Culprit of ancient die-off: Microbes

  • Updated: April 5, 2014 - 4:09 PM

Tiny microbes may have been responsible for the largest extinction event our planet has ever seen.

These ocean microbes of death were so small, that 1 billion of them could fit in a thimble-full of ocean sediment, and yet, they were almost responsible for killing off all the life on our planet, scientists suggested.

The end-Permian extinction was the most catastrophic mass extinction the Earth has ever seen. It started roughly 252 million years ago — long before the dinosaurs — and it continued for 20,000 years. By the time it was over, nearly 90 percent of all life on Earth had been destroyed, scientists say.

“It was not as dramatic as the impact that probably killed the dinosaurs, but it was worse,” said Gregory Fournier, an evolutionary biologist at MIT. “Things were very close to being over for good.”

Scientists have struggled to understand exactly what caused the long, slow, mass die-off in this dark era of our planet’s history. The geologic record tells us there was a sharp uptick of C02 levels at the time. That would have caused the oceans to acidify and the Earth to heat up, making the environment inhospitable for most forms of life. But what actually caused the C02 levels to rise has remained a mystery.

The first clue that microscopic microbes could be involved in the greatest die-off the Earth has ever known came when MIT geophysicist Dan Rothman was looking at how carbon levels grew during this time. “The growth was like what you might see in a real estate bubble, or a financial bubble,” he said. “If the C02 came from the sudden combustion of a coal field in Siberia it wouldn’t behave this way.”

To figure out which microbe might have a hand, Rothman took his research to Fournier, who had published a paper about Methanosarcina in 2008. The paper showed that sometime in the past 400 million years, Methanosarcina was the recipient of a gene transfer that allowed it to produce methane more efficiently than ever before. Fournier worked to date the gene transfer more specifically and found it most likely occurred about 250 million years ago.

It was the first time anyone had suggested microbes might be involved with the end-Permian extinction, but far from the first time that microbes have been accused of changing the chemistry of our planet. For example, photosynthetic microbes are responsible for creating the first oxygen in the Earth’s atmosphere. Fournier put it this way: “Microbiologists like to say, ‘Microbes rule the Earth, and we just live on it.’ ”

Los angeles times

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