Collapse of simple life forms linked to mass extinction 200 million...( A mass extinction about 200 million y...)

A mass extinction about 200 million years ago, which destroyed at least half of the species on Earth, happened very quickly and is demonstrated in the fossil record by the collapse of one-celled organisms called protists, according to new research led by a University of Washington paleontologist.

"Something suddenly killed off more than 50 percent of all species on Earth, and that led to the age of dinosaurs," said Peter Ward, a UW Earth and space sciences professor.

Evidence indicates the massive die-off was linked with an abrupt drop in productivity, the rate at which inorganic carbon is turned into organic carbon through processes such as photosynthesis. The waning productivity coincided with a sharp decline in radiolaria (included among protists), which was the focus of the new research. One example of productivity, Ward explained, occurs in the spring when fertilizer washes into waterways and triggers large algae blooms. The processes at work in that scenario were reversed 200 million years ago, he said.

There is no definitive evidence yet on what caused the demise of so many species, Ward said. However, the suddenness of the event is similar to two better-known mass extinctions one 250 million years ago at the end of the Permian period that killed some 90 percent of all species, the other 65 million years ago at the end of the Cretaceous period that sent the dinosaurs into oblivion.

The extinction 200 million years ago, at the boundary between the Triassic and Jurassic periods, killed the last of the mammal-like reptiles that once roamed the Earth and left mainly dinosaurs, Ward said. That extinction happened in less than 10,000 years, in the blink of an eye, geologically speaking.

Ward is the lead author on a paper detailing the evidence, published in the May 11 edition of the journal Science. Others participating in the research are James Haggart and Howard Tipper of the Geological Survey of Canada in Vancouver, British Columbia; Elizab
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
9-May-2001