Ancient whodunit may be solved

Evidence left at the crime scene is abundant and global: Fossil remains show that sometime around 252 million years ago, about 90 percent of all species on Earth were suddenly wiped out — by far the largest of this planet’s five known mass extinctions. But pinpointing the culprit has been difficult, and controversial. Now, a team of MIT researchers may have found enough evidence to convict the guilty parties — but you’ll need a microscope to see the killers.

The perpetrators, this new work suggests, were not asteroids, volcanoes, or raging coal fires, all of which have been implicated previously. Rather, they were a form of microbes — specifically, methane-producing archaea called Methanosarcina — that suddenly bloomed explosively in the oceans, spewing prodigious amounts of methane into the atmosphere and dramatically changing the climate and the chemistry of the oceans.

Volcanoes are not entirely off the hook, according to this new scenario; 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. Via Ancient whodunit may be solved: Methane-producing microbes did it!

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