What was the cause of Earth’s largest mass extinction?

Massive ocean-warming El Niño events played a key role in driving the largest extinction event in Earth's history, which took place approximately 252 million years ago, according to new research.

The study, published in the journal Science and co-led by the University of Bristol and China University of Geosciences (Wuhan), sheds light on the extreme environmental shifts that occurred during the Permian-Triassic period, ultimately leading to the devastation of life on land and in the oceans.

Unknown cause of mass extinction

For years, scientists have linked the mass extinction to enormous volcanic eruptions in what is now Siberia. These eruptions released vast amounts of carbon dioxide, accelerating climate warming and triggering the collapse of ecosystems at both land and at sea.

However, one mystery remained: why did life on land, including plants and typically resilient species like insects, suffer as badly as marine life?

“Climate warming alone cannot drive such devastating extinctions because, as we are seeing today, when the tropics become too hot, species migrate to the cooler, higher latitudes,” explained co-lead author Alexander Farnsworth, a senior research associate at Bristol.

“Our research has revealed that increased greenhouse gasses don’t just make the majority of the planet warmer, they also increase weather and climate variability , making it even more ‘wild’ and difficult for life to survive.”

Unpredictable climate swings over decades

The study reveals that the problem during the Permian-Triassic catastrophe was not simply the extreme heat but also the unpredictable swings in climate conditions over decades.

“Most life failed to adapt to these conditions, but thankfully a few things survived, without which we wouldn’t be here today. It was nearly, but not quite, the end of life on Earth,” said co-lead author Yadong Sun, a paleoclimatologist at the China University of Geosciences.

The temperature fluctuations during this period were uncovered by analyzing oxygen isotopes in the fossilized teeth of conodonts - tiny, extinct, swimming organisms.

Evidence of drastic climate change

The researchers found a significant collapse in temperature gradients, particularly in low and mid-latitude regions, revealing just how dramatically the climate changed.

“Essentially, it got too hot everywhere. The changes responsible for the climate patterns identified were profound because there were much more intense and prolonged El Niño events than witnessed today," said Farnsworth. "Species were simply not equipped to adapt or evolve quickly enough."

Extreme El Niño events

El Niño events, which are responsible for major shifts in weather patterns and temperatures today, were much more extreme and long-lasting during the Permian-Triassic period.

For instance, recent El Niño events have caused North American heatwaves and record global temperatures, such as the June 2024 heatwave when temperatures were 15°C hotter than normal.

While today's El Niño events typically last one to two years, the Permian-Triassic crisis saw Mega-El Niño events persist for much longer, resulting in a decade of drought followed by years of flooding, making it impossible for most species to adapt.

Earth's climate in a state of crisis

Paul Wignall, a professor of palaeoenvironments at the University of Leeds and co-author of the study, emphasized that “the climate was all over the place,” making survival difficult.

This extreme climate variability also contributed to the frequent wildfires, as reflected in the abundance of charcoal found in rock layers from that era.

“ Wildfires become very common if you have a drought-prone climate. Earth got stuck in a crisis state where the land was burning and the oceans stagnating. There was nowhere to hide,” added David Bond, a palaeontologist at the University of Hull.

The research highlights why the Permian-Triassic extinction was so much more devastating than other volcanic events throughout Earth's history.

Deadly feedback loop

The researchers found that these mega-El Niños created a feedback loop, causing the dieback of vegetation.

Plants are essential for removing CO2 from the atmosphere and are the foundation of the food web. This means that their decline further exacerbated the buildup of atmospheric CO2, amplifying the warming effects of ongoing volcanism.

This feedback loop also helps explain a long-standing puzzle: why did the extinction on land occur tens of thousands of years before marine extinctions?

Devastatingly rapid climate change

“Whilst the oceans were initially shielded from the temperature rises, the mega-El Niños caused temperatures on land to exceed most species' thermal tolerances at rates so rapid that they could not adapt in time,” Sun explained. Only species capable of rapid migration had a chance to survive.

Mass extinctions are rare but pivotal events in Earth's history, reshaping life and evolution.

“The Permo-Triassic mass extinction, although devastating, would ultimately see the rise of dinosaurs becoming the dominant species thereafter, just as the Cretaceous mass extinction led to the rise of mammals, and eventually humans,” Farnsworth concluded.

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