American scientists have determined the event that caused the most devastating mass extinction on Earth millions of years ago.

The End-Permian Extinction, also known as the Permian-Triassic extinction event or the Great Permian Extinction, is the greatest known extinction event ever. This catastrophe took place approximately 252 million years ago and effectively wiped out 96 percent of marine species and 70 percent of terrestrial vertebrate species that existed back then.

And now, a team of geologists from the US Geological Survey and MIT has apparently managed to determine which event triggered that calamity – underground magma pulse in the region known as Siberian Traps, which released massive amounts of greenhouse gases into the atmosphere.

According to a study published in the Nature Communications scientific journal, the processes that triggered the extinction event can be divided into three distinct stages.

During the first stage, about 252.2 million years ago, large volumes of lava erupted over land, gradually solidifying and forming a vast, dense rocky layer.

Approximately 251.9 million years ago the second stage began, when subsequent lava eruptions were stalled by the aforementioned solidified magma layer and started spreading beneath it, heating sediments and thus releasing vast amounts of greenhouse gases into the atmosphere.

During the third stage, about 251.5 million years ago, the release of the gases slowed down while magma continued to flow into sediments.

"Large igneous provinces have always been blamed for mass extinctions, but no one has really figured out if they’re really guilty, and if so, how it was done. Our new work takes that next step and identifies which part of the large igneous province is guilty, and how it committed the crime," Seth Burgess, one of the study’s co-authors, told MIT News.