A rare CO chondrite meteorite was the probable impacter that struck Earth 66 million years ago, wiping out 75% of Earth’s species, including nonavian dinosaurs. These findings are published in Science Advances. Researchers at the University of British Columbia (UBC), Paris, Brussels and Vienna, used advanced nickel isotope analysis of samples to narrow down the composition of the deadly Cretaceous-Paleogene meteorite.

“Carbonaceous chondrites of the Ornans class are definitely not like the typical meteors you find in museum collections,” says Dr. Philippe Claeys, who worked on the study as a visiting professor at UBC.

“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 impacter was the smoking gun. The fine debris thrown into the atmosphere would have been the primary factor.”

Researchers from Institut de Physique du Globe and Université de Paris conducted high-precision nickel isotope measurements of samples collected over years from a thin layer of clay created across the globe by the impact.

“This is challenging work,” adds Claeys, a professor with Vrije Universiteit Brussel currently visiting the Pacific Center for Isotopic and Geochemical Research with Earth, Ocean and Atmospheric Sciences at UBC. “Only a minute fraction of the projectile is preserved in the planet’s KT clay layer because the entire meteorite vaporized upon impact.”

Many questions remain about the origins of the world-shattering meteorite. Potential sources include distant, debris-rich regions of the outer solar system or even the outer area of the asteroid belt near Jupiter.

A rare impacter

Carbonaceous chondrites make up only 5% of meteorites so far sampled on Earth. Carbonaceous chondrites of the Ornans class—CO chondrites—make up a tiny fraction of that group. They are some of the most primitive and untouched materials in the solar system.

“Being impacted by such a rare, distant projectile really underscores how unlucky the dinosaurs were,” says Claeys.

The Cretaceous-Paleogene impacter was roughly 10–15 kilometers or 6 miles wide. It hit at an estimated 64,000 km/h (40,000 mph), forming the massive Chicxulub crater. The impact zone is buried underneath the Yucatán Peninsula in Mexico.

Reference:
Georgy Makhatadze, The origin of Cretaceous-Palaeogene impactor revealed by nickel isotopes, Science Advances (2026). DOI: 10.1126/sciadv.aef4858.

Note: The above post is reprinted from materials provided by University of British Columbia.