January 20, 2005 5:22 PM PST

Global warming, not asteroid, cause of extinction?

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Two hundred and fifty million years ago, the majority of life on earth may have suffocated.

The "Great Dying," a catastrophic event that killed 90 percent of Earth's marine life and 75 percent of the life on land, was caused by a combination of warmer temperatures and lower oxygen levels, according to a recent study by researchers at the University of Washington.

In other words, the extinction was precipitated by global warming, rather than an asteroid collision, the reigning theory.

The findings, to be published in the magazine Science, are largely based on comparisons of fossils found in South Africa's Karoo Basin and in China. Chemical, biological and magnetic materials found in the fossils from both sites are quite similar. Further, there is a lack of evidence in the Karoo fossils pointing to a sudden collision between planetary objects.

"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," paleontologist Peter Ward said in a statement. "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."

Ward believes that continuous volcanic eruptions from an area known as the Siberian Traps bathed the planet in methane, which warmed temperatures. Concurrently, oxygen levels in the atmosphere dropped to 16 percent, the equivalent of living on a 14,000-foot mountain.

Scientists and the public have debated the causes and dangers of global warming for years. While a number of scientists believe that global temperatures rise and fall in cycles, many believe human activity is currently contributing to an upward spike in temperatures.

Either way, things are getting warmer. A spring-summer sea lane running across the top of Siberia is expected to open in a few years.

The mass extinction occurred at the boundary between the Permian and Triassic periods at a time when all land was concentrated in a supercontinent called Pangaea. The dinosaurs went extinct at a later time, but many reptiles expired in the Permian extinction. Later, the Permian creatures were reincarnated as Texas crude oil.

 

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