The end-Cretaceous mass extinction, which included the elimination of all non-avian dinosaurs, occurred after the impact of the Chicxulub asteroid and during a stretch of the Deccan Traps volcanism in western India. Although it is known that the impact is temporally linked to the extinction, the relative roles are hard to disentangle. To help resolve the scientific debate, researchers at Dartmouth College tried a new approach — they removed scientists from the debate and let computers decide. They developed a new modeling method powered by interconnected processors that can work through reams of geological and climate data without human input. They tasked nearly 130 processors with analyzing the fossil record in reverse to pinpoint events and conditions that led to the end-Cretaceous mass extinction.
The end-Cretaceous mass extinction was marked by both the Chicxulub asteroid impact and the ongoing eruptions of the Deccan Traps volcanoes.
About 66 million years ago, the end-Cretaceous extinction event eradicated roughly 75% of the animal and plant species on Earth, including whole groups like non-avian dinosaurs and ammonites.
Early theories attributing the event to volcanic eruptions have been eclipsed by the discovery of an impact crater in Mexico known as Chicxulub that was caused by a huge asteroid now thought to be primarily responsible for the extinction event.
The theories have begun to converge, however, as fossil evidence suggests a one-two punch unlike anything in Earth’s history: the asteroid may have slammed into a planet already reeling from the massive, extremely violent eruptions of volcanoes in the Deccan Traps.
But scientists still do not know — nor agree on — the extent to which each event contributed to the mass extinction.
So, Dartmouth College researchers Alexander Cox and Brenhin Keller decided to see what they would get if they let the code decide.
Their model suggested that the outpouring of climate-altering gases from the Deccan Traps alone could have been sufficient to trigger the global extinction.
The Deccan Traps had been erupting for roughly 300,000 years before the Chicxulub asteroid.
During their nearly 1 million years of eruptions, the 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’ve known historically that volcanoes can cause massive extinctions, but this is the first independent estimation of volatile emissions taken from the evidence of their environmental effects,” Dr. Keller said.
“Our model worked through 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 we see in the geologic record.”
“These amounts turned out to be consistent with what we expect to see in emissions from the Deccan Traps.”
The model did reveal a steep drop in the accumulation of organic carbon in the deep ocean around the time of the Chicxulub impact, which likely resulted from the asteroid causing the demise of numerous animal and plant species.
The record contains traces of a decrease in temperature around the same time that would have been caused by the large amount of sulfur — a short-term cooling agent — the mammoth meteorite would have ejected into the air when it collided with the sulfur-rich surface on that area of the planet.
The asteroid impact also would have likely emitted both carbon and sulfur dioxide.
However, the model found that there was no spike in the emissions of either gas at that time, suggesting that the asteroid’s contribution to the extinction did not hinge on gas emissions.
“In modern context, the burning of fossil fuels from 2000 to 2023 has pumped about 16 billion tons of carbon dioxide into the atmosphere per year,” Cox said.
“This is 100 times greater than the highest annual emission rate scientists project from the Deccan Traps.”
“While alarming on its own, it would still take a few thousand years for current carbon dioxide emissions to match the total amount that spewed forth from the ancient volcanoes.”
“Most heartening is that the results we achieved are broadly physically plausible, which is impressive given that the model could have technically run completely wild without stronger prior constraints.”
The results were published in the journal Science.
Alexander A. Cox & C. Brenhin Keller. 2023. A Bayesian inversion for emissions and export productivity across the end-Cretaceous boundary. Science 381; doi: 10.1126/science.adh3875
Source : Breaking Science News