Horizon (1964) s39e04 Episode Script

The Day the Earth Nearly Died

The world today teems with life Wherever you look, something is alive Then imagine 95% of all this dying in one go It's not a fantasy.
It did happen 250 million years ago It was the day, the earth nearly died The Karroo Basin in South Africa A region of hunting and inhospitable beauty This is an area where little grows and man and beast struggle to survive But it hasn't always been like this Almost 300 million years ago during what scientists called the Permian period it was an oasis The scene would have been low-lying plains perhaps with mountains in the distance meandering rivers, lots of plants around the sides of those rivers low plants like ferns and so on and then in the background some trees of very unusual type This was a time millions of years before the dinosaurs when strange and half forgotten creatures walked the earth They were called thorapsids half mammal, half reptile The first creatures ever to fullly conquer life on land In any one locality you'd find 50 or 60 different species of reptiles living side by side specialized on different diets, different habitats and so on This is the skull of dicynodon It's sitting with the top of the skull just here coming down to the snout This is a tortoise-like beak that sits under here Dicynodon was a hippo-sized plant eater Filled the niche of the cow in a modern day pasture except these would live in herds and roam around the Permian flood plains Its principle predator was dinogorgon, the king of the Permian jungle These were real terrors.
The first time the world had ever seen such top carnivores as they're called They had sabre teeth this sort of length and just like the famous sabre tooth cats of much later They would leap on the backs of these hippopotamus-sized plant just piercing through their thick skin tearing the flesh For 30 million years these strange creatures ruled the earth This was a thriving, stable world as complete in its own way as ours is today Then, around 250 millions years ago, almost every living thing suddenly died The fossil record shows that the rock beds at the end of the Permian period contained absolutely no fossils No signs of life at all This is the dead zone This zone represents what it was like here after the mass extinction We have never found anything that represents life in this zone This is what we would call barren There's no evidence of plant life there's no evidence of soils - and especially there's no evidence of animals This is completely dead We're going from this very rich place to a biological desert Form a place that's like a rainforest to a place that is composed of a few species eking out an existence Scientists call this utter destruction of life the Permian mass extinction Never in the history of the planet was there a catastrophe that was so widespread, so devastating and so all-inclusive The Permian mass extinction was far more terrible than the later extinction that wiped out the dinosaurs The dinosaurs extinction that happened 65 million years ago killed off maybe 60% of most of the species on the planet There's still plenty of life around But I get the sense that were one to go back to the Permian extinction right afterward you would see virtually nothing of life At the end of the Permian era 95% of all life died It was the biggest reverse in the forward march of evolution ever recorded Yet, until recently, almost nothing was known about this extraordinary event Nobody could explain why it had happened or even whether it would happen again Scientists have spent years digging in Permian rocks for clues Yet, wherever they looked they could find no evidence of the cause of death No footsteps, no finger prints It seemed as if the killer had arrived and departed without a trace Then in the early 1990s they stumbled on something Buried under the frozen wastes of Siberia are thousands of miles of lava It's an area known as the Siberian Traps Today the region is covered in snow and vegetation but below the surface are the ancient remains of the biggest and most destructive volcanic eruptions the world has ever witnessed 250 million years ago hundreds of thousands of square miles of Siberia caught fire One of the first scientists who looked at it in detail was Vincent Courtillot I probably would have seen a curtain of red glowing fire rising a mile high up in the atmosphere extending from end to end of the horizon over a distance of hundreds of kilometers It's a phenomenon known as a flood basalt eruption When the earth crusts splits apart and releases curtains of lava across an entire continent The eruptions can last for millions of years Nobody is quite sure why they happen You get a huge eruption and another and another and maybe a lull and another bunch of 10 and then another all together over a few hundred thousand years The earth is almost continuously spewing out lava - until after a million years or so, millions of cubic kilometers have erupted so this is a truly gigantic volcanic object thousands, tens of thousands of times larger than anything man has ever seen Courtillot now began to wonder what such a volcanic monster would do to life on earth Were the Siberian Traps the Permian killer? Though nobody had ever seen a flood basalt eruption he did have one clue Just over 200 years ago, in a region of Iceland called Laki a tiny but similar eruption altered the climate of the Northern Hemisphere Benjamin Franklin, the America Ambassador in Paris at the time recorded the effect on Europe's climate The skies were clogged with volcanic ash It was a summer when the sun never shone Snow fell during August That winter was one of the worst winters in living memory That winter of 1783/1784 there were strange fogs, brown fogs snow, unusual amounts of snow fell and actually the winter continued onto the next summer This was called the year without a summer There was no grape, no wine, the wheat didn't ripen and actually that foul weather was observed in North America and in Japan and China Using the evidence from Laki, Courtillot now built a model of how the Siberian Traps might have destroyed the world First there would have been eruptions sending thousands of tons of dust and ashes into the sky Slowly the sun would have been blocked out and temperatures would have fallen First we'll enter a winter, a volcanic winter the dust and the sulphur will cool the atmosphere after each eruption for years or tens of years It would have been like a nuclear winter lasting decades But that would have been just the beginning As the sky's cleared vast quantities of gas given off by the burning lava would have slowly wrapped the earth in a blanket of carbon dioxide an extremely powerful greenhouse gas Gradually, over thousands of years there would have been massive global warming The carbon dioxide will lead to a greenhouse effect and the cold will be replaced by unusual hot time So you get the double hit, you're cold for a while and then hot for a longer time So that altogether after a million years the earth would be different The climate would be different and a mass extinction would have happened It seemed as though Courtillot must have found the cause of the extinction Here was a truly massive destructive event that had happened at exactly the right time Yet the evidence was not as straight forward as it appeared In America, geologist Peter Ward was alos looking at the evidence He knew that to do so much damage the change in world temperatures would have had to have been rapid and dramatic You have to have a very sudden, but very large increase in temperature to have done the mayhem and the destruction that is this mass extinction Ward looked more closely at the data from the Siberian Traps He estimated the amount of lava they'd produced and used this to calculate how much carbon dioxide they would have emitted He then calculated what this would have done to world temperatures We've looked at the Traps, the Siberian Traps we've tried to estimate how much gas would have come out of them - and how much warming would that have done and it turns out that in the worst case scenario, and of course for the world it was a worst case they may have raised the temperature of the earth about 5 ¡ãC The geological record shows that when world temperatures rise abruptly by 4/5 ¡ãC many species will die but he could also see there was no evidence that such an increase would wipe out 95% of all life His calculation showed that to do that would require a much bigger increase in temperature, perhaps double Well, scientist estimate that a rapid temperature rise of maybe 10 ¡ãC is going to be necessary to kill off so many animals and plants and everything else 5 ¡ãC, the Siberian Traps with their 5¡ãC, it would have created certainly climate change but a massive extinction? I don't think so It seemed there was a flaw in Courtillot's theory The Siberian eruption would have been deadly but not that deadly Something even more catastrophic must have been at work In 1998 the search for clues took American geologist Mike Rampino to the Alps It's one of the only places in Europe where there are Permian fossils Rampino had been trying to understand the extinction for some years and thought one vital piece of information was missing Nobody knew with any certainty how long the extinction had taken He believed that if he could find this out he'd have a clue to its identity Was he looking for a hit-and-run killer or something slower? One of the things we'd like to know about the Permian mass extinction was how rapid it was how long did it take for those, all of those organisms to become extinct? He planed to use a radically new dating system It's based on the fact that the fossil record charting the end of the Permian era is preserved in a thin layer of rock If it could work out how long it had taken for this rock to be deposited he'd know how long the extinction had taken The Permian rocks lie just below the next geological period the Triassic This is the Permian/Triassic boundary, the boundary between the Permian rocks below us and the Triassic rocks above us and this is the boundary where the mass extinction takes place What we're trying to do here is to determine how long it took for the sediments at the boundary in which the mass extinction took place to be deposited Rampino's system relied on the observation that the earth's orbit round the sun alters minutely every 23,000 years This produces small changes in the climate This, in turn, produces distinctive bands in the rock one every 23,000 years Rampino took photos of the rock bands and fed them into a laptop When I digitally enhance the photographs I can manipulate the data to bring out the 23,000 year cycle and that gives me a time-frame in which to put the mass extinction It's like a giant tape measure dividing an entire mountain into a series of 23,000 year divisions Rampino then fitted the layer of rock containing the evidence of the extinction into this pattern of cycles It covered less than half a cycle, 8,000 - 10,000 years, far faster than anyone had thought possible What this tells me is that the mass extinction took place in an astonishingly short period of time less than 10,000 years and possibly instantaneously This means that that mass extinction was catastrophic To have destroyed so much of life so quickly the killer must have been extraordinarily violent Rampino could think of only one thing it could be A mass extinction that happens at less than 10,000 years is very abrupt It fits the picture of a large impact at the end of the Permian Rampino was now convinced a huge meteor had slammed into the earth 250 million years ago Shockwaves would have raced around the globe instantly killing everything within hundreds of miles When an asteroid or comet that large hits the earth it's the equivalent of a billion atomic bombs going off at the same time in the same place Almost immediately afterwards millions of tons of dust would have shut out of the sun It would all have happened very rapidly much faster than the climate changes caused by a flood basalt eruption Temperatures would have plummeted almost overnight Makes a huge crater and throws a tremendous amount of dust and debris up into the earth's atmosphere and you end up with a catastrophic situation for life on the planet Rampino's calculation suggested this would've been a far bigger, harsher, more rapid nuclear winter than anything the Siberian Traps could have caused Life would have rapidly become almost impossible A meteor from outer space sounds like science fiction but there has been a similar case Most scientists now accept that 65 million years ago the dinosaurs were wiped out by just such an event but the Permian meteor would have been even bigger The asteroid that hit the earth at the time of the dinosaur extinction was at least 10km diameter The Permian mass extinction is even more severe so the asteroid that hit it that time must have been even larger, perhaps 15km in diameter It seemed the perfect answer A meteor the size of Manhattan had wiped out most of life on earth Yet something didn't add up Nothing that size could hit the earth and not leave a trace The meteor that had wiped out the dinosaurs had left a giant fingerprint in the shape of a crater just off the coast of Mexico where was the Permian crater No matter where they looked nobody could find anything dating from the Permian era but then a scientist from London came up with a totally new idea Adrian Jones models the effects of impacts on the earth's crust He now suggested geologists were searching for the wrong thing In a conventional view of an impact we have a high speed asteroid which hits the earth's crust and makes a crater instantaneously which is very deep Immediately after the crater is formed this deep shape the compressed rock underneath the crater rebounds and the crater expands to be a much shallower shape So under normal circumstance there would be a large shallow crater but Johns believes that when a really massive meteor hits the earth something else happens too What we think happens is that in addition to the energy from the asteroid itself an enormous amount of energy is released when the crater here is transforming back to its shallow shape John's theory is that as the crust rebounds from the impact of the meteor it generates far greater quantities of heat than anybody had thought possible He built a computer model to see what would happen to a crater if this occurred The impact causes a deep crater This rebounds to create a wider, shallower one but then if the meteor is very large something new happens It melts the earth's crust and lava is released And the final part of the model shows that lava has filled the crater and flowed beyond the edges of the crater and the original crater structure we can see the walls here is completely drowned by the large volume of lava so that there's no outward shape of the crater visible from the surface It meant the Permian crater would have entirely filled with lava The reason nobody had found a crater was because there wasn't one It was a fascinating idea but was it also too neat? When a large meteor hits the earth it leaves more than one fingerprint It also leaves a trail of shattered rock and dust which are blasted around the globe by the force of the collision If John was right the Permian meteor should have left similar traces But despite looking in Permian rocks the length and breadth of the planet nobody could find a single trace of the meteor Greg Retallack was one of those involved in the search He concentrated his efforts in Antarctica There was definitely a missing piece to this whole thing and we struggled with, to find out what that was and the clue was in front of us actually for quite some time In the middle 1990s, he led an expedition to see what was there It was really the trip of a lifetime and it was something I'd wanted to do for about 15 years before The team spent weeks exploring the Permian rocks but one bed of rock in particular attracted his attention We knew it was the very latest Permian bed and inside that bed there were quartz grains that had some very unusual features Quartz is the most common crystal on earth It's most frequently white and translucent Most of the quartz is just like this grain that I'm on now and it's a very clear grain Looking through the microscope the light shines through it brightly, it looks white But some of these crystals weren't white or clear This quartz had a very strange set of parallel fracture-like fused planes running through it at several angles Something had shuttered the quartz Retallack knew that only a force of enormous size could create these patterns It seemed there must have been a huge meteor It looks as though he had found the traces everybody had been looking for Yet again, something didn't fit As Retallack looked further at the new evidence there was a surprise The meteor that had wiped out the dinosaurs had left huge quantities of shattered quartz It had also left traces of a metal mainly found in outer space called iridium It's a common component of meteors When a meteor wiped out the dinosaurs 65 million years ago it left abundant evidence of itself There's a thin deposit of rocks that fell out of the atmosphere after this huge explosion and it has within it bits of quarts that are shattered by the pressure and it has iridium which came from the asteroid itself Yet Retallack's samples contained very little of either of these materials One would expect if the meteor solution was the whole answer that we would get a bigger input of shot quartz and iridium at the Permian/Triassic boundary that at the one where the dinosaurs went extinct and it was the other way around No traces of iridium dust and not much shattered quartz It didn't add up For a meteor to kill 95% of all life on earth it should have been the size of Manhattan Yet the evidence suggested that if there had been a meteor at the end of the Permian era it had been far too small to destroy the world The Permian killer had, once again, eluded scientists Paul Wignall, a geologist at the University of Leeds, had always been doubtful about the meteor theory It's a nice theory, it nicely explains the end of the dinosaurs in the later extinction event, but for this particular extinction I just don't think there's any convincing Wignall suspected all the explanations for the extinction had been based on insufficient data He also knew there was one place he might find more Greenland It's a country known to contain Permian rock but always considered too difficult to explore In the late 1990s he took a gamble and flew out there Piled all our stuff onto a helicopter, flew out into this wilderness they dropped us in the middle of nowhere and left us there for several weeks Their first task was to find the Permian rock Nobody even knew where it was Some of us had never been there before and we weren't exactly sure where we needed to look We had a lot of exploration, a lot of wandering around to do before we knew what we were looking for But finally they found what they had come for It exceeded their widest dreams Instead of the usual narrow band of rock strata the sediments containing the record of the extinction stretched for meters above and below them It was one of the best records of the Permian mass extinction ever found We were astounded by just how much, how much cliff there was to examine The whole Permian extinction story seemed to be spread through tens of meters of cliff and the fossils that we could collect were showing us a beautiful detailed story that was telling us a lot more than we'd known previously about the timing of what was going on at this time Yeah.
come Yeah Even to the naked eye, one thing was blindingly obvious The meteor theorists had got the timing wrong The Greenland rock showed that the extinction had been a gradual event In fact, it appeared to drag on for tens of thousand of years We could see that the extinction wasn't occurring instantaneously, but in fact was spread over several, a certain amount of rock, so we could see it was being spread over a certain amount of time Wignall now suspected he was onto something big The expedition spent a month amassing samples They shipped back 20 crates of rock to Britain It seemed at last that the Permian killer might reveal its secret Back in Leeds, Wignall realized he'd stumbled on a treasure trove of fossils Buried in the rock samples were thousands of them Many so small they had to be extracted in an acid bath His team was overwhelmed by what they'd got We were so excited with this story that we were working weekends and just buckets and buckets of rocks all being broke down we, excitingly we were just sieving them through, getting all the fossils out Wignall's sediments began to reveal the most detailed account of the extinction ever uncovered There was just a huge range of little tiny fossils in these rocks which were telling us in fantastic detail just what was going on at this time and there was no need to guess anymore, we could actually see the order in which things were going extinct and get the full extinction story right from the beginning all the way through to the end For the first time he was able to work out exactly what had happened It was a complete surprise The extinction had occurred in 3 distinct phases The extinction crisis first begins on land and what we see is species of plants, species of animals start disappearing about 40,000 years this goes on for This was the first phase a period when some, but by no means all, land species died And then what happens next at about 40,000-45,000 years after the crisis has begun is that we see a really quite sharp, abrupt extinction in the seas at this time so this is the marine extinction event, much shorter and sharper than what we see on land So the second phase of the extinction was the abrupt death of virtually everything in the sea Then came the third phase as the extinction moved back to the land Following on from that we then see the culmination of the land extinction so we start losing all our typical plants and all our typical animals as well and this carries on to a point of about 80,000 years after the extinction began Three long, slow phases, sprawled over at least 80,000 years very different from how the meteor theorists had seen it Yet Wignall was still no closer to understanding why it had happened or what the killer was but he had found a clue Analysis of the rock showed that just after the marine extinction but before the final death of everything on the land there was a mysterious increase in a form of carbon, called carbon 12 This is normally produced by rotting plant and animal matter, but this was a huge increase, too big to be explained by that alone Wignall realized that here was a fresh piece of evidence, something that, if he could understand it might provide the key to the Permian riddle The Carbo12 increase is clearly telling us something.
It's a clue to the nature of the Permian extinction.
There's something mysterious going on at this time, but exactly what it is not immediately apparent The key to the puzzle would come from a totally unexpected quarter Gerry Dickens is a geologist working on new sources of energy He had no special interest in the Permian extinction but one evening, sitting in a bar, he ran into a friend We were just sort of chatting about what we were working on for the summer and he was telling me that he was working on trying to understand how you could get massive of 12 carbon quickly because some signatures had been found in the rock records and it was very difficult to explain, it didn't make any sense Dickens was curious Several years earlier he'd spent time on a drilling rig in the Gulf of Mexico prospecting for a new source of energy called methane hydrate It's a gas frozen in huge reservoirs just below the seabed Dickens knew this methane contained massive quantities of carbon 12 He also knew there were dozens of these methane hydrate reservoirs scattered around the world's coasts We find 'em for instance along the coast of south America, along central America all along the western coast of the US and Canada, indications round Australia, Indonesia essentially anywhere along continental margins where you get a lot of organic matter that decays at the bottom and produces methane Could these massive reservoirs of methane, he now wondered, be the source of the carbon 12 found in Permian rocks and if it was, how did it get there? Dickens started to investigate Naturally occurring frozen methane is unstable and difficult to extract, so samples were artificially created in a lab The big question is try to get methane from deep down in the ocean up to the atmosphere He put blocks of the man-made methane into warmed water The results were spectacular So it's disassociating deep down Dickens found that even small pieces of frozen methane released enormous quantities of gas rich in carbon 12 The experiment supported what he'd suspected the increase in carbon 12 could be the fingerprint of a massive methane release He found something else as well It would only take a small increase in water temperatures to melt the methane and release the carbon To explain the amount of carbon 12 that we see in the geologic record we need to warm up the bottom water by somewhere in the order of about 5 ¡ãC He published his results in 1999 He couldn't have anticipated their effect 5,000 miles away in England, however, Paul Wignall read Dickens's findings with growing interest Suddenly realized that in fact a lot of his ideas as to how to explain carbon 12 increases may actually apply to the story we're getting from Greenland.
It's a kind of a missing link in the story for the Permian extinction Wignall now began to speculate What would be the effect on the world's climate of so much methane? It's one of the most potent greenhouse gases known to man Wignall constructed a rough climate model using the carbon 12 as a guide to the quantities of methane It's not that straightforward to work out just how significant the impact of this methane release would be but it's possible to work out the volumes emitted using the evidence from the carbon 12 increase and these certainly suggest that there may have been sufficient methane going into the atmosphere to perhaps increase global temperatures by 4/5 ¡ãC 4/5 ¡ãC, not enough to kill the world, but then Wignall realized this was only part of the story For the methane to melt something must already have raised world temperatures 4/5 ¡ãC The methane would then have raised them a further 5 ¡ãC more to a total of 10 ¡ãC This would have been more than enough to kill practically every living thing Wignall slowly realized what the evidence from Greenland was telling him.
There had not been one Permian killer, but 2 Paul Wignall now put together the extraordinary story of what might have happened 250 million years ago It started, as many had thought, with the Siberian Traps Thousands of miles of lava flows would have burst from cracks deep in the earth's crust This was the first killer Imagine the world for dicynodon as he crawls out of his hole in South Africa and looks at the sky It may be a bit purple, it may be a bit blue or red because of the very distant volcanic eruptions in Russia He may feel it a bit warmer at first.
Year by year progressively this gets worse and worse There would have been a freezing winter followed by slow but steady global warming Gradually the world would have heated up by 4-5 ¡ãC On land some species died Then the sea must have headed up.
Marine life would also have died Then something new happened The hotter water would have released the second killer from the deep the methane This huge injection of greenhouse gas now pushed world temperatures up a further 5 ¡ãC The world was now 10 ¡ãC hotter A temperature rise of 10 ¡ãC may not sound very much but 10 ¡ãC would mean this part of the south of England would turn into the Sahara desert Almost all life in every shape and form across the surface of the globe would have died Here at long last was an explanation that tied up all the loose ends and accounted for all the evidence The cause of the Permian mass extinction may finally have been found It would take nearly 100,000 years for life on earth to begin to recover When it did, a new family of creatures ruled the world.
This was the birth of the age of the dinosaurs but geologists have found that one of the strange, half mammal/half reptiles of the Permian world did survive It was a cow-sized plant eater called lystrosaurus This strange looking creature is one of the most important animals that ever walked the earth because lystrosauras was the ancestor of all mammals and so, ultimately, of us We're only here today because this odd looking creature somehow clung to life during the mother of all distinctions