for National Geographic News
Prehistoric global warming periodically wiped out much of the planet's wildlife and created exceptionally well-preserved fossils of the remains, according to a new study.
The enormous death toll inflicted by episodes of lethal atmospheric changes may have prevented life on Earth from being wiped out altogether, the study's author adds.
Greg Retallack, geologist at the University of Oregon, presented his study this week at the Geological Society of America's annual meeting in Salt Lake City, Utah.
Retallack says huge releases of carbon dioxide and methane starved the Earth of oxygen, causing mass extinctions over the last 500 million years.
He adds that the resulting buildup of billions of dead prehistoric creatures may have acted as a carbon sink, reducing CO2 in the atmosphere and preventing the Earth from becoming as hot and lifeless as Venus.
"It was the widespread death and burial of animals and their carbon that created fossil bonanzas, the likes of which may have saved us from the heat sterilization experienced by our sister planet," Retallack said.
He bases his theory on a compilation of unusually well preserved fossils found around the world, including fish, crustaceans, insects, and other ancient life forms.
The fossil record indicates about 40 episodes of exceptional preservation, he saysepisodes that coincide with periods of global warming, when the Earth was low in oxygen.
"Lowered levels of oxygen can kill fish and other creatures and also preserve their carcasses from dismemberment and decay," Retallack said.
In some mass extinctions, the scientist says, greenhouse gases "ramped up to intolerable levels of more than ten times the modern level of atmospheric carbon dioxide."
Volcanic activity and outbursts of undersea gases are the prime suspects for these periods of lethal pollution.
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