Instant Genius - What mass extinctions can teach us about the future of life on Earth

Episode Date: September 14, 2023

Most of us are aware that an asteroid strike led to the extinction of the dinosaurs some 66 million years ago. But fewer are aware that this was just one of several mass extinction events to have occurred throughout the Earth’s history. In this episode we catch up Prof Michael Benton, a palaeontologist based at the University of Bristol and author of the new book Extinctions: How Life Survives, Adapts and Evolves. He tells us all about the previous extinctions that have changed the balance of life on Earth, how they happened and what we can learn about the future of the planet by studying them. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hello and welcome to Instant Genius, a bite-sized masterclass in podcast form. I'm Jason Goodyear, commissioning editor, the BBC Science Focus magazine. Most of us are aware that an asteroid strike led to the extinction of the dinosaurs some 66 million years ago. But few were aware that this was just one of several mass extinction events to have occurred throughout the Earth's history. In this episode, we catch up with Professor Michael Benton, a paleontologist based at the University of Bristol, an author of the new book, Extinctions, How Life Survives, Adapts and Devolves. He tells us all about the previous extinctions that have changed the balance of life on Earth, how they happened, and what we can learn about the future of the planet by studying them.

What are we talking about exactly when we talk about an extinction event? When we talk about an extinction event, we mean a time when lots of species die out at the same time. So I think people probably realize that species don't last forever, maybe they last for a million years, which is a huge amount of time. But in terms of the geological record, that's not a great deal, they disappear completely. And an extinction event is where many species, we can think of the end of the Ice Age, where, for example, mammoths and woolly rhinos and lots of other creatures disappeared probably because climates were changing. and then there were bigger events in the deeper geological time, mass extinctions, where a whole range of species disappear at the same time. So you mentioned there mass extinction, so let's have a look at those.

So how many have there been in the past? And do they have a strict scientific definition? It's quite hard to define mass extinctions in a way because each one is unique. Normally geologists would say there were the big five, as we call them, And the one that most people are familiar with is the last of those five, which was the extinction of the dinosaurs 66 million years ago. And sometimes people refer to the present crisis as the sixth extinction for that reason. It's difficult to give a precise definition. Obviously, in general terms, lots of species die in a short time.

But that's not good enough, of course. A scientific definition would immediately ask for, what do you mean by lots? and what do you mean by a short time? And when you realize that, in fact, the causes may be different, the dinosaurs were killed by an asteroid, other events were triggered by massive volcanic eruptions, then it may be easier to see why it's difficult to give an exact definition. So you mentioned there, the extinction of the dinosaurs, which I think if you were to mention a mass extinction to someone on the street, they'd say, oh, like the dinosaurs.

So you mentioned the asteroid impact that I think landed in the Yucatan in Mexico. How locked in is the science of that, you know? What do we know about what happened and how sure about that, are we? The end of the dinosaurs, you're absolutely right, is probably the best known and the best studied. It's not only because it's dinosaurs and the public and scientists as well love dinosaurs. They're a greater icon of extinction. Because it was the latest event, the one that happened near, to the present day, it means that the quality of data is better than for many of the older events

because we can date it, we can analyze it in many different locations. For a long time, there have been two competing hypotheses. Number one was massive volcanic eruptions in India, which generated huge volumes of lava, which are called the Deccan traps. They're in the Deccan region of India and the traps just refers to step-like scenery made up of enormous thicknesses of basalt lava, or the asteroid which hit the earth in the Yucatan Peninsula in Mexico. And for quite a long time, we couldn't really pick between the two and people, you know, went after their favorite or maybe said, well, maybe it was a bit of both. But there was a really nice definitive test done a couple of years ago.

And this depended on the fact that volcanic eruptions, lead to a sharp increase in temperature because of the release of greenhouse gases and so on, whereas an impact leads to cooling temperature because of the cloud of dust, which blanks out sun and leads to something equivalent to what used to be called nuclear winter. And in the rock record, because of the really good quality of dating, a team was able to demonstrate that there was a pulse of warming 200,000 years before, the end of the Cretaceous, which was the geological period during which the dinosaurs lived and died out. But there was a cooling event, bang on the very end of the Cretaceous 200.

So that 200,000 years could be discriminated. And it pretty much says, yes, these eruptions were happening. Yes, they may have perturbed life in its final stages towards the end of the Cretaceous. But the Cuda grass, the killer, was the asteroid. bang on the end of the Cretaceous period. So that's the sort of superstar mass extinction event. But let's have a look at some of these other ones that are perhaps less well known. Could you tell us a bit about those, please?

Yes, of course. The one that I've been most interested in was the third of the five, the middle one, which is at the end of the Permian. And in some ways it should be more famous than the end-Cretaceous one because it was much more severe. So all the estimates, although the dinosaurs disappeared, at the end of the Cretaceous, the Ammonites and various other favorite groups of fossils. In fact, the loss of species was only, well, only 50%, whereas at the end of the Permian,

this was 250 million years ago, this third of the big five extinctions, maybe wiped out as many as 95% of species. So putting it another way, it wasn't half of species survived, but only one in 20. So this was much more profound, and the impacts or the effects in terms of the way that one shaped life today are much deeper because the long-lived ecosystems in the oceans and on land were entirely reset because that was so serious. And the N-Permian event, then, it also marks the origins of modern ecosystems.

We can go back and we find that the typical creatures, is in the sea today, like the corals, the mollusks, the crustaceans, the fishes, they pretty much all date from the Triassic period, which followed the Permian. And on land, that marked the Triassic marked the beginning of the dinosaurs, which we don't think of as terribly modern, but also lizards and turtles and crocodiles and mammals and lots of other modern groups, conifers, they got going at that time. So it had that positive aspect as well, devastating for life, but positive in terms of the long term. How do we go about studying extinctions? I presume it's a lot of detective work. It is detective work, and I think for a long time, people were a little bit vague about when

they occurred. So the first piece in the jigsaw is to have a really good system of dating the rocks. and in fact that's improved greatly in the last 20 or 30 years. People may be familiar with radiometric or radioisotopic dating and the quality of the dating, the exact dating, using pairs of isotopes and rates of decay and replacement, has improved enormously. So the end-permium event that I mentioned, when I started studying it, people said, oh, well, maybe it was somewhere between 260 and 240 million years ago. We're not really sure. And with a span of 20 million years, of course,

it could have been a gradual event, or it could have happened in many pulses. We don't know. But the dating now is 251.9, blah, blah, blah. Many figures after the decimal points. So it's possible to date it with a precision of plus or minus maybe 50,000 years, which is kind of, you know, this is orders of magnitude improvement. But in fact, the first clues came long ago when people were wondering about collecting fossils

and they noticed up to this point we find fossils like trilobites and graptolites and brachio pods. And some listeners will be familiar with those. These are typical paleozoic fossils. After a point, we find different kinds of fossils like ammonites and sea urchins and more modern-looking fishes and this and that. And so people knew something that was going on, but without the precise dating, then it was very hard to be sure. And then beyond that, the next thing is to establish changing physical conditions. And I'll just mention one method for doing that. And this is using isotopes of oxygen and carbon.

So one of the first things that we typically do these days, after dating the rocks, after documenting the fossils that you find all the way through and trying to find that point of changeover, massive changeover, people analyze the rocks, particularly limestones where they can get them in marine sections or ancient soils and shells and bones in terrestrial sections where it's a bit more difficult. And the oxygen and carbon isotopes give information about the temperature changes. they can give some information about ocean acidification and other factors like that. And being able to document temperature and pH, the acidity of the ocean, a few other things like that can be really, really helpful in determining what the driver was,

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Today, in partnership with French acoustic specialist focal, name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So you mentioned earlier that 50% of animals on Earth were wiped out in the most recent event and 95 in the third one. So why does some species survive and others don't? This is really, really a great question, the question of who's the victim and who's the survivor. I think people have realized in a big event, particularly at the end of the Permian, it's maybe hard to say.

And to some extent, people have referred to all of these mass extinctions as, illustrating the field of bullets phenomenon, meaning referring to the First World War that the soldiers all jump out of the trenches and run towards the enemy and the field of bullets will kill them randomly. And you could be strong and well-fed and beautifully well-trained, but you just get killed like the rest. So there is an aspect of a mass extinction that maybe is so devastating that I think the other way people refer to this would be to say the normal rules of evolution may be suspended for a short time because the nature of that crisis is not within the normal experience of any of the species. And we know, of course, Darwinian evolution

works on species according to regularly and small-scale changes in their environment to which they can adapt and can be better or worse at surviving. I think, though, there are some general rules, though, that we can pick on, which might be of interest. So, number one, One, be widespread. The more geographically widespread you are on the earth, the more chances of surviving. Number two, have a generalist diet. If your diet is super specialized and we think of things like pandas and dodoes and numerous other extinct or threatened species, that's not great. Don't be too big.

And it's not so much the size, but it's the fact that big animals like elephants and dinosaurs tend to live in small population sizes. And that's not great either. So there's some survival tips that we've learned. Be geographically widespread, be willing to eat everything, and be present in large numbers. Don't be too big. So I guess this depends on how you look at it. But can extinction events ever be a good thing? It depends who's asking the question. That's a kind of philosopher's answer. But for human beings, we shouldn't take too much pleasure or be relieved by the fact that life recovers. Of course, recovers. But the fact is it maybe takes half a million or a million years to recover, and that is not a comfortable span of time for humans to think about, nor for any existing

species. But yes, the positive aspect in terms of the history of life could be said to be when there is a mass extinction, it releases the innovation in evolution. Because part of normal life, normal life going along without major perturbations in the wild, is there's a kind of inertia, there's a kind of conservatism, so that species establish their positions in the ecosystem, they maintain a certain kind of balance, and as normal conditions go on, there's no great dramatic shifts, and when one species kills another species, they tend to live in a kind of balance because it wouldn't be great for example, if the lions were super efficient and killed all their prey, because then that wouldn't be great if you're a lion. You rely on being able to find more prey. So, but yes, and that conservatism then means certain groups are held in certain positions as a kind of constraint, and that constraint is removed. And each species is typically capable of doing an awful lot more than it may normally do in nature. The body size can vary more. The diet could vary more, but species

live side by side and limit their activity. And then the big picture, of course, we can look at the origins of these major groups and the fact that mammals and birds became superabundant on the earth today is almost certainly due to the fact that dinosaurs and other things died out. And we can speculate what would the world be like if they had not died out. So let's fast forward today then, look at the picture today. What is the current picture of the extinction of animals on earth at the moment? You know, what does it look like? So we know about human-caused extinctions through the historical record,

and I think Western scientists began recording information from maybe four or five hundred years ago, and that's why we can talk about the extinction of the dodo, the extinction of the Great Ork or the passenger pigeon, or the quagga. But of course, we typically concentrate on birds and mammals, and there's probably endless numbers of species of invertebrates like insects and slugs and such like that we're completely unaware where we may have caused extinction, because sometimes they may have a restricted geographic spread,

and it just takes the planting of a crop on a tropical island or something, clearing of the rainforest, and then who knows what we've done, because where people have done small-scale studies, they discover there may be hundreds or thousands of species of insects living in a very small area, and we hardly even notice them. So, yeah, we can document it to some extent, and there's a great deal of effort going into that to understand actually what is the current rate of extinction. And there's a great range of estimates depending on whether you care about birds and mammals, where we think it's quite well documented, or whether you care about bacteria and slime molds and maybe less popular organisms where the documentation is quite poor. Nonetheless, I think for the visual organisms like tropical trees, birds, mammals, beetles, people have talked about the current rate of extinction being equivalent to some of these mass extinctions. of the past. And I think a number of writers in the field have called the current crisis, the six mass extinction, because it really does seem to be scaling with the event at the end

of the Permian or at the end of the Cretaceous period. So coming off the back of that, and let's look back into these past extinction events. And I think one of the key points in your book is the things that we can learn about the future of the earth, life on earth, from studying these previous events. So could you tell me a bit about that idea, please? Yes, and I think the best way to focus this is we ignore the N-Cretaceous extinction. Everybody likes the dinosaurs and impacts, but actually that was a one-off. And the N-permine event plus maybe 15 other extinction events of different sizes. The N-Permine was the biggest, but there were a number of others, including the Paleocene-Eosine-Thermal

maximum about 50 million years ago, which has been intensively studied, there's a whole bunch of crises of different scales that we call hyperthermals. That means over or excessive temperature, hyper. A hyperthermal in all cases seems to be driven by volcanic eruption on a large scale, on a scale that humans have not recorded, at least within recorded history. And the effects of these volcanic eruptions, wherever they occur on the earth, whether they're under the ocean, on land, northern hemisphere, southern hemisphere, the size of the eruption will determine the amount of gases that get released into the atmosphere. Of course, when we think about eruptions, we think about lava. And of course, that's very dramatic. And you see it swamping towns and

killing life. But the global effects actually come from the greenhouse gases that are released into the atmosphere, particularly carbon dioxide, methane, and water vapor. Those three and be spewed out by a volcano. And the amount depends on the size of the volcano, and the amount will determine the amount of change in the global temperature. With a small volcanic eruption, it'll just be a kind of local effect, but with a bigger one, it's global. And so there's a sort of predictability then,

because we've now identified these 15 events in the past, these hyperthermals. And we can more or less say, what scale of event are you looking for in terms of the amount of CO2, the amount of warming? So the amount of warming can be as little as 1 or 2 degrees C caused by these volcanic eruptions in the past, all the way up to maybe 15 or 20, 15 or 20, as happened at the end of the Hermion. And at the low end, well, that's what we're already experiencing pretty much due to human intervention. And at the high end, we've got these ancient examples.

So the way we say is these are experiments that have actually been run on the earth, and they can give us some information that we can use at the present time. There are obviously caveats because the distribution of continents was different in the past. The living creatures were different in the past. But there are some common features about the ways in which plants and animals respond to rising temperature. And the first really key point that people need to be clear about is that almost no plant or animal is happy at a temperature above 35 degrees C. We're always deluded or we always get the wrong impression because we think about, oh, there's all these wonderful microbes that can live in high temperatures and there are cactuses and there are other plants and animals that can survive in the desert. they are the extremes. They are tiny numbers and the majority of species in the ocean and on land

hate temperatures above 35. And 35 to 40, just to let you realize, it's like a hot shower. And you might think, oh, this is lovely. You know, we could live under this hot shower forever, and that would be fine. But what happens in the present day is if temperatures go up to those levels, plants and animals simply move away. And we learn from the past, crises, the equator empties of life. And so life moves away from the equator. And we're seeing it today as the Sahara Desert increases in size. Not only is it displacing human populations to the north and the south, but also plants and animals, of course, are moving. And it becomes lifeless. And this has happened in the past. And in a way, that's not a crisis immediately. Not everything

dies within half a year. But then you crowd out the temperate and polar latitudes, meaning that there's great loss of species. So we've kind of learned those big things, I think, from looking at these past events. And a lot of this is quite new research. Taking this to the extreme, then, should human beings be worried about our own extinction? We should be worried about our loss of numbers, the sizes of human populations may have to decrease in one way or another. Technology, of course, adaptation can take us only so far. And people are talking about that. But of course, can we afford to provide air conditioning for everybody? And then in providing air conditioning, we're eating up energy in a colossal way. Because to adapt to climate change, we all have to then

increase our carbon footprint massively to provide us with those sorts of conditions. Probably humans will survive, even though we generate these very high temperatures because we can adapt. But the mistake that is sometimes made is somehow assuming that all the billions of people on Earth can benefit from the high technology, and somehow we can accommodate everybody using those systems and at some point the crisis will completely hit. So the tension in politics between net zero and adaptation has to be resolved because the net zero question will always be there, even though people may complacently think, well, I've got air conditioning, my car has got air conditioning, I'm fine. Why don't other people get those things? Yeah, so in some ways,

that can sound a little bit gloomy? How optimistic are you about the future of the earth? I think the aim in my book is to talk about the glory of the life of the past and indeed the wonders of life today. Ever since Charles Darwin, even before him and long after, naturalists have gloried in the diversity of life. We look at this. We see wonderful television programs or we see it in nature ourselves. We can only be amazed at the power of evolution to overcome difficulties. And then looking at the life of the past, we discover organisms, the like of which we've never seen alive today.

So I've always loved being a paleontologist because it's a bit like exploring other worlds. You don't have to have the imagination of science fiction writer or artists to imagine other worlds. There they are, buried in the rocks. And we have a world full of dinosaurs and giant flying reptiles, the size of airplanes. and we have other worlds full of trilobites and other strange creatures that don't exist anymore.

And life has always bounced back. So perhaps we focus too much on our own immediate human concerns. I think it's good to broaden and look at nature in general. We are causing devastation here and there, but nature has an amazing way of recovering. But it's just the timescales. As a paleontologist, I'm very happy to think of timescales of millions of years. But of course, many people would be more. impatient and they would say, I want to see things improving by next year or within 10 years.

And we, yeah, that's not going to happen. But I'm sure that evolution, you know, we learn such fascinating stuff from the life of the past. And the more we look and the more smart methods we use to investigate it, the more we learn about how extraordinary life can be. Thank you for listening to this episode of Instant Genius. Brought to you from the team behind BBC Science Focus. That was paleontologist Professor Michael Benton. To read more about the topics we've just discussed, pick up a copy of his book, Extinctions, How Life Survives, Adapts and Evolves.

The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your preferred app store. You can, of course, also find us online at sciencefocus.com. This podcast is sponsored by name, audio and focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist vocal,

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