Earth’s largest mass extinction may be due to microorganisms

Nature : The most severe extinction event in the fossil record may not have been caused by overactive Siberian volcanoes, as had been previously proposed. Instead, tiny microbial organisms could be to blame. According to a recent study by Daniel Rothman of MIT and colleagues, about 250 million years ago large amounts of organic matter accumulated on the ocean floor and single-celled microbes called Methanosarcina evolved to eat it. As they ate, the microbes converted the marine organic carbon to methane and released it into the atmosphere in large quantities. Volcanoes may have still played a part by adding nickel to the ocean sediments, which would have aided the microbes’ digestion. But the researchers do not yet understand exactly why the increased levels of atmospheric methane led to what has been termed the “Great Dying” of both land- and ocean-dwelling animals at the end of the Permian period.