Chicxulub impact: How the dino-killing asteroid may have burned everything in an hour or two
A new study, published in the Journal of Geophysical Research: Biogeosciences, indicates that the asteroid impact that created the Chicxulub crater 66 million years ago turned Earth into a giant frying pan. The impact generated a thick layer of fine dust that trapped heat in Earth’s atmosphere, causing temperatures to soar and ignite worldwide wildfires that killed most land animals, including the mighty dinosaurs.
“We're in the realm where we might be essentially killing off everything within that first hour or two,” said lead author Brandon Johnson, a planetary scientist at Purdue University, in a statement. Simulations show that the impact-generated heat vaporized rock and ejected huge amounts of dust high into the atmosphere. After cooling, some rock vapor morphed into tiny rock droplets known as spherules that were blown away from the impact crater. During their descent toward the ground, the spherules behaved like mini meteorites, and their friction with air created an intense, sudden pulse of heat. Previous research indicated that the spherules turned the world into a heat chamber, hot enough to sizzle thick-skinned large animals but not hot enough to make plants burst into flames.
However, this doomsday picture changed in 2023 when scientists stumbled upon new evidence in rock layers that date back to the time of the dinosaurs' extinction. They found a layer of fine post-impact dust that could have formed from rock vapor that didn't condense into spherules. “It reinvigorated my interest in what happened to the leftover vapor—that's where this work started,” said Johnson. For the study, Johnson and his colleagues combined existing simulations of the Chicxulub impact with geological observations from the extinction dust layer.
They then calculated the amount of dust that impact could have released into the atmosphere, boosting Earth’s retention and release of heat energy from the falling spherules. They found that the dust blanket-induced heat was three and a half times more intense than that generated by the spherules alone, generating enough heat that killed animals and triggered global forest fires. The instant heat-induced death scenario also supports another popular extinction theory—a prolonged post-impact winter. “It seems counterintuitive,” Johnson said, “but actually it’s the same effect.”
Think of an insulated mug that can keep soup hot and iced coffee cold. Once spherules disappeared and fires ended, dust clouds blocked the sunlight for years, ushering in a long global winter. The researchers say global fires are mainly responsible for ending the reign of dinosaurs, but a more complete geological record is needed to say that for sure. For the moment North America seems to be the best place offering the incriminating evidence for the wildfires. But further away from the impact site in Mexico, the effects could have become weaker.
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