ANN ARBOR---Some 34 million years ago, almost 90 percent of the tiny, shell-bearing sea creatures living along the U.S. Gulf Coast were wiped out and replaced by completely new species of shellfish or mollusks. The same pattern was occurring worldwide, marking the largest global mass extinction since the dinosaurs disappeared. Until now, the cause behind the mass extinction event was a mystery.
Using a new technique that is revolutionizing the way scientists study ancient climate and temperature change, researchers at the University of Michigan and Syracuse University showed that colder winters along the Gulf Coast resulted in the mass extinction at what is known in geological time as the Eocene/Oligocene boundary. Their research is being published in the Oct. 19 issue of Nature.
Their findings are based on an analysis of the chemical composition of fossilized "ear stones," called otoliths, from a group of fish that survived the mass extinction event. The technique enabled the researchers to determine the temperature of the water during winters and summers, which had not been done before.
"We found that while the summer temperatures remained the same, winter temperatures dropped 4 degrees Celsius," says Linda C. Ivany, a visiting assistant professor of earth sciences at Syracuse University. "Paleontologists had always suspected that temperature changes had something to do with the extinction, but we couldn't prove it. Mean annual temperature records for the Gulf Coast that exist for that time period don't show any change. But they don't tell you about seasonal variations in temperature."
Ivany collaborated on the project with Kyger C. Lohmann, U-M professor of geological sciences, and William Patterson, assistant professor of earth sciences at SU. She began the project at U-M in 1998, when she was a Fellow of the Michigan Society and assistant professor of geological sciences.
Lohmann developed a method to collect tiny
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Contact: Nancy Ross-Flanigan
rossflan@umich.edu
734-647-1853
University of Michigan
17-Oct-2000