Researchers use the sharp fossilized teeth of lamprey-like creatures called conodonts to date the rock in which the mercury was deposited. Like most other creatures on the planet, conodonts were decimated by the catastrophe.

The eruptions propelled as much as 3 million cubic kilometers of ash high into the air over this extended period. To put that in perspective, the 1980 eruption of Mount St. Helens in Washington sent just 1 cubic kilometer of ash into the atmosphere, even though ash fell on car windshields as far away as Oklahoma.

In fact, Algeo said, the Siberian Traps eruptions spewed so much material in the air, particularly greenhouse gases, that it warmed the planet by an average of about 10 degrees centigrade.

The warming climate likely would have been one of the biggest culprits in the mass extinction, he said. But acid rain would have spoiled many bodies of water and raised the acidity of the global oceans. And the warmer water would have had more dead zones from a lack of dissolved oxygen.

“We’re often left scratching our heads about what exactly was most harmful. Creatures adapted to colder environments would have been out of luck,” Algeo said. “So my guess is temperature change would be the No. 1 killer. Effects would exacerbated by acidification and other toxins in the environment.”

Stretching over an extended period, eruption after eruption prevented the Earth’s food chain from recovering.

“It’s not necessarily the intensity but the duration that matters,” Algeo said. “The longer this went on, the more pressure was placed on the environment.”

Likewise, the Earth was slow to recover from the disaster because the ongoing disturbances continued to wipe out biodiversity, he said.