Burning fossil fuels helped drive Earth’s most massive extinction

The findings solidify the Great Dying as one of the best examples that we have from Earth’s history of what a changing climate can do to life on our planet
Last Updated : 20 November 2020, 02:21 IST
Last Updated : 20 November 2020, 02:21 IST

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Paleontologists call it the Permian-Triassic mass extinction, but it has another name: “the Great Dying.” It happened about 252 million years ago, and, over the course of just tens of thousands of years, 96% of all life in the oceans and, perhaps, roughly 70% of all land life vanished forever.

The smoking gun was ancient volcanism in what is today Siberia, where volcanoes disgorged enough magma and lava over about a million years to cover an amount of land equivalent to a third or even half of the surface area of the United States.

But volcanism on its own didn’t cause the extinction. The Great Dying was fueled, two separate teams of scientists report in two recent papers, by extensive oil and coal deposits that the Siberian magma blazed through, leading to combustion that released greenhouse gases like carbon dioxide and methane.

“There was lots of oil, coal and carbonates formed before the extinction underground near the Siberian volcanism,” said Kunio Kaiho, a geochemist at Tohoku University in Sendai, Japan, and lead author of one of the studies, published this month in Geology, which presented evidence for the burning of ancient fossil fuels by magma. “We discovered two volcanic combustion events coinciding with the end-Permian land extinction and marine extinction.”

The findings solidify the Great Dying as one of the best examples that we have from Earth’s history of what a changing climate can do to life on our planet.

Kaiho and his team retrieved samples from rock deposits in south China and northern Italy that formed around the time of the extinction, and they detected spikes of a molecule called coronene. That substance, Kaiho explained, is produced only when fossil fuels combust at extremely high temperatures — like those you might find in magma.

One potential issue with coronene, says Henrik Svenson, a geologist at the University of Oslo who was not involved in the work, is that it forms only at temperatures exceeding 2,100 degrees Fahrenheit, and to reach such temperatures, the fossil fuels would have had to be enveloped inside the magma, not just sitting next to it.

But the team’s findings are backed up by a Nature Geoscience study published last month that presents chemical evidence for the acidification of the oceans after the fossil fuel combustion and greenhouse gas release.

As the planet warmed, the oceans absorbed more and more carbon dioxide. This caused waters to acidify to the point that organisms like corals would have dissolved, explained Hana Jurikova, a biogeochemist at the University of St. Andrews in Scotland who led the study. Jurikova and her team discovered spikes of the element boron — a proxy for acidity levels — in fossil brachiopod shells found in rocks in Italy that stretch across the extinction boundary.

“For the first time, we’re able to explain what caused the extinction,” Jurikova said. “If you just increase the temperature, organisms often find a way to cope. But the problem is if you really change temperature and acidification, and maybe nutrients, that’s when your organisms will not be able to adapt.” Today, with sea-surface temperatures on the rise, the oceans are acidifying, and some shelled animals are already showing signs of their shells dissolving.

Svenson thinks the next step for geologists is field work in Siberia to get a handle on whether ancient magma interacted with the fossil fuel deposits as the new studies imply.

“A lot of this we simply do not know,” Svenson said.

While you may be tempted to draw an analogy between the Great Dying and today’s warming climate, there are significant differences. For one, the greenhouse gases emitted during the Permian-Triassic events were far greater than anything humans have produced. Also, the volcanoes released carbon dioxide 252 million years ago at a rate much slower than humans emit it today.

“The amount of carbon released to the atmosphere per year from the Siberian traps, it was still 14 times lower than the rate we have at the moment,” Jurikova said. “So, the amount of carbon we’re burning per year at the moment is much higher than during the largest extinction. I mean, that’s incredible, right?”

Published 19 November 2020, 22:43 IST

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