spores. And what they find at the end of the Permian is that there's a real abundance of fungal spores in the rock record and much more than sort of the background level. And so there's been various ideas put forward to explain this. But the idea is that at the end of the Permian there was this big extinction and that things were basically left lying around rotting on the earth and all the fungi were attacking them and so there's this wealth of

spores. So the more fungus is, the more evidence is for depletion and disintegration after this extinction. That's one of the ideas. I mean, there's always some controversy about it and some people think perhaps that it's just because other things have disappeared from the record, because some of the plants have died.

It means the fungal spores have become more prominent in the rock record. But the general consensus is that this was fungi that was surviving all this catastrophe and had plenty to on. Turning then to what caused it,

the people reached out, after the 1960, 70s and 80s and the meteorite the dinosaurs 65 million years ago, the Gulf of Mexico, looking for another bigger meteorite. Why did that not held up as a model for what might have caused that extinction 250 million years ago?

Well, like you said, it was quite a trendy thing a few years ago to try and find a meteorite to explain all extinctions because, you know, a big wham into the earth you can kill things off instantly. It's a good good shock tactic to get rid of a lot of things in an instant. But actually the evidence for a meteorite impact is pretty sparse. And there have been reports of some reports of iridium,

which is a special rare element that you sometimes find. We've got at the KT boundary at the end of the Cretaceous. And there are other places where people think they've found certain minerals that show evidence of impact and debris beds where there's evidence of impact. But it's all quite dubious. and there's a lot of people who don't believe it. So the meteor impact idea is still around,

but I don't think that there's substantial evidence. I'm not a supporter of it, I have to say, let's be controversial here. It hasn't got much of a contingent to that at the moment. No, I don't think so. I think there are more other plausible causes for the extinction. I only come back to why it happened, but just one thing was mentioned Richard Caulfield,

on by Mike Benton, and I'd just like to spell it out a bit more. and this is the supercontinent of Pangea. And this is, we're talking about this in the Permian, this is the time you're all talking about before we move on. Can you say what that was and why that was significant? Okay, well, at the end of the Paleozoic, the continents, there had been lots of smallish island continents throughout most of the Paleozoic.

Paleozoic started with a fairly large continent called, I think it was Panottia, then it broke apart, and they went their separate ways, gone Wanderland was over the South Pole. Towards the end of the Paleozoic, those continents through the mechanism of plate tectonics reassembled into one single supercontinent, Pangaea. And this is about when?

About 270 million years ago, approximately. So all the landmass of the planet was assembled into one landmass. Right, that's right. And around the equator, shaped as I've read, like a sort of kidney equally unbirth. So that was where all the land was and the rest was over. Right. And that had profound consequences. because as we've explained, a lot of these marine organisms lived on the continental shelves.

And if you have lots of continents, then you have lots of continental shelf area. If you assemble those continents into one supercontinent, you actually lose a lot of continental shelf area. And that brings us to the point really about the nature of the Permanetriassic extinction, because by the mid-Permian, things were looking a bit rocky for things which lived in the sea anyhow. because they'd lost a lot of habitat area just by the assembly of Pangaea, and then something else or several something else has happened. And if you actually look at the rock record of the mass extinctions at the permatratic boundary, and this is another piece of evidence which mitigates against an asteroid impact,

that seems that there is more than one extinction pulse, perhaps two, possibly even three, separated in time, but relatively close together in time. But let's stick with this dramatic and massive landmass, which is very, not only around the ages, but in the centre of it, extremes occurred which made life very difficult. Do you want to come in on that, Chene? Yes, on land. There were conditions like we've never known before, really.

This whole mass of Pangea presents us with a world that we really don't know today because today our continents all spread apart and we're sort of separated by seas. But in Pangean times, we had this massive landmass, like you say, there was this kidney bean shape across the equator. And inside this landmass or in the middle of the continent, it must have been incredibly dry. I mean, if you were in the middle of the continent, it would have been a very long way from the sea, from the edges.

So there's just no moisture would have got inside. So initially we're talking about deserts. But also, because this is a large landmass, and the land doesn't hold much heat. So it's like imagine going to Siberia or northern Canada, where in the middle of a large continent, mass and then in ten you know magnifying the the continental effect so the continent would have got extremely hot in the summer and then and then very very cold in the winter each hemisphere

in the relative seasons and so we had we believe we've got evidence and climate models also support the idea that there was really extreme seasonal extreme seasonal temperatures and pressures in the middle of these continents which would have made really an inhospitable climates I mean would you want to live in plus 50? in the summer and plus minus 50 in the degrees centigrade in the winter? Horrible place to live. So we've got the panjeer there, which is a factor. And we're not talking about, so that is a factor, Mike Benton.

The meteor doesn't seem to be much of a factor. Let's start to dig away to find out why this mass extinction occurred. As it were, the ground has been prepared. Now, what do you three think, this is the sort of centre of it? What happened to make this massive event a massive event? I think that people now focus on the Siberian traps. The Siberian traps are a massive area in Siberia, of course, of basalt lava. The word trap refers to step-like scenery, and traps are a particular kind of volcanic eruption.

We mustn't imagine a sort of pointy, plinyan volcano like Vesuvius. We have to imagine something more like the eruptions on Iceland, where there are fissures and vast amounts of lava come out. Now the reason that people hadn't linked the extinction to the Siberian traps for quite a long time was that the dating of those rocks was not that good, whereas through the 1990s it became clearer and clearer that these vast eruptions that cover a huge area in Siberia did actually happen right at the perma-traassic boundary, so the timing is right, which is helpful. But then added to that was what we know about volcanoes today.

And of course, people have studied modern volcanic eruptions. like Mount St. Helens, historical ones like Crackatoa over 100 years ago, and those have given volcanologists some physical factors, so they know what happens when a massive eruption happens. So the Siberian traps represent millions of cubic kilometers of lava. They were erupted over a certain amount of time, maybe as much as 100,000 or 500,000 years. That's still to be checked.

Not many people like to do fieldwork in science. Liberia because of the cold and the mosquitoes and all of the rest of it. And of course, until recently, it was rather difficult for non-Russians indeed to get in there. What happens when a volcano erupts? Whether it is a pointy explosive volcano or a fissure bubbling volcano, there's a production of a huge amount of gas. We know that that happens and those gases include almost anything you can think of, which, when mixed with water, gives you acid. So one consequence of any volcanic eruption is acid rain.

carbon dioxide is one of the main gases that comes out of volcanoes and the second effect is global warming because CO2 carbon dioxide is a well-known greenhouse gas now with normal volcanoes the scale of it is small enough that the earth can recover plants mop up the CO2 and there's no long-term effect one interpolation please allow me this just so listeners know this this lava that came out

is supposed to be many kilometres thick and covered an area about the size of Western Europe we're talking about that when you say massive that's what massive is absolutely massive no no you're quite right and yeah people sometimes use the analogy of the size of the European Union is one of these strange

measures whatever that means but huge huge amounts one of the biggest ever the global warming the acid rain those are two important phenomena and I think the reason that people feel that perhaps the clue to the extinctions maybe links with the volcanoes is partly there's nothing

else the evidence for impact is weak, to say the least, and the evidence that Pangaea on its own could have done this is even weaker, I think. Those effects, though, would have been spread over many years, so this is pulses of volcanic eruption repeatedly, so that the Earth perhaps wouldn't have had time to mop up and deal with it in the normal sort of feedback process. And there's a final element, which we can discuss in more detail in a moment, which I must just mention as the sort of kudegra. which is the production of methane hydrates from the deep ocean. I'll go across to Richard Corfield for that.

So we've got the money seems to be on the Siberian traps, the lava, more CO2 getting into the air, the acid rain. But that, as has pointed out, would have been normally, let us say, mopped off. You're not shaking your head, so I'm okay so far. I'm agreeing, and this pulse to volcanism would cause a pulse extinction. Yes, so that's okay. But something else happened then came in,

which accelerated this and Mike's mentioned it, I'm asking you to talk about Richard, which is the methane hydrates. Well, methane hydrates are the mass extinction mechanism of choice at the moment for paleontologists. It is currently as fashionable as asteroid impacts were in the 1980s. So it's no surprise to find methane hydrates being invoked at the biggest mass extinction of all time.

Methane hydrates are molecules of methane, CH4, which are locked in a cage of water ice, molecules H2O. They're not chemically bound together, so it's a non-stochimetric relationship. What happens is that these methane hydrates are metastable through a relatively narrow range of temperatures and pressure. They're formed in the present day on the continental shelves and also in the permafrost of places like as it happens, Siberia. I'll bear in mind that Siberia wouldn't be where it is today at the perma tracic boundary. It'd be much closer to the equator. But because of the stability,

of these methane hydrates is so volatile, if you like. If there's a relatively small amount of global warming or a relatively small decrease in the overlying pressure, the ice cage breaks down and releases the CH4, the methane into the atmosphere. And methane is actually a more potent greenhouse gas than carbon dioxide. And so one of the speculations which goes along with the Siberian trap volcanism is that it started global warming, which then warmed methane hydrate deposits

in any permafrost deposits that there were at the time, and also on the continental shelf around this supercontinent pangier in an ocean, which, by the way, is called pantherasa. And this outgassing would have accelerated this global warming and made things even more uncomfortable for things which in all probability were fairly uncomfortable anyhow by the end of the Permian. So we have the thing rolling.

Jane Price, would anything else add to this? Because we seem to have a list of consequences now. But the acid rain started to, from studies of hydrology, massive floods, vegetation being torn away. The circle isn't quite complete, is it, for what people are saying, caused this big thing? No, I mean, as I said before, in the Permian, we see sort of evidence on land for lush conditions and peat swamps

and sort of really sort of meandering rivers slowly meandering, lots of water around. And then at the Permanentraceous boundary, there is a change. There's a change on land. And we start seeing intense dry conditions. So we lose all this evidence of wet climate and everything becomes dry. And we see sort of rivers that seem to be very fast-flown,

but eroding fresh new land, according what we call braided rivers, really high-powered rivers, just coming down, eroding a new landscape. And in the oceans, what we see, if you go to some of the rock records where we can see these rocks that show us what conditions were like in the ocean,

say in China, we go from conditions of sort of, you know, lush sea floor, if you like, with high diversity sea floor, lots of fossils in. And then suddenly we see shales, mudstones, black in colour. So it looks like that suddenly the conditions on the ocean floor has changed and there's no oxygen there. Instead we get evidence for, you know,

nasty, dark, dank conditions, no oxygen. poor life, that kind of thing. And so the idea is that with all this carbon dioxide that's been pumped into the atmosphere, the ocean's become very sluggish because the earth is warming up and the ocean currents aren't flowing so fast. And so

the waters of the oceans just become stagnant. And maybe that's what affected a lot of the things that lived in the sea. Yeah, just to elaborate that point, the ocean circulation at the moment is thermohaline, which means it's driven by the sinking of cold, dense

water at the poles. That could have been the case in the late Paleozoic. If you have global warming, and bear in mind that this event, the Siberian trap event, is superimposed on generally warm climatic conditions at the end of the Paleozoic anyhow. So these methane hydrates would have been poised to destabilise, if you like. Then a certainly defensible consequence of that as an idea is that you would shut down your normal ocean circulation and go to something where deep waters were being formed in the low latitudes, I near the equator, where the oxygen level in the water would be much lower anyhow.

And this could have given rise to an increase in the oxygen minimum layer in the ocean, an increase in the thickness of it, so that it sholled onto the continental shells. And so you've got a situation where 250 million years of evolution had produced your brachyopods and your trilobytes, all used to a high-oxygen environment. And in geological terms, overnight, they were suffocated by what was happening caused by an event which started on land.

So can we summarise that model? Because I think you've gone around most of it, Mike Benton. Can you summarize what is the going model? And you suggested that the methane hydrates might be defashion like Astro? I hope they don't disappear as fast. Because it sounds very convincing, and I've just sort of got the hang of this. So can you just summarize this model, Mike Benton, before we move on? What is the consensus between the three of you?

that will do as to what happened about 250 million years ago to cause this massive extinction. The consensus can be summarised then at the moment by the term runaway greenhouse, which is a wonderful allegory, if you like. The greenhouse effect is the term we use, obviously, for global warming and all of those effects. And the runaway greenhouse is uniquely a case like this

where normal earth processes, primarily photosynthesis by plants, are not able to keep up mopping up the sea or two. and the greenhouse effect runs away with itself. So the sequence of events then is eruption of massive volcanic lavas, and we know about that, that definitely happened. We know that the consequences of eruptions are the production of carbon dioxide and other gases. So acid rain, we know, happened,

and there is evidence, as Jane described, of the wash-off of vegetation, the removal of soil, the extraordinary change in climatic conditions, the flow of these hugely powerful, torrents of water, just washing the land into the sea. The anoxia we know about because sediments were black, so the oceans did become stagnant. We know that. There is evidence for that. What we don't know is the methane hydrates. At the moment, that is a kind of deosex machina that we believe extra organic carbon is needed to pump into the atmosphere, and that's a real source that it could come from. The volcanoes are not enough. The killing of all of life is not enough. And so for the moment,

that's the weak link that people need to really work hard on to discover additional independent evidence. How do you work hard on it? What are you going to do to find out about these methane hydrates? Well, there is some evidence that methane hydrates may be implicated. A core was drilled in the 1980s in Western Austria and it drilled right through the permatrassic boundary. They went there specifically to drill through it

and it was in the right rock type limestones where they could make what are called carbon isotope measurements, which is simply a measurement of the ratio of carbon 13 to carbon 12. And what they've found is that there is an enormous enrichment in the light isotope of carbon, carbon 12, at the perma-traesic boundary. And carbon 12 is a well-known signature of methane hydrates, at least one of this magnitude. So there is evidence to support the possibility

of isotopically light carbon being added to the global, ecosystem in a very short amount of time in very large quantities. And equally there's also evidence to suggest that at the same time there was an increase in global temperatures of about 6 degrees centigrade. Jane Bronson? Yes. So on land we can see evidence for this because there is this fantastic change on land from the lush conditions in the Permian to really

desert-like conditions. So if you went back say 200 million years or even 240 if you like, just after the Permotriassic extinctions, you'd be walking in a very different landscape. Deserts, sand dunes, very little plant cover, all the glossopteris has gone, all the swamps have gone, no coal seams, no peat, no peat swamps. In the rock record, we just see these very barren rocks

that just tell us it was very desert-like, very little, very little around. And Mike will tell you there's very few animals living on the surface. So it's a very, very different world in just a very, a few million years. Can we talk about survival now? Was there a pattern in it, Richard, Richard Corfield? Did the little smaller one survive? Was there a pattern in it? Not really. One of the intriguing things about the permatrassic boundary is that a lot of groups suffered massive declines like 96 to 99% declines and they left perhaps one species where before there had been 100, which crossed into the Triassic. Now, these are colloquially called dead clades walking,

where a clade is a lineage. So it's an evocative phrase, which gives you an idea. Some groups became completely extinct, but they probably had been in decline anyway. And there was the so-called coal gap when the vegetation on land had been so denuded that no coal was formed for about six million years after the Permatriassic boundary. And it's quite a long period of time when not much happened. And the earth was, if you like, exploited by so-called opportunistic species. There was a particular type of plant which massively increased in abundance just one species. Lestrosaurus was the mammalite reptile, which enjoyed mastery of the earth in the early

Triassic. And similarly in the oceans, certain species it really exploited the vacated ecosystems. Langman. Yes, Richard mentioned the coal gap, and there was a coral gap as well. So in the seas as well, that whole major mode of life just went, because those corals that built the reefs went. And it took about 20 or 30 million years for new groups of corals to move in and take over that role, just as on land, apparently plants were so hit for six that it took 10 or 20 million years

for some of them to recover the habit of being trees. you know, that's the effect. And generally it's not selective. As Richard mentioned, it's a sort of scattergun. You know, you just kill off lots, 19 out of 20 are killed off, and there's no major groups disappear. We found in our studies in Russia

where we're able to follow through the sequences on land. So there's no survival of the fittest in a way, is that? Yeah, you're absolutely right, because this is what you find in mass extinctions. You'd think that there are certain, well, there is in one sense, but the kind of adaptations that all, organisms work on and hone to particular plants for their diet or for escaping a particular predator, well, they mean nothing when there's some vast crisis, when the physical conditions

are hugely different. The one character, or a range of characters that does ensure survival at all times is to have a broad diet and a broad distribution. So cockroaches will do well in normal times and in mass extinctions. But other than that, being large is also not a good thing, because that's normally associated with small population size, that kind of thing. Stephen does say. Can I bring you, Jane? She's, I'm going to come back to that survival of fittest thing because I just thought of it.

I think it's a good line. No, no, it's a good one. Jane, can you want to develop that, obviously? Well, I was just thinking about the plants, and I think the key thing about the plants is it's not necessarily survival of the fittest at that particular time, but later on it's survival of those that could adapt to the new conditions.

And in the plant record, we see a real clear distinction between, in the Triassic times, between those that were adapted to surviving the weight, before and they just went because they couldn't adapt to these new dry conditions, but a whole new series of plants came in. Where did they come from? I think they were there anyway, but this gave them an opportunity to diversify and evolve. And there are probably plants that you would recognize today.

So things like the conifers, certain types of ferns and plants that were able to carry on. The classic, if you think of the classic triassic tree is a monkey puzzle tree. and there are certain types of ferns and conifers and they had special adaptions to living in dry climates. So if we take fossils, we can see that, for example, they were full of resin, because resin helps them preserve moisture. They have very small leaves. So if you imagine like a juniper or cupresses, a cypressus, a cypress tree,

they have leaves on them, but they're very small and pressed close to the stem. And they're all really good adaptions for saving water, you know, in a dry climate. And what we call it is to matter, the breathing holes on the leaves, had special structures on them to close them up and stop them losing moisture. So there's a whole range of plants that took off after the Permian Triassic Boundy, that were particularly well adapted to surviving in these dry desert conditions. And then a lot of them are still here today.

I was just going to say that if Stephen Jay Gould were still here, He would want to mention at this point the role of chance in the history of life. And then Mike mentioned that just now. The things which became extinct at the Permanatrassic boundary, there was no rhyme or reason to it beyond the fact that they were sort of slightly specialized into ecological niches. And so a purely random event comes along, resets the clock of life for absolutely no reason. And whatever's left inherits the earth,

which is a recurring theme in the history of life and earth. Same thing happened at the Cretaceous tertiary boundary. Same thing happened at the end of the Ordovian. Do you want to come back to that, Mike Newton, and tell us about how you thought how life was different after this boundary, after this mass extinction. Jane has begun to talk about it. If you could develop that.

We tried to set up at the beginning of the program what it would like then. What's it like after then? I think Jane has described quite correctly the dry conditions. Now, they only persisted for a certain amount of time, but nonetheless that colored the nature of the recovery. I think that people have often wondered, how could you have such a devastating mass extinction that drives one in 20, well, 90 out of 20 species to extinction?

And yet life somehow did recover to replicate the kind of situations that had existed before. And the reason is, as Richard mentioned, that this scattering of one in 20 species that survived was across the whole diversity of life. So there were enough markers at different points across the ecosystem that allowed life to recover. but it seems that it, depending on how you describe recovery,

it took anything from 20 to 100 million years for life to get back to the diversity that it existed before. Through the Triassic, on land at least, and in the sea, life did by the end of the Triassic 50 million years later look more or less as it had done at the end of the Permian. It had recovered more or less. So in the sea... Was there any new stuff there that led to...

Well, there were new things. There were dinosaurs, for example. So it's very likely that having devastating... life, you have the dead clayed walking phenomenon, which is simply these holdovers, these chance survivors, they're there, so they have the opportunity. But they're a weak reflection. They're just a small sample of what existed before. And therefore, that seems to be a phenomenon of general interest that new groups can more readily push in in some sense. And the dinosaurs were an example. They came 30 million years after the event, but they came

into ecosystems that were still not completely reconstructed. And therefore, there were some gaps for large predators and various other kinds of organisms on land. Is there any pattern, Jane By the we can deduce from this? Any sense of these sort of things happen every 250 million years or whatever it is? Oh, well, search for the cyclicity in mass extinctions is one of the key things that we're all engaged in. But I don't look to Mike to this.

He's the expert on that, but I don't think anybody has ever found any cyclicity. But we are finding a kind of a pattern of events. I mean, personally, you know, because I'm interested in climate change, I think all of these are associated with a major climate change. There is an event of some kind that causes a climate change. And I think a lot of things, particularly plants, respond to that climate change. Plants respond to the climate change rather than the event itself.

And a marine fauner, too. You know, there are sort of consequences of the event. And the events seem to be quite interestingly common. This business about cyclicity in mass extinction has been knocking around for at least 20 years when Dave Rauppov and Jack Sipkoski published a very controversial paper and then lots of people went out and decided that 26 million year periodicity was to do with the earth being hit by regular showers of meteorites. At the moment that's been largely discredited,

but there still is a sense in which there is some kind of periodicity in the history of life. Nick Shackleton at Cambridge spent his entire career assembling climate records, and mostly these were on relatively short timescales up to 100,000 years, which demonstrated that the Earth's movement around the sun dominates the Ice Age, non-ice-age cycle. But once he'd assembled enough data, and it took him decades to do it, he did find that out at about 30 million years, there is some kind of climate cycle,

but there's absolutely nothing between that 30 million year cycle and the 100,000-year cycle. Mike. I'm very dubious about cyclicity's on that scale. I think people have certainly demonstrated that on the scales of tens and hundreds of thousands of years. There's no question. I think the great difficulty that people have had is partly by the practicalities and partly the reality. The practicality is that when you're looking at ancient time and trying to look for cycles on millions of years,

it's actually quite hard to date the rocks sufficiently accurately to really be sure. And it's well known that statisticians can find patterns in any string of random non. numbers, and I think that's partly what happened here. I think the Earth is not hit by regular showers of meteorites, as people had suggested, nor do I think there are regular cycles of climate on this kind of a scale. And I think we're looking at a unique event, and we can't say we can predict when the next one, like the N-Permian mass extinction, is going to happen. Well, thank you all very much indeed.

Thanks, Shane Francis, Richard Corfield, and Mike Benton. Could go for a long time. could go into all the other years and epochs. But we've got to move on. Oh, yes, next week. We'll be looking at the voyage of the Pilgrim fathers to New England from Plymouth. That was in 1620.

Thank you very much for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.com. com.com.