Study removes human bias from debate over dinosaurs' demise

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SEPTEMBER 28, 2023

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Study removes human bias from debate over dinosaurs' demise

by Dartmouth College

Credit: Pixabay/CC0 Public Domain

To resolve the scientific debate surrounding the extinction of dinosaurs and numerous other species 66 million years ago, Dartmouth researchers have implemented a novel approach: removing human scientists from the equation and allowing computers to make the determination.

The researchers have developed a new modeling method that utilizes interconnected processors to analyze vast amounts of geological and climate data, eliminating the need for human input. Their findings were published on September 29 in the paper titled "A Bayesian inversion for emissions and export productivity across the end-Cretaceous boundary," featured in Science.

The team directed nearly 130 processors to analyze the fossil record in reverse, aiming to identify the specific events and conditions that led to the Cretaceous-Paleogene (K-Pg) extinction event. This event paved the way for the dominance of mammals, including primates that eventually led to the emergence of early humans.

"Our intention was to approach this question without any preconceived hypotheses or biases," explained Alex Cox, the study's first author and a graduate student in Dartmouth's Department of Earth Sciences. "Most models operate in a forward direction. However, we adapted a carbon-cycle model to work in reverse, utilizing statistical techniques to discern the cause from the effect. We provided the model with only the minimum prior information necessary for it to work towards a specific outcome."

Cox emphasizes that the model's output supersedes personal beliefs or previous assumptions. "Ultimately, it doesn't matter what we think or what we previously thought. The model reveals how we arrived at the observations present in the geological record," he added.

The model underwent an examination of more than 300,000 potential scenarios involving carbon dioxide emissions, sulfur dioxide output, and biological productivity during the one million years prior to and following the K-Pg extinction. Using a form of machine learning called Markov Chain Monte Carlo, similar to how a smartphone predicts text input, the processors independently collaborated to compare, revise, and recalculate their conclusions until they converged upon a scenario that aligns with the evidence preserved in the fossil record.

Geochemical and organic remains within the fossil record undoubtedly portray the catastrophic conditions during the K-Pg extinction, named for the geological periods encompassing the cataclysm that spanned millennia.

The disruption caused by an unstable atmosphere, laden with light-blocking sulfur, airborne minerals, and heat-trapping carbon dioxide, resulted in massive die-offs of animals and plants worldwide. Fluctuating between freezing and scorching conditions, the collapse of food webs was evident.

While the effect of the extinction is clear, its cause remains unresolved. Early theories attributing the event to volcanic eruptions have been overshadowed by the discovery of the Chicxulub impact crater in Mexico, believed to have resulted from a colossal asteroid strike that played a primary role in the extinction. However, fossil evidence is beginning to suggest a dual impact unlike anything experienced in Earth's history, proposing that the asteroid collided with a planet already reeling from the violent eruptions of volcanoes in the Deccan Traps region of western India.

Nevertheless, scientists still lack consensus on the extent to which each event contributed to the mass extinction. Consequently, Cox and his advisor Brenhin Keller, Assistant Professor of Earth Sciences at Dartmouth and co-author of the study, opted to "allow the code to decide" and determine the outcome.

According to their model, the outpouring of climate-altering gases solely from the Deccan Traps could have been sufficient to trigger the global extinction event. The Deccan Traps had been erupting for approximately 300,000 years prior to the Chicxulub asteroid impact. Over the course of nearly one million years, these eruptions are estimated to have released up to 10.4 trillion tons of carbon dioxide and 9.3 trillion tons of sulfur into the atmosphere.

"While it has been historically known that volcanoes can induce mass extinctions, this study represents the first independent estimation of volatile emissions based on evidence from their environmental effects," remarked Keller, who published a paper last year highlighting the connection between volcanism and four of the five major mass extinctions on Earth.

"Our model independently worked through the data without human bias, determining the necessary amounts of carbon dioxide and sulfur dioxide to produce the observed disruptions in climate and carbon cycling within the geological record. These quantities align with our expectations for emissions from the Deccan Traps," Keller stated. He has conducted extensive research exploring the link between Deccan volcanism and the K-Pg extinction.

The model did identify a sharp decline in the accumulation of organic carbon in the deep ocean during the period around the Chicxulub impact. This decline likely resulted from the asteroid's impact, leading to the extinction of numerous animal and plant species. The fossil record contains evidence of a temperature decrease during this time, indicating