Ebb and flow of sea may have caused mass extinctions

June 16th, 2008 - 2:46 pm ICT by IANS  

Washington, June 16 (IANS) Crashing asteroids or volcanic eruptions are believed to have wiped out dinosaurs 65 million years ago and caused other mass extinctions. But a new study suggests that there have been other culprits as well, most notably the gigantic ebb and flow of oceans. “The expansion and contraction of ocean environments have profound effects on life on earth,” said Shanan Peters of the University of Wisconsin, author of the study.

Changes in ocean environments that have a bearing on sea levels exert a driving influence on rates of extinction - the vanishing of animals and plants - and generally determine the composition of life in the oceans, said Peters.

Since life appeared on earth 3.5 billion years ago, scientists believe as many as 23 mass extinctions took place. During the past 540 million years, five well-documented extinctions wiped out the bulk of marine plants and animals species.

In the case of dinosaurs, a crater suggests they were wiped out as the result of a large asteroid crashing into the planet.

But the causes of other mass extinction events have been murky, at best - scientists have been unable to pin down the exact causes.

“Paleontologists have been chipping away at the causes of mass extinctions for almost 60 years. Impacts aren’t associated with most extinctions. There have also been studies of volcanism and some eruptions correspond to extinction, but many do not,” said Peters, whose work was supported by the National Science Foundation.

Arnold I. Miller, paleobiologist at the University of Cincinnati, said the new study is striking because it establishes a clear relationship between the tempo of mass extinction events and changes in sea level and sediment.

Over the course of hundreds of millions of years, the oceans have expanded and contracted in response to the shifting of the Earth’s tectonic plates and climate changes.

There were periods of the planet’s history when vast areas of the continents were flooded by shallow seas, such as the shark and mosasaur-infested seaway that neatly split North America during the age of the dinosaurs.

As those seas drained, mosasaurs and giant sharks went extinct. The findings of the study appeared Sunday in the online edition of the journal Nature.

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