The 500-million-year history of life on Earth is a series of booms and busts. But while the busts, or extinctions, can be either sudden or gradual, the booms, or diversifications, of new organisms rarely occur quickly, according to a new study by a National Science Foundation (NSF)-funded scientist at the University of California at Berkeley. A paper on the subject appears in this week's issue of the journal Nature.

"This research has profound implications for our ongoing impact on Earth's fragile biotic communities and ecosystems," says Rich Lane, program director in NSF's division of earth sciences, which funded the research.

A statistical analysis of the rates of extinction and origination in the fossil record shows that life seldom rebounds rapidly from an extinction. The results imply that the diversification of life obeys "speed limits" set by evolutionary processes, said study author James Kirchner of UC-Berkeley.

"There seem to be biological mechanisms that limit diversification of new organisms and control which ones become successful enough to persist," he said. "Biodiversity is slow to recover after an extinction."

This apparent speed limit on the rate at which surviving organisms evolve and diversify has major implications for present- day extinctions.

"If we substantially diminish biodiversity on Earth, we can't expect the biosphere to just bounce back. It doesn't do that. The process of diversification is too slow," Kirchner said. "The planet would be biologically depleted for millions of years, with consequences extending not only beyond the lives of our children's children, but beyond the likely lifespan of the entire human species."

Kirchner has been mining a fossil database created by the late University of Chicago paleontologist Jack Sepkosk
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-292-8070
National Science Foundation
4-Jan-2002