March 20, 2008 -- The gigantic Deccan Traps eruptions 65 million years ago may have released colossal amounts of climate-chilling, dinosaur-freezing sulfur into the atmosphere, according to a new study.
If true, this would mean that the famous Chicxulub meteor impact played, at most, a supporting role in ending of the Age of Reptiles.
Gases from a series of eruptions of the Deccan Traps may have "battered away" at life on the planet at the time, leading to the mass extinctions, explained geologist Stephen Self of the U.K.'s Open University in Milton Keynes.
The severe cooling effect of the sulfur, which perhaps struck several times over hundreds of thousands of years and lasted for centuries each time, may have been the real cause of the mass extinction event at the end of the Cretaceous.
The new study is just one of a series by an array of researchers in the last two years investigating the Deccan Traps' role in the most famous turning point in Earth's history, sometimes called the K-T mass extinction event.
Self and his colleagues obtained an inkling of how much sulfur and chlorine gas was released by measuring the gases found inside tiny and rare air bubbles in mineral crystals within Deccan lava rocks. What they found suggests that the Deccan eruptions could have released from 3.6 to 5.4 teragrams (million metric tons) of sulfur dioxide for every cubic kilometer of lava.
Multiply that by the individual eruptive pulses of 1,000 cubic kilometers of lava at a time, and the truly gigantic amount of sulfur released into the atmosphere becomes apparent.
"A semi-persistent gas release of hundreds to thousands of teragrams of (sulfur dioxide) per year can be envisaged for each Deccan eruption," Self and his team report.
"There's plenty of it, and it would be pumped into the atmosphere," Self told Discovery News.
Unfortunately there are very few models to test what that amount of sulfur dioxide would do to Earth at that time, he said.
What's generally known is that unlike carbon dioxide, sulfur dioxide reflects sunlight back into space and is considered a climate cooler. But, whereas carbon dioxide can survive for centuries in the atmosphere, sulfur dioxide is washed out in a matter of months and years. So the cooling effect lasts only a little longer than the eruption.
Still to be evaluated are the effects of other gases released from the huge eruptions. Chlorine and other "halogen" gases like fluorine and bromine are released by lavas, but usually play minor roles in modern-day volcanic eruptions.
"Yet, given the colossal amounts of magma erupted, the amount of halogens delivered to the atmosphere may have been dramatic as well," suggests Bruno Scaillet of France's Université d'Orléans.
Nor it is clear that what was learned about gas releases from the 1991 Mount Pinatubo eruption in the Philippines is much help, according to Scaillet.
Despite being the largest eruption studied by modern science, it was an entirely different sort of volcano. What's more, it was on the order of a 1000 times smaller than the Deccan eruptions, he writes in a separate report in the same issue of Science.
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