We now know what killed everything in Earth’s worst mass-extinction event.

Science Alert lets us know that oceanographers have determined that the event that killed 70 percent of all land species and 96 percent of all marine species (not individuals – but whole species dying out) was, you might’ve guessed it, a global warming event kinda like the current one that smothered the seas:

It’s widely accepted that climate change is to blame – more specifically, that long-term volcanic activity in Siberia spewed so much material into the atmosphere that it wrapped the world in a shroud of ash for a million years, simultaneously blocking sunlight, thinning the ozone, dropping acid rain, and raising temperatures.

And we’re experiencing similar atmospheric warming again today – only much faster than the Great Dying, which showed warning signs for 700,000 years before the event itself.

“This is the first time,” said oceanographer Justin Penn of the University of Washington, “that we have made a mechanistic prediction about what caused the extinction that can be directly tested with the fossil record, which then allows us to make predictions about the causes of extinction in the future.”

The team conducted a computer simulation of the changes Earth underwent during the Great Dying. Prior to the Siberian volcanic eruptions, the temperatures and oxygen levels were similar to what they are today, so that gave them a good baseline to work from.

Then they elevated greenhouse gases in the model’s atmosphere to mimic the conditions following the eruption, which raised sea surface temperatures by around 11 degrees Celsius (by 20 degrees Fahrenheit).

Sure enough, this resulted in an oxygen depletion of around 76 percent – and about 40 percent of the seafloor, mostly at greater depths, was entirely depleted of oxygen.

To observe how this would affect marine life, the team plugged oxygen requirement data from 61 modern species into the simulation. It was a disaster.

“Very few marine organisms stayed in the same habitats they were living in – it was either flee or perish,” said oceanographer Curtis Deutsch of the University of Washington.

The hardest hit were creatures most sensitive to oxygen, with the most pronounced devastation at high latitudes far from the equator. When the team compared their result with the fossil record, it confirmed their findings.

This is because animals living in the warmer waters around the equator can migrate to higher latitudes, where they will find habitats similar to the ones they just left. But animals already living in higher latitudes have nowhere left to go.

The team’s research has been published in the journal Science.