Fine dust lofted by the Chicxulub asteroid impact may have trapped an intense pulse of heat near Earth's surface, igniting widespread fires and killing exposed animals within the first hours of the catastrophe 66 million years ago. A peer-reviewed modeling study published July 28 in the Journal of Geophysical Research: Biogeosciences proposes a mechanism that could help explain why the impact near today's Yucatán Peninsula eliminated about three-quarters of species, including all non-avian dinosaurs.
The roughly six-mile-wide asteroid vaporized more than 1,000 cubic kilometers of terrestrial material, according to earlier work cited by the Purdue University-led team. As the expanding plume cooled, some rock vapor condensed into molten droplets called spherules, about 250 micrometers across. Those particles spread around the planet and heated the air as they fell, producing thermal radiation, but previous calculations suggested that spherules alone might not have generated enough energy to ignite forests globally.
Lead author Brandon Johnson and colleagues added a layer of much finer dust to impact simulations, guided by geological observations of extinction-boundary deposits. The particles were about 2.5 micrometers wide, roughly one-tenth the diameter of the spherules and similar in size to smoke particles that can penetrate human lungs. The team's calculations indicate that this opaque global layer would have prevented most heat from escaping to space and redirected it toward the ground.
With the dust included, the modeled surface heat was 3.5 times stronger than the pulse from falling spherules alone. Purdue said the resulting thermal dose reached about 17 times a level considered fully lethal to humans and was sufficient to ignite grass, pine needles and lichen, and possibly wood. The study therefore suggests that animals able to shelter underground, underwater or behind other barriers had a major immediate advantage, before the same dust later blocked sunlight and contributed to a cold impact winter.
The authors say their result strengthens the case that the impact itself devastated land ecosystems rapidly, rather than extinction occurring only through a slower collapse of food chains. However, they do not claim the question is settled. Paleontologist Alfio Alessandro Chiarenza, who was not involved in the research, noted that the strongest geological evidence for fires currently comes from North America, so scientists have not yet demonstrated that wildfires covered the entire planet.
Future fieldwork must test the model against a more complete global rock record and determine whether fire signatures weaken with distance from Mexico. Such evidence could clarify which animals survived the first hours, which biological traits protected them, and how immediate heating interacted with years or decades of darkness, cooling and polluted air. The new study reframes fine dust as a possible agent of both extremes: first acting as an insulating lid that retained lethal heat, then as a sun-blocking veil that prolonged ecological disruption.
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