The Origins of Life on Earth

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It's the Ancients on History Hit. I'm Tristan Hughes, your host. And in today's podcast, where we are covering one of the biggest topics in the whole of history, in the whole of human history and prehistory, because we are talking...

of life on Earth. I'll say that again. We are talking about the beginning of life on Earth. We're going back billions of years. We're going to be covering millions of life from the tiniest beginnings at the bottom of oceans to the creation of super continents and ultimately up to the arrival of the dinosaurs now joining me to talk through this huge I was delighted to get on the podcast Henry G. Henry is a British paleontologist and he is the senior editor of the scientific journal Nature.

It was wonderful to get him on the podcast. He is quite a character. And without further ado, here's Henry. Henry, it is great to have you on the podcast today. Thank you, Tristan. Thanks for inviting me. You're very welcome indeed. I've never done a subject like this on The Ancients before. Very, very exciting. And talking about big topics of the world, the beginning of life on Earth. Henry, you can't get many topics bigger than this.

Well, when you're talking about the ancients, this is really, really ancient, so you couldn't really get much more ancient than this, except the birth of the entire universe, I suppose. But once you're looking that far back, there's hardly any distinction to be made between one and the other, I guess. Absolutely. I mean, we are going millions and millions and millions of years back and we're going to be covering millions of years of history.

And to start it all off, Henry, let's go right from the beginning, not the big bang, but tell us how life on earth, how does it begin and when? Are you sitting comfortably? Yes. Then I'll begin. Life on Earth actually began not long after the Earth formed. It's really quite indecently close to when life on Earth formed. The earliest is very, very controversial because the signs are very, very diffuse and difficult to interpret. the earliest life on earth that everyone agrees about.

is 3.4 billion years old, give or take. That's 3.4 thousand million. And that's a reef, a fossiliser of a reef. in Western Australia. So that's three and a half billion years old. But of course, by then, life had already been well established because this was a whole reef. It wasn't just a little blob of matter, living matter. Coral was still three billion years in the future, which is quite staggering. It was made of microbes, piles of microbes. Microbes would make...

a lawn on the ocean floor. And by microbes, I mean the kind of scum that you find on ponds, like pond scum, blue-green, oily, what we used to call blue-green algae, and we now call cyanobacteria. And they would form lawns on the ocean floor and then a storm would cover them with sand and then the cyanobacteria would form another layer. then there'd be more sand. So you'd have this layer of slime and sand and slime and sand, and they'd build these great cushion-like mounds called stromatolites.

and you'd get whole reefs of these. Stromatolites are still found occasionally in very salty seawater where no other creatures can live. There's still a few in Western Australia. But for three billion years, they were the masters of life on Earth. They were the rulers of life on Earth. But there are signs.

that stromatolites lived as long as 3.7 billion, basically by these little layer cake structures in rocks. And these are found in Greenland, which back then was in the tropics because of continental drift.

But they're disputed. Some people think they weren't stromatolites, they were just folds in the rock. But life must have been around at that time, and there are other traces. But the earliest trace of life on Earth, which is very disputed... is from a tiny grain, one grain of a mineral called zircon. Now zircon is a mineral. It's like cubic zirconia that you make flashy wedding rings out of. And this zircon was once upon a time a grain in a rock.

that has now completely worn away. So it's called detrital zirgen. It was basically what was left after the rock was eroded away. And inside this zirkan is a little smudge of graphite. inside this little hole and the chemistry of this smudge of graphite suggested that it once passed through a living organism. because of slight deviations in the variety and in the flavour of carbon within it. And that's 4.1 billion years old.

Now, the Earth formed 4.6 billion years old when the rest of the solar system formed. And for quite a long time, it was a ball of magma that spent its time... So a planet isn't just a jumble of rocks, it solidifies into layers. So there's this hot radioactive liquid metal at the core that spins and forms the magnetic field. And then all the light froth on the outside, which is the crust on the mantle.

But for hundreds of millions of years, the planets weren't orderly. There were lots more planets in the solar system than there are now, and they kept walloping into each other. So at some point quite early, the infant Earth was... a bit like infants in the playground whizzing around. It was smashed into by another planet about the size of Mars, which stripped away the whole of the crust.

And this planet disintegrated and for a while our Earth had rings like Saturn, very early in its history, until this detritus, this remains of this collision. agglomerated together and formed the Moon. Now, the Earth and the Moon system are really rather strange. The Earth is the only planet of its kind that has a satellite that is similar in composition to its own parent, and that's why the impact is still a hypothesis, but there's really no other way to explain it.

And then after that, things cooled down a bit, and the atmosphere, the crust cooled and became more solid, and things kept walloping into the Earth, but not quite as big, because by that time, the solar system... had got tidied up, and most of the things that hit other things had already hit the other things, and so it was more peaceful, and the Earth could cool down a bit without having its crust stripped away every five minutes.

In the atmosphere, it was unbreathable, methane, hydrogen, and a lot of other unpleasant things, but there was a lot of water vapour. Water is very, very common in the universe. But the outer solar system, a lot of the bodies are covered in ice. But closer to the sun, where we are, it can support liquid water. And when the earth cooled, all the water vaping in the atmosphere fell like rain. It just condensed into rain.

And it rained and it rained and it rained for millions and millions of years. In fact, it would have made Oldham look quite sunny. And there was the old comet occasionally walloped into the Earth, providing more ice and water and things. and then the earth was a world of water and it was in that that life began deep deep down in the deep ocean where a lot of minerals superheated would jet out from cracks in the crust. and provide the raw chemistry and the very porous rock surfaces.

in which life began. Now, how life began is one of the big conundrums. Nobody knows how life began. People have come up with all sorts of ideas. But the one I tend to favour in my book... is deep down in these hydrothermal vents, as they're called, these superheated, superpressurised jets of water.

mineral-rich jets of water would shoot out from gaps in the Earth's crust, and then they'd cool and become turbulent and settle down in crusts in the rock. The rock would... basically form pretty much instantly from these minerals as it met the really cold pressurised water. And in the tiny, tiny holes in the rocks, I mean, microscopic pores in the rocks, like pumice, basically, which is a volcanic rock, but it's full of little air bubbles, so it's actually quite light.

The rock, although very light, would provide a catalytic active surface, if you will. The thing that volcanic rocks do very well is catalyse organic chemical reactions that wouldn't otherwise happen. So if little organic molecules, and there were loads and loads of them around, we know because comets and asteroids are full of simple molecules, the simple ingredients for life.

They would get together in the rocks and form more complicated molecules. And life began in these tiny little gaps in rocks in the super-pressurized deep sea. And one thing that life tends to do quite quickly is form little membranes like soap bubbles. They form all the time, everywhere.

And once you have a membrane, you can have differences in the chemistry between one side of the membrane and the other. And when you have that, you have difference in electrical potential between one side and the other, just like a battery. And then what happens is you have little holes in the membrane, so the electrical potential can go from one side to the other and drive more chemical reactions.

And all life, all life, including you and me and everything we know, is based on this simple idea of electricity. The electrical potential across a little cell membrane is huge when you think that cell membranes are very tiny and the distance between one side and the other is tiny. It's like millivolt. It's like the amount of power in an electric guitar pickup in the wire that's generated when an electric guitar string twangs.

The electrical potential is in millivolts. So it's a hell of a lot of electricity is suddenly generated and that put the molecules to work. And that is how life began by these little electrically charged soap bubbles. Now, nobody really knows because, as I say, the earliest evidence for life is hundreds of millions of years later in just a little smudge in one tiny crystal of graphite to suggest that there was once a living organism passed that way. So we've got no actual fossils.

But that seems to be the most likely in terms of logic and chemistry that life began in the sea. The evidence suggests from what we see of the most primitive living organisms is that it was quite hot. The proteins and molecules we see in the very most primitive bacteria suggest that they started in somewhere pretty warm, well above boiling point. So you could say, how could life begin if the water was above boiling point? Well, it wasn't steam because it was under huge pressure.

So the steam under heat pressure in the water, it doesn't become a gas. It's superheated. So it stays in a liquid up to like 200 or 300 degrees. So everything we know points to an origin in a very hot, very high-pressure environment. And with the addition of volcanic rock surfaces to provide the...

milieu in which the early chemicals of life could come together without just diffusing into the ocean. And in these tiny little rocks that they didn't have anywhere to diffuse to formed nice little concentrates. That seems to make the most sense. Now, in my book, A Very Short History of Life on Earth, I tell it like a story, but in the footnotes, I give more or less evidential support. Now the origin of life I say is one of the areas where I'm basically making it up.

but I'm trying to make it up based on what evidence we have. So... That, I hope, is an answer to your question, but it would be only an answer. And you could get two scientists and you get three different opinions about the origin of life on Earth. Yeah, Henry, it absolutely is an answer, a really, really interesting answer as well.

Well, let's move forwards then from that. I mean, I guess there is still lots of debate, lots of theories, lots of we don't know about this next stage before we get to animals proper and all of that. But you mentioned... cyanobacteria earlier. So do we know how things go from these really, really small organisms at the deepest depths of the ocean? Do we know how they get to the shallow waters and you get the emergence of this cyanobacteria?

All we know is we can track them ecologically because the cyanobacteria form these layer cake-like mounds which are called stromatolites. And these are found to this day, and they're found very commonly, they're the earliest form of life. But by 3.7 to 3.4 billion, the life had spread from the very dark depths of the sea to the surface waters. and into the sunshine. And sunshine had two huge effects on life. One is the ultraviolet rays would be very toxic. So what evolved was sunscreen, pigment.

that would protect, that would absorb the ultraviolet light. and stop the bacteria burning up, because the one thing that is really good for cleaning, or getting rid of bacteria, is ultraviolet light. This is why the best way to clean your wet washing is to hang it up in the sunshine because the ultraviolet light will kill any bacteria in it. I mean, absolutely. That's what it does. It will kill it dead tautologically like well-known brands of bleak.

So what the bacteria did was evolve pigments to absorb that ultraviolet radiation. But one thing life does is turn a problem into an opportunity. So once the energy was absorbed... It could be used to do things. So the energy was used to create food. The earliest living forms, one of the things they did

was to do chemistry with compounds of iron and sulfur, of which there are lots in the deep sea. Using these little batteries, by pushing things to and from the membranes, they could get energy out of iron and sulfur compounds. But when they were up near the surface, they could use this fantastic new source of energy, sunlight. to split water into hydrogen and oxygen.

And that is the most efficient and best way to get energy out of the biosphere. And that's what plants still do today. It's called photosynthesis. And they use a green pigment called chlorophyll. which is why plants are green and why we also have the green movement and being more green. It's to do with plants. and plant growth, because that's how plants are at the bottom of the food chain, and including...

The plankton that live in the sea, you can see this from my T-shirt, but your listeners can't see this. I'm wearing a T-shirt which says, Happy Plankton, and it's got lots of cheer for little plankton, and one of them says, We're the bottom of the food chain! Hooray! So the modern food chain started with photosynthesis when plants used a pigment and bacteria, they use different pigments, but they still do the same thing to create energy out of water.

Water is one of the most abundant substances in the universe. The whole of the planet was completely covered in it. So when you have sunshine and a pigment that harnesses the sunshine and used it to split water... Bingo. Life really took off.

Unfortunately, there's a problem with water, and that's one of the byproducts. The hydrogen was used to shuffle throughout the membranes, but you get this gas called oxygen which comes off. Now, there wasn't any... free oxygen in the atmosphere or the ocean at the time there probably was a bit but really as a tiny tiny trace

And life had evolved in the complete absence of oxygen. And molecular oxygen is very, very highly chemically reactive. In fact, it's one of the most dangerous poisonous substances in the universe. So when oxygen was released, it caused the first mass extinction of organisms that died out. Now, there's still bacteria around for which oxygen is extremely toxic. One of them is botulism organism that you get Botox from. Botulinum toxin is actually one of the most poisonous toxins known.

and it actually paralyzes muscles, and that's why it's used in Botox, because in tiny quantities it paralyzes muscles, so people with Botox treatment have no lines, but they can't really talk, they can't move their faces very much. because their muscles are paralysed with this poison Anyway, the bacteria that botulinum toxin comes from is evolved in the complete absence of oxygen.

And it thrives in badly canned food. If the food isn't properly sterilised before it's canned and there's no air in it, these oxygen-hating organisms can thrive in such a thing. The earliest organisms, they weren't botulinum bacteria, but they were oxygen-hating bacteria. So the first mass extinction drove legions of these to extinction when oxygen was released into the atmosphere. So that was one of the first catastrophes of the Earth when oxygen was released.

But the next major activity happened also related to oxygen. roll the ancient tape of life forward from about 3.5 billion to 2.5 billion. And there was an event called the Great Oxidation Event. where for reasons not entirely clear, there was a huge pulse of oxygen released into the atmosphere.

Probably more than there is in the atmosphere today, which is 21% by volume. It's about a fifth of the air we breathe is oxygen. And then it subsided to something very, very small like 2%, which is still tiny. This is probably related to a lot of tectonic activity. The crust is divided into these tectonic plates. They're forever bashing into each other, sliding underneath each other and creating volcanic activity. And that builds new land because there wasn't any land to start with.

If you think about places like Iceland, you see new islands, volcanoes forming all the time, and these produce new islands. And that was basically how all the continents formed originally. So there weren't any continents. They all started as these volcanic eruptions from the bottom of the sea. But one thing that this new rock does when it comes above the atmosphere... is it absorbs carbon dioxide like anything. It really sucks it up. It's called weathering and it forms carbonate rock.

Now, when all the carbon dioxide is sucked up into the atmosphere and there's nothing for the oxygen to react with, The oxygen reacts with the rock, the carbon dioxide. But when all the carbon dioxide is sucked out of the atmosphere... That, of course, wipes out the greenhouse effect. Now we're all very concerned about the greenhouse effect now.

But in the earliest days of the Earth, the sun was actually much dimmer than it is now. It's been slowly increasing in brightness throughout the history of the Earth. But then it was much dimmer, and the only reason that the Earth had a liquid ocean was because it had lots of carbon dioxide in the atmosphere to fuel the greenhouse effect to keep the Earth much warmer than it otherwise would have been.

So when this pulse of continental mountain building happened about two and a half billion years ago, That sucked up all the carbon dioxide, chilled the Earth. and it went into the deep freeze. The Earth was completely covered in ice, and I mean completely, all the way from the poles to the equator, for 300 million years. Of course, one great thing about ice is that it tends to float, so there were still things happening in the bottom of the ocean.

But life, if it had a motto, would be whatever doesn't kill you makes you stronger. So that event fueled the next change. In the history of life, which was the bacterial cells got together into a new order of existence, which is they formed proper cells, nucleated cells. Talk us through this next stage in evolution. Is this nucleation of cells? ultimately ending up with, let's say, multicellular organisms. You're way ahead of me, Tristan. You're rushing ahead. OK, you slow me down. So...

What happens with bacteria is bacteria are famously sociable and gregarious. Now, we saw this with the stromatolites. They formed layers of bacteria all living together. But it wasn't just this one kind of bacterium cyanobacteria. There were all sorts of other bacteria. Because the thing about bacteria, there are two things. One is they...

can live on virtually anything, and different bacteria specialize on eating different things. Some live on methane, some live on iron and sulfur, some live on other things, and one bacteria's waste product. could be another bacteria's food. So they tended to live together in these communities where they would trade chemicals. So some would prefer other things.

And the other thing about bacteria that they do is they're really rather free and easy with their own genetic material. They would trade genes. like little kids swapping trading cards in the playground if kids still do that they did when i was a kid And that's what happens now if a bacterium comes across a new antibiotic. The way it will combat it is to pick up a little bit of DNA that happens to have a protein that breaks down the antibiotic.

So that's how antibiotic resistance happens really quickly because bacteria pick up antibiotic resistance genes from other bacteria. So you've got to think of bacteria as a community of different species swapping food, swapping waste. swapping information, swapping chatter. So bacteria always live in these communities. And some of them are very difficult to get rid of. That's one of the reasons that these things called biofilms, they're called, are so successful.

For example, in people who have cystic fibrosis, what happens in the lungs is their lungs get too full of mucus. and this mucus is a wonderful place for all kinds of bacteria to live in, so they form biofilms which are very, very, very hard to get rid of. And that's what happens inside. So biofilms still happen. These were the things that were coating the surface of the sea because there was nothing to eat them billions of years ago. There were no animals.

But what happened in the great oxidation event when the Earth went through this crisis? was bacteria took this communal living to another level, rather than having lots of little bacteria swapping stuff, but each one doing everything itself. They took a leaf out of Adam Smith and the wealth of nations. They formed communities where each bacterium would do the thing it was best at and leave the other jobs to different bacteria.

So bacteria started living in a common membrane where some, the cyanobacteria, would do what they were best at, which was... catching sunlight and getting the energy out of sunlight. And then there were other bacteria called the proteobacteria that were great at digesting food. And these were the distant ancestors of the things called mitochondria we have in our cells. There's a little tiny pink power packs that produce the energy.

And then there were bacteria that were good at accumulating all the genes and becoming the library and repository of all the DNA. And they pulled in all the genes from the cyanobacteria and the proteobacteria. So mitochondria and chloroplasts, the green bodies in plants, that harvest online, they still have DNA from their ancient origins, but not very much, because they've subcontracted all the DNA business to the nuclear.

And the thing you can do if you've done the Adam Smith Wealth of Nations is each sell. can do much more than the sum of its parts. It becomes much more efficient. It can do more things, more economically. It can go bigger. It can go further. It can digest more. It can acquire more resources. So in a world of dearth, in a world which is having difficulty, that's when nucleated cells evolved in that period about two and a half billion years ago.

Now, the great glaciation faded, as they all will, but it took hundreds of millions of years. And these nucleated organisms called eukaryotes, which is basically Greek for nucleated organism, you're a Greek. fan you probably worked all this out so so another another happy billion years went along where the eukaryote started to diversify. Now, most of them remain single-celled, like amoebas and things like that. But some of them became multicellular because that's another.

stage in organisation. Some of them glom together to become multicellular organisms. And about 900 million years ago, so we're going for billions to hundreds of millions now, so we're getting really close to modern days now, where a billion years ago, they started to form. what are recognisable as algae, you know, seaweeds, and early fungi, and the very, very earliest animals, sponges, appear about 900 million years ago.

And so the period between about 1.8 billion and 800 million years ago... is known as the boring billion to geologists. who really only get out of bed if they've got some world-shattering apocalypse to wake up to. So the Earth was quite happy for a billion years, slowly brewing and evolving these little creatures, some of which became multicellular.

But then there was another episode of continental fuss and brouhaha. Well, yeah, what happened is all these volcanoes, you remember all them making continents. The continents started to get bigger and bigger, and of course they keep moving around. Now, lots of small continents would glom together to become super continents, and then these would split apart, and then they'd come together to form a super continent. So there is a kind of super continent cycle.

with a period of about half a billion years. And this is explained really well in a book by a friend of mine called Ted Nealt, who's a geologist, and he's called his book Supercontinent, which he wants to assure people is not about pelvic floor exercises. And it explains the supercontinent cycle. So at about 850 million years ago, there was a supercontinent where most of the landmasses were concentrated called Rodinia. And that started to break up and riff.

And that formed a string of continents mostly around the equator. Now, the thing about the tropics is that's where weathering is really intense. I mean, if you've been to the tropics, you've seen tropical storms, you'll see how roads are just washed away by rain and heat and humidity. Well, that was always the case.

Now, what that weathering did was it did the same old thing. It sucked carbon dioxide out of the atmosphere and there were more ice ages. And these lasted for only 80 million years. They did cover the whole of the Earth, but only for 80 million years. Even though there was more land to weather, the sun was that much hotter by then. So that fuelled the next step change, which was the evolution of animals.

But the problem with animals, animals really perfected consuming oxygen this poison animals need oxygen and they need lots of oxygen but they couldn't evolve until there was enough oxygen to live on And although there was gradually more oxygen in the atmosphere and in the ocean, it wasn't very much. It was only enough for animals with very slow metabolisms to live on. And these animals are the sponges. Sponges are very, very simple animals.

They don't have any organs or tissues. They're just bundles of cells with lots of channels between them. And the sponge shells waft any old detritus. bacteria, waste products, rusty bikes, old brass bedsteads. leather boots, half-eaten pork pies, into them and metabolize them. And what that does is it frees the ocean of anything that decay bacteria can live on. So over tens of millions of years, the sponges made the ocean much nicer and less stagnant and have more oxygen in it.

And that allowed bigger animals to live in the ocean. There was another thing that was fuelled by the increase in oxygen, and that was the invention of the anus, which was one of the great underappreciated episodes in evolution. There's what happens in very simple animals like jellyfish. They have a hole at the top or the bottom or the side or wherever. There's really no distinction.

And that's where all the food goes in, but it's also where all the waste comes out. And it's a kind of diffuse wash of ammonia. And that's chewed up by decay bacteria all around, and that sucks out all the oxygen. that some organisms invented or evolved through gut. So all the food came in the mouth, but didn't go out of the mouth. It went all the way through and came out of the anus at the other end. And that allowed animals to grow bigger. And it produced pellets, fecal pellets.

And these, rather than washing in the atmosphere, drifted to the bottom of the sea. And, of course, the bacteria followed it. Whoosh! It was a race to the bottom. And all of a sudden... well, sudden in geological terms, the ocean became much more clear. The ocean cleared and was oxygenated, and that's when animals happened. And the thing about animals with a mouth at one end and an anus at the other end is for the first time they have a direction of travel.

And an animal with a mouth at one end and an anus at the other end can move around. And it's usually looking for something. And the something it's looking for is something to eat. And so they started eating all the slime that covered the ocean floor. And they started burrowing underneath the slime. And then when they'd made burrows and they'd eaten all the slime, which had a terrific effect on the ecology of the earlier, they started eating each other. And that's when the fun started.

Henry, we're going to keep going from there, but you've kind of answered it already, but I had to ask this question because it's amazing. It seems like these sponges, they changed the world. They did. During the writing of this book, When you write a book, you change because of the things you find. And I have a great appreciation for sponges. Things change all the time and knowledge changes. When I was writing the book,

There was only very tentative and controversial evidence that sponges existed as long as 900 million years ago, which they'd need to to work on this scenario. But as the book was finished and not yet published... I was happy to have on my desk at Nature a report of the first fossilised sponges about 900 million years old. These are still very controversial. Not everyone will believe them.

The thing about sponges is some sponges leave little mineralised spicules, they're beautiful tiny microscopic grains that they make out of calcite or silica. and these can be preserved in the rock. So the actual organic matrix of the sponge isn't there, but you see these little specules. But many sponges don't have these. They have more of a protein matrix that they're based on. And these are the same sponges that the Romans made bath sponges out of. These are bath sponges.

So the earliest sponges seem to have been the distant ancestors of bath sponges, and they only leave their signs of their passing as textures in the rock. the ripples in the rock of where they were. And that's why they're very distinctive, but it's still very, very controversial evidence. So that just got published while the book was in press. Yay for sponges, that's what I say. Yay for sponges indeed, Henry. It is absolutely astonishing.

And you mentioned how the fun really begins when animals start eating each other. So talk us through the next stages as it will. What goes next in this great evolution story? Well, after this whole episode of glaciation that lasted a mere 80 million years, that's when you start to see animals It seems to be that animals were the next stage in organisation. You have creatures that were not only eukaryotes, not only multicellular.

Not only sponges, but animals that could move around. They had muscles. and they could actually move from one place to the other and they had a mouth at one end and an anus at the other so they could eat things now this didn't mean that they all did this But the next phase of evolution was a really, really strange phase of early animal evolution. When the animals were soft-bodied and quite gentle things, some of them looked a bit like jellyfish. Some of them looked a bit like modern sea slugs.

They were large enough to be visible. I mean, they were the size of a saucer and segmented, but pancake flat and could move along like flatworms do on the ocean floor today. And there were some animals that seemed to stay where they were. They were perhaps colonial animals like... Some sponges are like many animals are, moss animals and all kinds of jellyfish and so on. And they look like plaited loaves.

and they reproduced by sending out suckers like strawberry plants to make baby plaited loaves all around them. There's evidence for this in some rocks now in Newfoundland. And these animals lived in what was called the Ediacaran period, called after Ediacara, a mountain range in South Australia, where these fossils of these animals were first found.

Now, the Ediacaran period was 60, 70 million years long, and the later Ediacaran animals look a bit more mobile than the earlier ones. You see things more like mollusks, like snails and slugs. and worms that were more mobile than the more plaited loaf kind. They look like fronds. They're found today in all kinds of remote... romantic locations such as South Australia, Northern Greenland and Leicestershire. So these rocks just crop up everywhere. But then was another cataclysm.

For reasons that are not really known, all the Earth's surface, all the crust was scrubbed into the ocean right down to bedrock by an intense burst of weathering. This was a puzzle for a long time. It came at the base of what's known as the Cambrian period. And this was a puzzle for Darwin because before the Cambrian period, there didn't seem to be any fossils.

But from the beginning of the Cambrian, there were loads and loads and loads of fossils as if animals had suddenly appeared, as if from nowhere. Now, this was before the Ediacaran fossils were found, which were all of soft-bodied creatures. And you've got to bear in mind that most fossils are formed from the hard parts of animals, the shells, the teeth, the bones, anything that's been mineralised.

Now, the Ediacaran animals were unmineralised and they're only preserved as very faint impressions on sandstone. But all of a sudden, at the beginning of the Cambrian period, there were mineralised animals. It was known as the Cambrian Explosion because it did seem to happen all at once. And for a long time, geologists wondered... because they seem to be what was known as erosional surfaces. There were surfaces from which it looked like things had been scrubbed.

And then there were these animals. So geologists thought maybe there was this lost period in Earth's history where all the rock that had been developed but was then scrubbed away. That was the period in which all the evolution happened. So the Cambrian explosion was actually slower. We just missed the bits where it was happening. But now there are very refined techniques of dating the rocks using radioactive decay of minerals. It really was explosive. And it happened like this.

When this massive erosional episode happened that scrubbed all the, I won't say soil, because there wasn't any soil, that happened later. all the surface rocks into the sea, that did two things. One is it raised the sea level a lot. And that made a lot more places for animals to live in because most creatures, even today, live in shallow seawater around continental margins, the continental shelf. That's where most things live.

And the other thing was, all this rock that was scrubbed into the heat was full of minerals. It was full of calcium minerals, calcium carbonate, because of all that carbonate rock that had been formed when carbon dioxide was weathering the rock. And calcium phosphate was another one. And this was a bonanza for animals that had started to eat each other.

Because they didn't have any teeth, they would sort of suck each other to death. And all the animals that were sucked to death couldn't do anything about it because they didn't have any armour. So all the minerals allowed for two things. It was an arms race. Animals that used to suck each other to death evolved teeth. so they could chew each other to death, and the animals that were being chewed evolved armour.

and it was usually shells made of calcium carbonate, and in the vertebrates, bones and teeth made out of calcium phosphate, which is what our teeth and bones are made out of. So all of a sudden, at the beginning of the Cambrian, there's an evolution of animals with hard parts that would fossilise well. coincidentally and it was all to do with animals starting to eat each other and in the cambridge you have the appearance in the fossil record of

Lots and lots of strange things we don't see today, like trilobites. Now, everyone knows trilobites. Every geologist, every rock hound will have a trilobite. And they're kind of like giant woodlice. And they lived in the sea and they were very common. They're very beautiful, very sophisticated creatures. But there were lots and lots of other kinds of creatures that are less well-known. Also, mollusks with hard shells, clams and snails started to appear.

Things like starfish and sea urchins, the echinoderms, the spiny skin creatures. And even at the end of the period, the first fish, and they were very soft-bodied fish to begin with. But at the end of the camp, heavily armoured fish evolved. And these armoured fish were armoured because they had a mortal enemy for millions of years.

which was a major driver of evolution. And these were these horrific giant sea scorpions called Eurypterids. And some of them were about 10 feet long with huge pincers and great big goggly eyes. And so as long ago as 1933, a famous paleontologist called Roma speculated that fish evolved armor as a defense against being eaten by these gigantic sea scorpions.

It's a good idea and it's highly likely. I mean, we don't have any proof, but all these things happened at the same time. In the Cambrian period, about 540 million years ago was this. Cambrian explosion, which was a sudden arms race driven by the sudden appearance of a lot of calcium minerals in the sea and all the animal groups. Actually, nature loves its exceptions. For a long time, all the animal groups that we now know today originated in the Chandra, except one.

The bryozoa, these moss animals, which most people haven't heard of, but they form little colonies. Some things which look like seaweed, called dead man's fingers, are actually tiny colonies of these colonial animals. But another scientific report that appeared while this book was finished showed they were Cambrian bryozoa. So even that whole embarrassing gap in evolution has now been plugged in. So all the major animal groups and quite a lot of groups that we don't have today.

originated in the Cambrian, and that was basically the start of modern times. That was what you would call late antiquity. It's 540 million years ago, the Cambrian explosion. Hi, we're Backmarket, the home of high quality, affordable, refurbished tech. Like this laptop. It can binge 18 episodes in one weekend. That is normal, right? This laptop can also write, game, design... Browse Private Browse

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hello if you're enjoying this podcast then i know you'll be fascinated by the new episodes of the history hit warfare podcast from the polionic battles and cold war confrontations to the normandy landings and 9-11 we reveal new perspectives on how war shaped and changed our modern world. I'm your host, James Rogers, and each week, twice a week, I team up with fellow historians, military veterans, journalists and experts from around the world to bring you inspiring leaders.

If the crossroads had fallen, then what Napoleon would have achieved is he would have severed the communications between the Allied force and the Prussian force, and there wouldn't have been a Waterloo. It would have been as simple as that. Revolutionary technology. At the time the weapons were tested, there was this perception of great risk and great fear during the arms race. that meant that these countries disregarded these communities' health and well-being to pursue nuclear weapons instead.

It's as though the world is incapable of finding a moderate light presence. It always wants to either swamp the place. in trillion-dollar wars, or it wants to have nothing at all to do with it. And in relation to a country like Afghanistan, both approaches are catastrophic. Join us on the History Hit Warfare podcast, where we're on the front line of military history. Well, beat that fall of the Western Roman Empire right there. Henry, the Cambrian explosion, huge, huge events in prehistory.

I've got to ask in the next big question. You probably know where I'm going to go with this. If we've got all of these animals now in the water that's teeming with life, when do we start to see animals? moving on to land? Well, Tristan, I'm glad you asked me that because, again, it was quite a long story with a lot of precursors. Creatures like fungi and algae tend to get together to form things like lichens.

And these are very resistant. And there is some evidence that lichens and fungi and other plant-like creatures were starting to inhabit fresh water, like lakes and ponds. About 1.2 billion years ago, there's evidence from rocks in Scotland of that age which were deposited in fresh water and may show communities of... little cells of algae and fungi and they would have started forming crust along the water line that would have become resistant to desiccation, which is the important thing.

But the thing about moving on to land, land was as hostile an environment to life as empty space. Because for a creature in the water, it doesn't have to worry about bearing its weight on land because it's supported by the water. It doesn't have to worry about breathing because it absorbs all the oxygen from the water through its surface or through gills, the wet membrane. It doesn't have to worry about getting rid of wastes which just diffuse into the water or just shoot out a pellet.

It doesn't have to worry about drying out. But on land, anything that gets above the waterline is going to be crushed, desiccated and asphyxiated in pretty short order. So some creatures started to do it, some bacterial slime, by having a coating of mucus, which would, like a spacesuit, protect it against desiccation. And if they were thin enough and wet enough, they could absorb oxygen from the dry air. slime and various encrusting lower organisms would start to colonize the shoreline.

And then in the late Cambrian, and a bit later than that, some actual plant. started to come ashore but very simple things like mosses and plants called liverworts which are a bit like mosses that you can still find today in very dark, damp places, like around shady waterfalls and places like that, and rocks that are covered in water a lot of the time.

These would start to colonise the intertidal zone. Now, the intertidal zone, where the land is covered by the sea twice a day and is completely dried out for twice a day, is a very tough environment for animals and plants to colonise. But they started to do that. And very, very slowly, there became a covering of plants.

over the land near water and slightly further away from water. The earliest plants evolved tough, woody tissues that allowed them to grow upwards, because once the plants had colonised the land, what they wanted was access to sunlight, and they would compete each other for access to sunlight, so they'd start to outgrow each other in height. by outgrowing each other in height we're talking about centimeters at this time But once you start having little plants growing on the land...

you can start having little animals. These have been now supported by mineralised skeletons, you know, like little crabs and lice and early types of insect and spiders and harvestmen. These started crawling on the land, fighting tiny to the death battles underneath the covering of plants which would screen them from the sun and conserve moisture.

Then slowly, slowly, slowly, soil starts to form. Soil is another great underappreciated... feature of evolution and one of the worries about deforestation is not so much getting rid of trees it's because trees have roots that keep the soil in place and once you get rid of the plants Soil is completely washed away and soil is necessary for holding water, for conserving life. It's full of life.

So once plants had roots and fungi attached to the roots that broke up the soil and there were dead plants and dead animals in the soil and bacteria in the soil and fungi in the soil, basically making compost out of rot. and organic matter, you started to have soil and that started to be colonized by tiny animals and plants and was a growing medium for plants. So it took a while for this to happen.

But, of course, what you're dying to know is when the first fish came on land. That took a while because fish were bigger and had more to support. Well, from the Cambrian onwards, fish, which were vertebrates, they had backbones, they'd evolved, through to the Devonian period, which was about 400 to 350 million years ago, or thereabouts. Someone's going to kill me for getting the times wrong, but I'm just working for memory here.

That was what we always used to call the age of fishes. The oceans were full of fishes of all kinds. Some were enormous. And, of course, it was all full of other predators, like these gigantic sea scorpions, which I mentioned. But the great thing about land... Life, as we've seen, turns problems in life. They've all been on management training courses. There are no problems and difficulties. They're just challenges and opportunities.

And land was a whole challenge and opportunity. It was difficult to colonize, but oh boy, if you could do it, you'd have it to yourself without all these other fishes bumping into each other and getting all crowded in the sea. Now, there was a group of fishes called lobe finned fishes because their fins were supported on little legs. Well, they were just like little legs, only they terminated in fins and not fingers. Some of these were quite big.

and they tend to live in very shallow freshwater and in the shallow seas. and they lived very close to the surface of the water, and they were ambush predators. They used to hang around until something would turn up, and then they'd just go snap and swallow it. So they were quite big. Some were kind of alligator-like.

in that they were flattened from top to bottom rather than side to side, like fishes tend to be. So they could cruise along the rivers with just their eyes showing, waiting for some unfortunate insect to fall into the water or another fish to come along. And these were the creatures that started to colonize the land, because if you're living in very shallow water, sometimes the water can be so shallow it disappears altogether.

So, while still in the water, some of them traded fins for digits. And at first, they weren't really worried about how many digits they had. Some of them had eight digits per limb, some had seven, some had six. And these appeared towards the end of the Devonian. Basically, they were fish with legs. They had legs, but they couldn't have lived for any length of time out of water because they still had internal gills.

But some of them had lungs. In fact, all fish evolved with lungs. It's just most of them have lost them and turned them into other things like hi-fi cabinets and swim bladders and other things. So they breathe through their gills. But some of these lobefin fishes started to trade their gills for lungs and actually only breathed air. Now, there's still fish that do this. They're distant relatives of what we call tetrapods, that is, four-legged animals.

When lungfishes were first found, they were mistaken for salamanders. Now the Australian lungfish has got scales and lives in rivers and looks very, very prehistoric. But the South American lungfish can only live in air. It's a fish, but it cannot live full-time underwater. It has to breathe air because it doesn't really have any gills worthy of the name.

So animals like this started living in the water margins and they started colonising the land and the land was full of wonderful insects to eat because they'd all been colonising the land. So you started to get what were the first amphibians, these animals that live first in the water, first in the land.

They were rather different from the amphibians we see today, frogs and newts. These evolved much later, but they were distant cousins of them. So they lived a kind of halfway existence. They could live on the land. but they were tied to the water for reproduction for a long time because they still had spawn or very soft-shelled eggs that had to be laid in water.

So that was the amphibians. They started to colonize the land around 360-ish million years ago, and there were quite a lot of different ones. There were some that were more... evolved for living in water and there were some that were evolved for living in land although back then they would have just seen it as a different kind of water it was just water of negative depth so they were kind of fish that lived out of water really and that's what the early amphibians

But Henry, soon enough, it seems to be a similar trend that we've been having with earlier times. There is a great natural event which almost stymies this. Well, there were all the time, but the first one was rather an abundance of life rather than a catastrophe, and that was the evolution of forest. Because once we started having little plants growing to enormous heights, I mean centimetres above the ground, they evolved hard woody tissues which could support much higher trees.

and the first forests evolved in the Devonian. Now, the forest trees didn't look much like trees now. The first forest trees were basically giant fungi. I mean, they were really weird. They were the sort of thing that the caterpillar in Alice in Wonderland would have sat on top of smoking his hash pie. But then the trees were relatives of little, what we now call weedy water plants, like horsetails. You know the field horsetail? Beautiful plant, absolutely persistent weed, only grows so high.

But back in the late Devonian, the Carboniferous period, they grew to 50 metres high. And there were other things which were club mosses, which now grow to a few inches high. They grew to 70 metres high. And this was during the Carboniferous. Now the clue's in the name. This was the period in Earth history where most of the Earth's coals formed.

And it happened because of the way that some of these club mosses called lycopods grew. They didn't have heartwood. They were supported by a rind of tissue on the outside. a bit like some giant reed, but they grew incredibly fast and very, very wastefully.

Because most trees now, they grow up and they stay up and they support their reproductive tissues and their leaves high above the ground. And the reproductive tissues, you know, the flowers and the fruit, They come each year, but you still have the whole structure. But that wasn't true with the first forest. They started in the ground and shot up like some very slow-moving fireworks.

until they were metres above the ground, and then they'd produce the fruiting bodies, which are like cones, and spread spores everywhere, and then the whole tree would just die. It wouldn't stay up to do it next year. It would just die. And it would just stay there rotting like a trunk without any branches and eventually collapse into the ground. And this would use an incredible amount of carbon, carbon dioxide.

So what happened with two things in the age of the coal forest is an immense amount of decayed and half-decayed plant matter was accumulated on the land. and it wouldn't look like a forest. I was trying to imagine what it would look like, and in the book it was more like a World War I battleground.

Because it had all these, like, if you see pictures of the First World War, you know, after the forests and woodlands have been battered, they just look like a bleak landscape with the occasional tree trunk sticking up. And because these plants didn't have... solid trunks, they had hollow trunks.

You had these craters sitting on the ground, like bomb craters all over the place, with trees everywhere. And the craters were great for little amphibians to lay their eggs in and insects to live in. But it wouldn't have looked much like a forest now. And in that period... Huge deposits of this vegetable matter were deposited from the Carboniferous and into the subsequent Permian period. And in fact, 90%...

It's staggering. 90% of all the world's coal reserves were formed in this one period of about 70 million years when the lycopods were evolving. But then they caused another catastrophe. Well, that and continental drift. We'll come to that. They use so much oxygen and so much carbon. that they precipitated another ice age. They pulled all the carbon.

You know we have to plant a tree to suck carbon dioxide out of the atmosphere. Well, you can have too much of a good thing. In the Carboniferous times, they sucked so much carbon out of the atmosphere, they created another ice age. But they only did it at the South Pole, because the continent... had come together after the fragmentation to form.

large continental land masses, and the one nearest the south, Gondwana, was over the South Pole, and they were glaciers over the South Pole. That was the Carboniferous Ice Age. It wasn't the whole planet. There were actually other rice ages which I haven't really talked about which were catastrophic and led to extinction and origination but I've kind of glossed over those.

But the carboniferous one was quite important because it coincided with the slow formation of another supercontinent. This is the one everyone's heard of, Pangaea. where almost all of the continents coalesced to form some gigantic landmass from the South Pole. It covered the South Pole almost to the North Pole. And if you looked at it, it would have formed a sea shape.

There was a great gulf called the Tethys Ocean which was about over the equator and that had incredible coral reefs but also absolutely terrific monsoon rains which were just spectacular. And one of the problems you get when you get a lot of little continents forming into one big continent. is you get less margins of the continent because the margins get glommed together and form mountain ranges. So that meant less room for animals to live in. So life was getting tough.

And also because after the Carboniferous, plants became less profuse. So less oxygen was being diffused into the atmosphere. So Pangaea was quite tough. There was less life in the sea and also breathing on land became quite tough. It was like breathing in at the high mountains. In the Carboniferous, the plants had produced so much oxygen. that even though the forests were damp,

they could be set alight by lightning strikes, even though they were damp, because there was so much oxygen, even wet sticks would burn. And because there was so much oxygen, that could fuel the growth of giant insects. So there were dragonflies the size of crows. and there were millipedes the size of magic carpet. And there are again these giant sea scorpions that kept coming to get their age-old prey, the tetrapods, which...

thought they could cunningly escape by evolving little legs and crawling onto land, but oh no, that's none of it. Some of the biggest of these sea scorpions lived on land during the coal measures times. But when Pangaea formed, all that was swept away. Life became much more difficult. What you tend to find in big continental landmasses is very far from the sea. They become deserts because there's no rainwater. And so the interior of Pangaea was a desert, very, very hot.

In the more temperate regions, plant life was less diverse than it was. And then this was leading up to the greatest catastrophe. of the last 500 million years. This was the siege of Constantinople and the burning of the Library of Alexandria. Thermopylae and all the catastrophes you can see in the ancient world, all rolled into one, squared. Pompeii as well, isn't it? Yeah, very much so. It is very similar.

Sometimes the volcanoes are not just caused by continents bashing into each other. Sometimes a plume of lava comes from very, very deep in the earth and rises upwards and punches a hole in the crust. And this is kind of what's happening in Hawaii now. Hawaii is in the middle of a continental plate, the Pacific plate. But what happened is there's a plume of magma that started to arise several million years ago. and punctures a hole in the crust, forming volcanoes.

What happens is that the plume of magma stays still, but the continental plate moves above it. puncturing it every so often a bit like a sewing needle puncturing material as it moves so you get a chain of islands you get what's called a volcanic island art So all the oldest Hawaiian islands have been eroded away to tiny atolls like Midway Atoll, and some of the islands that are kind of old like Kauai.

are very jungly and eroded and not much in the way of volcanoes. And then you get to the big island where there's still active volcanoes. which are creating new land. And just about to surface, there's the Loihi Sea Mount, which is a volcano in the act of coming to the surface. So this is what's called a magma plume, and these have happened many times, and some of them are really, really big. Well, towards the end of the Permian period, one of them punctured the surface in South China.

which was kind of a shame because South China was the land that time forgot. When Pangaea started to get dry, South China still had these Carboniferous-style coal forests, you know, as if it was living in some prehistoric path. But the magma plume wiped all that out, and it filled the atmosphere with carbon dioxide, acid rain, and noxious gases and the lot. Now, that wiped out a lot of life on Earth, but that was only the hors d'oeuvres.

that life was just beginning to recover from this when an even bigger magma plume punctured the earth inside what's now western Siberia, which was in the north of Pangaea. Now, that spewed an amount of battle almost as big as the continental United States over a period of half a million years to several miles deep. Now, that would have produced an immense amount of carbon dioxide spewed into the atmosphere, which caused the temperature to rise by about six degrees.

But also the carbon dioxide in the atmosphere would form carbonic acid in the atmosphere and that would be rained out as acid rain. And also it produced hydrochloric acid and that would form these little... chlorine compounds which would destroy the ozone layer. This is why we don't have chlorofluorocarbons anymore because they puncture holes in the ozone layer. But these can be produced naturally.

And so every kind of disaster that could happen, happened. And 95% of all creatures in the sea... and over 70% of all creatures on land were killed in this maybe half million year period. of the end Permian mass extinction, they were either dissolved by the acid or they were grilled by the sun or boiled or fried or asphyxiated or covered in lava.

So that was an immense disaster. Of the major mass extinctions that have punctuated the Earth's history that we know of in the past half billion years, that was by far the biggest. And it took the Earth several million, maybe 10 million years to recover from that. But recover it did, because it always does. Henry, that is absolutely mind-blowing. You have the extinction of all these herbivores, carnivores, omnivores, all of these species.

But it does beg the question, as you said there, how does life recover from this horrifying extinction event? Well, before this extinction event, in the Carbonism Permian, a new kind of animal had evolved, and these were the reptiles. And by reptiles, I mean that loosely. These reptiles include the ancestors of mammals and birds.

And they had come up with a new way of protecting their spawn. Now, frogs and toads and other amphibians lay their eggs in the water because they have to return to water to breed. There's still that last vestige of the sea in them. But the problem of having all this spawn around is it's a wonderful free snack for anything that comes along. So frogs now and amphibians in the past probably came up with all sorts of cheeky ways of avoiding this. They would either keep the spawn in their own bodies.

or the spawn would happen really quickly, or they'd lay it in little holes in tree branches where nobody could get to them. Amphibians do that now, so there's no reason why they didn't do this in the past. But another cheeky way that amphibians evolved was evolving spawn with hard-shelled eggs. So there was a layer of shell, which was probably more like kind of paper when it started. It was more kind of dry and papery.

is as well as just evolving protection, it evolved basically a whole life support system. that could resist desiccation. It was like a life support capsule. Because in it, the embryo had lots of yolk to nurture it while it was growing. And it also had another membrane that would take all the animals' waste. And it had a breathable membrane that would allow air in and out, but not water to escape. That's called the amnion.

And after that, it would have the shell, which would be mineralised to something. Now, we still have that. In fact, human babies are still like that. We have all of those membranes except for the shell. We still have the amnion in which the embryo is. When a pregnant woman says her waters have broken, that means the amnion has ruptured and she's ready to give birth.

So even though we don't actually lay eggs anymore, we still have all those membranes that the earliest amphibians turning into reptiles evolved. And before the mass extinction, some of the amphibians, most of them stayed around water and became quite large and predatory, but some of them made a stab of a much more land life because once you've evolved these eggs...

you don't have to lay them in water anymore. You can incubate them in a warm midden or in a nest or something like that. So some amphibians turning into reptiles became quite large herbivores and carnivores. But that was only a brief dalliance with land life for amphibians. The end perm in extinction got rid of all these very pretentious land-living amphibians and most of the reptiles and most of other things as well.

But in the Permian, there was quite an ecosystem of reptiles which were distant cousins of mammals. There were herbivores and carnivores, a whole ecosystem called the therapsids. which aren't therapists, or either theropsids, which are different. Don't talk to me about theropsids. But most of these were wiped out in the extinction. What happened after the extinction was a bit like what happens on a bomb site.

A bombsite or anywhere where there's been a catastrophe is soon colonised by what's called a disaster assembly. When you look at old bomb sites or building sites, you see the same plants, you know, like red-hot pokers and ferns and brambles and stuff. And these colonise things really quickly. Well, there was the same thing after the end permanent extinction, only on a bigger scale.

Hi, we're Backmarket, the home of high-quality, affordable, refurbished tech. Like this laptop. It can binge 18 episodes in one weekend. That is normal, right? This laptop can also write, game, design, browse... Private browse. And do everything a brand new laptop can. There's just one different... It costs up to 50% less because it's not new, it's verified refurbished, meaning it's been inspected by industry experts and comes with a year's warranty.

What is power? Is it a home EV charger that works while you sleep? Maybe it's a heat pump that pulls warmth from thin air. Or is it switching to solar, so energy companies can pay you for a change? Power is all of that, at the touch of a button. Hive's Ecotech range gives you the power to control your home energy. Hive. Know your power. T's and C's apply. Visit hivehome.com. Immediately after the end permanent extinction, nine out of ten animals was one kind of animal called Lystrosaurus.

which was one of these distant cousins of mammals. But these were happy-go-lucky, go-anywhere-eat-anything animals. I was trying to describe them. They were different kinds of Lystrosaurus. Some were quite small, like, you know, cat size. Some were as big as hippos, but they were different kinds of Lystrosaurus. because there are no pictures in the book it's a very small book i'm having to paint the pictures with words so i describe them as having the body of a pig

and the eat-anything attitude of a golden retriever, and the head of an electric can opener. So they had this kind of blade at the front, and little teeth that they just shoveled anything in. In the earliest Triassic, which was after the catastrophe, They lived everywhere. They lived in jungles, they lived in swamps, they lived in deserts, they ate anything and lived in burrows, which was probably a good way to keep out of catastrophe.

And the only other animals that survived used to sort of share Lystrosaurus burrows. And from Lystrosaurus and the few other animals that survived came all the animals we know today. And in the sea as well was the same. A lot of the ancient sea life The last trilobites died out in that catastrophe, for example, so we don't see any more of those. And all sorts of peculiar animals that we don't see any more died out. But on the land in the Triassic period,

That was a great big raspberry to the earth. I can do a raspberry now like this. Well, imagine that in terms of evolution. Because the Triassic period was the most amazing carnival of land life that has ever been. Lots of amazing kinds of reptiles with unpronounceable names evolved in the sea, on land. Some of them were really, really odd. Many of them took to the air. There was this really strange creature called Sharaviptery.

which had wings, but not on its front legs, on its hind legs. Its front legs were just sticking out of the front, and they were really weird creatures that we have no analogue of today, but they all lived and died in the Triassic. It was a real carnival of diversity. And amid all this diversity, several other new animals evolved. There were turtles.

But these were very, very varied. There were turtles that had plates on their belly but no shells. There were turtles that had shells and belly plates. There were turtles that didn't really have any shell plates or belly plates but had a turtle-like beak.

So there were turtles, pretend turtles, mock turtles, wannabe turtles, and teenage mutant ninja turtles. They all lived together in the Triassic, and the only turtles we have today are the ones still with us. The first true frogs evolved in the Triassic period. And so did the mammals from a distant cousin of Lystrosaurus. There were little carnivores called Cynodonts. and they specialised in being small with active metabolisms.

The earliest scientists were quite big, but they got smaller from large dogs to small dogs to cats to weasels to mouse to shrews. And as they got smaller, they got furrier and more and more nocturnal. And they just lived in all the nooks and corners for a long time and nobody noticed them.

And, of course, the other group of animals that evolved in the Triassic is everyone's favourite prehistoric animals, the dinosaurs. So I'm going to have a glass of water now, and you're going to ask me about dinosaurs. Well, Henry, we might have to save Dinosaurs in Debt for another podcast, but I will ask one question before we wrap up about them, of course.

Interesting, you mentioned their cynodons. I remember watching Walking with Dinosaurs when I was very young. And cynodons, I think they feature in that Triassic episode as one of the small mammals. Yes, they do. Mammals did evolve alongside the dinosaurs, but they were mostly very small. But in the way that sea animals saw the land as a new opportunity where nothing, the mammals found an entirely new place to live in that no other large animals were colonising. That was the night.

So they became small, they became warm-blooded, and they chased insects. And they weren't very good at seeing, but they had whiskers and fur and a very good sense of smell and touch.

and hearing. Mammals evolved a marvellous sense of hearing by a complete accident of the way their jaws were structured because all their jaw bones As they got smaller, a lot of the bones at the back of the jaw... got squeezed backwards to where the middle ear happens and they became the bones of the middle ear and that allowed mammals to hear much higher frequencies than other animals and it revealed to them an entire sensory universe.

that was previously close to them. They could hear the high-pitched squeaks of insects that they could capture. They could squeak to each other so high-pitched that no other animals could hear this private communication. And mammals made the night their own for 160 million years. While the dinosaurs were busy stomping around in the daytime and bumping into each other, the mammals were keeping well out of the way, waiting for their time to come.

Early dinosaurs of the Triassic, then. We'll talk in more depth about dinosaurs in the future, Pod, I've no doubt, because that'd be great to focus in on. Yeah, it would, because there's lots more to say. Well, exactly. Give us a taster, therefore, these early dinosaurs. Well, in the Triassic, there were lots and lots of amazing kinds of reptiles of all kinds, and a lot of them were kind of vaguely crocodile-y.

And there were some things that actually did look like crocodiles. They lived on four stumpy legs and had armour and lived in the sea and not lived in, well, some of them did live in the sea, lived on land and looked much like crocodiles. But there were some crocodile-like animals that actually evolved to live on their hind legs and evolved a kind of bipedal locomotion.

where their whole fulcrum was concentrated over the hips. So they had a short body forward of the hips and a long tail which counterbalanced it. And that made them really manoeuvrable. Now, there are many kinds of crocodile-like animal that were like that in the Triassic. But there was this one lineage, the dinosaurs. Now, they evolved in the last third of the Triassic. But they lived alongside a lot of animals that were more or less like them.

but they weren't the main event. They were like the second violins in the reptile orchestra behind the star soloist. but in front of the French horns and the timpani. They were okay, but they only lived in certain parts of Gondwana land and northern Pangaea. But as the Triassic progressed and some of the other herbivores and carnivores declined, dinosaurs quietly slotted in.

to take their place so by the end of the triassic there were all the familiar dinosaurs that we know about the big gigantic sauropods and the small fierce theropods, which eventually became things like T-Rex and Brachysaurus. But that was a long way. There was another great extinction at the end of the Triassic. Because Pangaea had started to drift apart, there was a rift.

A giant rift valley happened in what is now North America along the Appalachian mountain front, which is a kind of weak point in the earth. That part of North America keeps sticking together and keeps moving apart. It had done so in the past. So a huge rift valley, like a gash in the earth, opened between the Carolinas in the south to the Bay of Fundy, stripping apart eastern North America from what was then North Africa, which was joined to it.

And that produced lots of the usual volcanoes and carbon dioxide and the usual fuss and mess and disaster and created the Atlantic Ocean. So this was Pangaea starting to drift apart. So the end Triassic extinction was like the third or fourth most intense mass extinction in the Earth's recent history.

And that wiped out a lot of animals, including a lot of the fantastic Triassic reptiles. But the dinosaurs, by luck, And so for the Jurassic and Cretaceous, they had the world to themselves, with all the little mammals scarring around under their feet, trying not to be trodden on. Brilliant. Well, we will delve into that in more detail in due time. Like the Jurassic, the Cretaceous, amazing. Can't wait to talk about those.

But finally, as we wrap up, Henry, looking at this topic, and of course, today with climate change and global warming right at the forefront of things, looking at the beginning of life, looking at all of these events, these natural events, what lessons can we learn from this for today? I think what it's given me when I've written the book is to take a very long view of current events. I no longer listen to the news, Matt.

I'd rather listen to you talking about ancient history because I think one of the great disasters of the media is the 24-hour news cycle. Everything is so short-term. But when you look at the long-term, the Earth has been... subjected to cataclysm and life has always recovered. Now, climate change caused by human beings is absolutely real and is absolutely urgent. but it's happened very, very recently.

I mean, within the last 500 years at most, and in fact, most intensely in the last 200 to 300 during the Industrial Revolution, and perhaps mostly in the last 100 because of the internal combustion engine. But all these things are passing things, and it's not true to say that people haven't been doing anything about it because people have.

whether it's by the forces of the market because people choose to live more sustainably but this has been happening for a long time i mean in historical terms people no longer drive those big gas guzzling cars anymore and they haven't for a long time

And the internal combustion engine, invented in 1876, will be a thing of the past in about 20 years' time. The internal combustion will still be there, but it'll be as antique as manual typewriters. I mean, they're still there, but they're only kind of niche. So people are beginning to do things about it. Also, a lot of it's been driven by human population growth.

And that's beginning to slow down, partly because of increases in health and welfare. And the biggest change in the past hundred years has been the political and reproductive emancipation of women, which has only happened in the past hundred years. And because of that, women are now part of the workforce and can choose when to reproduce. Now, for all of the history of animals, females would become pregnant as soon as they were able and keep having babies until they couldn't do it anymore.

And that was true until quite recently. But now it isn't. And because of that, the population is coming down, or at least it's still going up, but it's going up more slowly. And all sorts of wonderful things have flowed from female emancipation. Longevity, health, welfare, education. So there are a lot of good things to say. Like in 1970, only one in five people in the earth completed primary education. Now it's one in two.

And it'll be everyone in the whole world, not just in what we patronisingly call the developed world. It'll be everywhere by 2030. And the population will peak in the 26s and then start to go down quite rapidly. So human beings will become extinct in the next few tens of thousands of years, but we can manage that decline. And as part of that, we can manage...

amelioration of climate. There will be changes, there will be flooding, there will be widespread migrations and a lot of problems and disasters, but these are economic and governmental. We are not seeing the sixth mass extinction. that people have talked about we are going that way but only if we keep doing what we've been doing for another 500 years

And people are already pulling back. They're already success stories in conservation. People are already knowing what to do. And the great thing about human beings is that human beings are the only species in the history of the earth, as far as we know, that are actually conscious of what we're doing.

I mean, the little bacteria that released huge amounts of lethal oxygen into the Earth's atmosphere, killing virtually everything, you know, two and a half billion years ago, they presumably didn't know what they were doing and yet they caused probably the biggest mass extinction of all time.

But we do know what we're doing, and we're doing something about it. And the problem is urgent and pressing, and it's very, very right that people are drawing attention to it. And the governments are falteringly, haltingly not very well. making promises but they are going in that direction um The human-caused spike in carbon dioxide is a bit like a tiny version of the N-permin extinction. You know, it's very, very brief.

The calm, dark side in the atmosphere now is higher than it's been for hundreds of thousands of years, but it won't last long. It'll be very, very brief. It'll be a spike. So I'm cautiously optimistic about the future. But then being a paleontologist, I'm cautiously optimistic over hundreds of thousands of years. I mean, the next century is going to be quite difficult. for a lot of people but i think we already have the tools

to manage it. As the science fiction writer William Gibson once said, the future is already here, it's just not widely implemented. So I think these are the lessons to draw, is that the earth... It's very resilient. We don't need to save the planet. The planet will quite happily carry on and could wipe out the whole of life if it wanted, if it were a thinking being.

What we need to do is save ourselves because the earth is always changing and what we need to do is be conservative with a small c and try and work to maintain our level of comfort and luxury and learn how to manage. the changes to come in a way that is equitable and comfortable for the greatest number of people.

So I'm not one of these people who goes around preaching doom and gloom because I think there is a way out of it. And the human beings will disappear in due course and the earth will just carry on. But we can manage things with a bit of goodwill. it can be done climate change is absolutely real it's really a big threat but it's not the end of the world that's a much bigger deal Henry, that's a really nice way to end our chat today. Last but certainly not least, your book.

on these millions and millions and millions of years. It is called... It's called A Very Short History of Life on Earth. And I have a copy here. This is the US copy, which is... It's very small. You can hold the whole of life in the palm of your hand. The UK copy is a bit bigger. But it's still got the same stuff in it. I think they read in smaller print in the US. The UK version is...

Out now, a very short history of life on Earth. Wherever books and audiobooks are sold, I narrate the audiobook, so that could be a draw or make you run screaming away. The US edition will be out by the time you broadcast this. And time is coming up to Christmas. And remember that rectangular gifts are always easiest to wrap. Exactly, exactly, exactly. And I've read it myself. It is a really easy, very, very fun read indeed. Very good read.

Henry, thank you so much for taking the time to come on the podcast today. Thank you very much for inviting me. I've enjoyed it thoroughly. Back to the Battle of Galgamella, I say. Absolutely, absolutely. I hope you've enjoyed this podcast. If you have and are looking for more fascinating ancients content, I mean, of course you are, then why not subscribe to our new ancients newsletter at the link in the description below.