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SAN FRANCISCO — The greatest extinction in the history of life may have been caused, in part, by ozone-depleting gases spewed in a massive volcanic eruption, a new study suggests. Geologists have found surprisingly high amounts of the elements fluorine and chlorine in Siberian lavas dating back 250 million years — when about 90 percent of marine species and 70 percent of terrestrial species went extinct. Benjamin Black, a graduate student at MIT, and his colleagues described their theory Dec. 13 in a poster presentation at a meeting of the American Geophysical Union
Researchers have long struggled to explain the “Great Dying” that occurred at the end of the Permian period. Some think that the extinction was a long, drawn-out affair caused by multiple factors — perhaps gradual changes in oceanic or atmospheric chemistry (SN: 5/28/05, p. 339). Others have blamed a single catastrophic event such as a belch of methane from the seafloor or an asteroid impact (SN: 2/24/01, p. 116) like the one thought to have wiped out the dinosaurs and other species 65 million years ago.
Volcanoes might be one of those calamities. In Siberia, around 250 million years ago, a series of massive volcanic eruptions spewed out lava over more than 2 million square kilometers [800,000 square miles]. Some scientists have blamed these eruptions, known as the Siberian Traps, for climatic changes that contributed to the extinction. Black and his MIT adviser, Lindy Elkins-Tanton, have been traveling to Russia for the past few summers to test such theories in the Siberian Traps.
The rocks contain tiny blobs of once-molten material, preserved like chemical time capsules from the earliest days of the eruption. Measuring the amounts of sulfur, chlorine and fluorine in those blobs, Black found surprisingly high levels of those elements — up to 0.75 percent chlorine and 1.95 percent fluorine, by weight, in one sample. That’s significantly more than the amounts found in similar deposits like the Deccan Traps in India and the Columbia River flood basalts in Washington and Oregon.
A mechanism of formation is considered in which minor hotspot volcanism is induced at, and flood basalt volcanism is triggered by seismic energy focused antipodal to, oceanic large-body impact sites
Grasby studied the formations with University of Calgary colleagues Benoit Beauchamp and Hamed Sanei. “We saw layers with abundant organic matter and Hamed immediately determined that they were layers of coal ash, exactly like that produced by modern coal burning power plants,” said Beauchamp. “Our discovery provides the first direct confirmation for coal ash during this extinction, as it may not have been recognized before,” added Sanei.