MIT professor of geophysics Daniel Rothman stands next to part of the Xiakou formation in China. His right hand rests on the layer that marks the time of the end-Permian mass extinction event. Samples from this formation provided evidence for large amounts of nickel that were spewed from volcanic activity at this time, 252 million years ago. (Photo courtesy of Daniel Rothman/MIT)

As extinctions go, they don’t come any bigger.

Some 250 million years ago, an event or series of events wiped out 90 percent of the Earth’s species. It happened over the course of about 60,000 years, the blink of an eye in geologic time.

Of the five great extinctions, this was The Big One. Brutal and indiscriminate, the so called “end Permian” extinction (at the end of the Permian period) claimed vertebrates and invertebrates alike from the land and from the sea, with no quarter given even to insects. That’s why it’s been called “The Great Dying.”

The cause, scientists have theorized, was a “mysterious disruption to the Earth’s carbon cycle.” That, in turn, had been attributed to massive Siberian volcanic activity, a dramatic trigger with a dramatic result.

But new research published this week has produced a new theory, less explosive but equally lethal: the damage was done by a microbe.

Called “Methanosarcina,” it blossomed in the seas and  pumped methane into the atmosphere, wreaking havoc with the climate and the chemistry of the oceans. The microbe flourished on a diet of nickel, multiplied like crazy and effectively suffocated the planet.

The research, published in the Proceedings of the National Academy of Science, is the work of seven MIT researchers, led by geophysicist Daniel Rothman and postdoc Gregory Fournier.

Under the headline, “ancient whodunit may be solved,” the work is explained for non-scientists by David L. Chandler at MIT News and at The Conversation.

According to the researchers, there’s genetic evidence that shows a change in Methanosarcina at that time, “allowing it to become a major producer of methane from an accumulation of organic carbon in the water.”

“Volcanoes are not entirely off the hook,” writes Chandler. “They have simply been demoted to accessories to the crime. 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 burst of methane would have increased carbon dioxide levels in the oceans, resulting in ocean acidification — similar to the acidification predicted from human-induced climate change. Independent evidence suggests that marine organisms with heavily calcified shells were preferentially wiped out during the end-Permian extinction, which is consistent with acidification.”

The theory has its skeptics. Mark Reichow at the University of Leicester, quoted at The Conversation:

argues that there is no evidence that the increased nickel came from Siberian volcanoes. Rothman agrees that current data cannot identify the source of the nickel.  “This is an interesting hypothesis,” he told The Conversation, “but I think that Great Dying was the doing of many ‘kill mechanisms’ rather than just a single mechanism suggested here,” Reichow said.

 

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