Volcanoes or asteroids? Artificial intelligence ends the debate about the extinction of dinosaurs

Free-thinking computers reverse-engineered the fossil record to determine the causes of the disaster.

Addressing the long-standing debate about whether a massive asteroid impact or volcanic activity caused the extinction of dinosaurs and many others Classify 66 million years ago, a team at Dartmouth College took an innovative approach: they kept scientists out of the debate and let computers decide.

Researchers report in the magazine science A new modeling method powered by interconnected processors capable of processing volumes of geological and climate data without human intervention. They commissioned approximately 130 processors to analyze the fossil record backwards to determine the events and circumstances that led to the discovery of the fossils. Cretaceous period– The Paleogene (K–Pg) extinction event paved the way for the lineage of mammals, including primates, that gave rise to the first humans.

A new perspective on historical events

“Part of our motivation was to evaluate this question without pre-established assumptions or biases,” said Alex Cox, first author of the study and a graduate student in Dartmouth’s Department of Geosciences. “Most models point to the future. We adapted a model of the carbon cycle to work in the other direction, using the effect to find the cause using statistics, giving it only minimal past information as it moved toward a particular outcome.”

“In the end, it doesn’t matter what we think or what we thought previously: the model tells us how we got to what we see in the geologic record,” he said.

The model analyzed more than 300,000 possible scenarios for carbon dioxide emissions, sulfur dioxide production, and biological productivity over a million years before and after the K-Pg extinction. Thanks kind of Machine learning Known as a Markov chain Monte Carlo — not unlike the way a smartphone predicts what you’ll type next — the processors worked together independently to compare, revise, and recalculate their conclusions until they arrived at a scenario that matched the outcome saved in the fossil record. .

Discover the causes of extinction

The geochemical and organic remains of the fossil record clearly illustrate the catastrophic conditions that occurred during the K-Pg extinction, so named in reference to the geological periods on either side of the Millennium Catastrophe. Animals and plants around the world have suffered mass die-offs as food webs collapse as an unstable atmosphere — laden with sunlight-blocking sulfur, airborne minerals and heat-trapping carbon dioxide — oscillates wildly between freezing and scorching conditions.

Although the effect is clear, the cause of the extinction has not been resolved. Early theories attributing the event to volcanic eruptions were overshadowed by the discovery in Mexico of an impact crater known as Chicxulub, caused by a miles-wide asteroid, now thought to be primarily responsible for the extinction. However, theories are beginning to converge, as fossil evidence points to a double whammy unprecedented in Earth’s history: the asteroid may have collided with a planet already suffering from the massive and extremely violent eruptions of the Deccan Traps volcanoes, in western India.

But scientists still don’t know — or agree on — how much each event contributed to the mass extinction. So Cox and his advisor Brenhen Keller, assistant professor of geosciences at Dartmouth and co-author of the study, decided to “see what you get if you let the code decide.”

Modeling results and volcanic forcing

Their model suggests that the release of climate-changing gases from the Deccan Traps alone could be enough to trigger global extinction. The traps went off about 300,000 years before the Chicxulub asteroid. During their nearly million-year eruptions, the Deccan Traps are estimated to have pumped up to 10.4 trillion tons of carbon dioxide and 9.3 trillion tons of sulfur into the atmosphere.

“We know historically that volcanoes can cause mass extinctions, but this is the first independent estimate of volatile emissions based on evidence of their effects,” said Keller, who published research last year linking four of five mass extinctions on Earth to being caused by volcanoes. “environmental.” .

“Our model analyzed the data independently and without human bias to determine how much carbon dioxide and sulfur dioxide would be needed to produce the climate and carbon cycle perturbations that we see in the geological record. “It shows that there is a lot of carbon dioxide in the atmosphere,” said Keller, who has worked extensively to study the relationship between the Deccan volcanism and the K-Pg extinction. “These amounts are consistent with what we would expect from Deccan Trap emissions.”

Asteroid impact and modern context

The model revealed a sharp decline in organic carbon accumulation in the deep ocean at the time of the Chicxulub impact, likely due to the fact that 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 a large amount of sulfur – a short-lived cooling agent – ​​that the giant meteorite would have thrown into the air when it collided with the massive meteorite. Sulfur-rich surface. In this region of the planet.

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

Conclusion: methodological innovation and future applications

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

“What’s even more encouraging is that the results we obtained are generally physically plausible, which is impressive given that the model could have been completely runaway technically without stronger prior constraints,” he said.

Cox said that connecting the processors reduced the time needed for the model to analyze this huge data set from months or years to hours. His and Keller’s method can be used to invert other models of Earth systems, such as climate or the carbon cycle, to evaluate geological events whose outcomes are well known, but not the factors that caused them.

“This kind of parallel inversion has never been achieved in Earth science models before. Our method can be scaled to thousands of processors, giving us a much larger solution space to explore, and is very robust to human bias,” Cox said.

“So far, people in our field have been more impressed by the novelty of the method than by our result,” he said with a laugh. “Any Earth system whose effect but not its cause we know is ripe for reversal. The better we know the outcome, the better we can describe the inputs that caused it.”