Life on Earth snuffed out by global warming
Leigh Dayton, Science writer
January 22, 2005
SUFFOCATING global warming is to blame for the worst mass-extinction on Earth, according to international researchers tracking the cause of the "Great Dying" 250 million years ago.
Until now, circumstantial evidence suggested that an asteroid wiped out more than 90 per cent of all marine life and almost 75 per cent of all land plants and animals, like that which took out the dinosaurs 65 million years ago.
But new geochemical and fossil data reported today in the journal Science indicates that continuous volcanic eruptions in Siberia set off runaway global warming with disastrous consequences.
According to the new view, long-term planet-wide warming dramatically reduced oxygen and nutrients in the oceans and on land.
"The severe global warming had a devastating effect," said Kliti Grice, an organic geochemist who led a team of researchers from Curtin University of Technology in Perth. "Life suffocated or starved."
Professor Grice -- along with her Chinese, American, British and German colleagues -- studied two 30m-long sediment cores, one drilled in Western Australia, the other in southern China.
They discovered tell-tale compounds that showed the ocean was poisoned with sulfide and the air was choked with hydrogen sulfide -- both consistent with global warming -- and this was kickstarted by the well-document Siberian eruptions.
In a second study, an American and South African group -- led by paleontologist Peter Ward of the University of Washington in Seattle -- pieced together the fossil records of land-animal extinctions from sites in South African, Europe and North America.
They discovered that a 10-million-year-long period of gradual extinctions led to a final extinction "pulse" 250million years ago.
Professor Ward said the pattern of extinction was
"eerily similar" to evidence about marine extinctions, providing a glimpse of what could happen with long-term global warming.
"Animals and plants, both on land and in the sea, were dying at the same time, and apparently from the same causes -- too much heat and too little oxygen," he added.
According to Professor Ward, early reptiles and amphibians were hard-hit during the Great Dying.
In Perth, paleontologist Kathleen Grey, of the Geological Survey of Western Australia, welcomed the "first concrete evidence" of what triggered the largest of the planet's five great extinction events.
While she said the new findings were "significant" and "hard", she predicted they would not settle the debate entirely as scientists often found it hard to give up their favourite theories.
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