The other environment has sediments composed mostly of calcium carbonate, which is produced by organisms living in the water—such as corals—and chemical processes. These waters are clear, as in the Caribbean.
The seas rise and fall as the climate shifts and as the Earth's tectonic plates move. As a result, these two types of marine environments expand and contract, Peters said.
The marine animals in them sometimes disappear when their shallow-water environments vanish or are dramatically altered.
"It is not just a matter of rising and falling sea level, it is the environmental consequences that go along with changes in sea level that I'm measuring in this study," Peters said.
He found that all five mass extinction events, and many of the smaller events in the fossil record, are associated with changes in sea level and sedimentation.
Shrinking Habitat
Wolfgang Kiessling, a paleontologist at Humboldt University in Berlin, Germany, is an expert on mass-extinction events.
While he doubts that changing sea levels alone drive mass die-offs, he said the study is important because it shows that habitat size is relevant to species diversity.
"The bigger habitat you have, the more species you can sustain—and when habitat shrinks, you get increased risk of extinction," said Kiessling, who was not involved in the study.
However, he added, changes in sea level alone are insufficient to explain the magnitude of mass-extinction events such as the one 65 million years ago, which wiped out the dinosaurs. (See "Volcano Theory of Dino Die-Off Gets New Support" [November 5, 2007].)
"There's got to be more," he said, "something like supervolcanoes, asteroid impacts. … "
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