Another view of mass extinctions is heard

A University of Washington paleontologist says most mass extinctions were caused by gradual climate change and not catastrophic asteroid impacts.

And that, said Peter Ward, means we might be in the midst of another mass extinction.

Other paleontologists, however, disagree with Ward and the dispute is turning into a full-scale academic brawl.

"It's a shoot-out at the OK Corral," said Ward, who presented his climate change theory during NASA's Astrobiology Science Conference in the nation's capital last week.

He says five major extinctions have occurred during the past 500 million years -- the Ordovician, the Devonian, the Permian, the Triassic and the Cretaceous. There has been widespread agreement that the Cretaceous extinction, which wiped out the dinosaurs 65 million years ago, was triggered by an asteroid impact.

"It's such a simple idea that for 20 years we just assumed the same was true for all extinctions," says Ward.

But he says there's mounting evidence the Permian extinction around 250 million years ago was caused by huge volcanic eruptions in Siberia, which led to catastrophic climate change. Ward believes such "greenhouse extinctions" are the rule and asteroid impacts the exception.

Copyright 2006 by United Press International