Dinosaurs died out within hours, new study suggests
Popular Science...
The reign of the dinosaurs undisputedly came to a dramatic conclusion 66 million years ago, after the six-mile-wide Chicxulub asteroid slammed into what is now Mexico’s Yucatán Peninsula. However, the exact timeline of their extinction remains a matter of debate. Did most of the Earth’s species die a slow death of starvation after a dust-choked atmosphere blocked sunlight and ushered in a prolonged winter? Or did they quickly incinerate from globe-spanning wildfires sparked by falling, superheated space rock debris?
According to new evidence published today in the Journal of Geophysical Research: Biogeosciences, the answer may be the flash-cooked scenario.
“We’re in the realm where we might be essentially killing off everything within that first hour or two,” said Brandon Johnson, a Purdue University planetary scientist and study co-author.
A truly global catastrophe
Chicxulub would have immediately wiped out all life within a wide radius of its impact along the Cretaceous–Paleogene boundary, the geological demarcation between the age of the dinosaurs and the Cenozoic era. Traveling at a rate of speed of about 12 miles-per-second, the asteroid struck Earth with the equivalent force of 100 teratons of TNT—more than one billion times the strength of the atomic blasts at Hiroshima and Nagasaki. The blast created a 62-mile-wide, 19-mile-deep cavity while generating two-mile-high tsunamis and 620 mph winds. Around 25 trillion metric tons of debris rocketed into the atmosphere, which then rained down on Earth as fiery missiles called spherules to set forests ablaze.
A large amount of material was also transformed into gaseous rock vapor that traveled high into the atmosphere. In 2023, researchers documented a fine layer of dust in North America that may have even started as the atmospheric vapor.
“It reinvigorated my interest in what happened to the leftover vapor—that’s where this work started,” Johnson recalled.
Instant death
Using the leftover vapor as a starting point, Johnson and his colleagues merged existing computer simulations of the Chicxulub event with data from the extinction-era dust kicked up by the crater. Based on these simulations, the atmospheric blanket of rock vapor would have been even more deadly than the superhot spherules. Acting like a thick blanket of insulation, the dust cloud may have heated surface conditions at least 3.5 times hotter than the rocky debris alone. This would have been more than enough to instantly kill vast numbers of animals, while igniting spontaneous fires around the world.
“This work of ours supports this idea that it really is the impact that was devastating to terrestrial life and caused the mass extinction,” argued Johnson.
At the same time, the study’s authors conceded their findings may still support the slow-starvation extinction theory.
“It seems counterintuitive, but actually it’s the same effect,” said Johnson.
He said that the situation worked like a thermos designed to both keep liquids hot or cold for hours. After the infernos sparked by falling superheated rocks died out, the lingering atmospheric dust would then have obscured sunlight and warmth for years or even decades.
Johnson and his study co-authors still theorize that forest fires were responsible for the vast majority of global deaths within a comparatively short period of time. They also say that more data is needed to truly confirm their theory. Right now, most of the Chicxulub event wildfire evidence is located in North America, meaning there were fewer blazes further from ground zero.
“It could be that we will eventually find the record of completely global wildfires,” suggested University College London paleontologist Alessandro Chiarenza (who wasn’t involved in the study). “We just don’t have it so far.”
Either way, the Chicxulub asteroid extinction event was as devastating as it was thorough—spelling doom for Earth’s dinosaurs no matter the timeline.
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