During the Permian-Triassic boundary 250 million years ago, the Earth was enjoying some of its warmest temperatures when it was interrupted by a catastrophic cooling event.
The new discovery shows how an Ice Age forced a massive die-off of most marine life, and not from global warming as once thought.
It also shows the role geological events have played on our climate, specifically volcanic eruptions.
While the Earth has gone through a number of extinction level events, the one that happened at the Permian-Triassic boundary was one of the deadliest.
Over 95 percent of marine life vanished from the face of the planet.
Scientists previously believed it was from a rise in temperatures that preceded Climate Change, but researchers from the University of Geneva and University of Zurich discovered the die-off arose from a mini ice age.
Dating the past
The researchers worked on layers found at the Nanpanjiang basin in southern China. Bjorn Baresel, a University of Zurich scientist, said they made several cross sections of the basin sediments to determine the exact positions of ash beds in the marine sediments.
Then they dated the sediments using the natural radioactive decay of uranium from the mineral zircon. Because it decays at a specific speed, they can be accurate to within 35,000 years.