Earth history is different from ordinary history: it’s much harder to nail down specific dates when everything happened millions of years ago and over huge, slow timescales. But it can be done, as shown by paleontologists who have pinpointed the exact date of the largest mass extinction to ever occur on earth. The end-Permian mass extinction, which their study calls the “most severe biodiversity crisis in earth history,” wiped out 95% of marine life and 70% of life on land about 252.28 million years ago.
This huge exodus of creatures from the planet happened pretty quickly, according to the study published last week in Science. It lasted less than 200,000 years, and some species may even have met their end within 20,000 years.
More from TIME: IPCC Report: Global Warming — and Changing Population — Will Worsen the Toll of Extreme Weather
That sounds like a long time, but it’s a blink of an eye in geological years. “That’s probably one of the more surprising things – that we’re getting an impression that this event happened very quickly,” University of Calgary geosciences professor Charles Henderson said. Henderson’s team figured out the specific timing of the extinction by examining crystals found in volcanic ash beds in South China in combination with 1,500 fossil species found in rock layers.
A major finding of the study was also that marine and land organisms disappeared from the earth at around the same time, which has been an ongoing debate among scientists. The crisis obliterated insects, forests, amphibians, reptiles, and mammal ancestors – probably the closest we’ve come to having life completely wiped off the face of the earth. All of this happened during the end-Permian, when a chunk of land called Pangea existed in place of the continents we know today. Recovering from this apocalypse started with reptile-like creatures: critters such as the pig-sized, horny-beaked Lystosaurus crept in first, and others – including the dinosaurs – found their place later on.
The scientists are putting the blame on familiar culprits: carbon dioxide and methane. They suggest that the massive release of these two gases came from volcanic lava flows called Siberian traps, which are now found in northern Russia. The flood basalts triggered carbon dioxide- and methane- induced global warming and caused ocean acidification, a drier climate, more forest fires, and soil erosion. With so many punches, it’s no wonder life got wiped out — and Henderson urges the public to use studies of extinction to better understand what’s happening to the earth’s biodiversity today.
More from TIME: Global Appetite for Frog Legs Could Contribute to the Amphibian’s Extinction
“If you ignore history you’re destined to repeat it – the rock record is replete with history,” he said. “Studying the end-Permian can help us understand a little bit about what’s going to happen in the present and what might happen in the future. These are the kinds of concerns we have today.”
But Henderson noted that while his team’s study was “very, very detailed” and used abundant species to verify their findings, their study area was still in only one part of the world. He is currently conducting research in Arctic Canada, extracting information from the rock record to construct other rich stories of why the world looks the way it does.
“That’s what the rock record’s there for – to tell us what’s happened in the past,” he said. “Every layer in the rock is like pages in a book. But they’re hard to open.”
More from TIME: Are Australia’s Koalas, Battling Climate Change and Chlamydia, on the Path to Extinction?
LIST: Top 10 Strange Mass Animal Deaths
Tara Thean is a TIME contributor. Find her on Twitter at @TaraThean. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.