Earth’s biggest mass extinction happened 10 times faster in oceans than on land, study finds

Scientists have found that Earth’s worst mass extinction event 252 million years ago happened rapidly in the oceans, while it panned out over a much longer, drawn-out period, on land.

According to research published in the journal PNAS, the end-Permian extinction event saw a vast majority of animal species go extinct, and the planet entered the early days of the Age of Dinosaurs when the dust settled. 

“Mass extinctions permanently altered life’s evolutionary trajectory five times in Earth’s history, and the end-Permian extinction was the greatest of these biotic crises,” the scientists, including those from Chicago’s Field Museum in the US, wrote in the study.

They said the marine version of this mass extinction took up 100,000 years out of the entire 3,800,000,000 years that life has existed – the equivalent to 14 minutes out of a whole year.

“This paper is the first really focusing on vertebrates and saying, ‘No, something was going on that was unique to the terrestrial realm,’” Ken Angielczyk, senior author of the study from Field Museum, said in a statement.

The scientists noted that this extinction event led to the death of close to 85 per cent of the species living in the oceans with experts across the world still learning about the patterns of which animals went extinct and which ones survived, and why.

“People assumed that because the marine extinction happened over a short period of time, life on land should have followed the same pattern, but we found that the marine extinction may actually be a punctuation to a longer, more drawn-out event on land,” explained Pia Viglietti, lead author of the study from Chicago’s Field Museum.

In the study, researchers analysed fossils from 588 remains of four-legged fossil animals that lived in what is now South Africa’s Karoo Basin at the time of the Permian mass extinction.

The scientists then created a database, separating the fossils by age and grouping together specimens by 300,000-year time intervals.

Using this approach, the researchers narrowed in on intervals, or “time bins” during which different species appeared and disappeared, to look at the bigger picture of life over time.

“By applying sampling methods to these bins, we can help correct for issues like having more or fewer specimens collected in different time intervals or places. Ultimately, it lets us quantify how much extinction is happening and how quickly new species are appearing,” Ms Viglietti explained.

Examining the fossil of a herbivorous land mammal called Lystrosaurus, the scientists got more clues that the Permian extinction looked very different on land than it did in the oceans. 

“Lystrosaurus is like a poster child for the end-Permian extinction that’s always been portrayed as this animal that flourishes in the aftermath of all this extinction and just takes over,” Ms Viglietti said. 

“We see Lystrosaurus appearing before the extinction even got started, it was already abundant. It got us thinking about what was driving that abundance – if Lystrosaurus just took over the barren landscape after other animals went extinct, or if the environment was changing and Lystrosaurus adapted to these changes that were causing extinction for all these other species. Our best guess is the latter,” the paleontologist added.

While it is still unclear why the mass extinction was slower on land than in the oceans, the scientists believe one reason could be that the seas managed to absorb chemical changes and stabilise themselves, up to a point.

“In today’s climate crisis, the oceans can absorb a lot of carbon dioxide or rise in temperature without people realising, and then all of a sudden you get sudden ecosystem breakdowns like ocean acidification and coral bleaching,” Ms Viglietti explained.

The scientists now suspect the same may have been the case for the end-Permian oceans.

They believe understanding this extinction event can also provide insights into the mass die offs that the Earth is currently undergoing due to climate change and habitat destruction.