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viernes, 29 de mayo de 2009

A Supervolcano's Fallout: Mass Extinction

This placid view of Gouchang, Guizhou, China belies the region's violent history. New evidence uncovered from ancient lava deposits there suggests a supervolcano eruption was the direct cause of the mid-Permian extinction, which killed massive amounts of marine life, 260 million years ago.

Carbon from a massive volcanic eruption caused a mass extinction on Earth 260 million years ago, according to a new study. It's the first definitive link between a volcano and extinction.

The study strengthens the case that so-called supervolcano eruptions lead to massive climate change and may be responsible for many of the most devastating mass murders in Earth's history.

Although not one of the "big five" mass extinctions, the mid-Permian extinction has long been considered an important, if puzzling, event. Scientists have eyed massive lava deposits in the Emeishan region of southwestern China as the murder weapon, but they've been unable to show a connection.

Now Paul Wignall of the University of Leeds and a team of researchers have found that a host of algae and other marine species died out suddenly, along with many land-dwelling animals, right after a huge eruption. Chemical evidence also revealed a sharp up-tick in atmospheric carbon at the time, possibly spewed into the atmosphere when lava infiltrated and cooked pre-existing coal seams. The team's work is published in the current issue of the journal Science.

Compared to some of the largest volcanic cataclysms in geologic history -- called Large Igneous Provinces (LIP)s -- Emeishan is small; its lavas cover "only" around 250,000 square kilometers (96,526 square miles), an area about the size of Colorado.

Still, it was enough to have a global impact on life and climate. And the team's discovery adds credence to the idea that several major mass extinctions may have been caused by LIPs.

"Every crisis in the past 300 million years coincides with a LIP eruption," Wignall said. "So there's clearly some connection." Researchers suspect that the Siberian Traps eruption, which occurred just 10 million years later, was responsible for the Permian-Triassic extinction, the worst mass dying of all time. And though they agree that the huge eruptions disrupted climate, views are split over whether it was global warming from the excess carbon, or global cooling from large amounts of sulfur dioxide (SO2), that did the killing.

"This is an important study, as it tries to link basaltic eruptions directly to the extinction," Henrik Svensen of the University of Oslo said. "It is difficult to know exactly what the organisms died from, if judging from the fossils themselves."

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