Volcanic activity eyed in "Great Dying" 250 million years ago
The Washington Post
WASHINGTON — Scientists call it "The Great Dying," a 250 million-year-old catastrophe that wiped out 90 percent of ocean species and 70 percent of land species in the biggest mass extinction in Earth's geologic history.
The cause of the cataclysm is a matter of great dispute among paleontologists, but research released yesterday offers new evidence that global warming caused by massive and prolonged volcanic activity may have been the chief culprit.
Huge amounts of carbon dioxide were released into the air from open volcanic fissures known to geologists as the "Siberian Traps," researchers said, triggering a greenhouse effect that warmed the Earth and depleted oxygen from the atmosphere, causing environmental deterioration and, finally, collapse.
A second set of findings suggested that the warming also crippled the oceans' ability to refresh their oxygen supply, causing the seas to go sterile, destroying marine life and allowing anaerobic bacteria (which do not require oxygen) to release poisonous hydrogen sulfide into the air.
The two reports, prepared independently, cast doubt on another theory: that "The Great Dying" was caused by the impact of an asteroid or comet like the one that triggered the extinction of the dinosaurs 65 million years ago. Both studies were published yesterday by Science Express, the online version of the journal Science.
"This is not a world that is happy and then goes 'bang!' " said University of Washington paleontologist Peter Ward, leader of one of the studies. "This is a world that's in trouble for a long time, and then it gets in even worse trouble."
Ward led a team of scientists in a seven-year project to chronicle 126 fossil skulls in a 1,000-foot-thick deposit of sedimentary rock in southeastern South Africa's Karoo Basin.
Ward said the team's excavations showed a steady decline in the number of species over about 10 million years, followed by a sudden plunge 250 million years ago at the boundary between the Permian and Triassic periods of geologic time. The interval corresponds to a period of prolonged volcanic activity over one-third of modern-day Siberia.
Temperatures climbed globally as carbon dioxide poured into the atmosphere and oxygen levels fell, forcing gasping animals to gather at sea level, he said. "And the plants are not dealing well with the heat" either, he added. "Eventually, the imbalance reaches a critical point and everything dies."
Labels: volcanoes-ancient vulcanism
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