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The physical environment can produce sudden shocks to the life of our planet through impacting space rocks, erupting volcanoes and other events.

But sometimes life itself turns the tables and strikes a swift blow back to the environment. New research suggests that the biggest extinction event on record may have been initiated by a small, but significant change to a tiny microbe.

The end-Permian (or PT) extinction event occurred 252 million years ago. It is often called the Great Dying because around 90 percent of marine species disappeared in one fell swoop. Similar numbers died on land as well, producing a stark contrast between Permian rock layers beneath (or before) the extinction and the Triassic layers above. Extinctions are common throughout time, but for this one, the fossil record truly skipped a beat.

"The end-Permian is the greatest extinction event that we know of," said Daniel Rothman, a geophysicist at the Massachusetts Institute of Technology. "The changes in the fossil record were obvious even to 19th Century geologists."

Understanding the cause of this biological devastation requires understanding the geochemical clues that go along with it. Chief among these clues is a sudden swing in the balance of carbon isotopes stored in rocks from that same time period.

If geologists can find what disrupted the carbon, they'll likely know what killed off so much of the Earth's life forms. Several theories have tried to explain the carbon perturbation as, for example, massive volcanism, or a drop in sea level, but none of these environmental causes have fully matched the data.

Rothman and his colleagues have identified a different culprit — one coming from biology rather than geology. They argue in the Proceedings of the National Academy of Sciences that the carbon disruption and, consequently, the end-Permian extinction were set off by a particular microorganism that evolved a new way to digest organic material into methane.

If it happened once, it can happen again. To read more, click here.