April 1, 2014
Mass Extinction During The Great Dying Caused By Microbial Methane
Brett Smith for redOrbit.com - Your Universe Online
Over 250 million years ago a mysterious event dubbed the Great Dying wiped out 90 percent of all species on Earth.
Scientists have debated the culprit behind this mass extinction event for years, and a new study from MIT researchers has concluded that countless, tiny microbes released catastrophic amounts of methane into the atmosphere – choking off species that could not adapt.
Previous research has fingered raging volcanoes releasing copious amounts of carbon dioxide as the perpetrator – but the new study has claimed that volcanic activity was simply an accessory to the crime. Published in the Proceedings of the National Academy of Sciences, the new research said heavy volcanic activity at the time caused a sudden release of nickel – a nutrient necessary for the growth of the methane-producing archaea called Methanosarcina.
In the study, scientists looked at three separate sets of evidence. First, geochemical data revealed a dramatic boost of carbon dioxide in the oceans at the time of the Great Dying. Second, genetic information indicates a change in Methanosarcina at that time, causing it to become a main producer of methane from the build-up of carbon dioxide in the water. Finally, sediments show an abrupt rise in the quantity of nickel deposited at precisely this time.
The carbon deposits indicate that something caused a substantial uptick in the quantity of carbon-containing gases, either greenhouse gas or methane, developed at the time of the mass extinction. Some scientists have said that these gases could have been released by the volcanic eruptions that created the Siberian traps, a substantial formation of volcanic stone produced by the biggest eruptions in Earth's known geological history. However, calculations by the MIT team demonstrated that these eruptions were not sufficient to account for the carbon seen in the sediments. Even more noticeably, the variations in the quantity of carbon over time don't fit the volcanic model, the study team said.
"A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease,” said study author Gregory Fournier, a post-doctoral researcher at MIT. "Instead, we see the opposite: a rapid, continuing increase."
“That suggests a microbial expansion," he added, as the growth of microbial populations is one of the few phenomena capable of boosting carbon production at the rate seen during this time.
To see which microorganisms were releasing all that methane, the study team created a detailed map of Methanosarcina’s genetic history, which revealed that it acquired a particularly fast means of making methane from another microbe around the time of the Great Dying. This would have allowed the microbe to experience an impressive growth spurt, rapidly going through a vast reserve of oceanic carbon in the process.
The final piece of the puzzle was a new analysis of sediments in China, which showed nickel increased dramatically after the Siberian eruptions, which would fuel Methanosarcina’s exponential growth.
While the new study isn’t the final nail in the coffin, "the cumulative impact of all these things is much more powerful than any one individually,” said study author Daniel Rothman, an MIT professor of geophysics.