9:59:59.000,9:59:59.000 Narrator: There is a theory that scientists once dismissed as absurd: 9:59:59.000,9:59:59.000 that long ago the earth became so cold, every inch of it was entombed in ice. 9:59:59.000,9:59:59.000 The whole planet became one vast snowball, 9:59:59.000,9:59:59.000 and it lasted for 10 million years. 9:59:59.000,9:59:59.000 [Theme Music] 9:59:59.000,9:59:59.000 Earth has no more terrible force than an ice age. 9:59:59.000,9:59:59.000 Only 5 times in its 4 billion year existance 9:59:59.000,9:59:59.000 has our planet suffered this kind of catastrophe. 9:59:59.000,9:59:59.000 No one is certain what started them, or why they happened, 9:59:59.000,9:59:59.000 but there is one thing about ice ages on which most scientists agree: 9:59:59.000,9:59:59.000 the conventional view is that no matter how ferocious the advance of the cold in any ice age, 9:59:59.000,9:59:59.000 there will always be parts of the world that are safe and warm. 9:59:59.000,9:59:59.000 The freeze spreads out slowly from the poles, 9:59:59.000,9:59:59.000 but never reaches the hottest part of the planet, the tropics. 9:59:59.000,9:59:59.000 It has long been assumed that this is a basic law of nature. 9:59:59.000,9:59:59.000 The tropics can never freeze. 9:59:59.000,9:59:59.000 But then, this basic law of nature can't explain what happened 600 million years ago in Namibia. 9:59:59.000,9:59:59.000 [Jazz Music] 9:59:59.000,9:59:59.000 Paul Hoffman is one of those defiant geologists who disputes the conventional view. 9:59:59.000,9:59:59.000 He has spent years trying to convince his colleagues about the snowball earth. 9:59:59.000,9:59:59.000 As a scientist, I was completely convinced it was right. 9:59:59.000,9:59:59.000 But I knew I was going to have a struggle on my hands. 9:59:59.000,9:59:59.000 Because any idea as radical as this is going to be difficult to get across, 9:59:59.000,9:59:59.000 and there are going to be skeptics for sure. 9:59:59.000,9:59:59.000 Narrator: The place Hoffman and his colleague, Dan Schrag, 9:59:59.000,9:59:59.000 come back to study again and again is Namibia. 9:59:59.000,9:59:59.000 It is not an obvious place in which to seek evidence of a catastrophic ice age, 9:59:59.000,9:59:59.000 it is a land of relentless heat. 9:59:59.000,9:59:59.000 One of those locations that has been in the tropics for hundreds of millions of years. 9:59:59.000,9:59:59.000 The conventional laws of nature say an ice age could never have penetrated here. 9:59:59.000,9:59:59.000 But lurking among these sun-baked rocks is something that the conventional laws of nature 9:59:59.000,9:59:59.000 cannot explain away. 9:59:59.000,9:59:59.000 600 million years ago, these hills were at the bottom of the ocean, 9:59:59.000,9:59:59.000 and lying on the old sea bed are mysterious boulders. 9:59:59.000,9:59:59.000 [Eerie Music] 9:59:59.000,9:59:59.000 Geologists call them drop stones, 9:59:59.000,9:59:59.000 and drop stones could only have been brought here by one thing: a glacier. 9:59:59.000,9:59:59.000 To recreate drop stones in the lab, first you need ice. 9:59:59.000,9:59:59.000 This is going to take a while. 9:59:59.000,9:59:59.000 Narrator: The ice needs to float on shallow water above a sandy sea floor. 9:59:59.000,9:59:59.000 This is to simulate a glacier as it flows off the land, onto the surface of the sea. 9:59:59.000,9:59:59.000 Because it is carved through the landscape, a glacier always collects a huge amount of rock debris. 9:59:59.000,9:59:59.000 The ice would then get filled up with all sorts of boulders and cobbles, 9:59:59.000,9:59:59.000 and in this case, we're just using some gravel, 9:59:59.000,9:59:59.000 which we can pour on top of this layer of ice in our tank here. 9:59:59.000,9:59:59.000 Narrator: Having recreated a boulder-filled glacier, you need to melt the ice. 9:59:59.000,9:59:59.000 [Crashing sound] 9:59:59.000,9:59:59.000 As the ice melts, the boulders are released. 9:59:59.000,9:59:59.000 While most of the ice has melted at this point, 9:59:59.000,9:59:59.000 you can see that all the rocks that the glaciers carried out to the ocean 9:59:59.000,9:59:59.000 are now dropped to the sea floor. 9:59:59.000,9:59:59.000 In addition to all of this--in the real world--boulders, 9:59:59.000,9:59:59.000 there would also be a lot of sand, and a lot of much finer gained sediment. 9:59:59.000,9:59:59.000 And so these rocks would get filled in with very fine-grained sediment as well. 9:59:59.000,9:59:59.000 Narrator: In a few thousand years, the fine-grained sediment will cement itself together to form rock. 9:59:59.000,9:59:59.000 With the boulders trapped inside. 9:59:59.000,9:59:59.000 And that's how drop stones are made. 9:59:59.000,9:59:59.000 All you need is a glacier. 9:59:59.000,9:59:59.000 The message from the drop stones suggests just one thing: 9:59:59.000,9:59:59.000 Namibia, in the tropics, a place that everyone says has been hot for hundreds of millions of years, 9:59:59.000,9:59:59.000 must once have been covered in ice. 9:59:59.000,9:59:59.000 The most compelling evidence here is the juxtaposition of a large boulder like this 9:59:59.000,9:59:59.000 enclosed within very fine and delicately layered sediment. 9:59:59.000,9:59:59.000 And so it's difficult, if not impossible to imagine any way to account for this 9:59:59.000,9:59:59.000 other than a very extensive glaciation. 9:59:59.000,9:59:59.000 But for 50 years, since the idea that an ice age must have smothered the tropics was first proposed, 9:59:59.000,9:59:59.000 it has been deemed so radical that most scientists have dismissed it as absurd. 9:59:59.000,9:59:59.000 The theory has its roots in the 1940s, when a young geologist called Brian Harland, 9:59:59.000,9:59:59.000 made a series of intrepid field trips deep into the arctic. 9:59:59.000,9:59:59.000 Conditions were very different then. 9:59:59.000,9:59:59.000 Man hauling in the old Scotch tradition. 9:59:59.000,9:59:59.000 It was cold, but, um, you get used to it. 9:59:59.000,9:59:59.000 You can get used to anything, really. 9:59:59.000,9:59:59.000 Narrator: In the arctic, Harland had ample opportunity to learn all there was to learn 9:59:59.000,9:59:59.000 about that tell-tale sign of glaciation, drop stones. 9:59:59.000,9:59:59.000 Glacier deposits were a very dramatic occurrence, very distinctive, easy to identify. 9:59:59.000,9:59:59.000 And when I saw them, I knew from my own experience that this is glacial. 9:59:59.000,9:59:59.000 I didn't have to think very hard about it. 9:59:59.000,9:59:59.000 Narrator: But it was when he returned from the arctic, armed with his new-found knowledge, 9:59:59.000,9:59:59.000 that Harland made his scientific breakthrough. 9:59:59.000,9:59:59.000 With his now expert eye, he analyzed rocks from all over the world. 9:59:59.000,9:59:59.000 What he discovered amazed him. 9:59:59.000,9:59:59.000 Almost everywhere he looked, in rocks formed about 600 million years ago, he found drop stones. 9:59:59.000,9:59:59.000 Classic evidence that there had once been thick ice, even on the hottest continents. 9:59:59.000,9:59:59.000 The drop stones were so wide-spread that Harland began to contemplate the unthinkable. 9:59:59.000,9:59:59.000 The fact is that we've got evidence of a global glaciation. 9:59:59.000,9:59:59.000 Narrator: He knew it made no sense. 9:59:59.000,9:59:59.000 He knew that at the peak of the last ice age, which ended just 10,000 years ago, 9:59:59.000,9:59:59.000 ice spread down to where New York is today, but no further. 9:59:59.000,9:59:59.000 But the evidence was staring Harland in the face. 9:59:59.000,9:59:59.000 Evidence which seemed to flout the laws of nature. 9:59:59.000,9:59:59.000 600 million years ago, the drop stones said, ice had spread over every continent. 9:59:59.000,9:59:59.000 Right across the tropics, to the equator itself. 9:59:59.000,9:59:59.000 It meant there must have been an ice age of unimaginable ferocity. 9:59:59.000,9:59:59.000 In fact, too unimaginable. 9:59:59.000,9:59:59.000 When Harland presented his theory of global glaciation, colleagues dismissed it as laughable. 9:59:59.000,9:59:59.000 The skeptics had a whole host of reasons why Harland had to be wrong. 9:59:59.000,9:59:59.000 Reasons that were utterly convincing, 9:59:59.000,9:59:59.000 as they were based on the most basic rules about how the world works. 9:59:59.000,9:59:59.000 For a start, it's a given that the tropics, that wide belt around the earth, 9:59:59.000,9:59:59.000 has always received the full glare of the sun. 9:59:59.000,9:59:59.000 As they have always basked in sunlight, so they must always have remained warm. 9:59:59.000,9:59:59.000 Even during the last ice age, geological evidence suggests the tropics were pleasantly hot. 9:59:59.000,9:59:59.000 And they had another reason why the snowball theory must be wrong. 9:59:59.000,9:59:59.000 There was a far simpler explanation for drop stones in the tropics, 9:59:59.000,9:59:59.000 one that was absolutely consistent with scientific knowledge, 9:59:59.000,9:59:59.000 and which didn't involve a ludicrous idea like the tropics freezing over. 9:59:59.000,9:59:59.000 Continents drift. 9:59:59.000,9:59:59.000 They scrape across the surface of the earth at about the same pace that your fingernails grow. 9:59:59.000,9:59:59.000 This means that in about 400 million years, continents can shift from one end of the globe to the other. 9:59:59.000,9:59:59.000 Obviously, the doubters said, 600 million years ago all the continents had drifted into icy polar regions. 9:59:59.000,9:59:59.000 Once there, glaciers would have formed, and drop stones would be common in all rocks of this area. 9:59:59.000,9:59:59.000 And after those drop stones had been formed at the poles, 9:59:59.000,9:59:59.000 the land and the drop stones would have been carried back down to the tropics by continental drift. 9:59:59.000,9:59:59.000 For years, this remained the accepted explanation for why drop stones appeared everywhere. 9:59:59.000,9:59:59.000 The only way to make the theory of a global glaciation credible 9:59:59.000,9:59:59.000 was for someone to make the impossible possible. 9:59:59.000,9:59:59.000 They would need to find a way for the tropics to freeze over. 9:59:59.000,9:59:59.000 And this is just what happened next. 9:59:59.000,9:59:59.000 [Counting in German] 9:59:59.000,9:59:59.000 [Explosion] 9:59:59.000,9:59:59.000 It was the 1960s, the height of the cold war. 9:59:59.000,9:59:59.000 The world was obsessed with calculating the odds of surviving a nuclear holocaust. 9:59:59.000,9:59:59.000 It was known that a series of massive nuclear explosions 9:59:59.000,9:59:59.000 would create clouds of dust, smoke and soot. 9:59:59.000,9:59:59.000 Sunlight would be blocked out. 9:59:59.000,9:59:59.000 Hypothetically, the earth would enter a nuclear winter. 9:59:59.000,9:59:59.000 A man-made ice age. 9:59:59.000,9:59:59.000 In the Soviet Union, finding out how severe this man-made ice age could be 9:59:59.000,9:59:59.000 became the task for one climatologist. 9:59:59.000,9:59:59.000 Mikhail Budyko was that man. 9:59:59.000,9:59:59.000 Long ago, probably 25 or 30 years, 9:59:59.000,9:59:59.000 I compiled a number of studies which could be used to describe origin of ice ages. 9:59:59.000,9:59:59.000 Narrator: What Budyko was to uncover would fly in the face of conventional wisdom. 9:59:59.000,9:59:59.000 He would show how those predictions, that the tropics couldn't freeze over, 9:59:59.000,9:59:59.000 were complacent and unfounded. 9:59:59.000,9:59:59.000 Budyko knew that because the land and oceans are dark, 9:59:59.000,9:59:59.000 they absorb most of the heat coming from our sun's rays, 9:59:59.000,9:59:59.000 and that is how our planet is warmed up. 9:59:59.000,9:59:59.000 But sheets of ice are white. 9:59:59.000,9:59:59.000 They reflect sunlight like a mirror. 9:59:59.000,9:59:59.000 So an ice-covered earth absorbs far less solar heat. 9:59:59.000,9:59:59.000 During an ice age, as the freeze spreads, the earth grows whiter. 9:59:59.000,9:59:59.000 More heat is reflected away, so less and less heat is absorbed. 9:59:59.000,9:59:59.000 And so the earth grows ever colder. 9:59:59.000,9:59:59.000 It means that potentially, the Earth could be 9:59:59.000,9:59:59.000 caught in an vicious circle of unstoppable freezing. 9:59:59.000,9:59:59.000 Budyko converted this hypothetical scenario into a mathematical formula, 9:59:59.000,9:59:59.000 and that formula produced a terrifying prediction. 9:59:59.000,9:59:59.000 The Earth's climate has a theoretical breaking point. 9:59:59.000,9:59:59.000 [Dramatic Music] 9:59:59.000,9:59:59.000 Narrator: As long as the ice sheets remain close to the poles, 9:59:59.000,9:59:59.000 the Earth is safe but if the freeze continues, 9:59:59.000,9:59:59.000 such as might happen in an nuclear winter, 9:59:59.000,9:59:59.000 they could advance down to about where Texas is today. 9:59:59.000,9:59:59.000 Once the freeze had reached that point, 9:59:59.000,9:59:59.000 so much of the Earth would be covered in white ice 9:59:59.000,9:59:59.000 but over half the solar heat that normally warms the planet 9:59:59.000,9:59:59.000 would be reflected back into space. 9:59:59.000,9:59:59.000 At that point, there wouldn't be enough heat left to warm up the Earth. 9:59:59.000,9:59:59.000 Once this happens, there could in theory, be a runaway freeze. 9:59:59.000,9:59:59.000 A freeze that nothing could stop. 9:59:59.000,9:59:59.000 Temperatures plummet, ice sheets spread across all the continents, 9:59:59.000,9:59:59.000 the oceans and eventually, even the tropics. 9:59:59.000,9:59:59.000 If this was ever to happen, the entire planet would be trapped in ice. 9:59:59.000,9:59:59.000 There would be a snowball Earth. 9:59:59.000,9:59:59.000 What was most disturbing about Budyko's calculations 9:59:59.000,9:59:59.000 was that an Earth encased in ice would reflect so much solar heat, 9:59:59.000,9:59:59.000 it could never warm up enough to thaw, ever. 9:59:59.000,9:59:59.000 It was one billion and twenty years ago that the system 9:59:59.000,9:59:59.000 will be stable for a very long time and possibly, 9:59:59.000,9:59:59.000 all life will disappear. 9:59:59.000,9:59:59.000 Narrator: This was Budyko's paradox. 9:59:59.000,9:59:59.000 He had shown that a runaway freeze could ice over the tropics in theory, 9:59:59.000,9:59:59.000 but he had also shown that it could never have happened in practice 9:59:59.000,9:59:59.000 because if it had, the world would still be a snowball today 9:59:59.000,9:59:59.000 and that would mean we would never have existed. 9:59:59.000,9:59:59.000 For 15 years, nobody could solve the paradox of the runaway freeze. 9:59:59.000,9:59:59.000 The snowball Earth theory remained a logical impossibility. 9:59:59.000,9:59:59.000 To resurrect the theory, believers would have to do two things. 9:59:59.000,9:59:59.000 First, they had to prove that ice really had reached 9:59:59.000,9:59:59.000 the hottest parts of the planet, the tropics and that the 9:59:59.000,9:59:59.000 dropstones hadn't arrived there merely through continental drift. 9:59:59.000,9:59:59.000 Second, they had to come up with a theory that offered 9:59:59.000,9:59:59.000 an escape from the runaway freeze. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 That was when a new scientist had entered the picture. 9:59:59.000,9:59:59.000 In the late 70s, Joe Kirschvink was one of geology's rising stars 9:59:59.000,9:59:59.000 and back then, he thought the idea of a snowball Earth was mad. 9:59:59.000,9:59:59.000 The willingness to accept a nutty idea like freezing the whole planet 9:59:59.000,9:59:59.000 really needs to be supported by incredibly strong evidence 9:59:59.000,9:59:59.000 and overall, if you had asked me to place a wager in the late 70s, 9:59:59.000,9:59:59.000 I would've been on the conservative side on that one. 9:59:59.000,9:59:59.000 Narrator: Kirschvink's conservatism came about because he believed 9:59:59.000,9:59:59.000 the simple conventionalist explanation of why there were dropstones at the equator today. 9:59:59.000,9:59:59.000 600 million years ago, he thought, all the continents must've been 9:59:59.000,9:59:59.000 up near the icy poles when the dropstones were formed. 9:59:59.000,9:59:59.000 There was however only one technique to test this theory, 9:59:59.000,9:59:59.000 and it just so happened that Kirschvink had dedicated 9:59:59.000,9:59:59.000 his entire professional career to that technique. 9:59:59.000,9:59:59.000 It involved magnets and Kirschvink is a man in love with magnets. 9:59:59.000,9:59:59.000 I have wiped out my credit cards so many times by playing with strong magnets, 9:59:59.000,9:59:59.000 I don't like to remember it. 9:59:59.000,9:59:59.000 Narrator: Few people realize it but every rock is a weak magnet. 9:59:59.000,9:59:59.000 Each one contain magnetic minerals and the direction 9:59:59.000,9:59:59.000 these minerals pull in is fixed forever the moment the rock is first formed and 9:59:59.000,9:59:59.000 what gives these minerals their magnetic direction is the magnetic field around the Earth's core. 9:59:59.000,9:59:59.000 This means that rocks formed at the poles will always have a 9:59:59.000,9:59:59.000 magnetic direction that points up and down. 9:59:59.000,9:59:59.000 Rocks formed at the equator will always have a 9:59:59.000,9:59:59.000 magnetic direction that points from side to side. 9:59:59.000,9:59:59.000 The rocks have the ability to preserve magnetic direction 9:59:59.000,9:59:59.000 because of magnetic minerals in them. 9:59:59.000,9:59:59.000 They act like little compass needles and will line themselves up. 9:59:59.000,9:59:59.000 Narrator: By finding a rock's magnetic direction, Kirschvink is able to 9:59:59.000,9:59:59.000 identify where in the world it was originally formed, 9:59:59.000,9:59:59.000 no matter where continental drift might've taken it in the millions of years that followed. 9:59:59.000,9:59:59.000 In the 1980s, Kirschvink heard of a team of Australians who had run 9:59:59.000,9:59:59.000 tests which they claimed showed evidence of glaciers in the tropics. 9:59:59.000,9:59:59.000 Ever the skeptic, Kirschvink decided to duplicate their tests on his own, more sophisticated equipment. 9:59:59.000,9:59:59.000 It meant examining dropstones from some of the hottest parts of Earth. 9:59:59.000,9:59:59.000 The question was were they already at the equator when they were 9:59:59.000,9:59:59.000 formed by the ice or had they been created at the poles 9:59:59.000,9:59:59.000 and then carried to the tropics by continental drift? 9:59:59.000,9:59:59.000 To answer the question, Kirschvink turned to his pride and joy: 9:59:59.000,9:59:59.000 a custom built, hyper-sensitive magnetometer. 9:59:59.000,9:59:59.000 It's an incredible instrument. 9:59:59.000,9:59:59.000 You lower the sample into the actual magnetometer chamber. 9:59:59.000,9:59:59.000 The weak magnetic field of the sample generates an electric current 9:59:59.000,9:59:59.000 and so it allows us to measure the magnetic moment of an extraordinarily weak magnet. 9:59:59.000,9:59:59.000 One billionth say the level of a ordinary hand magnet type thing. 9:59:59.000,9:59:59.000 Narrator: Attached to the magnetometer was a computer which plotted 9:59:59.000,9:59:59.000 each rock's origin on an electronic outline of Earth as seen from above. 9:59:59.000,9:59:59.000 The center of the circle represented the poles, the circumference, the equator. 9:59:59.000,9:59:59.000 If the dropstones had been formed at the poles, as Kirschvink and everyone else thought, 9:59:59.000,9:59:59.000 they would show up at the center of the circle on the computer. 9:59:59.000,9:59:59.000 If they had been formed at the equator, they would show up at the circle's edge. 9:59:59.000,9:59:59.000 The machine gave its answer. 9:59:59.000,9:59:59.000 The dropstones had been formed in the tropics. 9:59:59.000,9:59:59.000 600 million years ago, there must have been a snowball Earth. 9:59:59.000,9:59:59.000 Here's a fundamental theorem in science. 9:59:59.000,9:59:59.000 If a theory is in conflict with data, modify the theory. 9:59:59.000,9:59:59.000 There's so many wonderful, beautiful theories that have been slaughtered by a nasty little fact. 9:59:59.000,9:59:59.000 Narrator: But Kirschvink was racked by the insurmountable paradox of the runaway freeze. 9:59:59.000,9:59:59.000 That if a snowball Earth had ever happened, 9:59:59.000,9:59:59.000 then science said that we should still be entombed in ice today. 9:59:59.000,9:59:59.000 How do you get out of it? 9:59:59.000,9:59:59.000 Obviously, the climate modelers had assumed that that was 9:59:59.000,9:59:59.000 a irreversible step and that you would never get out of it 9:59:59.000,9:59:59.000 and yet, we're out of it now and if we'd been in it before, 9:59:59.000,9:59:59.000 at some point, we must've gotten out of it. 9:59:59.000,9:59:59.000 Narrator: To get out of the deep freeze, what Kirschvink needed was 9:59:59.000,9:59:59.000 a power that would stay hot, even when the whole planet had frozen over. 9:59:59.000,9:59:59.000 Something that Budyko hadn't thought of, something that could burn forever, something like hell. 9:59:59.000,9:59:59.000 Looking at an active volcano, realize that magma tens or hundreds of kilometers 9:59:59.000,9:59:59.000 below the surface couldn't care less whether there was a thin layer of ice over the oceans. 9:59:59.000,9:59:59.000 It would still emerge. 9:59:59.000,9:59:59.000 Narrator: Volcanos survive ice ages because they have a direct channel 9:59:59.000,9:59:59.000 to the molten rock deep within the Earth, 9:59:59.000,9:59:59.000 rock that reaches temperatures of over a thousand degrees but that would 9:59:59.000,9:59:59.000 only melt ice in their immediate area. 9:59:59.000,9:59:59.000 Kirschvink has spotted something else about volcanos. 9:59:59.000,9:59:59.000 They also produce gas 10 billion times a year. 9:59:59.000,9:59:59.000 One gas volcanos emit in huge quantities is carbon dioxide, 9:59:59.000,9:59:59.000 a gas that causes the greenhouse effect and global warming. 9:59:59.000,9:59:59.000 Today, carbon dioxide is being pumped into the atmosphere by both volcanos and industrial activities, 9:59:59.000,9:59:59.000 but what stops the Earth from overheating is that we have a natural way 9:59:59.000,9:59:59.000 of removing the excess carbon dioxide from the atmosphere. 9:59:59.000,9:59:59.000 Rain is the Earth's natural cleaning agent. 9:59:59.000,9:59:59.000 As it falls through the atmosphere, each droplet of rain 9:59:59.000,9:59:59.000 absorbs carbon dioxide and cleans the air but Kirschvink realized 9:59:59.000,9:59:59.000 that on a snowball Earth, there could've been no rain. 9:59:59.000,9:59:59.000 The snowball was so cold, all the water on the planet's surface was frozen solid. 9:59:59.000,9:59:59.000 Without liquid water, nothing could've evaporated into the air 9:59:59.000,9:59:59.000 so there would've been no clouds and without clouds, 9:59:59.000,9:59:59.000 there can be no rain. 9:59:59.000,9:59:59.000 There would've been nothing to stop the carbon dioxide from the volcanos 9:59:59.000,9:59:59.000 from building up over millions of years. 9:59:59.000,9:59:59.000 It would've caused global warming on an inconceivable scale. 9:59:59.000,9:59:59.000 Kirschvink came across calculations showing that after 10 million years without rain, 9:59:59.000,9:59:59.000 the atmosphere would've been 10% carbon dioxide. 9:59:59.000,9:59:59.000 Today, it's far less than 1%. 9:59:59.000,9:59:59.000 This extra carbon dioxide would've created a greenhouse effect 9:59:59.000,9:59:59.000 that raised the temperature to an average of 50 degrees Centigrade, 9:59:59.000,9:59:59.000 hotter than the Earth has ever been. 9:59:59.000,9:59:59.000 Hot enough to melt the ice. 9:59:59.000,9:59:59.000 Kirschvink: And that seemed to be a natural and plausible escape. 9:59:59.000,9:59:59.000 Certainly enough to break the snowball or the ice condition. 9:59:59.000,9:59:59.000 Narrator: Joe Kirschvink had cracked it. 9:59:59.000,9:59:59.000 He had found the way out of the runaway freeze, 9:59:59.000,9:59:59.000 a way that made perfect scientific sense. 9:59:59.000,9:59:59.000 A way that was consistent with the laws of nature. 9:59:59.000,9:59:59.000 Kirschvink: The realization that we may have found 9:59:59.000,9:59:59.000 the way out of the snowball, it was wonderful. 9:59:59.000,9:59:59.000 Narrator: By 1990, Kirschvink had evidence that the tropics 9:59:59.000,9:59:59.000 had frozen over for 10 million years and he had 9:59:59.000,9:59:59.000 come up with a theoretical escape route from the runaway freeze, 9:59:59.000,9:59:59.000 but the problem was it was just a theory. 9:59:59.000,9:59:59.000 He had no physical evidence to prove the ice had melted 9:59:59.000,9:59:59.000 because of an extreme greenhouse effect and without that evidence, 9:59:59.000,9:59:59.000 the snowball Earth theory continued to be ignored. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 In 1992, Paul Hoffman entered the story. 9:59:59.000,9:59:59.000 One of geology's most respected but open-minded figures. 9:59:59.000,9:59:59.000 He was to turn into one of the snowball Earth 9:59:59.000,9:59:59.000 theory's most fervent disciples. 9:59:59.000,9:59:59.000 I loved the snowball Earth theory. 9:59:59.000,9:59:59.000 I mean it's almost a religious ferocity with which 9:59:59.000,9:59:59.000 I want to get across this saga of Earth history with 9:59:59.000,9:59:59.000 so many twists and turns and events that are 9:59:59.000,9:59:59.000 so far outside our own experience. 9:59:59.000,9:59:59.000 Narrator: Hoffman's mission was to find that 9:59:59.000,9:59:59.000 hard evidence that had eluded Kirschvink. 9:59:59.000,9:59:59.000 The final piece of the puzzle that would 9:59:59.000,9:59:59.000 prove the snowball had ended because of the greenhouse effect 9:59:59.000,9:59:59.000 and he knew just where to start looking. 9:59:59.000,9:59:59.000 Namibia. 9:59:59.000,9:59:59.000 Hoffman was drawn to Namibia first by the dropstones 9:59:59.000,9:59:59.000 but even more by what sat immediately on top of them. 9:59:59.000,9:59:59.000 Towering directly above were huge formations called cap carbonates. 9:59:59.000,9:59:59.000 Calcium carbonate crystalized into rock. 9:59:59.000,9:59:59.000 These bizarre structures seemed to appear right out of the blue. 9:59:59.000,9:59:59.000 Above this line right here, ??, no more stones whatsoever 9:59:59.000,9:59:59.000 so the glaciation must've come to an abrupt end 9:59:59.000,9:59:59.000 and sitting directly on top is a thick pile of carbonate 9:59:59.000,9:59:59.000 and it's puzzled geologists for generations. 9:59:59.000,9:59:59.000 [Dramatic Music] 9:59:59.000,9:59:59.000 Narrator: What really puzzled geologists was that caps made 9:59:59.000,9:59:59.000 from calcium carbonate are usually formed in warm water, 9:59:59.000,9:59:59.000 but in Namibia, they had suddenly appeared on top 9:59:59.000,9:59:59.000 of an ice cold glacier. 9:59:59.000,9:59:59.000 What this indicates is that you go from glacial conditions 9:59:59.000,9:59:59.000 to an ocean that is warm in a flash. 9:59:59.000,9:59:59.000 Narrator: To most geologists, this instant change from 9:59:59.000,9:59:59.000 cold to hot defied their understanding 9:59:59.000,9:59:59.000 but Hoffman suspected it might be a huge clue. 9:59:59.000,9:59:59.000 That the sudden appearance of mountains of 9:59:59.000,9:59:59.000 calcium carbonate must somehow be connected to 9:59:59.000,9:59:59.000 the death of the snowball in a colossal greenhouse effect. 9:59:59.000,9:59:59.000 But how? 9:59:59.000,9:59:59.000 Hoffman needed someone to explain why 9:59:59.000,9:59:59.000 calcium carbonate would be formed not just because 9:59:59.000,9:59:59.000 of warm conditions in general but specifically in the 9:59:59.000,9:59:59.000 conditions created by a melting snowball Earth. 9:59:59.000,9:59:59.000 So he turned to a geochemist, Dan Schrag. 9:59:59.000,9:59:59.000 Painstakingly, they analyze the snowball's theoretical 9:59:59.000,9:59:59.000 final moments, stage by stage, 9:59:59.000,9:59:59.000 working out what chemical and climatic processes were at work. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 First, they realized that as the ice melted, 9:59:59.000,9:59:59.000 it would produce liquid water. 9:59:59.000,9:59:59.000 The water would then evaporate, and create clouds 9:59:59.000,9:59:59.000 and those clouds would cause a change in the weather, 9:59:59.000,9:59:59.000 the likes of which has never been seen by human eyes. 9:59:59.000,9:59:59.000 Daniel Schrag: When the ice is retreating, 9:59:59.000,9:59:59.000 this is probably the most spectacular climate change 9:59:59.000,9:59:59.000 in Earth's history. 9:59:59.000,9:59:59.000 In some ways, we're going from the coldest climate 9:59:59.000,9:59:59.000 the Earth's ever experienced to the warmest climate 9:59:59.000,9:59:59.000 the Earth's ever experienced. 9:59:59.000,9:59:59.000 We immediately say that this was the mother of all climate changes. 9:59:59.000,9:59:59.000 Narrator: The most elemental powers of nature 9:59:59.000,9:59:59.000 would be unleashed upon the Earth. 9:59:59.000,9:59:59.000 One would predict hurricanes of such intensity that are unimaginable 9:59:59.000,9:59:59.000 so it's quite possible you could've had waves of 9:59:59.000,9:59:59.000 100 meters in amplitude coming in and crashing 9:59:59.000,9:59:59.000 in on the shore. 9:59:59.000,9:59:59.000 It would be unbelievably violent. 9:59:59.000,9:59:59.000 Narrator: And above all, there would be rain. 9:59:59.000,9:59:59.000 The first rainstorms for millions of years. 9:59:59.000,9:59:59.000 Rainstorms that would last at least a century 9:59:59.000,9:59:59.000 and it wouldn't be just any rain. 9:59:59.000,9:59:59.000 The rainwater would react with the vast quantites 9:59:59.000,9:59:59.000 of carbon dioxide in the atmosphere and form carbonic acid. 9:59:59.000,9:59:59.000 This acid rain would then deluge the Earth. 9:59:59.000,9:59:59.000 The acid rain would pound the exposed rocks, 9:59:59.000,9:59:59.000 producing a violent chemical reaction. 9:59:59.000,9:59:59.000 It would break the rocks down into their constituent parts, 9:59:59.000,9:59:59.000 one of which was calcium. 9:59:59.000,9:59:59.000 This would then fuse with the carbon in the acid rain. 9:59:59.000,9:59:59.000 The result, mountains of calcium carbonate, 9:59:59.000,9:59:59.000 exactly as they could see right above the dropstones in Namibia. 9:59:59.000,9:59:59.000 Suddenly, it became clear that the natural expectation 9:59:59.000,9:59:59.000 of a prolonged global glaciation ending in extremely 9:59:59.000,9:59:59.000 high levels of carbon dioxide was that you would expect 9:59:59.000,9:59:59.000 these very unusual thick carbonate rocks should 9:59:59.000,9:59:59.000 immediately follow the glacial deposits. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 Narrator: Hoffman and Schrag had found the final evidence. 9:59:59.000,9:59:59.000 Schrag: The beauty of the snowball Earth theory is exactly that 9:59:59.000,9:59:59.000 it links the chemistry, the geology, the planetary science 9:59:59.000,9:59:59.000 and bam, bam, bam, all of the facts 9:59:59.000,9:59:59.000 are consistent with the predictions of the theory. 9:59:59.000,9:59:59.000 [Jazz Music] 9:59:59.000,9:59:59.000 Narrator: In 1998, Hoffman and Schrag made an 9:59:59.000,9:59:59.000 triumphal tour of the world's universities, 9:59:59.000,9:59:59.000 promoting the snowball theory, 9:59:59.000,9:59:59.000 and then someone threw a spanner in the works. 9:59:59.000,9:59:59.000 An entire scientific discipline, the biologists took one look 9:59:59.000,9:59:59.000 at the 10 million year long snowball Earth and said 9:59:59.000,9:59:59.000 it was quite simply impossible. 9:59:59.000,9:59:59.000 One scientist who had problems with the snowball was Guy Narbonne. 9:59:59.000,9:59:59.000 He like many other biologists could see there was a 9:59:59.000,9:59:59.000 fundamental problem reconciling the snowball Earth theory 9:59:59.000,9:59:59.000 with what he knew. 9:59:59.000,9:59:59.000 The geological evidence speaks very strongly 9:59:59.000,9:59:59.000 of ice sheets marching on the equator. 9:59:59.000,9:59:59.000 The biological evidence speaks very strongly of open water 9:59:59.000,9:59:59.000 being available at this whole time. 9:59:59.000,9:59:59.000 Narrator: Narbonne's problem was another set of nature's law. 9:59:59.000,9:59:59.000 Nothing less than the laws that governed life itself. 9:59:59.000,9:59:59.000 600 million years ago, when the snowball was set to have struck, 9:59:59.000,9:59:59.000 there was nothing living on the land. 9:59:59.000,9:59:59.000 It all existed in the sea and it was not life as we know it. 9:59:59.000,9:59:59.000 The most common organism on the planet was this. 9:59:59.000,9:59:59.000 Cyanobacteria. 9:59:59.000,9:59:59.000 This mass of cyanobacteria is so ancient, 9:59:59.000,9:59:59.000 it predates even the snowball. 9:59:59.000,9:59:59.000 The oldest fossils that we have in the world 9:59:59.000,9:59:59.000 are stromatolites and these are colonies like you see here. 9:59:59.000,9:59:59.000 They're made out of literally billions of cyanobacteria. 9:59:59.000,9:59:59.000 Narrator: What made cyanobacteria and more sophistocated 9:59:59.000,9:59:59.000 ancient organisms like green algae essential to the snowball 9:59:59.000,9:59:59.000 debate was that they photosynthesize. 9:59:59.000,9:59:59.000 Just like plants today under the water, these lifeforms 9:59:59.000,9:59:59.000 absorb sunlight and convert it into energy. 9:59:59.000,9:59:59.000 So these species' chances of surviving the snowball 9:59:59.000,9:59:59.000 would've depended on whether there was enough 9:59:59.000,9:59:59.000 sunlight for photosynthesis in the snowball seas 9:59:59.000,9:59:59.000 at a time when every inch of the planet was 9:59:59.000,9:59:59.000 allegedly covered in thick ice. 9:59:59.000,9:59:59.000 Light penetration through ice is not great if the ice 9:59:59.000,9:59:59.000 is more than a couple tens of meters thick. 9:59:59.000,9:59:59.000 Narrator: And that was the problem biologists pointed 9:59:59.000,9:59:59.000 to in Hoffman and Schrag's work. 9:59:59.000,9:59:59.000 Their calculations had reckoned on the snowball 9:59:59.000,9:59:59.000 producing ice sheets up to a kilometer thick, 9:59:59.000,9:59:59.000 and even in the warmest places around the equator, 9:59:59.000,9:59:59.000 they would've been tens of meters thick. 9:59:59.000,9:59:59.000 More than enough, biologists believe, to block out 9:59:59.000,9:59:59.000 any sunlight from the oceans and that meant death 9:59:59.000,9:59:59.000 to most things that depended on photosynthesis for life. 9:59:59.000,9:59:59.000 Narbonne: You cut off photosynthesis and within a few years, 9:59:59.000,9:59:59.000 let alone a few million years, mass extinction. 9:59:59.000,9:59:59.000 Narrator: It meant that many of the photosynthesizing 9:59:59.000,9:59:59.000 species should've become extinct 600 million years ago 9:59:59.000,9:59:59.000 and the trouble was they hadn't. 9:59:59.000,9:59:59.000 Cyanobacteria grow in rock-like colonies all over the tropics today 9:59:59.000,9:59:59.000 as do other photosynthetic plants, dating from before 9:59:59.000,9:59:59.000 the snowball like green algae. 9:59:59.000,9:59:59.000 For many biologists, there seemed to be only one possible conclusion: 9:59:59.000,9:59:59.000 there may have been a severe ice age but not a fully 9:59:59.000,9:59:59.000 fledged snowball that covered all the oceans 9:59:59.000,9:59:59.000 because lifeforms that should've died out are still with us. 9:59:59.000,9:59:59.000 Unless someone could find a way for marine life 9:59:59.000,9:59:59.000 to survive under a thick sheet of ice, 9:59:59.000,9:59:59.000 the whole theory would be back in the bin. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 Then along came the man from NASA, Chris McKay. 9:59:59.000,9:59:59.000 Chris McKay: I'm planetary scientist with an interest 9:59:59.000,9:59:59.000 in life in extreme environments. 9:59:59.000,9:59:59.000 In particular, environments that are cold and dry. 9:59:59.000,9:59:59.000 Several years ago, I saw the papers about the snowball Earth, 9:59:59.000,9:59:59.000 indicating the geological evidence that the Earth was ice covered 9:59:59.000,9:59:59.000 and had been ice covered for millions of years. 9:59:59.000,9:59:59.000 Plus the evidence that there are organisms (bacteria and green algae) 9:59:59.000,9:59:59.000 that survived this ice covered state and that's the puzzle. 9:59:59.000,9:59:59.000 How could these photosynthetic organisms survive? 9:59:59.000,9:59:59.000 Narrator: McKay was intrigued because it just so happened 9:59:59.000,9:59:59.000 he had visited a place on Earth today that was so cold, 9:59:59.000,9:59:59.000 it could actually be compared with the snowball of 600 million years ago. 9:59:59.000,9:59:59.000 Antarctica, the coldest place on Earth. 9:59:59.000,9:59:59.000 Here, temperatures can fall to -30. 9:59:59.000,9:59:59.000 Almost as severe as the snowball at its warmest point, the equator 9:59:59.000,9:59:59.000 and deep in Antarctica are the dry valleys where there are lakes 9:59:59.000,9:59:59.000 smothered by an ice sheet many meters thick. 9:59:59.000,9:59:59.000 McKay: We think these little lakes represent a good 9:59:59.000,9:59:59.000 model for looking at the snowball Earth. 9:59:59.000,9:59:59.000 Could there be life underneath the ice cover on a snowball Earth? 9:59:59.000,9:59:59.000 Narrator: Scientists were eager to discover if there was 9:59:59.000,9:59:59.000 enough light for life to survive in the water below the thick ice. 9:59:59.000,9:59:59.000 They were about to be astonished. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 There was light, lots of it 9:59:59.000,9:59:59.000 even though over head, 9:59:59.000,9:59:59.000 the ice was five meters thick. 9:59:59.000,9:59:59.000 There was so much light, 9:59:59.000,9:59:59.000 the water was filled with plant life and bacteria, 9:59:59.000,9:59:59.000 including two organisms dating from the time 9:59:59.000,9:59:59.000 of the snowball that would've needed sunlight to live. 9:59:59.000,9:59:59.000 McKay: When we're diving in the lakes 9:59:59.000,9:59:59.000 and swimming around, there's life in the water. 9:59:59.000,9:59:59.000 There's bacteria, cyanobacteria 9:59:59.000,9:59:59.000 but there's also green algae. 9:59:59.000,9:59:59.000 Narrator: And McKay had a hunch as to why this 9:59:59.000,9:59:59.000 photosynthetic life could survive. 9:59:59.000,9:59:59.000 It was something about the nature 9:59:59.000,9:59:59.000 of the ice itself. 9:59:59.000,9:59:59.000 McKay: The transparency of this ice is very high 9:59:59.000,9:59:59.000 and it's due to the fact that it's freezing very slowly 9:59:59.000,9:59:59.000 underneath this thick ice cover. 9:59:59.000,9:59:59.000 Now let's imagine this snowball Earth where 9:59:59.000,9:59:59.000 there's also a thick ice cover, 9:59:59.000,9:59:59.000 the ice on the bottom is freezing very slowly as well, 9:59:59.000,9:59:59.000 it should have the same optimal properties 9:59:59.000,9:59:59.000 as this clear, clean ice. 9:59:59.000,9:59:59.000 Narrator: By freezing slowly, water rejects impurities 9:59:59.000,9:59:59.000 such as salt or dirt which make it cloudy. 9:59:59.000,9:59:59.000 So the ice becomes clean and transparent. 9:59:59.000,9:59:59.000 Because of this transparency, 9:59:59.000,9:59:59.000 life giving sunlight would've been reaching down 9:59:59.000,9:59:59.000 into the snowball seas. 9:59:59.000,9:59:59.000 McKay realized that even at its height, 9:59:59.000,9:59:59.000 there would've been havens around the snowball's 9:59:59.000,9:59:59.000 equator where the ice was thin enough 9:59:59.000,9:59:59.000 for photosynthetic life to cling on below but there was more. 9:59:59.000,9:59:59.000 Although disciples of the theory accept 9:59:59.000,9:59:59.000 the snowball would've been death to most things, 9:59:59.000,9:59:59.000 they argue whatever life did survive 9:59:59.000,9:59:59.000 would've emerged into a new world almost 9:59:59.000,9:59:59.000 devoid of competition. 9:59:59.000,9:59:59.000 The perfect conditions for an explosion of evolutionary change. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 These fossils show the new species which appeared 9:59:59.000,9:59:59.000 soon after the time of the snowball. 9:59:59.000,9:59:59.000 All display a massive increase in size and complexity 9:59:59.000,9:59:59.000 from the simple organisms that lived before. 9:59:59.000,9:59:59.000 These are the first multi-cellular lifeforms. 9:59:59.000,9:59:59.000 Even those with some questions about the snowball theory 9:59:59.000,9:59:59.000 recognize a new climate after a mass extinction 9:59:59.000,9:59:59.000 could be a spur for evolution. 9:59:59.000,9:59:59.000 [Music] 9:59:59.000,9:59:59.000 But if the snowball can change the course of life on the planet, 9:59:59.000,9:59:59.000 there remains one final question. 9:59:59.000,9:59:59.000 No one knows why the snowball happened 9:59:59.000,9:59:59.000 or if it could happen again. 9:59:59.000,9:59:59.000 The sun is hotter than it was 600 million years ago 9:59:59.000,9:59:59.000 and is getting hotter all the time. 9:59:59.000,9:59:59.000 Climate trends would have to change dramatically. 9:59:59.000,9:59:59.000 If it ever did happen again, 9:59:59.000,9:59:59.000 it almost certainly wouldn't be for millions of years 9:59:59.000,9:59:59.000 but if it ever did, that would mean death to almost everything 9:59:59.000,9:59:59.000 including us. 9:59:59.000,9:59:59.000 [Music]