Volcanoes or asteroids? AI ends debate over dinosaur extinction – Issues.fr

Dartmouth scientists used an innovative computer model to suggest that volcanic activity, not an asteroid impact, was the primary cause of the mass extinction that ended the age of dinosaurs. This revolutionary approach opens up new possibilities for studying other geological events.

Free-thinking computers have reconstructed the fossil record to determine the causes of a catastrophe.

To address the long-standing debate over whether a massive asteroid impact or volcanic activity led to the extinction of dinosaurs and many other species 66 million years ago, a team at Dartmouth College took an innovative approach: It took scientists out of the debate and left them Computers decide.

Researchers report in the journal Science about a new modeling method based on interconnected processors that is capable of processing large amounts of geological and climate data without human intervention. They tasked nearly 130 processors with reverse analysis of the fossil record to identify the events and conditions that led to the discovery of the fossils. Cretaceous-Paleogene extinction event (K-Pg), which paved the way for the descent of mammals, including primates, that would lead to the emergence of the first humans.

A new perspective on historical events

“Part of our motivation was to evaluate this question without predetermined assumptions or biases,” said Alex Cox, lead author of the study and a graduate student in the Department of Earth Sciences at Dartmouth. “Most models point to the future. We adapted a model of the carbon cycle to work in reverse, using the effect to use statistics to find the cause and giving it only the bare minimum of prior information as it moves toward a specific outcome.

“Ultimately, it doesn’t matter what we think or what we thought before: the model shows us how we got to what we see in the geological record,” he said.

The model analyzed more than 300,000 possible scenarios of carbon dioxide emissions, sulfur dioxide production and biological productivity in the millions of years before and after the K-Pg extinction event. Using a type of machine learning called Markov Chain Monte Carlo—not unlike the way a smartphone predicts what you’ll type next—the processors worked together independently to compare, verify, and recalculate their conclusions, until they arrived at a scenario consistent with the result obtained in the fossil record. .

Discover the causes of extinction

The geochemical and organic remains of the fossil record clearly reflect the catastrophic conditions that occurred during the K-Pg extinction event, named in reference to the geologic periods on either side of the millennial catastrophe. Across the world, mass extinctions of animals and plants occurred as food webs collapsed in an unstable atmosphere that—laden with sun-blocking sulfur, airborne minerals, and trapping carbon dioxide heat—fluctuates wildly between freezing and scorching temperatures.

Although the effect is clear, the cause of the extinction is unclear. Early theories that attributed the event to volcanic eruptions were overshadowed by the discovery of an impact crater in Mexico called Chicxulub, caused by a kilometer-sized asteroid that is now believed to be the main culprit in the extinction. But theories are beginning to converge as fossil evidence points to a double whammy unprecedented in Earth’s history: The asteroid may have crashed into a planet already affected by the massive and extremely violent eruptions of the Deccan Traps volcanoes in western India.

But scientists still don’t know – or disagree – about the extent to which each event contributed to the mass extinction. So Cox and his advisor Brenhin Keller, assistant professor of geosciences at Dartmouth and co-author of the study, decided to “see what you would get if you let the code decide.”

Modeling results and volcanic impacts

Their model suggested that the release of climate-changing gases from the Deccan Traps alone may have been enough to trigger global extinctions. The traps erupted about 300,000 years before the Chicxulub asteroid. It is estimated that the Deccan Traps pumped up to 10.4 trillion tons of carbon dioxide and 9.3 trillion tons of sulfur into the atmosphere during their nearly million-year eruptions.

“We know from the past that volcanoes can cause mass extinctions, but this is the first independent estimate of fugitive emissions based on evidence of their impact on the environment,” said Keller, who published an article last year noting that Four of the five mass extinctions on Earth were caused by volcanism.

“Our model analyzed the data independently and without human bias to determine the amount of carbon dioxide and sulfur dioxide required to produce the climate and carbon cycle disruptions that we see in the geological record. These amounts turned out to be consistent with what we expect from emissions from the Deccan trap,” said Keller, who has worked extensively to study the connection between Deccan volcanism and the K-Pg extinction.

Asteroid impact and modern context

The model showed a sharp decline in deep-sea organic carbon accumulation at the time of the Chicxulub impact, likely because the asteroid caused the disappearance of many animal and plant species. The record contains evidence of a drop in temperature around the same time, thought to have been caused by the large amount of sulfur – a short-term coolant – that the mammoth meteorite would have thrown into the air as it collided with the sulfur-rich surface. in this area of ​​the planet.

The asteroid impact would also likely have released carbon dioxide and sulfur dioxide. However, the model found that there was no peak in emissions of either gas at this time, suggesting that the asteroid’s contribution to extinction did not depend on gas emissions.

Conclusion: methodological innovation and future applications

In the modern context, Cox said, burning fossil fuels released about 16 billion tons of carbon dioxide into the atmosphere annually between 2000 and 2023. This is 100 times higher than the highest annual emission rate predicted by scientists for the Deccan traps. While this is alarming in itself, it would still take several thousand years for current carbon dioxide emissions to reach the total amount released by ancient volcanoes, Cox said.

“Most encouragingly, the results we obtained are overall physically plausible, which is impressive given that the model could technically have gotten completely out of control without stronger prior constraints,” he said.

Connecting the processors reduced the time it took for the model to analyze such a huge data set from months or years to hours, Cox said. His method and Keller’s can be used to invert other models of the Earth system, such as climate or the carbon cycle, to assess geological events whose consequences are well known, but not the factors that caused them.

“This type of parallel inversion has never been achieved before in geoscience models. “Our method can scale to thousands of processors, giving us a much larger solution space to explore, and it is quite robust to human biases,” Cox said.

“So far, people in our field have been more fascinated by the novelty of the method than by the conclusion we reached,” he laughed. “Any Earth system whose effect is known but not the cause is ripe for reversal. The better we know the outcome, the better we can characterize the input that caused it.


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