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An eruption-fueled extinction?

Wednesday, 11 January 2012
by Jennifer Chu

The Siberian Traps were created about 250 million years ago by massive volcanic eruptions. The lava that covered the land formed flat plains as it cooled. Photo: NASA Earth Observatory

Enormous volcanic eruptions may have triggered the worst extinction in Earth’s history.

Around 250 million years ago, the most devastating mass extinction in Earth’s history marked a definitive end to the Permian geologic period. The global event extinguished more than 90 percent of the planet’s marine species and 70 percent of its terrestrial species. Exactly what caused the collapse has been an ongoing puzzle for scientists: Their theories have included massive volcanic eruptions, an asteroid impact and the formation of the supercontinent Pangaea.

Now researchers at MIT and elsewhere have found fresh evidence that the mass extinction may have been triggered by enormous volcanic eruptions that gave rise to the Siberian Traps, a wide expanse of volcanic rock in present-day Russia. The researchers discovered that these eruptions spewed vast amounts of gases into the atmosphere, possibly setting off a cascade of environmental effects that led to the end-Permian collapse. The team published their findings this week in the online edition of Earth and Planetary Science Letters.

Lead author Benjamin Black, a PhD student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says emissions of sulfur, chlorine and fluorine from the Siberian Traps could have been up to one million times the amount released from all of today’s volcanoes in a typical year. While the volcanoes that generated the Siberian Traps likely erupted over an extended period, the total amount of gases released provides scientists tangible evidence for a potential cause of the end-Permian extinction.

“We have concrete numbers that we can put on these gases that would have been erupting about 250 million years ago,” Black says. “These numbers give us a much better chance of being able to evaluate whether the Siberian Traps caused the extinction.”

Black worked with former MIT professor Linda Elkins-Tanton, director of the Department of Terrestrial Magnetism at the Carnegie Institution for Science in Washington, D.C., to measure the amount of gas trapped in volcanic rock obtained from the Siberian Traps. Three years ago, the team trekked to central Siberia, a region composed of flood basalts — remnants from immense lava eruptions hundreds of millions of years ago that blanketed the area and hardened into rock formations.

“When you go in by helicopter, you see trees until the horizon, but then there’s a river, and suddenly you see these immense cliffs of black basalts,” Black says. “In some places, if you’re very lucky, you can see them sitting directly on the Permian sedimentary rocks.”