Shadow Of Extinction

It is old news, I admit. Two hundred and fifty-one million years old, to be precise. But the story of whathappened then, which has now been told for the first time, demands our urgent attention. Its implications aremore profound than anything taking place in Iraq, or Washington, or even (and I am sorry to burst your bubble)Wimbledon. Unless we understand what happened, and act upon that intelligence, pre-history may very soonrepeat itself, not as tragedy, but as catastrophe.

The events which brought the Permian period (between 286 and 251 million years ago) to an end could not beclearly determined until the mapping of the key geological sequences had been completed. Until recently,palaeontologists had assumed that the changes which took place then were gradual and piecemeal. But threeyears ago a precise date for the end of the period was established, which enabled geologists to draw directcomparisons between the rocks laid down at that time in different parts of the world.

Having done so, they made a shattering discovery. In China, South Africa, Australia, Greenland, Russia andSpitsbergen, the rocks record an almost identical sequence of events, taking place not gradually, but almostinstantaneously. They show that a cataclysm caused by natural processes almost brought life on earth to anend. They also suggest that a set of human activities which threatens to replicate those processes could exertthe same effect, within the lifetimes of some of those who are on earth today.

As the professor of palaeontology Michael Benton records in his new book, When Life Nearly Died, the marinesediments deposited at the end of the Permian period record two sudden changes.1 The first is that the red orgreen or grey rock laid down in the presence of oxygen is suddenly replaced by black muds of the kinddeposited when oxygen is absent. At the same time, an instant shift in the ratio of the isotopes (alternativeforms) of carbon within the rocks suggests a spectacular change in the concentration of atmospheric gases.

On land, another dramatic transition has been dated to precisely the same time. In Russia and South Africa,gently deposited mudstones and limestones suddenly give way to massive dumps of pebbles and boulders. But thegeological changes are minor by comparison to what happened to the animals and plants.

The Permian was one of the most biologically diverse periods in the earth's history. Herbivorous reptilesthe size of rhinos were hunted through forests of tree ferns and flowering trees by sabre-toothed predators.At sea, massive coral reefs accumulated, among which lived great sharks, fish of all kinds and hundreds ofspecies of shelly creatures.

Then suddenly there is almost nothing. The fossil record very nearly stops dead. The reefs die instantly,and do not reappear on earth for ten million years. All the large and medium-sized sharks disappear, most ofthe shelly species, and even the great majority of the toughest and most numerous organisms in the sea, theplankton. Among many classes of marine animals, the only survivors were those adapted to the near-absence ofoxygen.

On land, the shift was even more severe. Plantlife was almost eliminated from the earth's surface. Thefour-footed animals, the category to which humans belong, were nearly exterminated: so far only two fossilreptile species have been found anywhere on earth which survived the end of the Permian. The world's surfacecame to be dominated by just one of these, an animal a bit like a pig. It became ubiquitous because nothingelse was left to compete with it or to prey upon it.

Altogether, Benton shows, some 90% of the earth's species appear to have been wiped out: this represents bythe far the gravest of the mass extinctions. The world's "productivity" (the total mass ofbiological matter) collapsed.

Ecosystems recovered very slowly. No coral reefs have been found anywhere on earth in the rocks laid downover the following 10 million years. One hundred and fifty million years elapsed before the world once againbecame as biodiverse as it appears to have been in the Permian.

So what happened? Some scientists have argued that the mass extinction was caused by a meteorite. But theevidence they put forward has been undermined by further studies. There is a more persuasive case for adifferent explanation. For many years, geologists have been aware that at some point during or after thePermian there was a series of gigantic volcanic eruptions in Siberia. The lava was dated properly for thefirst time in the early 1990s. We now know that the principal explosions took place 251 million years ago,precisely at the point at which life was almost extinguished.

The volcanoes produced two gases: sulphur dioxide and carbon dioxide. The sulphur and other effusionscaused acid rain, but would have bled from the atmosphere quite quickly. The carbon dioxide, on the otherhand, would have persisted. By enhancing the greenhouse effect, it appears to have warmed the worldsufficiently to have destabilised the superconcentrated frozen gas called methane hydrate, locked in sedimentsaround the polar seas. The release of methane into the atmosphere explains the sudden shift in carbonisotopes.

Methane is an even more powerful greenhouse gas than carbon dioxide. The result of its release was runawayglobal warming: a rise in temperature led to changes which raised the temperature further, and so on. Thewarming appears, alongside the acid rain, to have killed the plants. Starvation then killed the animals.

Global warming also seems to explain the geological changes. If the temperature of the surface waters nearthe poles increases, the circulation of marine currents slows down, which means that the ocean floor isdeprived of oxygen. As the plants on land died, their roots would cease to hold together the soil and looserock, with the result that erosion rates would have greatly increased.

So how much warming took place? A sharp change in the ratio of the isotopes of oxygen permits us to replywith some precision: six degrees centigrade. Benton does not make the obvious point, but another author, theclimate change specialist Mark Lynas, does.2 Six degrees is the upper estimate produced by the UN's scientificbody, the Intergovernmental Panel on Climate Change, for global warming by 2100.3 A conference of some of theworld's leading atmospheric scientists in Berlin last month concluded that the IPCC's model may haveunderestimated the problem: the upper limit, they now suggest, should range between 7 and 10 degrees.4 Neithermodel takes into account the possibility of a partial melting of the methane hydrate still present in vastquantities around the fringes of the polar seas.

Suddenly, the events of a quarter of a billion years ago begin to look very topical indeed. One of thepossible endings of the human story has already been told. Our principal political effort must now be toensure that it does not become set in stone.

George Monbiot's book The Age of Consent: aManifesto for a New World Order is published by Flamingo.

References:

1. Michael J. Benton, 2003. When Life Nearly Died: The Greatest Mass Extinction of All Time. Thames andHudson, London.

2. Press Release issued by Mark Lynas, 17th June 2003. "New Evidence Warns of Global Warming'Catastrophe' this Century".

3. Eg Robert Watson, chairman IPCC, 20th November 2000. Report to the Sixth Conference of the Parties ofthe United Nations Framework Convention on Climate Change.

4. Fred Pearce, 4th June 2003. GlobalWarming's Sooty Smokescreen Revealed. New Scientist.