Free-thinking computers reverse engineered the fossil record to determine the cause of the cataclysm.
To address the long-standing debate about whether a massive asteroid impact or volcanic activity caused the extinction of the dinosaurs and numerous others seed 66 million years ago, a team at Dartmouth College took an innovative approach. They removed scientists from the discussion and left decisions to computers.
The researchers report in the journal science This is a new modeling technique that leverages interconnected processors to process sets of geological and climate data without human input. They tasked about 130 processors with reverse analysis of the fossil record to pinpoint the events and circumstances that led to the accident. Cretaceous period– The Paleogene (K-Pg) extinction event paved the way for the rise of mammals, including primates, which led to early humans.
A new perspective on historical events
“Part of our motivation was to evaluate this question without any predetermined assumptions or biases,” said Alex, lead author of the study and a graduate student in Dartmouth College’s Department of Earth Sciences.・Mr. Cox stated. “Most models move forward. We adapt our carbon cycle models to run in the opposite direction, using effects to find causes through statistics and minimizing Only limited advance information was given.
“Ultimately, it doesn’t matter what we think or what we thought before. The model will explain how we arrived at what we see in the geological record. “It shows,” 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.some kind of machine learning Known as Markov Chain Monte Carlo – similar to how a smartphone predicts what you’ll input next – processors work together independently until they arrive at a scenario that matches the results stored in the fossil record. We compared, revised and recalculated our conclusions. .
Unraveling the cause of extinction
Geochemical and organic debris in the fossil record clearly capture the catastrophic conditions during the K-Pg extinction, named for the geological epochs on either side of the millennia-long cataclysm. I did. Under an unstable atmosphere rich in sulfur that blocks the sun, floating minerals, and carbon dioxide that traps heat, food webs collapse, conditions fluctuate wildly from frigid temperatures to scorching heat, and plants and animals around the world die on a large scale. I was disappointed.
Although the effects are clear, the causes of extinction remain unresolved. Early theories attributing the event to a volcanic eruption were overturned by the discovery of an impact crater in Mexico known as Chicxulub. This crater was caused by an asteroid several miles wide, which is now believed to be the primary cause of this extinction event. But the theories are starting to converge, as fossil evidence suggests a one-two punch unlike any other in Earth’s history. The asteroid may have struck the planet, which was already reeling from a large and very violent volcanic eruption in the Deccan Traps 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 Brehin Keller, a Dartmouth assistant professor of geosciences and co-author of the study, decided: “Let’s see what we can get if we let the code decide.”
Modeling results and volcanic effects
Their model suggested that the outflow of climate-altering gases from the Deccan Trap alone could have been enough to cause a global extinction. Trap erupted approximately 300,000 years before the Chicxulub asteroid. During their roughly 1 million years of 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.
“While it has been known historically that volcanoes can cause large-scale extinctions, this is the first time that volatile emissions have been independently estimated based on evidence of environmental impact.” Professor Keller said. Last year, he published a paper linking four of Earth’s five mass extinctions to volcanoes. Volcanic activity.
“Our model independently processed the data without human bias and determined the amounts of carbon dioxide and sulfur dioxide needed to cause the disruptions to the climate and carbon cycle seen in the geological record. . These amounts were found to be consistent with what would be expected to be seen in emissions from the Deccan Traps,” said the study, which investigates the link between Deccan volcanism and the extinction of K-Pg. said Keller, who has done extensive research for this purpose.
Modern background with asteroid impact
The model revealed a sharp decline in deep-sea organic carbon accumulation around the time of the Chicxulub impact. This is likely due to the asteroid causing the extinction of many plant and animal species. The record includes evidence of a near-contemporaneous temperature drop that may have been caused by large amounts of sulfur (a short-term coolant) that would have been released into the air when a giant meteorite struck a sulfur-rich surface. It is included. in that region of the globe.
Asteroid impacts also likely released both carbon and sulfur dioxide. However, the model found that there was no sudden increase in the amount of either gas released at that time, suggesting that the asteroid’s contribution to extinction was independent of the amount of gas released.
Conclusion: Methodological innovation and future applications
Cox said that in the modern context, from 2000 to 2023, fossil fuel combustion pumped around 16 billion tonnes of carbon dioxide into the atmosphere annually. This is 100 times more than the project with the highest annual emission rate of scientists from the Deccan Traps. While that in itself is alarming, Cox said it will still be several thousand years before current carbon dioxide emissions match the amount emitted by ancient volcanoes.
“What is most encouraging is that the results we have achieved are largely physically valid. We are aware that without strong prior constraints, the model could have technically run completely out of control. “When you think about it, this is impressive,” he said.
By interconnecting the processors, Cox said, the time it takes for models to analyze such huge data sets has been reduced from months or years to hours. His and Keller’s method inverts other Earth system models, such as climate and carbon cycles, to assess geological events whose outcomes are well known but the factors that led to them are unknown. You can use it.
“This kind of parallel inversion has never been done before in earth science models. Our method can be scaled up to include thousands of processors, allowing us to explore a much wider solution space. and is very resistant to human bias,” Cox said.
“So far, people in our field have been more fascinated by the novelty of our methods than by the conclusions we’ve reached,” he laughed. “Earth systems where we know the effects but not the causes are ripe for reversal. The better we know the outputs, the better we can characterize the inputs that caused them.” .”
Reference: “Bayesian Inversion of Emissions and Export Productivity Across the End-Cretaceous Boundary,” by Alexander A. Cox and C. Brenhin Keller, September 28, 2023. science.
DOI: 10.1126/science.adh3875