The asteroid that ended the age of dinosaurs 66 million years ago was not an ordinary space rock. New research published in Science Advances has identified the Chicxulub impactor as a CO-type carbonaceous chondrite, one of the rarest and most primitive types of meteorite known, and in doing so, has revised the understanding of how the impact triggered a mass extinction.
How they identified it
The challenge is that the entire 10-to-15-kilometer-wide (6-to-9-mile-wide) asteroid vaporized on impact. Only a minute fraction of its material was preserved in a thin layer of clay found at the Cretaceous-Paleogene boundary in locations around the world.
An international team led by Georgy Makhatadze at the Institut de Physique du Globe de Paris and Frédéric Moynier used high-precision nickel isotope analysis on samples from Denmark, Spain, and Italy. Nickel isotopes provide a distinctive chemical fingerprint that can distinguish between different families of meteorites. By comparing the K-Pg boundary samples against a large collection of known meteorites, the team narrowed the impactor’s identity to a CO chondrite, a carbonaceous chondrite of the Ornans class.
Carbonaceous chondrites account for only about 5 percent of meteorites that fall to Earth. The Ornans subclass is a tiny fraction of that group, composed of some of the most pristine, least-altered material from the early solar system. Philippe Claeys, a visiting professor at the University of British Columbia and co-author on the study, put it bluntly: “Being impacted by such a rare, distant projectile really underscores how unlucky the dinosaurs were.”
A revised extinction mechanism
The identification has implications beyond classification. CO chondrites are relatively depleted in volatile elements, including water and sulfur, compared to other carbonaceous chondrites that had previously been proposed as the impactor’s composition.
This matters because a leading theory held that sulfur released from the asteroid itself contributed to the global cooling that followed the impact. Sulfate aerosols in the stratosphere can block sunlight for years. But if the impactor was sulfur-poor, that mechanism becomes less likely.
Instead, the team argues, the fine debris blasted into the atmosphere when the asteroid struck may have been the primary driver of the deadly climate disruption. Claeys noted: “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 be the primary factor.”
Origin and context
The CO chondrite’s composition suggests it originated in the outer solar system, likely in the outer asteroid belt near Jupiter. It struck Earth at roughly 64,000 kilometers per hour (40,000 miles per hour), carving the Chicxulub crater beneath what is now the Yucatan Peninsula in Mexico.
The extinction that followed eliminated approximately 75 percent of all species, including all non-avian dinosaurs. Earlier research had established that the impactor was a carbonaceous-type asteroid through ruthenium isotope analysis. The new nickel isotope work goes a step further, pinning down the specific subclass and refining the understanding of what made the impact so devastating.
The study was conducted in collaboration with Vrije Universiteit Brussel and the University of Vienna, with samples collected over many years from K-Pg boundary sites across Europe.
Sources
- Makhatadze, G.V., Moynier, F., Brun, L.-A., Goderis, S., Claeys, P., Koeberl, C. “The origin of the Cretaceous-Palaeogene impactor revealed by nickel isotopes.” Science Advances (2026). DOI: 10.1126/sciadv.aef4858
- ScienceDaily: “Scientists identify the rare meteorite that killed the dinosaurs“