March 6 (UPI) -- New research suggests the Permian-Triassic extinction event was caused by a brief ice age, 250 million years ago.
The ancient rock strata known as the Permian-Triassic boundary boasts evidence of one of the greatest mass extinctions in Earth's history. Some 95 percent of marine species disappeared from the planet.
Until now, scientists believed the mass extinction was the result of global warming. But new research suggests the mass extinction occurred during a brief period of extremely frigid temperatures prior to warming.
The latest revelations are the result of close analysis of sediment layers found in southern China's Nanpanjiang River basin. The ancient layers allowed researchers from the universities of Geneva and Zurich, in Switzerland, to recount the shifting biodiversity and climate history during the Permian and Triassic periods.
"We made several cross-sections of hundreds of meters of basin sediments and we determined the exact positions of ash beds contained in these marine sediments," researcher Bjorn Baresel explained in a news release.
Researchers recovered zircon crystals from ash layers trapped in the sediment cross-sections, allowing them to develop a more accurate timeline. Zircon incorporates uranium, which decays into a lead at a fixed rate over time.
"This is why, by measuring the concentrations of uranium and lead, it was possible for us to date a sediment layer to an accuracy of 35,000 years, which is already fairly precise for periods over 250 million years," said researcher Urs Schaltegger.
Analysis of the newly dated layers showed a significant reduction of seawater levels during the extinction event. The only explanation for such a dramatic decrease in water levels is a sudden increase in ice. The ice age lasted just 80,000 years, but the extreme cold was enough to kill off the majority of marine species.
Ash deposits suggest an uptick in volcanic activity and the release of sulphur dioxide into Earth's atmosphere blocked out the sun and triggered the brief ice age.
"We therefore have proof that the species disappeared during an ice age caused by the activity of the first volcanism in the Siberian Traps," Schaltegger concluded.
Researchers detailed their analysis of the Permian-Triassic extinction event in the journal Scientific Reports.