The reign of the dinosaurs inarguably came to a dramatic conclusion 66 million years ago, after the six-mile-wide asteroid Chicxulub slammed into what is now Mexico’s Yucatan Peninsula. However, the exact timeline of their extinction remains a topic of debate. Did most of Earth’s species slowly starve to death after a dust-clogged atmosphere blocked sunlight and caused a prolonged winter? Or were they quickly incinerated by worldwide wildfires sparked by falling superheated space rock debris?

According to new evidence published today in the Geophysical Research Journal: Biogeosciencesthe answer may be the quickly prepared stage.

“We’re in the realm where we could essentially be killing everything in that first hour or two,” said Brandon Johnson, a planetary scientist at Purdue University and co-author of the study.

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 dinosaurs and the Cenozoic era. Traveling at a speed of about 12 miles per second, the asteroid slammed into Earth with the force equivalent to 100 teratons of TNT, more than a billion times the force of the atomic explosions at Hiroshima and Nagasaki. The explosion created a cavity 62 miles wide and 19 miles deep and generated two-mile-high tsunamis and 620 mph winds. About 25 trillion metric tons of debris were launched into the atmosphere, which then rained down on Earth in the form of burning missiles called spherules to set forests on fire.

A large amount of material was also transformed into gaseous rock vapor that traveled high into the atmosphere. In 2023, researchers documented a thin layer of dust in North America that may have even started as atmospheric vapor.

“This rekindled my interest in what happened to the leftover steam; that’s where this work began,” 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 extinction-era dust kicked up by the crater. According to these simulations, the atmospheric layer of rock vapor would have been even deadlier than the superhot spherules. Acting as a thick layer of insulation, the dust cloud may have heated surface conditions at least 3.5 times more than the rock debris alone. This would have been more than enough to instantly kill large numbers of animals and at the same time cause spontaneous fires around the world.

“This work of ours supports the idea that it really was the impact that was devastating to terrestrial life and caused the mass extinction,” Johnson argued.

At the same time, the study’s authors admitted that their findings may still support the slow starvation theory of extinction.

“It seems contradictory, but it’s actually the same effect,” Johnson said.

He said the situation worked like a thermos designed to keep liquids both hot and cold for hours. After the infernos caused by falling superheated rocks died out, lingering atmospheric dust would have obscured sunlight and heat for years or even decades.

Johnson and his study’s co-authors still theorize that wildfires were responsible for the vast majority of global deaths in a comparatively short period of time. They also say more data is needed to truly confirm their theory. Right now, most of the wildfire evidence from the Chicxulub event is in North America, meaning there were fewer fires farther from ground zero.

“It could be that we will eventually find the wildfire record completely global,” suggested University College London paleontologist Alessandro Chiarenza (who was not involved in the study). “We just don’t have it so far.”

Either way, the Chicxulub asteroid extinction was as devastating as it was complete: It spelled doom for Earth’s dinosaurs regardless of the timeline.

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