By analyzing nickel isotopes preserved in the 66-million-year-old debris left by the Chicxulub impact, researchers conclude that the asteroid responsible for Earth’s last mass extinction most likely belonged to an exceptionally rare class of primitive meteorites called carbonaceous chondrites of the Ornans type (CO chondrites).
This painting depicts an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatan Peninsula in what is today southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth. Shown in this painting are pterodactyls, flying reptiles with wingspans of up to 50 feet, gliding above low tropical clouds. Image credit: Donald E. Davis / NASA.
Carbonaceous chondrites make up only 5% of meteorites so far sampled on Earth. CO chondrites make up a tiny fraction of that group.
They are some of the most primitive and untouched materials in the Solar System.
“CO chondrites are definitely not like the typical meteors you find in museum collections,” said Professor Philippe Claeys, a researcher at Vrije Universiteit and the University of British Columbia.
“A CO contains much less volatile elements — like carbon, zinc, water and particularly sulfur — than other classes of meteorites we’ve discovered so far on Earth.”
“It doesn’t alter our theory of what caused the extinction event, but it makes it less likely that sulfur contained in the impactor was the smoking gun.”
“The fine debris thrown into the atmosphere would have the primary factor.”
In their study, Professor Claeys and colleagues conducted high-precision nickel isotope measurements of samples collected over years from a thin layer of clay created across the globe by the Chicxulub impact.
“This is challenging work. Only a minute fraction of the projectile is preserved in the planet’s KT clay layer because the entire meteorite vaporized upon impact,” Professor Claeys said.
Many questions remain about the origins of the Chicxulub impactor.
Potential sources include distant, debris-rich regions of the outer Solar System or even the outer area of the asteroid belt near Jupiter.
“The Chicxulub impactor was roughly 10 to 15 km,” Professor Claeys said.
“It hit at an estimated 64,000 km/h forming the massive crater.”
“The impact zone is buried underneath the Yucatán Peninsula in Mexico.”
“Being impacted by such a rare, distant projectile really underscores how unlucky the dinosaurs were.”
The study was published today in the journal Science Advances.
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Georgy V. Makhatadze et al. 2026 The origin of Cretaceous-Palaeogene impactor revealed by nickel isotopes. Science Advances 12 (29); doi: 10.1126/sciadv.aef4858
