Dartmouth scientists have 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 the dinosaurs. This pioneering approach opens new horizons for investigating other geological events.
Free-thinking computers reverse-engineered the fossil record to determine the causes of the disaster.
To address the long-standing debate about whether a massive asteroid impact or volcanic activity caused the extinction of dinosaurs and many other creatures. Classify 66 million years ago, a team at Dartmouth College took an innovative approach, keeping scientists out of the debate and letting computers decide.
Researchers report in the magazine Sciences A new modeling method powered by interconnected processors that can work through sets of geological and climate data without human intervention. They commissioned approximately 130 processors to analyze the fossil record backwards to determine the events and conditions that led to this. Cretaceous period– The Paleogene (K–Pg) extinction event paved the way for the rise 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 a pre-specified hypothesis or bias,” said Alex Cox, first author of the study and a graduate student in Dartmouth’s Department of Geosciences. “Most models move in a forward direction. We have adapted the carbon cycle model to work in the other direction, using forcing to find cause through statistics, and giving it only minimal prior information as it works toward a particular outcome.”
“In the end, it doesn’t matter what we think or what we previously thought — the model shows 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 in the million years before and after the K-Pg extinction. Through 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 came up with a scenario that matched the result preserved in the fossil record.
Discovering the causes of extinction
Geochemical and organic remains in the fossil record clearly show the catastrophic conditions that occurred during the K-Pg extinction, named after the geological periods on either side of the catastrophe that lasted thousands of years. Animals and plants around the world have suffered massive die-offs as food webs collapse as an unstable atmosphere — laden with sun-polluting sulfur, airborne metals, and heat-trapping carbon dioxide — swings wildly from freezing to scorching conditions.
While 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 of an impact crater in Mexico known as Chicxulub that was created by a miles-wide asteroid now believed to be primarily responsible for the extinction event. However, theories are beginning to converge, as fossil evidence suggests a one-two punch unlike anything in Earth’s history: the asteroid may have collided with a planet already suffering from massive, extremely violent volcanic eruptions in the Deccan Traps in western India.
But scientists still don’t know — and don’t agree — 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 influx of climate-changing gases from the Deccan Traps alone could be enough to trigger global extinction. The traps exploded approximately 300,000 years before the Chicxulub asteroid. During the 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.
“We have known historically that volcanoes can cause mass extinctions, but this is the first independent estimate of volatile emissions drawn from evidence of their environmental impacts,” said Keller, who published research last year linking four out of five mass extinctions on Earth. Volcanoes.
“Our model worked through 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. “Our model worked through the data independently and without human bias to determine the relationship between the Deccan volcanism and the K-Pg extinction,” said Keller, who has worked extensively to study the relationship between the Deccan volcanism and the K-Pg extinction. “These quantities turned out to be consistent with what we would expect to see in emissions from Deccan traps.”
Asteroid impact and modern context
The model has revealed a sharp decline in organic carbon accumulation in the deep ocean around the time of the Chicxulub impact, which was likely the result of the asteroid causing the demise of many animal and plant species. The record contains traces of a drop in temperature around the same time that could have been caused by a large amount of sulfur – a short-lived cooling agent – that the massive meteorite would have thrown into the air when it struck the sulfur-rich surface in that region of the planet. .
The asteroid impact would also likely release both carbon dioxide and sulfur. However, the model found that there was no rise in emissions of either gas at that time, suggesting that the asteroid’s contribution to the extinction was not contingent on gas emissions.
Conclusion: Methodological innovation and future applications
In the modern context, Cox said, burning fossil fuels from 2000 to 2023 resulted in about 16 billion tons of carbon dioxide being pumped into the atmosphere annually. This is 100 times greater than the highest annual emission rate scientists expect from the Deccan traps. Although alarming in itself, it will take a few thousand years for current carbon dioxide emissions to match the total amount emitted by ancient volcanoes, Cox said.
“What’s even more encouraging is that our results are physically plausible at scale, which is impressive given that the model could have been quite technically runaway without stronger prior constraints,” he said.
Connecting the processors has shortened the time it takes for the model to analyze such a huge data set from months or years to hours, Cox said. His method and his method of inverting models of other Earth systems – such as those of climate, or the carbon cycle – can be used to evaluate geological events whose outcomes are well known, but not the factors that led to those events.
“This type of parallel inversion has never been done in Earth science models before. Our method can be scaled to thousands of processors, giving us a much wider solution space to explore, and is completely resistant 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 ready to capsize. The better we know the outputs, the better we can describe the inputs that caused them.”
Reference: “Bayesian inversion of emissions and export productivity across the End-Cretaceous boundary” by Alexander A. Cox and C. Brynhen Keller, September 28, 2023, Sciences.
doi: 10.1126/science.adh3875
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