Roughly 66 million years ago, a massive asteroid crashed into Earth, leaving a crater 12 miles deep by 110 miles wide. The catastrophic collision plunged the planet into a dark, cold winter, and in the aftermath of this disaster, known as the Chicxulub impact, 75 percent of living species, including the non-avian dinosaurs, went extinct.
Scientists generally agree on this version of events, but they’ve long debated what mechanism triggered the global winter that ultimately led to this mass extinction.
Now, they have a new theory: When the asteroid struck what is now Mexico’s Yucatán Peninsula, it sent tiny particles of pulverized granite into the atmosphere. This silicate dust blocked out sunlight, which meant plants couldn’t photosynthesize. And, as a result, several plant-eating animals starved, which would have led more species to disappear.
Based on the results of new paleoclimate modeling—published Monday in the journal Nature Geoscience—photosynthesis came to a halt around the globe within two weeks of the asteroid impact. Photosynthesis did not ramp up again for 620 days, and it did not reach its pre-impact rate for roughly four years, according to the modeling.
The dust particles may have remained in the atmosphere for as long as 15 years and could have contributed to a 27 degree Fahrenheit drop in global temperatures, per the paper.
“The asteroid didn’t kill all the dinosaurs in one go, but it was a more stealthy murderer, which triggered a war of attrition that led three out of every four species to die,” says Steve Brusatte, a paleontologist at the University of Edinburgh who was not involved in the new study, to the Guardian’s Ian Sample.
The new paper is unlikely to be the final word on what killed the dinosaurs. However, while past research has focused on the sunlight-blocking powers of sulfur and soot in the asteroid’s aftermath, this is one of the first studies to look more closely at dust.
“The effects of the dust were not well known,” says study co-author Pim Kaskes, a geologist at Vrije Universiteit Brussel, to the New York Times’ Miriam Fauzia. “Most of the work that has been done used very coarse-grained material that rains very rapidly out of the atmosphere or extremely fine particles that also rain down relatively quickly.”
So, researchers took a closer look at the dust’s impact by examining fine-grain samples from Tanis, a heavily studied geological formation in North Dakota that contains fossils and debris from the aftermath of the Chicxulub impact. After measuring the size of the dust grains at the site, they ran that data through a computer climate model and factored in soot and sulfur particles.
They found the fine silicate dust that got lofted into the air was between 0.8 and 8 micrometers in diameter—thinner than a strand of human hair. Sulfur and soot likely played a role in the global winter, too, however, these particles likely didn’t linger in the atmosphere for as long as the dust did, per the modeling.
This suggests fine dust particles may have played a bigger role in the mass extinction than previously understood.
“The dust-induced disruption in photosynthetic activity is huge, much larger than what we anticipated before this research,” says study co-author Cem Berk Senel, a planetary scientist at the Royal Observatory of Belgium, to Live Science’s Stephanie Pappas.
A global winter driven by dust would explain how plants and animals that could survive while dormant—for example, as a seed or in hibernation—were able to withstand the extinction event. But it doesn’t demonstrate how marine plants survived, per the Times.
More work is needed to definitively determine the exact “killing mechanisms” that followed the asteroid, as Senel tells Nature News’ Katharine Sanderson. Other scientists agree, adding that the team’s new dust measurements will contribute to the development of more accurate paleoclimate models of the Chicxulub impact moving forward.
But, more than likely, there was “no single silver bullet” that killed off most life on Earth, says David Kring, a planetary scientist at the Lunar and Planetary Institute who was not involved in the research, to the Washington Post’s Carolyn Y. Johnson. The asteroid impact also sparked wildfires, tsunamis and acid rain. As such, it was probably a “potpourri of environmental effects” that caused the mass extinction, Kring tells the publication.