The biggest catastrophe in the history of life on Earth resulted from one of the most titanic volcanic outpourings on record, new research concludes.
At the close of the Permian period around 252 million years ago, more than 90 percent of all marine species and roughly 75 percent of all land species vanished. New high-precision analysis of ancient lavas determines this extinction followed the start of massive volcanic eruptions in what is now Siberia, researchers report online August 28 in Science Advances. The finding clinches what paleontologists have long suspected: Volcanic gases prompted environmental changes that made the planet uninhabitable for most life.
The researchers have “found the smoking gun for this extinction event,” says geoscientist Richard Ernst of Carleton University in Ottawa.
The Siberian Traps eruptions spewed more than 3 million cubic kilometers of molten rock (SN: 1/15/11, p. 12), enough to bury the United States to the height of the Eiffel Tower. Scientists knew this volcanism took place around the time of the Permian extinction but couldn’t determine whether the Siberian eruptions were the cause of the die-off or just a coincidence.
Resolving this issue required precisely dating both the volcanic eruptions and the extinction itself, says Seth Burgess, a geochronologist at the U.S. Geological Survey in Menlo Park, Calif. In China, Burgess and MIT geologist Samuel Bowring collected rocks left over from an ancient island chain. The rocky layers contain fossilized evidence of the Permian extinction as well as ash blasted from nearby volcanoes.
The ash holds zircon crystals, which naturally form with small amounts of uranium that gradually decays into lead. Comparing the relative number of uranium and lead atoms in the zircons provided precise dates for the Permian extinction, the researchers reported last year in theProceedings of the National Academy of Sciences.
Unlike explosive eruptions, the Siberian Traps contain few zircons (SN: 1/10/15, p. 12). After painstakingly scouring the remnants of the ancient Siberian lava flows, the researchers found and precisely dated 192 crystals.
The precise dates peg the Siberian volcanism to around 300,000 years before the Permian extinction and suggest that the eruptions continued for at least 500,000 years after the die-off. The volcanism probably released huge amounts of carbon dioxide and other volatiles into the air, which caused extreme climate change and acidified the oceans (SN Online: 6/14/12).
“We can now say that this largest preserved magmatic event in Earth’s history preceded the onset of mass extinction,” Burgess says. “We’ve never really been able to say that before.”
A big puzzle still remains, says Stanford paleontologist Jonathan Payne. Life took around 5 million years to start recovering from the extinction. “Yet all the evidence we have now suggests that the Siberian Traps ended millions of years earlier,” he says. “We still don’t understand why the Earth system remained unstable for so long after the main pulse of Siberian Trap volcanism appears to have ended.”