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ARTICLE VIEW:
The ‘Great Dying’ wiped out 90% of life, then came 5 million years
of lethal heat. New fossils explain why
By Laura Paddison, CNN
Updated:
6:02 AM EDT, Wed July 2, 2025
Source: CNN
Around 252 million years ago, life on Earth suffered its most
catastrophic blow to date: a known as the “Great Dying” that wiped
out around 90% of life.
What followed has long puzzled scientists. The planet became lethally
hot and remained so for 5 million years.
A team of international researchers say they have now figured out why
using a vast trove of fossils — and it all revolves around tropical
forests.
Their , published Wednesday in the journal Nature Communications, may
help solve a mystery, but they also spell out a dire warning for the
future as humans continue to heat up the planet by burning fossil
fuels.
The Great Dying was the worst of the five mass extinction events that
have punctuated Earth’s history, and it marked the end of the Permian
geological period.
It has been attributed to a period of volcanic activity in a region
known as the Siberian Traps, which released huge amounts of carbon and
other planet-heating gases into the atmosphere, causing intense global
warming. Enormous numbers of marine and land-based plants and animals
died, ecosystems collapsed and oceans acidified.
What has been less clear, however, is why it got so hot and why
“super greenhouse” conditions persisted for so long, even after
volcanic activity ceased.
“The level of warming is far beyond any other event,” said Zhen Xu,
a study author and a research fellow at the School of Earth and
Environment at the University of Leeds.
Some theories revolve around the ocean and the idea that extreme heat
wiped out carbon-absorbing plankton, or changed the ocean’s chemical
composition to make it less effective at storing carbon.
But scientists from the University of Leeds in England and the China
University of Geosciences thought the answer may lie in a climate
tipping point: the collapse of tropical forests.
The Great Dying extinction event is unique “because it’s the only
one in which the plants all die off,” said Benjamin Mills, a study
author and a professor of Earth system evolution at the University of
Leeds.
To test the theory, they used an archive of fossil data in China that
has been put together over decades by three generations of Chinese
geologists.
They analyzed the fossils and rock formations to get clues about
climate conditions in the past, allowing them to reconstruct maps of
plants and trees living on each part of the planet before, during and
after the extinction event. “Nobody’s ever made maps like these
before,” Mills told CNN.
The results confirmed their hypothesis, showing that the loss of
vegetation during the mass extinction event significantly reduced the
planet’s ability to store carbon, meaning very high levels remained
in the atmosphere.
Forests are a vital climate buffer as they suck up and store
planet-heating carbon. They also play a crucial role in “silicate
weathering,” a chemical process involving rocks and rainwater — a
key way of removing carbon from the atmosphere. Tree and plant roots
help this process by breaking up rock and allowing fresh water and air
to reach it.
Once the forests die, “you’re changing the carbon cycle,” Mills
said, referring to the way carbon moves around the Earth, between the
atmosphere, land, oceans and living organisms.
Michael Benton, a professor of paleontology at the University of
Bristol, who was not involved in the study, said the research shows
“the absence of forests really impacts the regular oxygen-carbon
cycles and suppresses carbon burial and so high levels of CO2 remain in
the atmosphere over prolonged periods,” he told CNN.
It highlights “a threshold effect,” he added, where the loss of
forests becomes “irreversible on ecological time scales.” Global
politics currently revolve around the idea that if carbon dioxide
levels can be controlled, damage can be reversed. “But at the
threshold, it then becomes hard for life to recover,” Benton said.
This is a key takeaway from the study, Mills said. It shows what might
happen if rapid global warming causes the planet’s rainforests to
collapse in the future — scientists are very concerned about.
Even if humans stop pumping out planet-heating pollution altogether,
the Earth may not cool. In fact, warming could accelerate, he said.
There is a sliver of hope: The rainforests that currently carpet the
tropics may be more resilient to high temperatures than those that
existed before the Great Dying. This is the question the scientists are
tackling next.
This study is still a warning, Mills said. “There is a tipping point
there. If you warm tropical forests too much, then we have a very good
record of what happens. And it’s extremely bad.”
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