Life on our planet faced a stern test during the Cryogenian Period that lasted from 720 million to 635 million years ago when Earth twice was frozen over with runaway glaciation and looked from space like a shimmering white snowball. Life somehow managed to survive during this time called "Snowball Earth," and a new study offers a deeper understanding as to why. Fossils identified as seaweed unearthed in black shale in central China's Hubei Province indicate that habitable marine environments were more widespread at the time than previously known, scientists said Tuesday. The findings support the idea that it was more of a "Slushball Earth" where the earliest forms of complex life — basic multicellular organisms — endured even at mid-latitudes previously thought to have been frozen solid.
The fossils date from the second of the two times during the Cryogenian Period when massive ice sheets stretched from the poles toward the equator. This interval, called the Marinoan Ice Age, lasted from about 651 million to 635 million years ago.
"The key finding of this study is that open-water — ice-free — conditions existed in mid-latitude oceanic regions during the waning stage of the Marinoan Ice Age," said China University of Geosciences geobiologist Huyue Song, lead author of the research published in the journal Nature Communications.
"Our study shows that, at least near the end of the Marinoan 'Snowball Earth' event, habitable areas extended to mid-latitude oceans, much larger than previously thought. Previous research argued that such habitable areas, at best, only existed in tropical oceans. More extensive areas of habitable oceans better explain where and how complex organisms such as multicellular seaweed survived," Song added.
The findings demonstrate that the world's oceans were not completely frozen and that habitable refuges existed where multicellular eukaryotic organisms — the domain of life including plants, animals, fungi and certain mostly single-celled organisms called protists — could survive, Song said.
Earth formed approximately 4.5 billion years ago. The first single-celled organisms arose sometime during roughly the first billion years of the planet's existence. Multicellular organisms arrived later, perhaps 2 billion years ago. But it was only in the aftermath of the Cryogenian that warmer conditions returned, paving the way for a rapid expansion of different life forms about 540 million years ago.
Scientists are trying to better understand the onset of "Snowball Earth." They believe a greatly reduced amount of the sun's warmth reached the planet's surface as solar radiation bounced off the white ice sheets.
It is widely believed that atmospheric carbon dioxide levels plummeted just prior to these events, causing the polar ice caps to expand and hence more solar radiation reflected back to space and the polar ice caps expanded further.
The fossils date from the second of the two times during the Cryogenian Period when massive ice sheets stretched from the poles toward the equator. This interval, called the Marinoan Ice Age, lasted from about 651 million to 635 million years ago.
"The key finding of this study is that open-water — ice-free — conditions existed in mid-latitude oceanic regions during the waning stage of the Marinoan Ice Age," said China University of Geosciences geobiologist Huyue Song, lead author of the research published in the journal Nature Communications.
"Our study shows that, at least near the end of the Marinoan 'Snowball Earth' event, habitable areas extended to mid-latitude oceans, much larger than previously thought. Previous research argued that such habitable areas, at best, only existed in tropical oceans. More extensive areas of habitable oceans better explain where and how complex organisms such as multicellular seaweed survived," Song added.
The findings demonstrate that the world's oceans were not completely frozen and that habitable refuges existed where multicellular eukaryotic organisms — the domain of life including plants, animals, fungi and certain mostly single-celled organisms called protists — could survive, Song said.
Earth formed approximately 4.5 billion years ago. The first single-celled organisms arose sometime during roughly the first billion years of the planet's existence. Multicellular organisms arrived later, perhaps 2 billion years ago. But it was only in the aftermath of the Cryogenian that warmer conditions returned, paving the way for a rapid expansion of different life forms about 540 million years ago.
Scientists are trying to better understand the onset of "Snowball Earth." They believe a greatly reduced amount of the sun's warmth reached the planet's surface as solar radiation bounced off the white ice sheets.
It is widely believed that atmospheric carbon dioxide levels plummeted just prior to these events, causing the polar ice caps to expand and hence more solar radiation reflected back to space and the polar ice caps expanded further.
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LearningTranscript
00:00Humans, animals, in fact all life on Earth, are only here by chance.
00:1099% of all the species that ever lived have been wiped out in a series of catastrophes.
00:18Disasters that change the course of evolution.
00:23650 million years ago, the Earth froze.
00:29It pushed life to the verge of extinction.
00:34But if this disaster hadn't happened, then life today would be little more than microscopic slime.
00:44This is the story of Snowball Earth.
00:59It's almost impossible to comprehend the immense time scale of our planet's lifetime.
01:11So imagine the whole of Earth's history compressed into a single day.
01:18At midnight on our clock, four and a half billion years ago, the planet was born.
01:28Minutes later, the proto-planet Theia smashed into the infant Earth.
01:39And our moon was formed.
01:46At 4 a.m., the first primitive life appeared.
01:50By 8 a.m., the continents were surrounded by shallow seas full of simple bacteria.
01:59Over the next three billion years, bacteria colonized the oceans.
02:05Then, at 8.27 p.m., 650 million years ago, disaster struck.
02:15The planet froze.
02:19Temperatures plummeted many degrees below freezing.
02:24Ice spread down from the poles and crept towards the equator.
02:30Eventually, the entire planet was locked in a straitjacket of ice, a snowball Earth.
02:38Life had only just got started.
02:41Now it seemed doomed.
02:45Earth remained icebound for 25 million years before it finally thawed.
02:52Some microorganisms did survive
02:55and made the biggest evolutionary leap forward in the history of the planet.
03:02The catastrophe almost wiped out life on Earth, but instead kick-started evolution,
03:08creating life as we know it, including us.
03:15How did all of this happen?
03:17And how on Earth did scientists figure it out?
03:21There are no traces of the ancient ice sheets left.
03:24They're long gone.
03:26But there are still clues that can tell us about this dramatic ancient ice age.
03:37This evidence is hidden away in some of the world's most remote places.
03:43These are the Flinders Ranges in the Australian outback.
03:49Today, it's one of the hottest and driest places on Earth.
03:54So it's ironic that this is where geologist Jim Gehling
03:57is searching for evidence of the coldest period in history.
04:05The area is so vast, the best way to investigate is from the air.
04:12There's a disaster story written in these layers of rock.
04:16You just have to know how to read it.
04:19It's really like looking at a book made of rock.
04:23Every single layer has a secret on it.
04:26We look at these rocks as though they're a history book.
04:30Gehling has located an unusual rock formation in a dried-up creek bed.
04:40It's the evidence Gehling has been looking for.
04:45A 650-million-year-old rock called a dropstone.
04:51A dropstone is an exotic piece of rock.
04:54They shouldn't be mixed in with mud and sand.
04:56They should be together in boulder beds or gravel beds.
05:00But there they sit.
05:02The rock may look insignificant,
05:04but it's a major clue to the powerful forces that created the frozen world of snowball Earth.
05:11This rock shouldn't be here.
05:13It's sitting in a rock composed of mud, silt, sand, and gravel.
05:19And normally that's impossible.
05:24A dropstone has been transported here from thousands of miles away.
05:30There's only one force that can carry rocks like this around the globe,
05:35and that is ice.
05:44There's not a lot of ice in Australia today.
05:48So to investigate how ice could have moved rocks around the world in the ancient past,
05:53glaciologist Shad O'Neill scales the sheer walls of the Matanuska Glacier in Alaska.
06:02It's the closest we can get to our distant icy past.
06:09It's much smaller than the ancient glaciers, but it still operates in the same way.
06:16We're taking a look at the rocks that are being transported down the valley by the glacier.
06:23And to do that, we need to go down there.
06:32Glaciers are nature's bulldozers.
06:35They smash everything in their path.
06:39They gouge stones and rocks from high up in the mountains and carry them down the valley.
06:44Rocks as big as buses can be transported for miles across the landscape by a glacier.
06:50The longest glaciers are hundreds if not thousands of kilometers long,
06:54so you can move rocks over long distances.
07:00When the ice melts, it deposits debris at the base of the glacier.
07:05This glacier is only a few hundred feet thick, but it can still carry thousands of tons of rock.
07:12The glacier brought all this stuff down from the mountains,
07:16and when the glacier melts away, it ends up looking like a building site that's been bulldozed.
07:23It's exactly the same process that transported dropstones to the Flinders Ranges.
07:30But there's one important distinction.
07:32The Matanuska Glacier transports rocks over 24 miles.
07:38The glaciers of 650 million years ago carried them for many thousands of miles.
07:45Here's a great example of a rock that was picked up by the glacier,
07:50carried down valley, and then deposited.
07:53Very similar to what you'd find in Australia, where glaciers used to be in the past.
07:59The Flinders Ranges dropstones show that Australia was once covered in ice.
08:06But they don't prove that the whole world was frozen over,
08:10because the continents were not always where they are today.
08:16The Earth's surface is in constant, very slow motion,
08:21and it pushes the continents around the planet.
08:25So where were they 650 million years ago?
08:30And where was Australia?
08:33Perhaps it was closer to the South Pole,
08:36and the dropstones came from Antarctic glaciers.
08:41The answer to that question comes from another brutal desert.
08:51Death Valley in the American Southwest.
08:55Geologist Joe Kirschfink coined the term Snowball Earth.
09:00He's been gathering evidence to prove it actually happened for the past two decades.
09:06Death Valley has a series of rocks that are extremely important for understanding Earth history.
09:11It's a treasure chest.
09:19Like the Flinders Ranges, it's not the kind of place you'd expect to find evidence of ice.
09:25Yet scattered among the sediments of an ancient seabed are more glacial dropstones.
09:31Every time I come here I see new things.
09:34There are those big boulders, and I see one at the bottom, and they're all dropstones.
09:38You can see that they're coming in from the top.
09:40This is one of the best places in the world to see this type of geology.
09:45The dropstones Kirschfink has discovered here
09:48date back to the same period as those found in the outback.
09:53650 million years ago, two of the hottest places on the planet today,
09:58Death Valley and the Australian outback, were covered in ice.
10:03And what's more, Kirschfink can tell where these two deserts were at the time of the Big Freeze.
10:10The answer is in the rocks themselves.
10:14Every rock has a unique magnetic signature that enables scientists to zero in on their point of origin
10:21with great accuracy.
10:25To study this signal, Kirschfink drills cores from the rocks containing the dropstones
10:30and measures their magnetic field.
10:36The Earth's magnetic field is formed by electric currents flowing in the middle of the planet.
10:43The pattern of that field allows us to measure the latitude that a rock forms at.
10:49Once they know the latitude at which a rock formed,
10:52scientists can figure out where on the planet it came from.
10:57When a glacier dumped these dropstones here, Death Valley was inside the tropics.
11:04Rock cores from dropstones in the Australian outback had an even more stunning tale to tell.
11:10A group started studying the magnetism in the Flinders Ranges
11:14and they thought they had a very stable magnetization that
11:17they said, well, wait a minute, something might be relevant there.
11:21The rock's magnetic signal revealed that 650 million years ago,
11:26Australia had been in a completely different place than it is today.
11:35When the planet was in the grip of the Big Freeze, Australia was near the equator.
11:42Here was the proof the scientists were looking for.
11:47It was wonderful. It was the first time anywhere that we had proven that the glaciers were on the equator.
12:01Ice sheets along the equator, Earth's warmest climate zone, could mean only one thing.
12:08If you have ice at the equator, then the whole of the globe must have been covered by ice.
12:12And so you have to envisage a completely white planet, a giant snowball.
12:19The planet was locked in a deep freeze by the greatest ice age in the history of the Earth.
12:26The entire Earth would have looked like Antarctica looks today.
12:31Even areas as desolate like this in Death Valley with nothing on it would be under several hundred meters of ice.
12:42What was to become of the single-celled organisms trapped beneath the thick crust of snow and ice?
12:50Their future was not a bright one.
12:55This was the greatest ice age that this planet has ever known.
13:01You have to imagine a planet whose oceans were not only capped by ice near the poles,
13:07but that ice had grown across the entire planet and all but shut down its living systems.
13:15650 million years ago, the planet was shutting down.
13:21Life on Earth seemed destined for total extinction.
13:26Somehow, something had plunged the whole planet into a catastrophic deep freeze.
13:34The question was what?
13:408.27 p.m. on our 24-hour clock, representing the history of the Earth.
13:47650 million years ago, the planet faced climate catastrophe, a global deep freeze.
13:56But what made it happen?
13:59Snowball Earth wasn't the first time the planet was frozen, and it wouldn't be the last.
14:06Our planet is struck by an ice age roughly every 100,000 years.
14:11Ice sheets and glaciers expand, reshaping the landscape, but normally stop before reaching the equator.
14:18650 million years ago, that rule was broken.
14:24Most ice ages are triggered by changes in the planet's orbit around the sun.
14:30The further the Earth moves away from its star, the colder it gets.
14:36But factors like orbit and rotation aren't enough to explain ice stretching right down to the equator.
14:43That would have taken something far more dramatic.
14:48The smoking gun turned out to be our atmosphere.
14:53Specifically, greenhouse gases like carbon dioxide.
14:58Too much greenhouse gas causes global warming,
15:03but normal levels of CO2 provide the Earth with a moderate climate.
15:08A greenhouse gas is any kind of gas which has the capacity to convert the sun's rays into heat.
15:14These gases are amazingly effective, making this planet the warm planet that it is today.
15:24But it's a delicate balancing act.
15:29If levels of CO2 grow too high or too low, the climate will spiral into chaos.
15:36Too much, and the planet warms. Too little, and it cools.
15:42Carbon dioxide is a very important gas.
15:45It's both our dilemma and our solution when it's there in too great a proportion that overheats the Earth,
15:53which of course we're worried about today.
15:56However, in the time leading up to Snowball Earth, we had the opposite problem.
16:00There wasn't enough carbon dioxide.
16:03And the Earth began to cool to a point where there was a runaway refrigeration
16:08that locked this Earth up in an icy crust.
16:14Gehling believes that a drop in carbon dioxide levels caused the Snowball Earth disaster.
16:20Something was removing the CO2 on a huge scale.
16:24And there's only one process capable of doing that.
16:28Weathering.
16:30It occurs when carbon dioxide mixes with water vapor to form acid rain.
16:37When acid rain falls on rocks, it reacts with minerals, locking the CO2 in the water that runs off.
16:45It then washes down the rocks.
16:47It then washes down to the sea, where it helps form solid limestone.
16:52Carbon dioxide that was once in the atmosphere is now locked in rock on the seafloor.
16:58When weathering occurs at a great rate, you strip away rocks with acid rain.
17:05And that takes carbon dioxide out of the atmosphere and makes sure that it's locked away in the ocean.
17:11Weathering happens more quickly in hot and humid locations.
17:17Normally, at least some of Earth's landmasses are too far north or south for weathering to be a major factor.
17:27But 650 million years ago, all the Earth's landmasses, from Death Valley to Australia,
17:34were clumped together into one big supercontinent at the equator.
17:39A hot, humid zone with the greatest rainfall on Earth.
17:45The weathering process went into overdrive.
17:48CO2 levels crashed, and so did the Earth's temperature.
17:55You have carbon dioxide being taken out of the atmosphere,
17:58and, as a result, the Earth inevitably has to cool.
18:03Normally, the Earth's plants and animals balance the levels of carbon dioxide in the atmosphere,
18:09ensuring it's neither too hot nor too cold.
18:13But 650 million years ago, life on land was yet to evolve.
18:19In the oceans, life was still a mystery.
18:21650 million years ago, life on land was yet to evolve.
18:26In the oceans, life was still emerging as simple, single-celled bacteria.
18:32In fact, the bacteria were actually making the situation worse.
18:37650 million years ago, this was a world of cyanobacteria.
18:41Bacteria that formed a slime layer on the seafloor.
18:46Cyanobacteria are tiny organisms that have been around on this planet for 3 billion years before Snowball Earth.
18:54But, at this time, they were particularly important.
19:00These cyanobacteria sucked even more carbon dioxide from the oceans
19:05and locked it into limestone reefs called stromatolites.
19:08Some of this ancient carbon dioxide is still locked up in fossilized reefs, like these in southern Australia.
19:17When Jim Galing pours a weak acid onto them,
19:20the ancient carbon dioxide that has been locked away for hundreds of millions of years is released.
19:27What you'll see is an effervescence.
19:30Those white bubbles are carbon dioxide that had been locked up in these stromatolites.
19:35A carbon dioxide that had been locked up in these stromatolites being released back into the atmosphere.
19:43Rather than stabilizing the carbon dioxide levels, the cyanobacteria were depleting them further.
19:51In combination with weathering, they sucked the carbon dioxide out of the atmosphere and temperatures dropped.
19:59Even then, the planet might have avoided a total freeze.
20:05Until a catastrophic chain reaction pushed it to the point of no return.
20:178.27 and 30 seconds in the evening on our clock of Earth history.
20:22Snowball Earth, 650 million years ago and counting.
20:28Ice was advancing from the poles.
20:31It happens during all ice ages.
20:35Normally, it stops, but not this time.
20:39Instead, it just kept on marching towards the equator.
20:44As it did, it triggered a chain reaction that pushed the primitive life in the ocean to a point of no return.
20:50A chain reaction that pushed the primitive life in the oceans to the edge of extinction.
21:00The Earth's surface is made up of land, open ocean and ice.
21:05These surfaces all reflect sunlight differently, and that's the key to what happened next.
21:20Here in the Arctic, geophysicist Don Perovich heads for the boundary where the sea ice meets open water.
21:28It's a point scientists call the lead edge.
21:33And one of the best places to study how the Earth tipped over into the catastrophic deep freeze.
21:40This is the place where the ice that's frozen to the shore meets the open Arctic Ocean.
21:45But it's more than that. The lead is where there's water, the lead's where there's light, and so the lead's where there's life.
21:52We see whales going by and seals and birds flying above. It's an incredibly productive area.
22:01Here, Perovich can compare the reflectivity, or albedo, of two very different surfaces.
22:09The sea ice and open ocean.
22:15His sensor measures the amount of sunlight hitting the snow and the amount it reflects back.
22:23Sea ice is the most reflective surface on the planet.
22:29It reflects 85% of the sunlight that hits it.
22:33If we were to just go out there, just 100 yards away to the lead, the albedo would be less than 10%.
22:41And what's interesting about this is this snow-covered ice has the largest albedo of any naturally occurring surface on Earth.
22:50And the open ocean has the smallest.
22:53So right here, we have a contrast between the best natural reflector and the worst natural reflector.
23:01Open sea reflects very little light back into space.
23:05It absorbs the energy in the sunlight, keeping the planet warm.
23:11Scientists believe that 650 million years ago, the opposite happened.
23:18Earth's best reflector, sea ice, was replacing its worst reflector, sea water.
23:26When enough ice had formed, the remaining ocean couldn't absorb enough heat.
23:31So the Earth cooled.
23:34So more sea ice built up.
23:36That reflected more sunlight.
23:39The Earth got colder, and that made still more ice.
23:44It was the point of no return.
23:47Let's say we grow a little bit more ice.
23:51So we're replacing the worst reflector with the best reflector.
23:55We'll cool things off, and we'll get more ice, and we'll cool it off more, and it builds upon itself.
24:01A runaway freezing effect, capable of turning the whole planet into an ice ball.
24:07It's an idea no one even considered until a few decades ago.
24:12Scientists only discovered it was possible when they were studying another kind of disaster altogether.
24:23A nuclear war.
24:26During the Cold War, researchers predicted that a nuclear war could push enough smoke and dust into the atmosphere
24:33to block out the sun and initiate a global freeze.
24:44Russian climate modeler Mikhail Bodiko was investigating this scenario when he made a chilling discovery.
24:56He calculated that if the ice sheets spread beyond 30 degrees latitude, as far south as New Orleans,
25:03they would reflect so much of the sun's energy that the Earth would reach an irreversible tipping point.
25:12So when we have a system like the Earth with these feedbacks,
25:17one of the things that's talked about a lot is tipping points.
25:20You can think of it as you're in a boat rocking back and forth, not much changes until you go too far,
25:26and then you're in a new state.
25:28And Bodiko's work said that if we move the ice down far enough,
25:32we'd reach a tipping point and cover the whole Earth with it.
25:37Bodiko calculated that if the ice ever reached this tipping point,
25:41the planet would no longer absorb enough heat to keep the ice in check.
25:46The planet would be entombed in ice from pole to pole.
25:51The theory is that 650 million years ago, this was exactly what happened.
25:57Instead of the world we have today, we'd have something that looked like this.
26:03A vast expanse of white, of blocks of ice tilted every which way, covered by snow.
26:09The sheer totality of the snowball Earth disaster is hard to imagine.
26:16Eventually, the ice sheets collided, clamping their icy jaws shut at the equator.
26:23It seemed that nothing could survive in this frozen wasteland.
26:29And yet, life managed not only to survive this disaster, but thrive.
26:34And triggered the greatest evolutionary leap in our history.
26:45650 million years ago,
26:488.28 p.m. on our clock representing the Earth's history.
26:54Deep beneath the ice sheets, single-celled organisms, the only life on the planet,
26:59faced a tough choice, adapt or die.
27:03Bacteria that had evolved over 3 billion years now faced extinction.
27:10But what would happen to life if snowball Earth repeated itself today?
27:16Could we survive the same conditions?
27:19As ice sheets spread down from the poles, supplies of fresh water would freeze solid.
27:24Crops and livestock would perish worldwide.
27:30Industry would grind to a halt.
27:36You could not run a nuclear power plant long enough to get through the snowball.
27:42Many experts believe that humanity could find ways to live through a short-term ice age.
27:47But the odds of surviving a snowball Earth are next to nothing.
27:53If humans ever experience a snowball Earth,
27:57we will quite bluntly be out of control.
28:02There is no way we could stop it.
28:05It would be easier to live on the surface of Mars,
28:09probably, than on the surface of Earth during a snowstorm.
28:12It would be easier to live on the surface of Mars,
28:15probably, than on the surface of Earth during a snowball.
28:18The thick layer of ice covering the planet would become humanity's tombstone.
28:25650 million years ago, the only life facing extinction was single-celled bacteria.
28:36Even their survival seemed improbable.
28:38But here we are. Life clearly did survive.
28:42The question is how?
28:50The quest to learn how ancient organisms kept evolution alive
28:55has brought this lone microbiologist to Whiteout Glacier in southern Alaska.
29:02Here, Hazel Barton studies how life could survive a global deep freeze.
29:09Her mission is to find signs of life in some very dead-looking frozen caves.
29:17People used to think that caves were devoid of life, that there was nothing in there.
29:21But it turns out they're actually teeming with microorganisms.
29:26Barton searches for modern-day microbes living in this ice cave
29:30to learn how their ancient ancestors survived the mother-of-all climate disasters millions of years ago.
29:39If you look on the edge of the cave, you can see all the particle dust that's got lodged in the ice.
29:46And it creates a surface that the microbes can actually live on.
29:51This cave runs underneath the glacier.
29:54Inside, it's four degrees below freezing.
29:58Organisms that live in conditions this harsh are rightly called extremophiles.
30:04Barton takes samples of the microbes buried in freezing rock sediments at the base of the glacier.
30:12I'm looking for some sediments that might contain microbes
30:18that have never been exposed to the heat.
30:22So the thing we remember about these bugs is that they love the cold
30:27and they've actually evolved to live in those cold conditions.
30:29And because of that, if I was to take them outside right now into the heat of the sunlight, they'd die.
30:34It would be like taking us into the middle of the desert and dropping us off there.
30:38Barton believes this cave can shed light on how microbes adapted to conditions during Snowball Earth.
30:48The majority of surfaces exposed on Earth would probably have looked something like this.
30:55So we're looking at the kind of conditions that organisms that survived that period would have been living on.
31:01They're not just living on the ice, they're living in it too.
31:07Sunlight penetrates a few feet into the ice, and that's enough for the microbes to flourish.
31:16We're still pretty close to the entrance right here, so I think there's definitely a lot of sunlight energy
31:22and enough for cyanobacteria to grow on.
31:26And they're probably in the ice, they're living in the ice right now.
31:37The deeper Barton goes into the cave, the darker and colder it gets.
31:42But even here, life hangs on.
31:46This is a community that looks like cyanobacteria.
31:49They're incredibly resistant to all kinds of stress that you would put them under.
31:56They can survive it.
31:58During Snowball Earth, the ice was thousands of feet thick.
32:06Barton finds similar conditions hundreds of feet deeper into the cave.
32:12Here there is hardly any light at all.
32:14But even in this dim, icy world, Barton finds microbes thriving.
32:24So what we're looking at are microorganisms that have to adapt and generate energy when there is no sunlight.
32:31So what they do is they pull energy from the rock itself.
32:36They actually chew into the rock to get that energy.
32:38Outside, Barton trains her field microscope on the sample she's collected.
32:43She believes the ancient microbes had similar structures to the cyanobacteria and were consummate survivors.
32:55We're seeing cyanobacteria.
32:57There's a whole community living in that ice.
33:02Cyanobacteria really are these amazing organisms.
33:05Cyanobacteria really are these amazing organisms.
33:08They're very, very adaptive.
33:10They're one of the most ancient forms of life on our planet.
33:13They can survive some really extreme conditions.
33:16Cyanobacteria have evolved amazing survival mechanisms.
33:22If our cells freeze, they burst their walls.
33:25If they dry out, they die.
33:27But cyanobacteria have evolved a cell structure that prevents rupturing in some of the most extreme conditions on Earth.
33:37They've changed the structure of their DNA so it doesn't get damaged.
33:42If you were to take us and dry us, then our DNA would be irreparable.
33:47You do that to a cyanobacteria and you just have to add water a hundred years later.
33:52And within a few hours, it's starting to carry out photosynthesis.
33:56It's starting to do this again.
33:59Just as some could cope with dry conditions, others could cope with ice.
34:05As the ice rolled over them, most microbes died.
34:11But the hardiest survived.
34:14Over time, strains evolved that thrived in the cold and dark.
34:20To become the ancestors of every living thing on Earth today.
34:27Everybody thinks about these global catastrophes like it's going to wipe out all life.
34:33And it's like, no, these microorganisms have been going through similar things for billions of years.
34:38And they're adaptive and they change.
34:41And then they fill the niche that's left behind.
34:45Barton's research proves that even in the most extreme conditions, in the ice, in the dark, life finds a way.
34:53Short of an object the size of Mars hitting the planet, you know, life will go on on Earth.
34:59And events that we may think are, you know, catastrophic, just simply turn over a new leaf and we start seeing a different form of life on Earth.
35:08The only reason we are here today is because life adapted and survived.
35:15But for life to move on and evolve, the Earth had to melt.
35:19But what force could have broken through the 25 million year icy hell?
35:25The answer was hidden deep within the Earth itself.
35:29But it was about to burst through to the surface.
35:428.35 p.m. on our Clock of Earth's History.
35:49The planet's surface has been locked in ice for almost 25 million years.
35:55But then, at 8.37 p.m., something remarkable happened.
36:00The ice sheets began to recede.
36:03Something was warming the Earth.
36:06But it wasn't the Sun.
36:10The thing that would save the planet was actually inside the Earth itself,
36:15buried deep below the ice.
36:33This is Mount Augustine, Alaska, in the Aleutian Islands, one of the most volcanic regions on the planet.
36:40Mount Augustine has been active for over 40,000 years and is still erupting today.
36:48Volcanologist John Power heads there to learn how volcanoes could have saved us from the global deep freeze.
36:56Because volcanoes are the only things on the planet hot enough, strong enough, to thaw a frozen world.
37:10We're on our way to Augustine Volcano.
37:13It's one of the most active volcanoes in the region.
37:16Last erupted in 2006.
37:19It all comes to play here at Augustine.
37:22A fiery hell lies under Mount Augustine.
37:27During the last eruption in 2006, 17 billion tons of molten lava and ash exploded into the atmosphere.
37:36So much material spewed out in the blast, the volcano actually increased its own height.
37:45We're about 100 feet higher than the summit of the volcano was prior to the eruption.
37:51This is some of the newest land in North America.
37:54Using his field thermometer, John Power takes the temperature from just below the surface.
38:00We've got a temperature of about 95, 96 degrees centigrade.
38:05So the summit of the volcano is still very hot.
38:09If you wanted to cook some potatoes, fry up some eggs, this would be exactly the spot to do it.
38:14Mount Augustine is hot, but it's hard to believe that a volcano, even one this powerful,
38:20could punch through an ice sheet several thousand feet thick.
38:23Where we are now has been covered with glacial ice as recently probably as 10, 15, 20,000 years ago.
38:30This was all underneath a glacier at that point in time.
38:37When Power examined volcanic rocks here, he found evidence that 24,000 years ago
38:43an eruption smashed its way up through the ice.
38:46There is absolutely no problem for a volcano like Augustine or its neighbors to erupt through an ice sheet.
38:52It could be either several kilometers or several miles thick.
38:57We know it's possible because we've seen it happen.
39:00In 1996, the Grimsvatn volcano in Iceland erupted right through a glacier.
39:08It punched its way to the surface through more than half a mile of ice.
39:12The torrents of hot gases and ash blew a giant hole in the glacier.
39:18The heat of the eruption was so great, it produced a giant melt,
39:22where five hours of flash floods carried 45,000 tons of water a second.
39:29But on a global scale, that's nothing.
39:33When the whole world was frozen, a few hundred million tons of ice melted.
39:37On a global scale, that's nothing.
39:40When the whole world was frozen, a few little holes wouldn't have made much difference.
39:57But volcanoes have another formidable weapon in their arsenal.
40:00They spew out more than just lava and rocks.
40:04Volcanoes also produce huge amounts of greenhouse gases.
40:12Carbon dioxide is one of the very dominant species of gas that is coming out of volcanoes.
40:17There have been times when we've had certainly, you know,
40:20thousands of tons per day coming out of this volcano.
40:23Mount Augustine is dwarfed by the volcanoes that broke through the ice of the glacier.
40:27It's dwarfed by the volcanoes that broke through the ice of snowball earth.
40:33Scientists believe that thousands of them ejected billions of tons of carbon dioxide into the atmosphere.
40:43Over a period of around a million years, this caused carbon dioxide levels to rise,
40:49reversing the depletion that created snowball earth,
40:53and tipping the balance in the opposite direction.
40:58Carbon dioxide rapidly built up in the atmosphere,
41:02until it got to a critical point, where we had a super meltdown of the ice,
41:08and that was the death knell of snowball earth.
41:11The carbon dioxide rich atmosphere trapped the sunlight,
41:16increased temperatures, and finally melted the ice.
41:20After a 25 million year freeze, snowball earth was over.
41:26As the ice sheets retreated, something remarkable happened.
41:30The greatest leap in the evolution of life the world has ever seen.
41:35A leap that would lead directly to us.
41:44635 million years ago, the earth was saved from a global deep freeze by volcanoes.
41:50Volcanic eruptions released billions of tons of carbon dioxide into the atmosphere.
41:57The CO2 captured the heat of the sun, warming the world and melting the ice.
42:04After a 25 million year freeze, snowball earth was over.
42:11In the oceans, single-celled organisms had survived freezing conditions beneath the ice.
42:16But they were about to undergo the most extraordinary change, and fast.
42:22Roughly 3 million years after snowball earth ended,
42:26the new warm climate triggered an evolutionary explosion unlike any other.
42:32Single-celled bacteria evolved into multi-celled creatures.
42:39The first ever complex organisms.
42:43The first ever complex organisms, and the ancestors of all animals, including us.
42:57Snowball earth must have been the closest thing to extinction of early life on earth that we had.
43:03And yet we know creatures survived.
43:05And it can't be a coincidence that very soon after the waning stages of this earth-wide ice age,
43:14we get the first large creatures.
43:17It really seems as though that series of environmental catastrophes
43:22spawned the kind of biology that could give rise to multi-cellularity.
43:28Snowball earth wasn't a catastrophe for life.
43:31In fact, it kick-started evolution.
43:34The key to this revolution was oxygen.
43:38Before the snowball, oxygen levels were only 1%,
43:42too little to support more complex organisms.
43:45After the deep freeze, levels rocketed to 21%.
43:52Scientists believe the boost in oxygen levels was the result of ice age chemistry.
43:58During snowball earth, the sun's ultraviolet rays reacted with water molecules in the ice
44:05to produce a chemical called hydrogen peroxide.
44:09This chemical remained locked in the frozen water until temperatures rose and the ice began to melt.
44:17The hydrogen peroxide broke down, releasing huge quantities of oxygen into the air and oceans.
44:24The quantum leap in oxygen levels now provided the fuel for life to evolve,
44:30from single to multi-celled organisms.
44:35Global ice ages are really the bookmarks of evolution.
44:40It can be no coincidence that the evolution of animals
44:45was preceded by the largest ice age that the earth has ever experienced.
44:49The first multi-cellular organisms were the size of pinheads.
44:53These tiny embryonic creatures are the oldest multi-cellular fossils on the planet,
44:59the first links in the evolutionary chain that eventually leads to higher animals and humans.
45:06Over millions of years in the new oxygen-rich atmosphere,
45:10these creatures became more and more complex.
45:14In Australia, Jim Gehling studies the fossil remains of the creatures
45:19that inherited the planet after snowball earth.
45:25After snowball earth, we see a revolution in the history of life from the fossil record,
45:31because for the first time, we see large creatures,
45:35creatures that any human being would be able to identify.
45:39We see large creatures, creatures that anyone can see with the naked eye.
45:45They are the first animals on earth.
45:48This primitive sea creature is one of the first complex multi-cellular organisms.
45:54It lived and died around 50 million years after the end of snowball earth.
46:01It's absolutely complete, you can see the gut, you can see the head end,
46:05where the segments are wrapped around it,
46:08these incredibly fine segments just wrapped over the sea floor.
46:11All the animals on the planet, including us, are descended from creatures like this.
46:20You're looking at the first life forms which had patterns of cells and body plans
46:27that were the same as ours, head, a tail, a belly, a back,
46:33even though they're not necessarily our direct ancestors,
46:37these are the first creatures that represent the line of biology that gave rise to us.
46:45All over the planet, similar organisms were evolving,
46:49making the leap from primitive to complex life.
46:55There'd been life on this planet for more than 3 billion years,
47:01and it was really only the snowball event that kick-started complex life.
47:06If it hadn't been for this ice age, this would have been slime world forever
47:10and we wouldn't be sitting here talking about it.
47:13So, if you want to put your finger on one point in the history of life
47:17that made a big difference, that was snowball earth.
47:22From slime to all life on earth in all of its frantic, colourful glory,
47:28every living thing on the planet is likely the direct result
47:33of a catastrophic deep freeze that threatened to destroy life on earth,
47:39but ended up creating life as we know it.
47:44We owe our existence to the greatest climate disaster the planet has ever known.
47:51Without snowball earth, we would not be here.
47:57The Earth is on the brink of extinction.
48:01The Earth is on the brink of extinction.
48:05The Earth is on the brink of extinction.
48:09The Earth is on the brink of extinction.
48:13The Earth is on the brink of extinction.
48:17The Earth is on the brink of extinction.
48:21The Earth is on the brink of extinction.
48:24The Earth is on the brink of extinction.