Nearly 90 percent of all species on Earth were suddenly wiped out about 252 million years ago, making it the largest mass extinction in the planet’s history, and according to a new study, tiny climate-changing microbes might have been the killers, not asteroids, volcanoes or raging coal fires as previously believed.
The study, conducted by a team of researchers at Massachusetts Institute of Technology, or MIT, said that Methanosarcina, a form of methane-producing microbes, suddenly flourished in abundance in ancient oceans, ejecting huge amounts of methane into the atmosphere, dramatically changing the planet's climate and the chemistry of its oceans.
“The reason for the sudden, explosive growth of the microbes, new evidence shows, may have been their novel ability to use a rich source of organic carbon, aided by a sudden influx of a nutrient required for their growth: the element nickel, emitted by massive volcanism at just that time,” the researchers said in a statement.
According to the study, published in the Proceedings of the National Academy of Science, volcanoes while not totally free of blame, have been demoted to accessories to the crime. Earlier studies have suggested that something caused a significant uptick in the amount of carbon-containing gases -- carbon dioxide or methane -- produced at the time of the mass extinction.
While some researchers have suggested that these gases might have been produced by volcanic eruptions, the MIT researchers say that such eruptions were not large enough to account for the carbon seen in the sediments. In addition, MIT's scientists say, the changes observed in the amount of carbon over time also do not fit the volcanic model.
“A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease,” Gregory Fournier, a researcher at MIT, said in the statement. “Instead, we see the opposite: a rapid, continuing increase. That suggests a microbial expansion.”
The genomic analysis of Methanosarcina revealed that the organism had acquired a particularly fast means of producing methane -- through gene transfer from another microbe. Under the right conditions, this genetic acquisition helped the microbe undergo a dramatic growth spurt, rapidly consuming a vast reserve of organic carbon in ocean sediments.
The study also revealed that nickel served as the mineral nutrient to support Methanosarcina, providing the fuel for the microbe’s explosive growth. According to the researchers, the burst of methane would have increased carbon dioxide levels in the oceans, resulting in ocean acidification.
“While no single line of evidence can prove exactly what happened in this ancient die-off, the cumulative impact of all these things is much more powerful than any one individually,” Daniel Rothman, a professor of geophysics at MIT, said. “While it doesn’t conclusively prove that the microbes did it, it does rule out some alternative theories, and makes a strong and consistent case.”