The world’s worst mass extinction event wiped out almost all marine animals and more than two-thirds of land animals, but scientists are still trying to wrap their heads around what caused all those creatures to die off about 252 million years ago.

One team has a new hunch, and it’s not a humongous asteroid strike or the single eruption of an enormous volcano that destroyed the atmosphere, with calamitous consequences for the rest of the ecosystem. Instead the researchers say that tremendous heat released the greenhouse gases trapped in rock and that those gases caused climate changes that killed much of the world’s animals.

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The researchers studied a large area of volcanic rock in Russia known as the Siberian Traps, where there was a lot of previous intense volcanic activity. They used geological clues to look into the region’s past and better understand the processes at work there millions of years ago.

“Broad, flat volcanoes likely dispelled significant volumes of lava, ashes and gas, while pushing sulfur dioxide, carbon dioxide and methane to dangerous levels in the environment,” Syracuse University explained in a statement. “But that’s only part of the story.”

It wasn’t the generous amount of lava flowing out of the volcanoes and onto the Earth’s surface that killed off more than 95 percent of marine species and about 70 percent of terrestrial ones. The process was related but different: Magma creeped upward and pushed its way into the small voids between existing rock, with the intense heat releasing gas into the atmosphere.

When it comes to mass extinctions, “their abrupt nature necessitates a similarly short-lived trigger,” and that’s why volcanic activity in places like the Siberian Traps, called large igneous provinces, is often blamed, according to a study in the journal Nature Communications. But those rock regions persist much longer than a mass extinction event, so a specific period of magmatism “must be responsible for driving deleterious environmental effects.”

This research points to heat from the molten rock affecting other sediment in a process called contact metamorphism, “likely liberating the massive greenhouse gas volumes needed to drive extinction.” Those greenhouse gases would have sent carbon into the ocean and raised sea temperatures, which would account for the huge impact on marine life during the mass extinction 252 million years ago — known as the end-Permian event, because of its occurrence at the end of the Permian geological period, or as the Great Dying. The event was “a critical inflection point in the evolutionary trajectory of life on Earth” because it was so severe.

The authors note greenhouse gas emissions are believed to be a common culprit of extinction events

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New data show “surface lava flows erupted too early to drive mass extinction,” researcher James Muirhead said in the Syracuse statement. “Instead, there was a subinterval of magmatism … that triggered a cascade of events causing mass extinction.”

The team hopes to use what they’ve found to investigate other mass extinction events, to determine whether they might also be connected with magma activity at large igneous provinces.

Getting to the bottom of these prehistoric events help us understand how life on Earth evolved in the way it did, lead author and U.S. Geological Survey geologist Seth Burgess said in the statement: “Mass extinction can take 10,000 years or less — the blink of an eye, by geological standards — but its effects on the evolutionary trajectory of life are still observable today.”