AGU press contact: Sasha Warren, [email protected] (UTC-6 hours)

Purdue University press contact: Brittany Steff, [email protected] (UTC-5 hours)

Researcher contact: Brandon C. Johnson, Purdue University, [email protected] (UTC -5 hours)

WASHINGTON - 66 million years ago, the six-mile-wide Chicxulub asteroid crash-landed in Mexico's Yucatán Peninsula and changed life on Earth forever. The reign of the dinosaurs ended, and only creatures that could shelter in burrows or shallow waters survived into the age of mammals that followed.

Friction between the atmosphere and debris falling back to earth from the impact caused an intense heat pulse in the immediate aftermath. A new study has found that a thick, global blanket of dust likely insulated the atmosphere, trapping and radiating enough heat down to the surface to ignite worldwide wildfires and burn even the thickest-skinned animals to a crisp.

"We're in the realm where we might be essentially killing off everything within that first hour or two," said Brandon Johnson, a planetary scientist at Purdue University and lead author of the study. This result reinvigorates the decades-long debate around whether it was the asteroid impact or another after effect that killed the dinosaurs.

The study will appear Tuesday 28 July in Journal of Geophysical Research: Biogeosciences, AGU's journal for research on the biogeosciences of the past, present, and future Earth.

The fiery aftermath of an impact

When Chicxulub hit the Earth, we know from geology and impact simulations that the resulting temperatures, pressures, and release of energy vaporized rock, kicking an enormous cloud of dust and rock vapor - literally gaseous rock - high into the atmosphere. Some rock vapor cooled and condensed into tiny rock droplets known as spherules that flew away from the impact crater, then careened back to the surface like mini meteorites. On the way down, the friction between the air and the falling spherules generated an intense pulse of heat.

Previous studies suggested that the spherules had an effect like turning on a world-wide broiler - radiating enough heat to sizzle thin-skinned animals without shelter, but not enough for plants to suddenly burst into flames.

For a while, this moved researchers away from the idea that the immediate effects of the Chicxulub impact caused the extinction. However, in 2023, new evidence from layers of rock recording the dinosaurs' extinction event in North America unearthed another piece of evidence in the story: a layer of extremely fine post-impact dust that could have formed from rock vapor that didn't condense to form spherules. "It reinvigorated my interest in what happened to the leftover vapor - that's where this work started," Johnson said.

Combining previous simulations of the Chicxulub impact with geologic observations from the extinction dust layer, the new study calculated the amount of dust in the atmosphere after impact and, crucially, how that dust layer would boost Earth's retention and release of heat energy from the falling spherules. With the dust blanket, the heat at the surface would have been 3.5 times more intense than with the spherules alone - enough to kill animals and start spontaneous forest fires.

"This work of ours supports this idea that it really is the impact that was devastating to terrestrial life and caused the mass extinction," said Johnson.

A flash in the pan or a slow decline?

The same dust driving Johnson's global fires theory also supports another popular extinction idea: that dinosaurs might also have starved to death through a prolonged post-impact winter.

"It seems counterintuitive," Johnson said, "but actually it's the same effect." Similar to how an insulated mug can be used to keep both soup hot and iced coffee cold, once the spherules finished falling and the fires petered out, massive dust clouds could have blocked warmth from the Sun for years to decades and caused a global winter.

Johnson and his co-authors believe global fires were the bigger killer, but only a more complete geologic record can pin that down. To date, the best evidence for wildfires during the extinction event comes from North America, but it's possible that the effects were weaker or different further away from the impact site in Mexico.

"It could be that we will eventually find the record of completely global wildfires," said Alfio Alessandro Chiarenza, a paleontologist at University College London who was not involved with this study. "We just don't have it so far."

This matters because the extinction of the dinosaurs is the best record we have of how entire ecosystems respond to disaster. Knowing whether animals burned alive quickly or starved slowly over decades is important for interpreting the impact a major disruption like Chicxulub had on evolution and ecosystem recovery.

"It would be great to figure out which animals survived right at the impact and what their biological features were," Chiarenza said. "This could finally tell us why some animals made it when others, like the dinosaurs, didn't."

Notes for journalists:

This study appears in Journal of Geophysical Research: Biogeosciences, an AGU journal. View and download a PDF of the study here. Neither this press release nor the study is under embargo.

Paper title:

"Heat and wildfires during the K-Pg mass extinction enhanced by fine dust"

Authors:

• Brandon C. Johnson, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, USA.
• Alexandria V. Johnson, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA.
• Shigeru Wakita, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA.
• Douglas S. Robertson, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.

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Purdue University has also published a web story on this study: www.purdue.edu/newsroom/2026/Q3/dinosaur-killing-asteroid-also-created-a-dust-cloud-that-insulated-earth-charbroiling-cretaceous-creatures