killed dinosaurs:For decades, scientists have hotly debated whether an asteroid strike or a massive volcanic eruption ended the reign of the dinosaurs 66 million years ago. At that time, about three-quarters of all life on Earth, including all non-avian dinosaurs, died out, bringing the Cretaceous Period to a dramatic end. Now scientists have developed a new way to identify the real dinosaur killer: let a computer crack it.
The team reports in the Sept. 17 issue of the journal Science that the results of the computational work show that the Deccan Traps eruption produced enough gas to trigger the extinction event. 29. These eruptions lasted for about a million years and spewed vast quantities of gas-filled lava in what is now western India.
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“The goal is not to approach this problem from the point of view of ‘Let’s blame the volcano and explain why’ or ‘Let’s blame the asteroid and explain why,’ but to reduce human harm in the process,” Dartmouth said. Commitment or bias.” Computational geologist Alexander Cox. The idea is to use evidence from the crime scene to work backwards. Scientists have hard evidence: Cores drilled into deep-sea sediments contain geological data that show the release of deadly gases into the atmosphere, especially carbon dioxide, which warms the planet, and sulfur dioxide, which acidifies the oceans. But Cox said the gas could come from an asteroid burning rocks on the planet’s surface or from eruptions in the Deccan Traps.
Cox said previous efforts to understand the source of the gas have focused on timing and studied the pulses of molten rock during the Deccan Traps eruption (SN: 02/21/19). But “we can only make a best guess at [the lava’s] initial gas content.” Estimates of carbon dioxide concentrations in lava, for example, vary by orders of magnitude, he said. “So we’re addressing this problem from a gas emission perspective, not from a lava flow perspective.”
To determine the relative contribution of each possible culprit, Cox and Dartmouth geologist C. Brenhin Keller used a statistical model called the Markov Chain Monte Carlo method. This method systematically considers the probabilities of different scenarios of gas emissions from different sources and gradually moves towards possible solutions as simulation results approach geological observations. Cox said the researchers’ approach is particularly powerful because they use 128 different processors to run the scenarios in parallel. “All processors compare their performance at the end of each model run, just as classmates compare answers.” This parallel computation means that a computation that would have taken a year takes only a few days. Cox and Keller used observational data collected from three cores drilled into deep-sea sediments, each dating back 67 million to 65 million years. These sediments contain foraminifera, marine-dwelling microorganisms whose carbonate shells contain different isotopes, or forms, of carbon and oxygen. The chemical composition of these shells records the chemistry of the ocean at the time of their formation and can therefore be used as a proxy to infer past global temperatures and how many organisms flourished in the ocean and how much carbon moved between atmospheres. , Sea and land (SN: 16.1.20).
Computer simulations showed that the amount of gases released into the atmosphere by the volcanic activity was sufficient to explain the changes in temperature and carbon cycles inferred from the foraminifera data in the boreholes. As for the asteroid impact that created the giant Chicxulub crater in what is now Mexico, it likely did not produce significant amounts of carbon dioxide or sulfur dioxide, the analysis found (SN: 1/25/17).
But many scientists are not convinced that these findings provide a definitive answer to this long-standing and complex question. “It’s an elegant way to solve this problem,” said Sierra Petersen, a geochemist at the University of Michigan in Ann Arbor. Modeling in this way allows the freedom to find consensus solutions while considering multiple proxy registrations. But as with any model, the output depends on the input. “
Peterson points out that foraminifera shells are not a perfect proxy for ancient temperatures: the ratio of oxygen isotopes in foraminifera shells changes not only with temperature but also with seawater composition. Different temperature proxies can cause the model to reproduce different patterns of gas release, Peterson said. As for the culprits behind the mass extinction, she added: “It’s a bit of an exaggeration to say that this study shows that the impact didn’t cause the extinction. I think they show that the impact probably wasn’t related to the massive [gas] release.” But she said that was not the case. The asteroid may still have other lethal effects on Earth’s environment. In fact, Chicxulub’s impact “caused many harmful effects beyond the carbon dioxide and sulfur dioxide emissions investigated in this study,” says paleoclimatologist Clay Tabor of the University of Connecticut in Storrs. I said.
This included large amounts of soot and dust that were thrown from the crushed rock by the impact, he said. Previous research suggests that this dust can reduce the amount of sunlight reaching Earth by 20 percent, leading to cold winters that quickly kill plants and destroy habitats (SN: 7/17/20).
In addition, the new study shows that asteroid impacts had no long-term effects on Earth’s carbon cycle, based on carbon isotope data recorded in foraminiferal shells millions of years after the extinction. But at the moment of impact, the creatures suddenly dropped in numbers, Tabor said. “The rapid changes caused by the Chicxulub impact may have been responsible for its impact on life.”
“Both the many geochemical records covering [the extinction event] and this modeling effort do not represent the changes associated with the Chicxulub impact very well,” he said. “This impact probably released much less carbon dioxide and sulfur dioxide than the Deccan trap, but it was released almost immediately,” Tabor said. So while the asteroid impact released less gas overall, the release rate was still potentially devastating.