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24 September 2014
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Paul Wignall from Leeds University has pieced together a radical theory of what killed 95% of all life on Earth in the Permian era
First shown: Thursday 5 December 2002
The Day The Earth Nearly Died
Coming up on Horizon
Archaeologists search the Amazon for The Secret of El Dorado.

The Day The Earth Nearly Died - questions and answers

Can we estimate how much life there was on Earth before the Permian extinction events?

We have no way of knowing how densely the Permian world was inhabited or how large the different animal populations were because the fossil record is too patchy and inaccurate. However we do know that what was significant about the Permian world was that, for the first time, practically every ecological niche was occupied. This was a self-sustaining world as complete, in its way, as ours is today. In fact this was the first time such a complete array of creatures had existed.

Moreover we know that some of these creatures were in the process of evolving into mammals and were, therefore evolutionarily, extremely sophisticated. The early dinosaur period, which followed the Permian extinction, was much less sophisticated. In this sense, the Permian extinction marks a step back in evolution. Indeed it's doubtful the early dinosaurs - which were evolutionarily rather primitive - would have been able to find a niche in the world had the more advanced animals of the Permian world not been wiped out. In other words, the Permian extinction probably cleared the way for the dinosaurs and if there hadn't been a Permian extinction, there may not have been any dinosaurs.

What proportion of plants and animals survived the end of the Permian?

The Permian extinction wiped out around 95% of all life on earth. By contrast the extinction which ended the reign of the dinosaurs killed a mere 65% of all life. Almost all scientists agree the Permian extinction was the biggest recorded event of its kind in the history of the world.

What new information does this insight into Permian extinction offer on dinosaur extinction, 200 million years later?

The Permian extinction, and the later K/T extinction which wiped out the dinosaurs, have led some scientists to suggest that extinctions are a normal part of evolution; that the extinction of one species clears the way for the next. Thus the extinction of the Permian's thorapsids, or mammal-like creatures, cleared the way for the early reptilian dinosaurs, and the extinction of the dinosaurs cleared the way for mammals. If this is true then evolution is not a smooth process of advance but is marked by steps and even reverses.

It may also be true that there is an intimate relationship between the evolution of life and the physical/geological development of the earth. In other words as the earth has undergone geological change, so have the animals that have lived on it. Geology and evolution go hand in hand, each throwing light on the other.

What theories are there for how such a large animal as lystrosaurus could have weathered the climate warming by 10°C?

Lystrosaurus was a herbivore and is believed to be the ancestor of every mammal now on Earth. Nobody really knows why some animals survived the extinction and others didn't. In particular we can only guess at why lystrosaurus was the only thorapsid (mammal-like creature) to survive. Paleontologists speculate, from looking at its fossil remains, that it may have had a particularly well adapted jaw or mouth which enabled it to eat tough woody vegetation and thus survive in desert like conditions. This is only an informed guess.

Why does Greenland have such useful geological records for this period?

The Permian geological record is extremely patchy across the world. This is partly because it was such a long time ago (roughly 290 million - 250 million years ago) and has been overlain or disrupted by later geological activity, and partly because many parts of the Permian world - and in particular most of what is now Europe and North America - were hot and desert like and the fossil record vaporised. Thus the Permian rocks in Britain, for instance, are mostly a red sandstone which contains no fossils; some of the bst examples of this are along the dorset coast in the cliffs around budleigh salterton.

One of the results of this absence of Permian fossils in Europe and North America is that, for many years, scientists were extremely ignorant about the Permian period. This ignorance has been exacerbated by the fact that, by a perverse set of accidental circumstances, the best Permian fossil records tend to be in some of the most physically or politically challenging places which have been extremely expensive or politically difficult to visit. As a result it's only in recent years that scientists have begun to collect accurate data on the period.

Does the theory rule out the possibility of an asteroid sparking off the extinction period? Could the extensive movement of continents since then not have erased any huge impact crater?

The debate about what caused the Permian extinction remains unresolved. The weight of evidence currently tends to discount a large meteor as the culprit and to favour a multicausal explanation: probably volcanism and methane. But new evidence could, once again, turn all this on its head. It is possible that somebody may, one day, find the crucial evidence of a meteor impact that is currently missing. It may be that the impact crater, for instance, has been buried under later geological activity, or is hidden on the bottom of an ocean. All we can say for sure is that nobody has yet found all the usual indicators of a large meteor impact. That doesn't mean they do not exist.

Is there any pattern emerging in the timing of such mass extinctions?

No. There is no apparent pattern to the timing of the different extinction events in the Earth's history. However, if it's true that the geological evolution of the Earth is related to the evolution of life on Earth, then if, in the future, geology becomes a predictive science then we may be able to predict future extinctions. Indeed to the extent that we are correctly predicting global warming we may already be partly along this road. What we don't know, with any certainty, is how adaptable life, in all its different guises, is to change.

How much of a threat to global climate change is there still from sub-sea methane hydrate?

The existence of huge reservoirs of frozen methane hydrate around the world's coasts is a relatively recent discovery and nobody knows quite how unstable it is or what it would take, today, to melt it. Scientists calculate that a global increase of 10°C might have been sufficient to release frozen methane hydrate during the Permian period but nobody knows whether that would be sufficient under today's conditions. What is clear, however, is that should it be released, huge quantities of greenhouse gases would escape into the atmosphere and the world would very rapidly warm up.

More information
University of Bristol
Palaeontology Research Group
San Francisco State University
The Permo-Triassic Extinctions
University of California, Berkeley
Museum of Paleontology
University of Rochester
Dept of Earth Sciences
US Geological Service
Gas hydrates
The Geological Society
Flood basalt eruptions
When Life Nearly Died
MJ Benton, 2003, Thames & Hudson, London and New York
Mass Extinctions and Their Aftermath
A Hallam and PB Wignall, 1997, Oxford University Press
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