Siberian Traps erupt

The Siberian Traps are a vast pile of volcanic rock covering much of northern Siberia, produced by one of the largest volcanic episodes in Earth's history. The eruptions began about 252 million years ago and went on for roughly a million years, with the main pulses close to the end of the Permian. Lava spread over an area of more than 2 million square kilometers, and the original volume was at least several million cubic kilometers. The name comes from the Swedish word for stairs, trappa, because the stacked lava flows form a stepped landscape.

The cause lies deep in the planet. Most geologists link such huge outpourings of basalt to a hot plume of rock rising from the mantle, though the details remain debated. What made these eruptions deadly was the geology above. The magma rose through a thick region of coal, carbonate rock and salt-bearing sediment in Siberia. Heat from the intrusions cooked these rocks, releasing huge amounts of carbon dioxide, methane, sulfur gases and halogens. This is a reason the event is thought to have been so much worse than many other lava floods.

Precise radiometric dating of zircon crystals, work led by scientists including Seth Burgess and Samuel Bowring, shows that the eruptions started shortly before the mass extinction and kept going through it. The gases warmed the planet, acidified the oceans and starved the seas of oxygen. Sulfur may have caused short cold snaps, and damage to the ozone layer may have added stress on land. The timing makes the Traps the leading suspect for the Great Dying, though scientists still discuss how much each effect contributed.