The Permian-Triassic extinction event, also known as the "Great Dying", was the largest mass extinction in Earth's history. It occurred about 252 million years ago. So, what exactly happened? A series of factors caused the extinction, including massive volcanic eruptions, global warming, and ocean acidification. The extinction wiped out more than 95% of all species, including most vertebrates. The extinction marked the end of the Permian period and the beginning of the Age of Dinosaurs
What caused the extinction?
Volcanic eruptions:
Released carbon dioxide into the atmosphere, which caused global warming and ocean acidification
Ocean acidification:
Made the oceans toxic and fatal to much marine life
Lack of oxygen:
Caused large-scale deoxygenation of the oceans
Metal and sulfide poisoning:
Caused widespread poisoning of the oceans
What did the extinction lead to?
A revolution in ecosystems, with birds and mammals becoming dominant over amphibians and reptiles.
Approximately 251.9 million years ago, the Permian–Triassic (P–T, P–Tr) extinction event (PTME; also known as the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying) forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras It is Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is also the greatest known mass extinction of insects. It is the greatest of the "Big Five" mass extinctions of the Phanerozoic. There is evidence for one to three distinct pulses, or phases, of extinction.
The scientific consensus is that the main cause of the extinction was the flood basalt volcanic eruptions that created the Siberian Traps, which released sulfur dioxide and carbon dioxide, resulting in euxinia (oxygen-starved, sulfurous oceans), elevated global temperatures, and acidified oceans. The level of atmospheric carbon dioxide rose from around 400 ppm to 2,500 ppm with approximately 3,900 to 12,000 gigatonnes of carbon being added to the ocean-atmosphere system during this period. Several other contributing factors have been proposed, including the emission of carbon dioxide from the burning of oil and coal deposits ignited by the eruptions; emissions of methane from the gasification of methane clathrates; emissions of methane by novel methanogenic microorganisms nourished by minerals dispersed in the eruptions; longer and more intense El Niño events; and an extraterrestrial impact which created the Araguainha crater and caused seismic release of methane and the destruction of the ozone layer with increased exposure to solar radiation.
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What caused the extinction?
Volcanic eruptions:
Released carbon dioxide into the atmosphere, which caused global warming and ocean acidification
Ocean acidification:
Made the oceans toxic and fatal to much marine life
Lack of oxygen:
Caused large-scale deoxygenation of the oceans
Metal and sulfide poisoning:
Caused widespread poisoning of the oceans
What did the extinction lead to?
A revolution in ecosystems, with birds and mammals becoming dominant over amphibians and reptiles.
Approximately 251.9 million years ago, the Permian–Triassic (P–T, P–Tr) extinction event (PTME; also known as the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying) forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras It is Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is also the greatest known mass extinction of insects. It is the greatest of the "Big Five" mass extinctions of the Phanerozoic. There is evidence for one to three distinct pulses, or phases, of extinction.
The scientific consensus is that the main cause of the extinction was the flood basalt volcanic eruptions that created the Siberian Traps, which released sulfur dioxide and carbon dioxide, resulting in euxinia (oxygen-starved, sulfurous oceans), elevated global temperatures, and acidified oceans. The level of atmospheric carbon dioxide rose from around 400 ppm to 2,500 ppm with approximately 3,900 to 12,000 gigatonnes of carbon being added to the ocean-atmosphere system during this period. Several other contributing factors have been proposed, including the emission of carbon dioxide from the burning of oil and coal deposits ignited by the eruptions; emissions of methane from the gasification of methane clathrates; emissions of methane by novel methanogenic microorganisms nourished by minerals dispersed in the eruptions; longer and more intense El Niño events; and an extraterrestrial impact which created the Araguainha crater and caused seismic release of methane and the destruction of the ozone layer with increased exposure to solar radiation.
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TVTranscript
00:00Since the Earth was formed billions of years ago,
00:06it's been hit by a series of disasters.
00:09250 million years ago,
00:15the largest volcanic eruptions the planet has ever seen
00:19nearly erased all life on Earth.
00:22It was the greatest mass extinction in the history of the planet.
00:28But without it, humans could never have evolved.
00:34This is the story of the planet of fire.
00:53Over the last 4.5 billion years,
00:56all life on Earth has lurched from one terrible disaster to the next.
01:01It's difficult to grasp the immense timescale of the events that shaped us.
01:06So imagine Earth's history compressed into the 24 hours of a single day.
01:13At 1040 in the evening, that's 250 million years ago,
01:18all life on the planet faced extinction.
01:22Earth was in a period of prehistory called the Permian.
01:27A cataclysmic event kick-started a deadly chain reaction
01:33that wiped out nearly all animal and plant species on the planet.
01:38It was called the end-Permian extinction
01:41and was the greatest die-off in the history of the planet.
01:4695% of all creatures around the globe were wiped out.
01:53According to South African paleontologist Roger Smith,
01:58it was Earth's darkest hour.
02:01The end-Permian extinction was as dramatic as a mass extinction could be.
02:06Since the beginning of life on Earth,
02:08there has been no other one that has come close to the 95% of species on Earth,
02:14both in land and sea, disappearing within a very short space of time.
02:19It was a catastrophic wipe-out and changed the course of evolution.
02:25We humans are only here today because of the 5% of creatures who survived.
02:30Had it not been for those few survivors,
02:33those few animals which were pre-adapted or able to get through that great drought,
02:39we would not have had life on Earth.
02:44What happened? How did it happen?
02:47It's a mystery that's puzzled scientists
02:50since evidence of the catastrophe was first discovered almost half a century ago.
02:58Figuring out what caused the extinction
03:01is a key element to understanding the evolution of life on Earth.
03:10In the Karoo Basin, South Africa,
03:13Smith studies an area that was once teeming with animals that predate the dinosaurs.
03:19But 250 million years ago, this would have looked a very different place.
03:24Rainfall in the mountain areas were feeding Mississippi-sized rivers
03:28which meandered themselves slowly across the plains.
03:33This was a fully developed, stable ecosystem.
03:40Small plant-eating creatures called dictadon thrived here,
03:44scurrying around in the vegetation.
03:47Huge herds of cow-sized herbivores called dicynodonts grazed on the plains.
03:59But a vicious killer stalked the herds.
04:04The herds were hunted down by the dictadon,
04:07and the herds were killed by the dictadon.
04:11But a vicious killer stalked the herds.
04:20Over 150 million years before T. rex,
04:23Gorgonopsian was Earth's deadliest carnivore.
04:31Armed with serrated interlocking teeth,
04:34this ferocious animal was the ancient world's top predator.
04:40But all these creatures were doomed.
04:45None of them survived the mass extinction.
04:49What killed them?
04:56Clues to how the Permian world died
04:59lie buried in the rocks of South Africa's Karoo Basin.
05:03Under this scrub, paleontologists have unearthed layers of ancient fossils
05:08and paleontologists have unearthed layers of sedimentary rock
05:12from this turbulent time.
05:14Now, sedimentary rocks like this are characterized by layers,
05:18each layer representing a point in time when deposition was taking place.
05:23The oldest layers are at the bottom and the youngest layers at the top.
05:29These rocks are like a time machine,
05:33taking us back a quarter of a billion years.
05:39One layer, higher up this formation,
05:42offers clues to what ended the Permian world.
05:47Here we're sitting at the very top of the Permian
05:50and this particular interval
05:53shows us something very dramatic in the rock record.
05:56Below me we have green and bluish-gray rocks
06:00that clearly suggest that the environment was wet.
06:05These rocks are littered with fossils,
06:08but just above this layer it's a very different story.
06:15Suddenly everything turns red
06:17and that reddening is an indication of drying,
06:21rapid drying and warming.
06:25These red rocks reveal a sudden and dramatic rise in temperature
06:31and mark the point in time when life on Earth nearly died.
06:38The fossils tell us at this point
06:40there is virtually nothing left on Earth
06:43and we go into a dead zone.
06:47Life had almost ceased to exist, and not just here.
06:52The dead zone of red rock is found all around the world.
06:57This meant that 250 million years ago
07:01the climate change and mass extinction was global.
07:06Something huge, on a planet-wide scale,
07:10pushed temperatures up by 20 degrees Fahrenheit
07:13and killed virtually all life on Earth.
07:2010.40 p.m. on our clock of the Earth's history.
07:25250 million years ago the planet was in climate free fall.
07:31Scientists have discovered that temperatures rose by about 20 degrees.
07:38The sudden and dramatic global warming
07:40changed the course of evolution on Earth.
07:44It caused a mass extinction so devastating
07:47that some scientists thought it must have been caused by something extraordinary,
07:51something extraterrestrial.
07:55Could it have been an asteroid strike?
08:03They knew a cosmic impact would have sent billions of tons of dust
08:07high into the atmosphere,
08:10blocking out the sun,
08:13stopping plant growth,
08:16reducing temperatures,
08:18and causing the food chain to collapse.
08:23An extinction from an asteroid strike would have happened within decades.
08:29But that's not the story the rock evidence is telling us.
08:35Over the last decade, Professor Paul Wignall
08:38and researchers at Leeds University in England
08:41have been examining rocks from the dead zone
08:44around the time of the devastating mass extinction.
08:48They've collected thousands of samples
08:51and taken hours of video on their expeditions to Greenland.
08:56The rocks confirm a period of climate change and much more.
09:01They record the story of mass extinction on land and sea
09:07and provide a clearer picture of the die-off than ever.
09:13The extinction is like the biggest fossil crime scene of all time.
09:17The great thing about Greenland is that we have such a great record
09:20at the crime scene, if you like.
09:23There's just a huge amount of information to be collected,
09:26so it provides us with an extremely detailed record of what happened,
09:30probably one of the best records of that time interval.
09:33What's more, these Greenland rocks build a solid case
09:36against the asteroid impact theory.
09:40One of the most obvious clues would be that the extinction should occur extremely fast,
09:44that within days and weeks of an impact,
09:47everything will essentially drop dead in a matter of years.
09:50So that should be razor sharp when we see it in a fossil record.
09:53We should see just an abrupt line or termination,
09:56and that's not what we see.
10:00Instead, Wignall's rocks show that the extinction happened
10:03over a period of 100,000 years,
10:09far too long to be the result of a meteor strike.
10:15The Greenland team's discovery meant that something else
10:19must have caused the catastrophic extinction.
10:24And geologist Mike Benton thinks he knows what.
10:29He believes the disaster began deep beneath the Earth's surface.
10:38If it's not impact, then the next most obvious dramatic event
10:42is initiated by volcanic eruptions of some kind.
10:46So you obviously look for some center of volcanic eruptions.
10:52Volcanoes are nature's ultimate destructive force.
10:56Fueled by unimaginable pressure deep within the planet,
11:00they shoot molten rock and toxic gases high into our atmosphere.
11:07In 1975, the eruption of the Greenland volcano
11:10In 1975, the eruption of Mount Tolbochik in Russia
11:14was so huge the plume of ash and debris was visible from space.
11:25But geologists know that volcanic eruptions were far bigger
11:29and more powerful 250 million years ago
11:33because they found the aftermath in eastern Russia.
11:38Today, deep beneath the frozen wastes of one of the most remote corners of the Earth,
11:43Siberia, is evidence of the catastrophe that nearly killed off life.
11:49A vast expanse of ancient lava flows,
11:52forming a bleak landscape called the Siberian Traps.
11:57The Siberian Traps are a style of volcanism which we don't see on Earth today.
12:00They represent the biggest style of volcanism
12:03that the Earth ever experiences or produces.
12:07Earth's ancient volcanic eruptions dwarf anything we might witness today.
12:15At the end of the Permian period,
12:17millions of cubic miles of magma built up beneath the Siberian crust.
12:24The entire region began to bulge upwards.
12:28And then, like a giant blister, the Earth erupted,
12:32spewing out vast amounts of lava,
12:36flooding the area under a sea of molten rock.
12:41It was a type of volcanic eruption called a flood basalt.
12:49Here was the force behind the eruption.
12:53Here was the force behind the mass extinction.
12:57250 million years ago,
12:59the Siberian flood basalt released enough lava
13:03to cover an area the size of the United States,
13:06under one mile of molten rock.
13:12Siberia has long since cooled.
13:15But Iceland is still one of the world's most geologically active places.
13:19Here, Mike Benton researches the terrible impact
13:22even a small flood basalt could have had.
13:26We're here in the middle of a lava field in Laki, in Iceland,
13:30because this is a very well-documented historical basalt eruption
13:34that can act as a good analogy for the Siberian traps.
13:39In 1783, a vent eruption happened here,
13:43which lasted for about eight months.
13:4617-mile-long volcanic vents
13:49shot fountains of lava 4,000 feet into the air.
13:57But it was tiny compared to the Siberian eruptions.
14:03The eruption was so large,
14:05that it was impossible to measure the size of the eruption.
14:10But it was tiny compared to the Siberian eruptions.
14:15Even so, it was a disaster.
14:20Volcanoes produce three things.
14:23The lava is one. That will kill things locally.
14:25But it produces ash and, most importantly, gas.
14:29Now, the lava goes a relatively short distance.
14:31The ash will go further, flying through the air.
14:34But what really kills are the gases.
14:37The Laki eruption produced huge quantities of sulfur dioxide.
14:44It's a gas which has a deadly impact on the environment.
14:50When it mixes with water vapor in the atmosphere,
14:53it turns into sulfuric acid and falls to earth as acid rain.
15:00That has a terrible effect, as was recorded by the people at Laki,
15:04where they reported that it burned people's eyeballs,
15:07that it made it hard for them to breathe,
15:09because it congested their lungs.
15:12Livestock suffered lesions and burning of their skin,
15:15and plants were killed off.
15:18The whole food chain began to collapse.
15:24And that was just the start.
15:27Some sulfuric acid didn't fall back to earth.
15:31It stayed in the atmosphere in small droplets.
15:39These reflected sunlight away from the planet, cooling its surface.
15:46The cooling following the Laki eruption was catastrophic.
15:49It killed more people than the immediate damage by sulfuric acid.
15:54It created very cold winters for two or three years after the eruption,
15:58not just on Iceland, but throughout much of northern Europe.
16:01People reported crop failures and death as a result.
16:07Benton's analysis of the Laki eruption has shown that
16:10the cooling effect produced by volcanic sulfur dioxide is deadly,
16:17and that the effects can be felt thousands of miles away.
16:22Imagine how devastating the Siberian traps must have been.
16:29Laki spewed out gas and lava for eight months
16:32and covered an area of about 200 square miles in molten rock.
16:41The Siberian traps erupted for nearly half a million years.
16:45They produced about two million square miles of lava.
16:54That's 200,000 times larger than Laki.
17:02Using Laki as a model, Benton can begin to reconstruct the chain of events
17:06that turned the Siberian eruptions into a global catastrophe.
17:10The most likely sequence of events starts with these massive eruptions in Siberia,
17:14with lava spreading over thousands of square kilometers,
17:18square miles of landscape,
17:20and causing destruction and devastation wherever they went.
17:25The eruptions released billions of tons of sulfur dioxide into Earth's atmosphere,
17:32which created a huge amount of sulfur dioxide.
17:35The sulfur dioxide into Earth's atmosphere,
17:40which created acid rain and volcanic winters,
17:43and sent global temperatures plummeting.
17:50Around the world, the climate change killed plants,
17:55and the food chain fell apart.
17:59Where the plants failed, herbivores like Dicynodon starved,
18:04and where they starved, the carnivores that ate them died too.
18:09Ten percent of species perished.
18:12But this was just the beginning.
18:16Another gas, released by the Siberian traps,
18:20was about to make things much, much worse.
18:2810.40 p.m. on Earth's evolutionary clock,
18:32250 million years ago.
18:36A series of giant volcanic eruptions have plunged the planet into chaos.
18:43The sulfur dioxide released by the Siberian traps
18:46has devastated animal and plant populations.
18:53In England, paleontologist Paul Wignall
18:55conducts post-mortems on the victims of the Permian extinction.
19:02These fossils he collected in Greenland
19:05definitely felt the effects of volcanic gases.
19:12The first things that start suffering in the entire fossil record
19:15is the plant record.
19:17We start seeing a change in the composition of plants.
19:22And also we start to see the appearance of some very strange mutated spores.
19:32The fossilized plants reveal a world struggling to adapt to climate change.
19:41They also record the effects of a second deadly volcanic gas,
19:47carbon dioxide.
19:50Looking at the surfaces of leaves
19:52and the number of little holes that are in the surfaces of leaves
19:55is actually a monitor of how much carbon dioxide there is.
19:59Plants need carbon dioxide to create energy.
20:03They breathe it in through tiny holes on the back of their leaves.
20:08The more carbon dioxide in the atmosphere,
20:10the fewer holes the plant needs to absorb it.
20:17When scientists studied fossilized leaves dating back 250 million years,
20:22they discovered a sudden dramatic reduction
20:25in the number of breathing holes.
20:29It seemed that at the start of the extinction,
20:31levels of carbon dioxide surged.
20:38And that meant one thing.
20:42The Siberian Trap eruptions must have released billions of tons of CO2.
20:48This greenhouse gas changed global cooling into global warming.
20:54Scientists calculate that the amount of carbon dioxide in Earth's atmosphere
20:58at the time of the eruptions was 20 times higher than it is today.
21:04More than enough to seriously affect the climate.
21:08It was global warming gone mad.
21:11The result of these Siberian Trap eruptions was a rise in global warming.
21:15The result of these Siberian Trap eruptions was a rise in global temperature
21:18of at least 5 degrees centigrade.
21:21And they happened episodically,
21:22so that it may be there were pulses repeated and repeated of temperature rise.
21:29A rise of 5 degrees centigrade, that's about 10 degrees Fahrenheit,
21:33may sound small to us,
21:36but it had a massive impact on the Earth's climate.
21:41Warming Earth's atmosphere affects how rain is generated
21:44and where it falls.
21:47By raising Earth's temperature, volcanic CO2 altered global weather systems.
21:53In equatorial regions, it simply stopped raining.
22:00In South Africa, the Karoo Basin felt the full impact of this change in climate.
22:07Its lush flood plains became a scorched desert.
22:12Paleontologist Roger Smith studies how this rapidly changing landscape
22:17impacted the Karoo's inhabitants.
22:23And he's just discovered one of the victims.
22:32Here we have an in-situ skull of Dasanodon.
22:36It's one of the last of the big cow-sized herbivores of the Permian period.
22:41And at this level, which is just below the extinction,
22:44this represents probably the last gasp of the Permian herbivores.
22:52The global warming marked an evolutionary watershed in Earth's history.
23:00Animals and plants suffered drought and starvation.
23:0635% of them perished.
23:11But the fallout from the Siberian traps was only just beginning.
23:16The rise in global temperatures triggered a domino effect
23:20and unleashed the next terrible phase of extinction,
23:25this time in the oceans.
23:3310.40 p.m. on the Earth's clock, 250 million years ago.
23:41Massive volcanic eruptions first released sulfur dioxide that cooled the planet,
23:48then carbon dioxide that heated it up.
23:55The sea-sawing climate killed animals and plants by the millions.
24:01Extinction ruled the land.
24:05It was the first terrible phase of the extermination of virtually all life on Earth,
24:12but a critical moment in the story of man's evolution.
24:18The future of life hung by a thread, but not everywhere.
24:28So far, the oceans had escaped unscathed.
24:35The oceans at the end of the Permian were teeming with life.
24:39There were quite complex reefs made up of corals and various other kinds of creatures
24:44that were fixed to the seabed.
24:46There was rich life, there were sharks swimming in the shallows,
24:49the water would have been pale blue like any typical tropical sea.
24:53So, at a distance, it would have looked like a modern coral reef, perhaps.
24:58But climate change was about to end this.
25:05Paleontologist Paul Wignall has found evidence
25:08of the next deadly phase of the mass extinction,
25:13the death of the oceans.
25:19This is a really nice example of rocks that we get from Greenland.
25:22The evidence is, first of all, they're very black,
25:24which is typical when you have no oxygen around.
25:26But even more telltale is these lovely golden crystals,
25:29which we can see on the surface.
25:31And this is pyrite, or fool's gold,
25:33and we'd only find this if there was no oxygen around on the seafloor.
25:38It's an important breakthrough.
25:41Fool's gold can only form in an environment that lacks oxygen.
25:47Its discovery in 250 million-year-old rocks means only one thing.
25:55Somehow, the Earth's oceans had lost their oxygen.
26:03It was clear that there was something major going on
26:06which hadn't been discovered before.
26:09What we could see was a sudden lack of oxygen
26:11at the end of the Permian mass extinction.
26:13It's a completely new extinction phenomenon.
26:17It's then that we realized that we were now looking
26:19at a very different way of killing life in the seas.
26:27But lower oxygen levels alone can't explain
26:30why so many species died in the oceans.
26:36It's a mystery that research at Green Lakes National Park
26:39in upstate New York has helped to solve.
26:45Marine geologist Lee Kump has discovered the process
26:48that he thinks was responsible for the extermination
26:51of nearly all marine life 250 million years ago.
26:57We're here at Green Lake because we view this as a microcosm
27:00of the ocean that may have existed at the end of the Permian
27:04at the time of this great mass extinction.
27:07It's a really unique habitat here that's unusual in terms of most lakes.
27:12It's like a typical lake at the surface,
27:15but lurking down below is this poisonous water.
27:21The lake looks normal.
27:23But under the surface it's dying,
27:25just like the ancient Permian oceans.
27:31The water is stagnating.
27:34Its oxygen levels dropping.
27:39Over the past five years, Kump and divers from Penn State University
27:43have been monitoring the lake's slow death.
27:48At the bottom, they've found strange colonies
27:50of purple sulfur bacteria.
27:53An organism that only lives in water rich in a highly toxic gas
27:57called hydrogen sulfide.
28:02Hydrogen sulfide is a waste product produced by bacteria
28:06which thrive in water which has no oxygen.
28:10Once the oxygen level drops,
28:12then to the point where there's no oxygen left,
28:15then organisms that can't stand oxygen
28:17begin to thrive.
28:19And these organisms have a waste product,
28:21hydrogen sulfide, that is poisonous to air breathing life.
28:26Hydrogen sulfide is a vital ingredient in the formation of fool's gold.
28:32The large amounts of fool's gold
28:34discovered in the 250 million year old Greenland rocks
28:37suggest that the same process that's happening in this lake
28:41was happening in the Permian oceans.
28:44Kump and his team research the rising levels of hydrogen sulfide in the lake.
28:50They do this by measuring the growth of purple sulfur bacteria.
28:55Recording the changing depth at which it can be found.
28:59They know they've found it when they pull out pink water.
29:05We're looking for the pink water because actually
29:08it's the pink water that's the most toxic.
29:12We're looking for the pink water because
29:14that's indicative of where these purple sulfur bacteria live.
29:17So this is our marker of where these organisms
29:20have a very large population density.
29:22There are so many there that they create this pink water.
29:27Below this toxic layer of pink water,
29:30oxygen breathing animals cannot survive.
29:35Kump has charted the changing depths
29:37at which pink water can be found in Green Lake.
29:42Ready?
29:45Oh yeah, that's rotten eggs.
29:48That's nasty stuff.
29:51He's discovered that as oxygen levels in the lake drop,
29:55the amount of poisonous hydrogen sulfide increases
30:00and the pink water can be found closer to the surface.
30:05It means that the poison is rising up through the water,
30:09killing all of the oxygen breathing animals who live there.
30:15The Green Lakes are just a small expanse of water,
30:18but imagine it on a global scale.
30:21If we were to take a satellite picture of the Permian Ocean,
30:24the regions that are green today would have been pink
30:27when viewed from space because of the abundance
30:30of the purple sulfur bacteria.
30:33Kump's Green Lakes research gives us an insight
30:36into what was happening in the world's oceans
30:38at the time of the mass extinction.
30:43Rocks from the same period tell us that it was a global phenomenon.
30:48Oceans and seas were starved of oxygen
30:51and saturated with poison.
30:55Something major must have happened
30:57to trigger the removal of oxygen.
31:01But what?
31:04In the Green Lakes, it's caused by stagnating water.
31:09The water has stopped circulating.
31:13And recently, researchers have discovered that 250 million years ago,
31:18the same thing happened on a global scale.
31:24Normally, oxygen dissolves into seawater at the surface.
31:29It's then transported by current
31:31circulating between the equator and the poles.
31:37Sunlight at the equator warms the seawater.
31:42As this warm water moves towards the poles,
31:45it cools and sinks,
31:47carrying its dissolved oxygen down with it,
31:50allowing the oceans and its inhabitants to breathe.
31:55This same process was happening 250 million years ago.
32:02But then the Siberian Trops came along
32:05and raised Earth's temperature by about 10 degrees.
32:10The significance of that for the world as a whole,
32:13and particularly the oceans,
32:15is the way it affects circulation in the world's oceans.
32:18It's a bit like leaving a goldfish bowl in the window in bright sunshine.
32:22The water there, it warms up, it loses its oxygen,
32:25and it essentially stagnates.
32:27And so if you magnify that to an oceanic scale,
32:29then that's effectively what we think is happening
32:31in the oceans at the end of the Permian.
32:37The evidence suggests that 250 million years ago,
32:41the rapid global warming created by volcanic gases
32:45warmed not only the atmosphere,
32:47it also warmed the oceans.
32:52They stopped circulating oxygen and stagnated,
32:55becoming breeding grounds
32:57for poisonous hydrogen sulfide-producing bacteria.
33:04We think that the warming then led to the development
33:07of the build-up of hydrogen sulfide in the deep ocean.
33:10This built up to such large concentrations
33:12that it invaded into the shallow part of the ocean
33:15and displaced all of the air-breathing organisms
33:18from those environments,
33:20and eventually providing them no place of shelter.
33:27Climate change triggered by the Siberian Traps
33:30had already killed around a third of all species on land.
33:36By raising the temperature of Earth's oceans,
33:39it then caused the death of virtually all life in the sea.
33:44But the killing wasn't finished.
33:48Lurking at the bottom of the oceans was another killer,
33:53one that would wipe out practically everything else on Earth.
34:05250 million years ago,
34:07the Siberian Trap eruptions rocked the Earth
34:10and covered an area the size of the United States
34:13in thick molten rock.
34:18They set in motion a chain of events
34:21that would wipe out virtually every species on Earth.
34:27Volcanic sulfur dioxide created acid rain and sudden winters.
34:36Next, carbon dioxide raised the planet's temperature so high
34:40the food chain collapsed.
34:48Then the oceans warmed,
34:50and the oxygen levels dropped.
34:55As a result, bacteria filled the water with lethal hydrogen sulfide,
35:02turning the planet's seas into one big kill zone.
35:08Together, they cut global animal and plant populations
35:11by a staggering 70 percent in just 50,000 years.
35:18Now, the animal and plant species that managed to survive
35:22suffered a final blow.
35:29In Iceland, geologist Mike Benton is searching for clues
35:33to this final deadly wave of extinctions.
35:36There is a mystery to understand how the production of carbon dioxide
35:39and the sudden rise in global temperature of about five degrees
35:42could have caused such a catastrophic event.
35:47A sudden rise in global temperature of about five degrees
35:50wouldn't in itself kill life in the catastrophic way we see.
35:54Something else must have caused that massive scale of extinction
35:58that we know happened that time.
36:02The gases released from the Siberian Traps
36:05triggered global warming that wiped out species
36:08first on the land, then in the oceans.
36:14But then temperatures increased again
36:18by another ten degrees.
36:24The result, a catastrophic second wave of extinction on the land.
36:29Scientists know that carbon dioxide released by the traps
36:32caused the first leap in global temperatures.
36:36But the second jump remained a puzzle.
36:41They needed to find something even stronger than CO2
36:44that could accelerate global warming on an unprecedented scale.
36:48And they found the answer to this mystery
36:51hidden in the depths of the ocean
36:54off the coast of Santa Barbara, California.
36:59About a mile offshore, Dr. Ira Leifer,
37:02a climatologist from the University of California,
37:05is on his way to monitor an unusual phenomenon.
37:10He's going to look for clues that could help us
37:14He's on his way to monitor an unusual phenomenon.
37:20He's looking for another greenhouse gas.
37:24Not carbon dioxide, but methane.
37:28This area is where methane, from deep within the earth,
37:32rises through the earth's crust until it reaches the seabed
37:36and then through the water column
37:39to reach the sea surface as bubbles.
37:44You can find these bubble seeps in coastal areas all over the planet.
37:50But this one's proximity to Southern California
37:53has given scientists a unique opportunity
37:56to monitor one closely.
38:01Diving deep into the cold Pacific waters,
38:04Leifer's students collect methane samples
38:07straight from a vent in the seafloor.
38:10The samples show that when it comes to global warming,
38:13methane is a super gas.
38:16Methane is a very potent greenhouse gas,
38:19perhaps 20 to 25 times more potent
38:22on a molecule-per-molecule basis than CO2.
38:27That means if we add one molecule of CO2 to the atmosphere
38:30and one molecule of methane, that methane has 25 times the effect.
38:35The amount of methane released by seeps like this one in Santa Barbara
38:39is too small to explain the additional 10 degree temperature rise
38:43recorded towards the end of the mass extinction.
38:49But there's another source of the gas that might.
38:54In the deep ocean, the most unexplored and least understood part of our world,
38:59there are vast quantities of a substance called methane hydrate.
39:05It's methane gas frozen in the cold water at the bottom of the sea.
39:11Today, there's an estimated 30 trillion tons of methane
39:15locked away in ice on the seabed.
39:19If it turned into gas, there would be a global disaster.
39:25Leifer thinks that this may be what happened 250 million years ago.
39:31If we look at this massive extinction as comparable to a genocidal crime
39:37on an unimaginable scale, and we ask ourselves,
39:41who are the criminal suspects? Who's responsible?
39:45We'd look at the evidence.
39:47And at the top of the short list is methane hydrates
39:50because of the vast size and their known instability.
39:56Frozen methane is ultra-sensitive to heat.
39:59Raising its temperature by even a few degrees can destabilize it
40:04and trigger the release of this powerful greenhouse gas.
40:09If the atmosphere warms for any particular reason,
40:13the ocean will warm, methane hydrate will release methane,
40:16this will warm the atmosphere, leading to warmer temperatures
40:19and even more methane hydrate releasing its methane to the atmosphere.
40:24A positive feedback cycle.
40:30250 million years ago, billions of tons of volcanic gases
40:34produced by the Siberian traps triggered one of these cycles.
40:41The eruptions increased global temperature by 10 degrees.
40:47Enough to thaw the frozen methane hydrate at the bottom of the oceans
40:51and release billions of tons of potent greenhouse gas
40:55into the Earth's atmosphere.
41:00The temperature went up another 10 degrees.
41:06The world was now 20 degrees hotter.
41:10Life couldn't adapt to the increase in heat
41:13and the sudden change in climate.
41:16Now nearly all life died out.
41:20First to go, the remaining vegetation.
41:23Next, the frozen methane hydrate.
41:26The remaining vegetation.
41:28Next, the few surviving herbivores.
41:33And with them, the last of the carnivores vanished.
41:41Earth's food chain was more than broken.
41:44It hardly existed at all.
41:47Yet in spite of the overwhelming series of catastrophes,
41:51new life and eventually humans do evolve.
41:56We owe our existence to an unlikely group of four-legged heroes.
42:06250 million years ago,
42:09the planet had been brought to its knees by savage volcanic eruptions.
42:15The toxic gases they released created worldwide climate chaos
42:22and wiped out most life on Earth.
42:27For the planet's dominant species, there was no hope of survival.
42:33For something like a Gorgonopsian,
42:35it would have seen a world which would be changing.
42:38The various animals that it was eating would be becoming rarer.
42:42It would be getting a heck of a lot hotter.
42:44So terminal times for the Gorgonopsians and all around it as well.
42:50For these fearsome predators and for most living things,
42:53it was the end of the line.
42:56But in evolutionary terms, it was a new beginning.
43:01Catastrophes can reset the evolutionary clock.
43:04That means that evolution, the whole direction of evolution,
43:07perhaps will change because the dominant species disappear.
43:12And then other species that were taking a less significant role
43:16before the event have their chance.
43:19250 million years ago,
43:21the mass extinction provided a priceless evolutionary opportunity
43:25to a small burrowing animal.
43:30These are cynodons.
43:33They'd been a favorite snack for Gorgonopsians.
43:37But by burrowing underground, they'd stayed out of their predators' reach.
43:42And it proved to be a useful habit
43:44when climate change scorched the Earth's surface.
43:48Tubers and roots underground provided them with food and water.
43:54In South Africa's Karoo Basin,
43:56paleontologist Roger Smith has made an important discovery.
44:00We're looking at a burrow cast in the early Triassic.
44:03And we know from fossils that have been found in the ends of these casts
44:07that they are cynodon.
44:10Cynodons were digging burrows
44:12during the end-Permian extinction event.
44:16And it's very likely that that was one of the reasons
44:20why it was able to survive the great drought at that time.
44:25After the mass extinction,
44:27these cynodons went on to become
44:29one of the dominant species in the New World.
44:33Without them, we wouldn't be here today.
44:36One of the cynodon lion eventually became a mammal.
44:39And had it not been for the survivor through the cynodon lion,
44:43mammals would not have existed and evolved, and nor would we.
44:47So we have a lot to thank the cynodons for.
44:54A quarter of a billion years ago,
44:56life suffered a devastating blow.
45:01Only today,
45:02only to bounce back with new species and ecosystems.
45:07But the same kind of catastrophe
45:09that gave our earliest ancestors its chance could happen again.
45:16Eruptions like Iceland's Larki
45:18come roughly every 20 million years.
45:22Gigantic ones like the Siberian Traps are rarer still.
45:27They happen every few hundred million years.
45:30But they do happen.
45:32It might shock people to realize
45:34that the Earth can cause extreme devastation.
45:37And of course, there's nothing that human beings
45:40with all their technology could do to counter that.
45:43So that if there were to be an eruption today
45:46on the scale of Siberian Traps,
45:48it would be hard to know how large numbers of human beings
45:52could protect themselves from it.
45:54So very likely there would be unbelievable death and destruction.
45:58Nobody would be safe.
46:03But the biggest threat to mankind's future
46:06might not be a naturally occurring phenomenon.
46:09For the first time in history,
46:11the dominant species on Earth
46:13is upsetting the delicate balance of its own ecosystem.
46:19Our production of carbon dioxide
46:21is having a catastrophic impact on Earth's systems.
46:27We have the potential to release 2,000 or 3,000 gigatons
46:30of carbon dioxide to the atmosphere
46:32in the next couple centuries.
46:34When we look at the Siberian Trap volcanism,
46:37we're talking about maybe similar quantities
46:40of carbon dioxide released,
46:42but over millennia to maybe a million years.
46:45And so we're taking the whole Siberian Trap event
46:49and compressing it into the timescale of human activity,
46:53one or two centuries, and that's scary.
46:57It's already causing the planet to heat up,
47:00and scientists fear the runaway global warming of the past
47:04could happen again in the future.
47:08With more than 30 trillion tons of methane
47:11locked up as hydrates on the seafloor,
47:13the potential for another hydrate meltdown
47:16is as real today as it was 250 million years ago.
47:22But this time, we would have started it.
47:26I'm sure if we carry on what we're doing today
47:28in terms of pollution, we will cause a catastrophe,
47:30but how quickly is the big question.
47:34The end Permian extinction
47:36was one of the most important chapters
47:39in the story of the evolution of life.
47:42It nearly wiped out life itself
47:44from the face of the planet.
47:47The few survivors became our direct ancestors.
47:52Without this mass extinction event,
47:54we probably wouldn't be here at all.