送交者: cornbug 于 2005-1-23, 13:02:35:
可能是因为全球变暖而不是大行星撞地球所至。
Global Warming May Have Caused Extinction -Study
Thu Jan 20, 2:05 PM ET
Science - Reuters
WASHINGTON (Reuters) - Global warming (news - web sites) and not a giant asteroid may have nearly wiped out life on Earth some 250 million years ago, an international team of scientists said on Thursday.
The mass extinction, known as the "Great Dying," extinguished 90 percent of sea life and nearly three-quarters of land-based plants and animals.
There has been recent evidence that a big asteroid or meteor hit the Earth and triggered the catastrophe, but researchers say they now have evidence that something much more long-term -- global warming -- was the culprit.
Kliti Grice of Curtin University of Technology in Perth, Australia, and colleagues studied sediment cores drilled off the coasts of Australia and China and found evidence the ocean was lacking oxygen and full of sulfur-loving bacteria at that time.
This finding would be consistent with an atmosphere low in oxygen and poisoned by hot, sulfurous, volcanic emissions, they wrote in a report published in the journal Science.
A second team led by Peter Ward at the University of Washington looked at fossil evidence in South Africa and found little evidence of a catastrophe and instead signs of a gradual die-off.
They examined 126 reptile and amphibian skulls from the Karoo Basin in South Africa, where there is an exposed piece of dried sediment from the end of the Permian Era and the beginning of the Triassic, 250 million years ago.