Microscopic villain may be culprit in ancient mass extinction

Posted Apr 3, 2014 by Martin Laine
Something killed off 90 percent of the Earth’s living species 250 million years ago. The prevailing theory has been that increased volcanic activity caused drastic changes in the Earth’s climate and the species could not adapt fast enough.
José-Luis Olivares/MIT
Now a team of MIT researchers have found evidence that the real culprit is a methane-producing microbe called methanosarcina, according to an article on the MIT News website. Their findings have been published in the Proceedings of the National Academy of Sciences.
While increased volcanic activity would result in the trapping of greenhouse gases causing global warming, depletion of the ozone layer, and an increase in acid rain, it would not be drastic enough to explain the rapid rate of extinction.
“A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease,” said Gregory Fournier, a post-doctoral fellow at MIT. “Instead we see the opposite: a rapid, continuing increase. That suggests a microbial expansion.”
The researchers base their conclusions on three sets of evidence: the rapid rise of carbon dioxide in the oceans at the time; development of methanosarcina’s ability to convert organic carbon in the water into methane; and sediment showing increased amounts of nickel.
“A lot of this rests on the carbon isotope analysis,” said lead researcher Daniel Rothman, a geophysics professor at MIT. He said the data was strong and clear for this geological period. “If it wasn’t such an unusual signal, it would be harder to eliminate other possibilities.”
But in order for a microscopic species to create enough methane to cause extinction, there would have had to be huge proliferation in their numbers. This is where the nickel comes in, because the methanocarcina would have needed the right combination and amounts of mineral nutrients to fuel their growth, and nickel was key to that.
The team points to great deposits of nickel that resulted from a series of in Siberia that occurred at about the same time.