Sixty-six million years after the impact that ended the Cretaceous, researchers have finally pinned down the exact type of asteroid that struck Earth — and it is one of the rarest kinds known.
The Chicxulub impactor, the 10-kilometer-wide asteroid that carved a 200-kilometer crater in the Yucatán Peninsula and drove 75% of Earth's species to extinction, has long frustrated scientists trying to identify its origin. Most impactors leave only trace elements behind. But a new isotopic analysis, published in Science Advances, has matched the debris layer to a specific and unusual meteorite class: a CO chondrite.
CO chondrites are a subtype of carbonaceous chondrite — primitive meteorites that contain organic compounds and water-bearing minerals. What makes them special is their isotopic fingerprint: they carry a distinct ratio of chromium, titanium, and nickel isotopes that matches the 66-million-year-old geological layer found at the K-Pg boundary worldwide. CO chondrites make up less than 0.5% of all known meteorites, making this one of the rarest impactors ever identified.
Knowing the exact type of asteroid that caused the end-Cretaceous extinction helps scientists assess the risk of future impacts. Most near-Earth objects are of different types, but if a rare CO chondrite were on a collision course, its high dust and sulfur content would make it far more destructive than an ordinary chondrite of the same size. The same isotopic technique can now be applied to other impact layers, potentially revealing whether Earth has been hit by similar objects at other points in its history.
Understanding the dinosaur killer is not just a historical exercise — it is a tool for preparing for the next one.