In a paper published Jan. 20 by Science Express, the online version of the journal Science, the researchers say they have found no evidence for an impact at the time of "the Great Dying" 250 million years ago. Instead, their research indicates the culprit might have been atmospheric warming because of greenhouse gases triggered by erupting volcanoes.

The extinction occurred at the boundary between the Permian and Triassic periods at a time when all land was concentrated in a supercontinent called Pangea. The Great Dying is considered the biggest catastrophe in the history of life on Earth, with 90 percent of all marine life and nearly three-quarters of land-based plant and animal life going extinct.

"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," said UW paleontologist Peter Ward, lead author of the paper. "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."

The paper is to be published in the print edition of Science in a few weeks. Co-authors are Roger Buick and Geoffrey Garrison of the UW; Jennifer Botha and Roger Smith of the South African Museum; Joseph Kirschvink of the California Institute of Technology; Michael De Kock of Rand Afrikaans University in South Africa; and Douglas Erwin of the Smithsonian Institution.

The Karoo Basin of South Africa has provided the most intensively studied record of Permian-Triassic vertebrate fossils. In their work, the researchers were able to use chemical, biological and magnetic evidence to correlate sedimentary layers in the Karoo to similar layers in China that previous rese
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
20-Jan-2005