- The biggest-ever mass extinction of life on Earth may
have been accompanied by the smell of rotten eggs or decomposing cabbage,
geologists said yesterday.
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- At the end of the Permian era, 251 million years ago,
95% of all life went extinct - and the killer might have been foul-smelling
hydrogen sulphide.
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- Life has been wiped out on a massive scale at least five
times in geological history. The biggest, the Permian mass extinction,
opened an evolutionary doorway for the age of the dinosaurs, which also
ended in a mass extinction 65 million years ago, probably by collision
with an asteroid.
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- "The end-Permian is puzzling," Professor Lee
Kump of Penn State University told the Geological Society of America, meeting
in Seattle. "There is no smoking gun, no compelling evidence of asteroid
impact."
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- The deep oceans of the Permian were anoxic, that is,
they carried no dissolved oxygen. If sea levels rose, then many creatures
would have died. A second theory was that for some reason, surface and
deep water mixed, bringing anoxic water to the surface. The decomposition
of creatures in the deep ocean could have caused a carbon dioxide crisis;
the gas is lethal in high concentrations to many animals. However, "plants,
in general, love carbon dioxide, so it is difficult to think of carbon
dioxide as a good kill mechanism," Prof Kump said.
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- But hydrogen sulphide gas could have been the great exterminator.
Humans can smell the gas at concentrations in parts per million million.
At the bottom of the Black Sea today there are concentrations at 34 parts
per million: a toxic brew for any oxygen-consuming creature. The poisonous
soup of the Black Sea is locked away under a layer of relatively clean
water.
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- Prof Kump added that 251 million years ago, as levels
of oxygen in the atmosphere fell, the levels of hydrogen sulphide and carbon
dioxide in the oceans would have begun to poison sea and air.
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- He is looking for evidence in the form of photosynthetic
sulphur bacteria in the end-Permian rocks.
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- EducationGuardian.co.uk © Guardian Newspapers Limited
2003
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- http://education.guardian.co.uk/higher/sciences/story/0,12243,1077287,00
.html
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