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01-21-2005, 04:27 PM
Volcanoes 'wiped out life on Earth, not giant asteroid'
By Roger Highfield, Science Editor
(Filed: 21/01/2005)
An asteroid impact did not cause the "Great Dying", when most of the planet's species became extinct 250 million years ago, scientists say today.
Instead, two new studies suggest high temperatures, toxic gases and low oxygen triggered by intense volcanic activity were to blame.
The Great Dying, the Permian-Triassic extinction, is considered the biggest catastrophe in the history of life on Earth, with 90 per cent of all marine life and almost three quarters of land-based plant and animal life becoming extinct.
Evidence has been building that the impact of a comet or asteroid triggered the extinction. But two teams point to an alternative culprit - global warming triggered by greenhouse gases from volcanoes.
"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," says Dr Peter Ward of the University of Washington, Seattle, the head of one team.
"Animals and plants on land and in the sea died at the same time, apparently from the same causes – too much heat and too little oxygen."
The researchers used chemical, biological and magnetic evidence to correlate sedimentary layers in the Karoo Basin of South Africa to similar layers in China that previous research has tied to the marine extinction at the end of the Permian period.
Karoo fossils disclosed two patterns, one showing gradual extinction over 10 million years leading to a sharp increase in extinction rate that lasted another five million years. Evidence from the marine extinction is "eerily similar" to what researchers found in Karoo.
But the team found nothing in the Karoo that would indicate an asteroid hit around the time of the extinction, though it looked specifically for impact clays or material ejected from a crater left by such an impact.
More on this Story (http://news.telegraph.co.uk/news/main.jhtml?xml=/news/2005/01/21/wvolc21.xml)
By Roger Highfield, Science Editor
(Filed: 21/01/2005)
An asteroid impact did not cause the "Great Dying", when most of the planet's species became extinct 250 million years ago, scientists say today.
Instead, two new studies suggest high temperatures, toxic gases and low oxygen triggered by intense volcanic activity were to blame.
The Great Dying, the Permian-Triassic extinction, is considered the biggest catastrophe in the history of life on Earth, with 90 per cent of all marine life and almost three quarters of land-based plant and animal life becoming extinct.
Evidence has been building that the impact of a comet or asteroid triggered the extinction. But two teams point to an alternative culprit - global warming triggered by greenhouse gases from volcanoes.
"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," says Dr Peter Ward of the University of Washington, Seattle, the head of one team.
"Animals and plants on land and in the sea died at the same time, apparently from the same causes – too much heat and too little oxygen."
The researchers used chemical, biological and magnetic evidence to correlate sedimentary layers in the Karoo Basin of South Africa to similar layers in China that previous research has tied to the marine extinction at the end of the Permian period.
Karoo fossils disclosed two patterns, one showing gradual extinction over 10 million years leading to a sharp increase in extinction rate that lasted another five million years. Evidence from the marine extinction is "eerily similar" to what researchers found in Karoo.
But the team found nothing in the Karoo that would indicate an asteroid hit around the time of the extinction, though it looked specifically for impact clays or material ejected from a crater left by such an impact.
More on this Story (http://news.telegraph.co.uk/news/main.jhtml?xml=/news/2005/01/21/wvolc21.xml)