for National Geographic News
A surge of undersea volcanic activity about 93 million years ago sapped the oceans of oxygen, triggering a mass extinction of marine life, a new study finds.
The catastrophic event buried a thick mat of organic matter—from large clams to single-celled algae—on the seafloor, which today is a major source of oil.
The new findings allow scientists for the first time to directly pinpoint undersea magmatism—the formation of rock from cooling magma—in the dino-era carnage.
The research also opens a window onto the way Earth responds to large inputs of greenhouse gases, experts say.
(Explore an interactive on the greenhouse effect.)
At the time of the mass die-off, Earth's climate was warm and muggy, and ocean circulation was sluggish, according to study co-author Steven Turgeon, an earth scientist at the University of Alberta in Edmonton, Canada.
Palm trees grew on the North Slope of Alaska and carbon dioxide levels were 3 to 12 times higher than today's concentrations. The carbon dioxide spike was mostly a result of increased volcanic activity linked to Earth's rapidly shifting tectonic plates, Turgeon said.
"And now we have this magmatic pulse that happened at that time—a huge one by what we can tell—and that's what caused this chain reaction to drive the oxygen from the ocean and cause this mass extinction," he said.
(Related: "Mass Extinctions Due to Sea Level Changes, Study Says" [June 16, 2008].)
Turgeon and colleague Robert Creaser report their findings in tomorrow's issue of the journal Nature.
Scientists have long suspected that undersea volcanism could be responsible for the marine mass extinction, an anoxic—or oxygen-depleting—event known as the OAE2. But until now the evidence was "sketchy," Turgeon noted.
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