It might be hard to imagine today, but life on Earth hasn’t always had an go of things. The volcano that is thought to have wiped out the dinosaurs dramatically hindered the ability for many animals to survive, and it’s largely considered to be the most catastrophic thing life on Earth has ever had to endure.

It wasn’t.

The dinosaur-killing space rock that struck the Gulf of Mexico just shy of 66 million years ago wiped out roughly 75% of life on Earth, but something else happened even further back in Earth’s timeline that was even more dire and dramatic. An incredibly catastrophic event dating back some 250 million years snuffed out a whopping 90% of Earth’s life. It’s known among scientists as the “Great Dying,” and a new study suggests that a massive volcano in what is now Siberia was the trigger that started Earth’s largest mass extinction event.

Researchers knew a colossal volcano erupted in around the same time as the Great Dying, but determining whether the two were connected and to what extent was the subject of debate. This new work, which was published in Nature Geoscience, used samples from Earth’s crust to detect how the ancient eruption may have affected the Earth.

What they discovered was that a wealth of chemical elements was present in the geological record of Earth around the time of the eruption. After, however, the chemicals are nowhere to be found, suggesting that a massive chemicals including chlorine and iodine was shot into the upper reaches of Earth’s atmosphere. That would have spelled doom for just about anything living on Earth at the time.

“We concluded that the large reservoir of halogens that was stored in the Siberian lithosphere was sent into the Earth’s atmosphere during the volcanic explosion, effectively destroying the ozone layer at the time and contributing to the mass extinction,” Michael Broadley of the Centre for Petrographic and Geochemical Research explains.

Without a stable atmosphere to protect the Earth’s surface from the ravages of the Sun, life was rapidly snuffed out. The few life forms that were able to sustain themselves until the atmosphere could rebuild itself were the lucky ones, and managed to pass on their DNA. Every living thing we see on Earth today is ultimately a descendent of the species that found a way to survive.

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