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The event that killed the dinosaurs 66 million years ago might be the most famous mass extinction ever, but it's not the only one in Earth’s history, nor is it the worst... not by a long shot.

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The event that killed the dinosaurs might be the most famous mass extinction ever. And scientists are pretty sure they've identified the scene of the crime: a meteor crater in the Gulf of Mexico.

But that event sixty-six million years ago is neither the only one in Earth's history, nor the worst. Not by a long shot. Scientists studying a remote swath of land in Russia have pieced together clues about an extinction event that makes the demise of the dinosaurs look tame.

The extinction event in question happened at the end of the Permian period, which was a geologic span of time that ran from about 299 million to 252 million years ago. This was before the dinosaurs, but not so far back that life on Earth would have seemed totally alien. There were no birds or mammals, but there were reptiles, amphibians, ferns, and insects.

Granted, some Permian creatures -- like Dimetrodon look pretty strange to us now, but you'd still be able to walk around and see plants and animals you could put a name to. But at the end of the Permian, a lot of life suddenly went extinct. Like, a lot.

Within no more than two hundred thousand years, most of the marine and terrestrial species on Earth vanished. Estimates vary, but more than 90% of all species may have disappeared. It would take about 8 to 9 million years for.

Earth's ecosystems to really recover. This extinction was so dramatic that scientists have nicknamed it “The Great Dying”. There have been a handful of hypotheses over the years to explain this massive die-off.

Some researchers have proposed another big asteroid, like the one that would kill off the dinosaurs. But one place on Earth seems to stand out as the most likely scene of the crime: a massive volcanic region in Russia known as the Siberian Traps. The rock underneath this area of Siberia is relatively stable -- it's not on a tectonic plate boundary, like many volcanoes are.

But about the same time as the Great Dying, a massive pulse of magma from deep inside the Earth — known as a mantle plume — melted through the crust. The plume triggered the biggest volcanic eruptions ever known, which may have lasted more than a million years, and covered an area bigger than Greenland in lava. After the initial eruptions, there was a quiet period for a while, followed by one big, final burst of activity.

These eruptions happened at pretty much the same time as the mass extinction, and scientists think this volcanic activity is a pretty likely explanation for what happened. The eruptions could have spewed massive amounts of carbon dioxide and methane into the Earth's atmosphere, changing the chemistry of the Earth's air and water. The oceans, for instance, would have abruptly become more acidic and as much as ten degrees warmer -- and would have lost almost all of their oxygen.

If that seems bad, you're right! But there's still some details to work out. Sure, we found a site of massive volcanic activity, and it's about the right age.

But the timeline actually isn't quite right for the initial burst of eruptions at the Siberian Traps to have caused the Great Dying. By the time the extinction event started, the traps had already been erupting for about three hundred thousand years and had spewed out two-thirds of their magma. Also, this kind of massive eruption has happened in other times and in other places.

Some of those are associated with mass extinctions, but not all. So does that let the Siberian Traps off the hook? One leading hypothesis, published in 2009, proposes that it was volcanic activity but, remarkably, it might have not been those huge initial eruptions.

Remember that quiet period? During that period, magma was still flowing, but instead of erupting dramatically, it spread underground, intruding in between layers of existing rock to form what are known as sills. Visible today in places like river banks, the sills look kind of like the frosting in between the layers of a giant cake.

As the magma spread out, it heated and altered the surrounding rocks in a process known as contact metamorphism. These existing rocks, put downs by millions of years of geologic activity, contained quite a bit of carbon, and even included coal beds. The intruding magma would have effectively “cooked” all these rocks, creating and releasing greenhouse gases like carbon dioxide and methane.

They would also have released a type of chemical called halocarbons, which would have stripped the ozone layer, just like CFCs in more recent years. And researchers have calculated that the contact metamorphism generated four to nine times more carbon dioxide than the lava itself contained. In 2017, researchers took a closer look at the start of this quiet, deadly period.

And they were able to pin the timing down to line up with the onset of the mass extinction, thanks to very precise radiometric dating, which uses the steady decay of radioactive elements like a clock to estimate the age of rocks and other materials. This research would explain why it took 300,000 years for the extinction to start. The big eruptions, though dramatic, may not have brought up enough carbon dioxide by themselves, nor did they cook as much of the underground rock as the sills.

And all that carbon dioxide, once released from the cooking rocks, would be enough to change the Earth's atmosphere, leading to warmer temperatures and acidic, de-oxygenated oceans. And from there to the most staggering loss of life our planet has ever seen. This may be the best smoking-gun evidence we ever get to tie the Great Dying to a place on Earth that you could actually theoretically visit.

And it's a bunch of volcanic rock in Siberia. Thanks for watching this episode of SciShow, and thanks to our channel members for your support. Did you know you can become a member of this very channel?

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