( New discoveries about the timing and sp...)India's smoking gun: Dino-killing eruptions

The Deccan Traps of India are one of Earth's largest lava flows ever, with the potential of having wreaked havoc with the climate of the Earth - if they erupted and released climate-changing gases quickly enough. French and Indian geologists have now identified a 600-meter (2000-foot) thick portion of the lava that may have piled up in as little as 30,000 years - fast enough to have possibly caused a deadly global climate shift.

"Our working hypothesis is that the majority of the total volume of lava might have been erupted in only a few major events spread over only a small fraction of millennia," said Anne-Lise Chenet of the Laboratoire de Paleomagnetisme, Institut de Physique du Globe de Paris (IPGP).

To test that hypothesis, the researchers have combined already known ages of the traps gathered from radiometric dating with magnetic fields frozen in the rocks. Volcanic rocks record information about the Earth's magnetic field with magnetic minerals that align with Earth's field like millions of tiny compasses before the lava cools. When the lava solidifies, the compasses are locked in place.

Lava layers that erupted within two or three centuries of each other will record similar magnetic fields, explains Chenet. Longer than that and the natural changes in Earth's magnetic field start to show up. The team also incorporated information about the lava's chemistry, the way it flowed and piled up and the red weathered soils between lava layers to estimate the timing and number of major volcanic pulses.

All that information points to the 600 meters (2000 feet) of lava pouring out in as little as 30,000 years. This is enough to have possibly released a climate-altering amount of sulfur gases, says Chenet. An estimate of just how much gas is still be
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Source:Geological Society of America