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About 252 million years ago, a natural disaster struck the planet, wiping out more than 90% of all life.
The mass extinction that ended the Permian is known as the Great Extinction and was the worst of the five global catastrophic events in Earth's history, even more devastating than the event caused by a giant asteroid that wiped out the dinosaurs.
The most plausible explanation offered so far is that carbon dioxide released by volcanic activity in an area known as the Siberian Traps caused a sudden warming of the planet. The emissions across the vast area in what is now Russia, which was about the size of Australia, resulted in higher temperatures, acid rain and ocean acidification.
However, a mega El Niño effect, similar but more intense and longer-lasting than the climate phenomenon experienced today, could have played a crucial role, according to new research published Thursday in the journal Science.
"What we show is that it was a climate-driven extinction crisis. It wasn't just the warming, it's how the climate responded," said study co-author Paul Wignall, a professor of paleoenvironments at the University of Leeds in the United Kingdom.
"If conditions were bad but constant, life could have evolved to cope with them. But the fact is that it kept swinging from one extreme to the other for decades."
The research team built a computer model of the global climate at the end of the Permian. It showed that as global temperatures rose, El Niño events, a climate pattern that originates in the Pacific Ocean but affects weather around the world, increased in size and duration.
This phenomenon caused temperatures to rise dramatically, causing alternating periods of flooding and scorching drought. This caused forest fires that would have wiped out many species of animals around the world over a period of about 100,000 years.
El Niño events on a large scale
Today, an El Niño event, which affects wind patterns and ocean currents, typically lasts between nine and 18 months and occurs every two to seven years. Alex Farnsworth, a senior research associate at Britain's University of Bristol and joint lead author of the study, said that during the warmest phases of the extinction, an El Niño episode would have lasted 10 years.
The El Niño of 252 million years ago is thought to have originated in the Panthalas Ocean, a body of water much larger than the present-day Pacific Ocean that could trap more heat, which in turn would have amplified and sustained the effects of El Niño.
He added that volcanic activity remained an important factor, but was not sufficient on its own to explain the scale of the biological catastrophe that was unfolding. The planet had experienced similar episodes before, but they had not caused a mass extinction.
"The volcanism was the main culprit here, but there was a feedback mechanism on the ocean dynamics that caused these much stronger El Niños to start developing and then (the two things) worked together," Wignall said.
A prolonged and intense El Niño also explained why extinctions started on land before they occurred in the ocean, the study found.
"While the oceans were initially shielded from the temperature increases, the mega-El Ninos caused temperatures on land to exceed the thermal tolerances of most species so quickly that they could not adapt in time," said co-lead author Yadong Sun, a researcher at the China University of Geosciences in Wuhan, in a press release.
"Only species that could migrate quickly could survive, and there weren't many plants or animals that could do that."
A major reason the end-Permian extinction was so severe was that mega-El Ninos created incredibly warm conditions in the tropics. These conditions spread rapidly to higher latitudes, wiping out most of the vegetation and destroying the ability of vegetation to remove carbon dioxide from the atmosphere.
"You're losing all the trees at this point, which is astonishing. Nothing would have grown higher than your knees in the early Triassic," Wignall said, referring to the geologic period following the extinction when the ecosystem began to recover.
Past changes in temperature can be determined in a variety of ways: from plant and animal fossils, sediment cores and ice, and, for more recent changes, tree rings and coral. These proxy data can be used to build computer models that help scientists reconstruct and understand what past conditions and climate systems were like.
Farnsworth said the team's climate model, which took months to run multiple simulations, was better than its predecessors at piecing together what was happening because of new, detailed temperature data gleaned from fossils of tiny eel-like creatures known as conodonts, collected and analyzed over a long period of time. That data showed how temperatures rose at different latitudes as the mass extinction unfolded.
The ratio of two different oxygen isotopes, or variants, in the fossilized tooth material of the conodonts, which were common in the ocean at the time, depended on temperature, he added.
According to Alfio Alessandro Chiarenza, a Royal Society Newton International Fellow in the Department of Earth Sciences at University College London, it would be interesting to find evidence in the fossil record of how organisms - including trilobites, early amphibians, reptilian mammal ancestors and early crocodilians - were affected by the extinctions, and which aspects of their biology were most severely affected by these climatic upheavals.
"This study provides another example of how complex and interconnected climate-environment dynamics are and how such processes can radically affect the ecological balance - a serious warning in light of our current ecological crisis," said Chiarenza, who was not involved in the study.
Resonance with the current climate crisis
Some researchers believe we are in the midst of a sixth mass extinction and that the end-Permian mass extinction can provide lessons for the current climate crisis.
The study shows that El Niños currently cause coral bleaching and massive fish kills. However, the ecological impact and future development of El Niños in a warming climate are unknown.
However, Wignall said the world was a different place geographically 252 million years ago: home to a vast supercontinent called Pangaea and a huge ocean, possibly making it more susceptible to the carbon dioxide spewed out by supervolcanoes.
"The end-Permian is the biggest crisis in Earth's history from the standpoint of life, but I don't think we'll ever get anywhere near those conditions again because (Earth then) was a very strange planet with a continent on one side and a giant ocean on the other," he said.
"The planet was really vulnerable then."
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