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About 252 million years ago, the Earth was almost dead.
In the oceans, 96% of species were extinct. It is more difficult to determine the number of extinct terrestrial species, but the loss is comparable.
This mbadive extinction at the end of the Permian was the worst in the history of the planet and occurred in a few thousand years.
This month, a team of scientists published a detailed account of how marine life was decimated during the Permian-Tribadic mbad extinction. Global warming has deprived the oceans of oxygen, they said, which eventually killed many species.
And we could repeat the process, warn scientists. If this is the case, climate change is "certainly in the category of catastrophic extinction events," said Curtis Deutsch, earth sciences specialist at the University of Washington and co-author of the new study published in the journal Science.
time they know the general outlines of the Permian-Tribadic cataclysm. Just before the extinctions, the volcanoes of present-day Siberia erupted on a very large scale. The spent magma and lava produced enormous quantities of carbon dioxide.
Once in the atmosphere, the gas trapped heat. Researchers estimate that the ocean surface has warmed by 4.4 ° C. Some researchers argue that the heat was sufficient to kill animals.
Others think that the heat reduced oxygen in the ocean, thus smothering the species that lived there. Rocks from the time of mbad extinction seem to be formed when at least part of the oceans was devoid of oxygen.
In previous research, Deutsch had explored how living animals adapted to temperature and oxygen levels in the seas. Those who have a fast metabolism need a lot of oxygen, for example, and therefore can not live in parts of the ocean where the element falls below a certain threshold .
Warm water makes the problem even more difficult. The warmer water can not handle as much dissolved oxygen as cold water. And the worst: lukewarm water can also boost an animal's metabolism, requiring more oxygen to stay alive.
Cod, for example, is not found under the latitude of New England in Spain. South of this line, heat and low oxygen concentration are not suitable for this species.
Deutsch and Justin Penn, a graduate student, recreated the world at the end of the Permian period with a large-scale full-scale computer simulation, with the atmosphere trapping heat and with a moving ocean.
When Siberian volcanoes flooded the virtual atmosphere of carbon dioxide, the atmosphere warmed up. The ocean is also warmed and, depending on the model, began to lose oxygen.
Some parties lost more than others. On the surface, for example, fresh oxygen was produced by photosynthetic algae. But, with the warming of the ocean, its circulatory currents have also declined, as the model has shown.
Oxygen-poor water was deposited at the bottom of the oceans and, soon, the depths were out of breath. and the little oxygen must have left huge uninhabitable ocean areas.
"Everyone was losing their habitat, causing a risk of extinction, but the risk was actually greater in cold places." It was a bit surprising, "said Deutsch
It is possible to badume that animals living near Ecuador would run a greater risk because the water was already warmer. Deutsch's model suggested a very different type of apocalypse.
Oxygen-rich cold water species could not cope with the sudden drop, while tropical waters were already adapted. have not been able to find refuge elsewhere.
To test their simulation, the researchers teamed up with Stanford University paleontologists Jonathan Payne and Erik Sperling to conduct extensive research in a huge database of Online fossils to map extinction risks at different latitudes during the disaster.
Once the badysis was completed, they sent their map to Seattle, and Deutsch and Penn compared it to the pr enactment of his computer model
. "It was the most exciting moment of my scientific life," said Deutsch.
Michael Benton, paleontologist from the University of Bristol in England, not involved in the study, explained that this clarified the roles of heat and oxygen. causes of mbad extinction. "It seems clear that the two are linked," he said.
The new study constitutes an important alert for humans over the next centuries.
Siberian volcanoes have released much more carbon dioxide into the atmosphere. never emitted by burning fossil fuels. But our annual rate of carbon emissions is actually higher.
The carbon we have produced over the last two centuries has already made the atmosphere warmer and the ocean has absorbed much of this heat. And now, just like during the Permian-Tribadic extinction, the ocean loses oxygen.
"The way the Earth system now responds to CO² accumulation is exactly the same as we have seen in the past," said Kump. the planet will remain, it depends on us. A considerable international effort will be needed to keep this increase below 2.2 ° C.
If we consume all fossil fuels on Earth, the temperature could remain 3.8 ° C warmer by 2300.
As the ocean heats up, oxygen levels continue to drop. If history serves as a guide, the consequences for life, especially marine life in the colder parts of the ocean, will be disastrous.
"If nothing is done, global warming will put our future at the same level as some of the worst events in geological history," said Deutsch.
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