The First Life on Earth

Today we’re going back to the beginning – no Romans, Celts, Egyptians or Macedonians in sight. Billions of years of prehistory as we look at the emergence of life on Earth. From the rise of the earliest microscopic membranes to the arrival of the dinosaurs. Tristan Hughes is joined by Henry Gee to journey through several billion years of history; from the rise of the earliest microscopic membranes to the arrival of the dinosaurs. MORE Rise of Humans with Henry Gee Listen on Apple https://podcasts.apple.com/no/podcast/rise-of-humans/id1520403988?i=1000702067254&l=nb Listen on Spotify https://open.spotify.com/episode/1vXxIXCruQh4w90EuawE6E Jurassic America Listen on Apple https://podcasts.apple.com/rs/podcast/jurassic-america/id1520403988?i=1000700771214&l=hr Listen on Spotify https://open.spotify.com/episode/0W4Id2RpIYL3ZoUIPSnVcB Presented by Tristan Hughes. Audio editor is Aidan Lonergan, the producer is Joseph Knight. The senior producer is Anne-Marie Luff. All music courtesy of Epidemic Sounds The Ancients is a History Hit podcast. Sign up to History Hit for hundreds of hours of original documentaries, with a new release every week. Sign up at https://www.historyhit.com/subscribe. Hosted on Acast. See acast.com/privacy https://acast.com/privacy for more information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Tristan Hughes?

  Ever wondered why the Romans were defeated in the Teutoburg Forest? What secrets lie buried in prehistoric Ireland? Or what made Alexander truly great? With a subscription to History Hit, you can explore our ancient past alongside the world's leading historians and archaeologists. You'll also unlock hundreds of hours of original documentaries with a brand new release every single week, covering everything from the ancient world to World War II. Just visit historyhit.com/subscribe.

• 0:32Speaker 01

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• 1:11Speaker 02

  Hey, we're Nick and Jack, hosts of The Best One Yet. Behind every episode, there's research, emails, spreadsheets, and our shared Google Doc, the headline hammer. With Google Workspace with Gemini, Google's AI is built right into the premium versions of tools we already use, like Gmail, Docs, and Sheets. No new tools or extra logins, just personalized AI for the way we work. That means less time on the work around the work and more time finding the stories worth talking about. Get AI tools for work. Upgrade to Google Workspace with Gemini at go.O.gle/workspacewithGemini. That's go.O.gle/workspacewithGemini.

• 1:44Speaker 03

  In Our Time is a world-class seminar every week. Why was Jeremy a lonely snail? What were lines doing in York in the third century? I'm Misha Glennie, and every week I'm joined by expert guests to explore the ideas that shape our world.

• 2:00Speaker 04

  It's one of the first times, really, that you consistently see someone painting teeth. I know that sounds bonkers.

• 2:04Speaker 05

  If I was going to define mathematics, I would say it's the study of structure.

• 2:08Speaker 03

  In Our Time, listen on bbc.com or wherever you get your podcasts. Tea or coffee? Love a cup of tea.

• 2:18Speaker 03

  Hello and Happy New Year. Welcome to

• 2:21Tristan Hughes?

  2026 on the ancients is gonna be a good one. We've got some awesome episodes already lined up. Our January schedule is done. We've recorded it all and cannot wait to share those episodes with you. But we are kicking off 2026 and the new year with one of my favourite ever episodes. Over the five years, five and a half years that we've been doing the podcast. And actually, this is an episode that so many of you have found deep in the ancients archive. And you've been requesting time and time again that we get this guest back on at every opportunity. You want more of this guest. He's none other than Dr. Henry G.

• 3:01Tristan Hughes?

  The brilliant Dr. Henry G, who we have now had on since doing this first interview with him all those years ago. We've had him on several times since because he is a fan favourite. He's funny and he makes these stories that we cover with him going millions of years back into prehistory. He makes them really interesting and easy to follow, big, complex topics as well. And we did quite a big topic for our first ever interview with Henry G. We covered hundreds of millions of years of history of life on earth, the origins of life on earth. Going from the earliest single cells at the bottom of the deepest, darkest oceans

• 3:43Tristan Hughes?

  to the rise of animals with backbones, the first fish, fossil fish with backbones, to plants and trees and animals taken to the land, ultimately to the rise of the dinosaurs. Henry covers all of this in this really fun and fascinating interview. I really do hope you enjoy. If you've never listened to an interview of Henry G before, well, you are in for a real treat. So really excited to get this one out of the archive, to share with you, to kick off 2026. Here is Henry G, Dr. Henry G, talking through the origins of life on earth. Let's go.

• 4:29Tristan Hughes?

  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?

• 4:41Speaker 06

  Well, are you sitting comfortably?

• 4:44Tristan Hughes?

  Yes.

• 4:44Speaker 06

  Then I'll begin. Life on Earth actually began not long after the Earth formed. In fact, it's really quite indecently close to when life on Earth formed. The earliest, it's 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, fossilized of a reef in Western Australia. So that's three and a half billion years old.

• 5:26Speaker 06

  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, of living matter. It wasn't a coral reef. 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.

• 6:09Speaker 06

  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. And 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.

• 6:54Speaker 06

  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 zircon. It was basically what was

• 7:33Speaker 06

  left after the rock was eroded away. And inside this zircon is a little smudge of graphite, in other words, pencil lead, inside this little hole with this zircon. 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

• 8:13Speaker 06

  of the solar system formed. And for quite a long time, it was a ball of magma that spent its time. Solidifying into layers, 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

• 8:55Speaker 06

  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, it's 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

• 9:38Speaker 06

  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 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

• 10:23Speaker 06

  water vapour in the atmosphere fell like rain. It just condensed into rain.

• 10:29Speaker 06

  And it rained, it rained and it rained for millions and millions of years. In fact, it would have made Oldham look quite sunny. And it was, and there was the odd 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.

• 11:07Speaker 06

  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 volcanic rock, but it's full of little air bubbles, so it's actually quite light. The rock, although very light, would provide

• 11:52Speaker 06

  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, and 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 superpressurised 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

• 12:34Speaker 06

  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 millivolts. It's like the amount of power in an electric guitar pickup in the wire that's generated

• 13:17Speaker 06

  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 past that way. So we've got no actual fossils. But that seems to be the most likely in terms of logic and chemistry, uh, that life began in the sea.

• 13:59Speaker 06

  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 suggests that they started in somewhere pretty warm, well above boiling point. So you could say, how could life began if the water was above boiling point? Well, it it wasn't steam because it was under huge pressure. So the steam underheats pressure in water, it doesn't become a gas, it's superheated. So it stays in a liquid up to like two or three hundred degrees. So everything we know points to an origin in a very hot, very high pressure environment.

• 14:40Speaker 06

  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, so 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,

• 15:24Speaker 06

  is an answer to your question, but it would be only an answer. And you could get two scientists and you'd get three different opinions about the origin of life on Earth.

• 15:33Speaker 03

  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 knows 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 like the shallow waters and you get the emergence of this cyanobacteria?

• 16:03Speaker 06

  All we know is we can track them ecologically because the cyanobacteria formed 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, pigments that would protect, that would absorb

• 16:45Speaker 06

  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, tortologically, like well-known brands of bleach. 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.

• 17:28Speaker 06

  The earliest living forms, one of the things they did was to do chemistry with compounds of iron and sulphur, 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 sulphur 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're about the green movement and being more green.

• 18:12Speaker 06

  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 for my t-shirt. But you can't, 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.

• 18:53Speaker 06

  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.

• 19:35Speaker 06

  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. Uh, 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 it actually, 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 paralyzed with this poison. Anyway, the bacteria that botulinum toxin comes from is evolved in the complete absence

• 20:19Speaker 06

  of oxygen, and it thrives in badly canned food. If the food isn't properly sterilized before it's canned and there's no air in it, these oxygen-hating organisms can thrive in such a thing. So, uh, 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, uh, roll the ancient tape

• 21:01Speaker 06

  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,

• 21:44Speaker 06

  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,

• 22:26Speaker 06

  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.

• 23:08Speaker 06

  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,

• 23:51Speaker 06

  which is they formed proper cells, nucleated cells.

• 24:02Speaker 02

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• 24:04Speaker 07

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• 25:38Tristan Hughes?

  Talk us through this next stage in evolution. Is this this nucleation of cells? Does this ultimately ending up with, let's say, multicellular organisms?

• 25:46Speaker 06

  You're way ahead of me, Tristan. You're rushing ahead.

• 25:49Tristan Hughes?

  OK, you slowed me down.

• 25:51Speaker 06

  So what happens with bacteria is bacteria are famously sociable and gregarious. Now, we saw this with the stromatolites, they form 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 specialise on eating different things. Some live on methane, some live on iron and sulphur, 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.

• 26:36Speaker 06

  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. 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,

• 27:20Speaker 06

  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

• 28:05Speaker 06

  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.

• 28:48Speaker 06

  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 cyanobacteria and the proteobacteria. So mitochondria and chloroplasts, the green bodies in plants that harvest sunlight, they still have DNA from their ancient origins, but not very much because they subcontracted all the DNA business to the nucleus. And it lived in a common membrane.

• 29:27Speaker 06

  And the thing you can do, if you've done the Adam Smith Wealth of Nations, is each cell 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.

• 30:07Speaker 06

  And these nucleated organisms called eukaryotes, which is basically Greek for nucleated organism. You're a Greek fan. You've probably worked all this out. So. So another, another happy billion years went along where the eukaryotes started to diversify. Now, most of them remained single celled, like amoebas and things like that. But some of them became multicellular because that's another stage in organisation. Some of them glommed 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

• 30:49Speaker 06

  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

• 31:34Speaker 06

  episode of continental fuss and bruhaha. 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 supercontinents, and then these would split apart, and then they'd come together to form a supercontinent. So there's a kind of supercontinent 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 Neild, who's a geologist, and he's called his book Supercontinent, which

• 32:16Speaker 06

  he wants to assure people is not about pelvic floor exercises. It's, and it explains the supercontinent cycle. So at about 850 million years ago, there was a supercontinent where most of the land masses were concentrated, called Rodinia. And that started to break up and rift. And that formed a string of continents mostly round 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.

• 32:57Speaker 06

  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 eighty million years. They did cover the whole of the earth, but only for eighty million years. Even though there was more land to weather, the sun was that much hotter by then. So that fueled 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.

• 33:39Speaker 06

  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. Uh, sponges are 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.

• 34:19Speaker 06

  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. Uh, there was another thing that was fueled by the increasing oxygen, and that was the invention of the anus, which was one of the great underappreciated episodes in evolution.

• 34:53Speaker 06

  Because what happens in very simple animals like jellyfish, they're basically cup shaped. 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. But some organisms invented or evolved a 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.

• 35:35Speaker 06

  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.

• 36:18Speaker 06

  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 early earth. They started eating each other and that's when the fun started.

• 36:34Tristan Hughes?

  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.

• 36:43Speaker 06

  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. But 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 nine hundred 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 nine hundred million years old. These are still very controversial. Not everyone

• 37:23Speaker 06

  will believe them. The thing about sponges is some sponges leave little mineralised speckles, 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 speckles. But many sponges don't have these. They have a 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

• 38:05Speaker 06

  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. So yay for sponges, that's what I say.

• 38:23Tristan Hughes?

  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 were. What goes next in this great evolution story?

• 38:40Speaker 06

  Well, after this whole episode of glaciation that lasted a mere eighty 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.

• 39:21Speaker 06

  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, you know, 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.

• 40:05Speaker 06

  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 sixty, seventy 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.

• 40:49Speaker 06

  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.

• 41:32Speaker 06

  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 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 seemed 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

• 42:13Speaker 06

  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

• 42:55Speaker 06

  today, live in shallow seawater round continental margins, the continental shelf. That's where most things live. And the other thing was, all this rock that was scrubbed into the, 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.

• 43:38Speaker 06

  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 Cambrian, 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 hand will have a trilobite.

• 44:21Speaker 06

  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 skinned 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 Cambrian, 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.

• 45:02Speaker 06

  And these were these horrific giant sea scorpions called euryptorids. 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 armour as a defence 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

• 45:47Speaker 06

  loves its exceptions. For a long time, all the animal groups that we now know today originated in the Cambrian, except one, the Bryozoa, these moss animals, which most people haven't heard of, but they 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. 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

• 46:28Speaker 06

  would call late antiquity is 540 million years ago, a Cambrian explosion.

• 46:34Tristan Hughes?

  Well, beat that fall of the Western Roman Empire, right there. Henry, the Cambrian explosion, huge, this huge event in 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, there's teeming with life, when do we start to see animals moving on to land?

• 46:56Speaker 06

  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 freshwater, like lakes and ponds, about 1.2 billion years ago. There's evidence from rocks in Scotland of that age, which were deposited in freshwater, and they show communities of little cells

• 47:36Speaker 06

  of algae and fungi. And they would have started forming crusts along the waterline 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 you just diffuse into the water or just shoot out of pellets. It doesn't have to worry about drying out.

• 48:20Speaker 06

  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. And so very slowly, 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 plants started

• 49:03Speaker 06

  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 colonize 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 colonize. 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.

• 49:48Speaker 06

  The earliest plants evolved tough, woody tissues that allowed them to grow upwards, because once the plants had colonized 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 mineralized 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

• 50:30Speaker 06

  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,

• 51:13Speaker 06

  basically making compost out of rock 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 four hundred to three hundred and fifty million years ago or thereabouts. Uh, someone's going to kill me for getting the time wrong, but I'm just working from memory here. That was what we always used to call the age of fishes.

• 51:57Speaker 06

  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 light. 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, uh, little, well, they were just like little legs, only they

• 52:39Speaker 06

  terminated in fins and not fingers. Some of these were quite big, and they tended 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

• 53:22Speaker 06

  can be so shallow it disappears altogether. So whilst 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. Uh, and these appeared towards the end of the Devonian. These kind of, 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 hyphae cabinets and swim bladders and other things. So they breathe through their gills. But some of these lobe-finned fishes started to trade their gills for lungs

• 54:07Speaker 06

  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. Uh, when lung fishes 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 colonizing the land and the land was full of wonderful insects to eat because they'd all been colonizing the land.

• 54:49Speaker 06

  So you started to get what were the first amphibians, these animals that lived first in the water, first in the land. Now, 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

• 55:32Speaker 06

  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 there were kind of fish that lived out of water really, and that's what the early amphibian.

• 55:51Speaker 02

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• 56:26Speaker 03

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• 56:37Speaker 03

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• 57:26Tristan Hughes?

  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.

• 57:37Speaker 06

  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 forests. Because once we started having little plants growing to enormous heights, I mean, oh, centimetres above the ground, they evolved hardwoody 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 pipe. But then the trees were relatives of little, what we now call weedy water plants, like

• 58:22Speaker 06

  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's 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.

• 59:06Speaker 06

  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 fruits, 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 firework. Until they were metres above the ground and then they produced 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.

• 59:47Speaker 06

  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 was 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 have looked like a forest, I was trying to imagine what it would look like and in the book it was more like a World War One 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.

• 1:00:31Speaker 06

  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, ninety percent is staggering. Ninety percent of all the world's coal reserves were formed in this one period of about seventy million years when the lycopods were evolving. But then they caused another catastrophe. Well, that and continental drift, we'll come to that.

• 1:01:12Speaker 06

  They used 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 continents 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 there were glaciers over the South Pole. That was the Carboniferous Ice Age. It wasn't the whole planet.

• 1:01:52Speaker 06

  There were actually other ice 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 C 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.

• 1:02:37Speaker 06

  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.

• 1:02:59Speaker 06

  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 carpets.

• 1:03:42Speaker 06

  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 Colm measures times. But when Pangaea formed, all that was swept away. The life became much more difficult. What you tend to find in big continental land masses 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. And in the more temperate regions, plant life was less diverse than it was.

• 1:04:24Speaker 06

  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 and 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 punctures 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.

• 1:05:08Speaker 06

  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 arc. 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.

• 1:05:52Speaker 06

  And just about to surface, there's the Lohehe 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 past. But the magma plume wiped all that out and it filled the atmosphere with carbon dioxide, acid rain and noxious gases and the lot.

• 1:06:34Speaker 06

  Now, that wiped out a lot of life on Earth, but that was only the aurore. 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 basal 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

• 1:07:18Speaker 06

  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 ninety-five percent of all creatures in the sea, and over seventy percent 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,

• 1:08:00Speaker 06

  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 ten million years to recover from that. But recover it did, because it always does. Henry, that is absolutely mind-blowing. And 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 Carboniferian Permian,

• 1:08:45Speaker 06

  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

• 1:09:27Speaker 06

  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. But another consequence of that 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 on all the

• 1:10:12Speaker 06

  animal's wastes, so it wouldn't poison itself. 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 mineralized to some extent. 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.

• 1:10:55Speaker 06

  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. And carnivores, but that was only a brief dalliance with land life for amphibians. The end Permian 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.

• 1:11:39Speaker 06

  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 bomb site or anywhere where there's been a catastrophe is soon colonized by what's called a disaster assemblage. 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 colonize things really quickly. Well, there was the same thing after the end Permian extinction, only on a bigger scale.

• 1:12:22Speaker 06

  Immediately after the end Permian extinction, nine out of 10 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-sized, 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 described 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.

• 1:13:03Speaker 06

  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 anymore died out.

• 1:13:48Speaker 06

  But on the land, in the Triassic period, that was a great big raspberry to the earth. Um, 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 Sharoviptorix, which had wings but not on its front legs, on its hind legs. Its front legs were just little sticking out at 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.

• 1:14:34Speaker 06

  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 plate. 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. And they all lived together in the Triassic. And the only turtles we have today are the ones still with us. Uh, 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 Sinodons. And they specialised in being small with active metabolisms.

• 1:15:20Speaker 06

  The early Sinodons 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 nocturnal. And they just lived in the looks 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.

• 1:15:46Speaker 03

  Well, Henry, we might have to save dinosaurs in depth for another podcast, but I will ask one question before we wrap up about them, of course. Interesting, you mentioned they're sinodons. I remember watching Walking with Dinosaurs when I was very young. And sinodons, I think they feature in that Triassic episode, so on the small mammals.

• 1:16:02Speaker 06

  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 jawbones,

• 1:16:44Speaker 06

  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.

• 1:17:27Tristan Hughes?

  Well, Henry, talk to us a bit about these early dinosaurs of the Triassic then. We'll talk in more depth about dinosaurs in the future, Paul, I've no doubt, because that'd be great to focus in on.

• 1:17:37Speaker 06

  Yeah, it would, because there's lots more to say.

• 1:17:39Tristan Hughes?

  Well, exactly. Give us a taste of, therefore, these early dinosaurs.

• 1:17:42Speaker 06

  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

• 1:18:27Speaker 06

  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 soloists, 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

• 1:19:08Speaker 06

  dinosaurs that we know about, the big gigantic sauropods and the small fierce theropods, which eventually became things like T. rex and brachiosaurus, but that was a long away. 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

• 1:19:54Speaker 06

  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, survived. And so for the Jurassic and Cretaceous, they had the world to themselves with all the little mammals staring around under their feet, trying not to be trodden on.

• 1:20:33Tristan Hughes?

  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, 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?

• 1:20:59Speaker 06

  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 much. 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,

• 1:21:39Speaker 06

  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.

• 1:22:23Speaker 06

  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 is being 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's coming down, or at least it's still going up, but it's going up more slowly.

• 1:23:04Speaker 06

  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 nineteen seventy, 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 the, what we patronizingly call the developed world. It'll be everywhere by twenty thirty. And the population will peak in the twenty sixes 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

• 1:23:49Speaker 06

  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 five hundred 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.

• 1:24:33Speaker 06

  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. The human caused spike in carbon dioxide is a bit like a tiny version of the end term in extinction. You know, it's very, very brief. The carbon dioxide 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 and then things will carry on. So I'm cautiously optimistic about the future, but then being a paleontologist, I'm cautiously optimistic over hundreds of thousands of years.

• 1:25:15Speaker 06

  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 is 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

• 1:25:52Speaker 06

  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.

• 1:26:33Tristan Hughes?

  Well, there you go. There was a throwback to our first ever episode with Dr. Henry G, covering the origins of life on Earth. You can listen to part two of that interview now. We recorded that in the last few months. It's just gone out and that episode is titled The Age of Dinosaurs, where we go from the beginning of dinosaurs right through to the end. Thank you for listening to this episode of The Ancients. Please follow the show on Spotify or wherever you get your podcasts. That really helps us and you'll be doing us a big favour. If you'd also be kind enough to leave us a rating as well, we'd really appreciate that. Don't forget, you can also sign up to History Hit for hundreds of hours of original documentaries with a new release every week.

• 1:27:13Tristan Hughes?

  Sign up at historyhit.com/subscribe. That's all from me and I'll see you in the next episode.

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