Chicxulub asteroid impact created 2-year cloud of dust that may have killed the dinosaurs

Sharmila Kuthunur
Wed, November 1, 2023

Dinosaurs look on as an asteroid plumets through the sky.

66 million years ago, a large asteroid crashed into Earth near Mexico's Yucatán Peninsula, sparking a frigid global winter that led to the mass extinction of dinosaurs who had reigned over the planet for over 160 million years.

"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," Steve Brusatte, a paleontologist at the University of Edinburgh unaffiliated with the new study, told Guardian's Ian Sample.

Scientists generally agree the Chicxulub impact wiped out 75% of all species on Earth, but precisely what caused the extreme and abrupt shift in climate following the event has been an open question. Now, new research pins it down to very fine dust particles that were blasted into the atmosphere due to the impact. A layer of dust blanketed Earth for up to 20 years, "in which the first five to eight years are the most severe," Cem Berk Senel, a postdoctoral researcher in planetary science at the Royal Observatory of Belgium and his team write in the new study.

Related: Asteroid that killed the dinosaurs: Likely origin and what we know about the famous space rock

In the first year after the impact, global temperatures dropped by more than 10 degrees Celsius (18 degrees Fahrenheit).

Previous research focused on two other contributors to the long, dark winter that followed: Soot and sulfur, which absorb and block sunlight more effectively than dust. However, a 66-million-year-old rock sample Senel and his team collected in North Dakota, about 1,800 miles (3,000 km) north of the Chicxulub crater, shows a lot more fine dust particles than expected, suggesting dust played a bigger role in the cataclysmic event than previously thought.

The change in Earth's history from what geoscientists call the Cretaceous period to the Palaeogene period is recorded in a 4.3-foot-thick (1.3 meters) part of the collected rock, which formed at the time of the Chicxulub event. After measuring the sizes of particles in this section of rock, Senel and his team used the data to simulate post-impact climate. The simulation predicted a blanket of dust particles between 0.8 and 8 micrometers in diameter formed just a week after impact.

Within two weeks, that blanket, which researchers suspect hovered in Earth's atmosphere longer than soot and sulfur, stopped plants from photosynthesizing for up to two years. The shut down in turn starved species relying on them, including non-avian dinosaurs, according to the new study.

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The new study underscores the thus-far overlooked role of dust particles in the global impact winter. However, it's unlikely to be the final word on whether soot or dust caused the cooling, as variations in climate models could lead to different results.

The new study, for instance, explains how hibernating plants and animals could have survived the two-year-period without photosynthesis, but it doesn't explain how freshwater organisms survived the impact.

So more research is needed to better understand the "exact killing mechanisms" after the Chicxulub impact, said Senel.

This research is described in a paper published Oct. 30 in the journal Nature Geoscience.

Dust Doomed the Dinos, Scientists Say

Isaac Schultz
Thu, November 2, 2023 

A paleoart illustration of a Dakotaraptor steini navigating the fallout of the Chicxulub impact.


We all know how the story goes: a large asteroid falls to Earth from space, slamming into the Yucatán Peninsula with 100 million megatons of force. The impact spawned tsunami waves best measured in miles and kicked up dust, soot, and sulfur that blotted out the Sun, causing the death of about 75% of Earth’s species, including all dinosaurs but the ancestors of birds.

Now, a team of scientists posit that silicate dust played a larger role in the mass extinction than previously estimated. Using paleoclimate simulations and details of the material kicked up by the impact, the researchers determined that fine dust may have stayed in Earth’s atmosphere for up to 15 years following the asteroid impact, which could have cooled the Earth significantly—by about 27°F (15°C). The team’s research was published this week in Nature Geoscience.


Paleoclimate models showing the distribution of dust immediately after and 5 days after the impact.

Paleoclimate models showing the distribution of dust immediately after and 5 days after the impact.

The Chicxulub impact was so intense it left 50-foot ripples on the seafloor and caused debris to rain down as far north as North Dakota—which is where the recent team collected fine-grained material from the impact for sampling. The site is called Tanis, and is famous for being rich with fossilized creatures that died in the immediate fallout of the asteroid impact. Data previously taken from Tanis revealed that the event happened in springtime, 65 million years ago.

“We specifically sampled the uppermost millimeter-thin interval of the Cretaceous-Paleogene boundary layer,” said Pim Kaskes, a geochemist at Vrije University Brussel in Belgium and co-author of the study, in a Royal Observatory of Belgium release. “This interval revealed a very fine and uniform grain-size distribution, which we interpret to represent the final atmospheric fall-out of ultrafine dust related to the Chicxulub impact event. The new results show much finer grain-size values than previously used in climate models and this aspect had important consequences for our climate reconstructions.”

The researchers stated that more studies of the K-Pg boundary—the geological layer that includes the fallout of the Chicxulub impact—would help clarify exactly how life rebounded in the months and years after the event.

More: Dinosaurs Were Already in Big Trouble Before the Asteroid, More Evidence Suggests