Scientists Pinpoint a Rare CO Chondrite as the Meteorite That Wiped Out the Dinosaurs

When you picture the asteroid that ended the reign of the dinosaurs, you probably imagine a massive, blazing rock slamming into Earth, spewing sulfur and fire. Recent research, however, hints that the cosmic culprit might have been something far more nuanced—a very rare type of space rock called a CO chondrite.

Teams from the University of British Columbia, Paris, Brussels and Vienna dug deep into the thin, worldwide clay layer that was deposited right after the Cretaceous‑Paleogene (K‑Pg) impact. By measuring the subtle variations in nickel isotopes preserved in that layer, they were able to narrow the identity of the impactor to a CO‑type carbonaceous chondrite, a class that makes up only a few percent of the meteorites that ever reach Earth.

“Carbonaceous chondrites of the Ornans class are definitely not like the typical meteors you see in museum displays,” explains Dr. Philippe Claeys, a visiting professor at UBC and co‑author of the study. “They contain far less volatile stuff—think carbon, zinc, water and especially sulfur—than most other meteorites.” That detail matters because the old narrative often blamed massive sulfur releases for the Earth’s rapid cooling and acid rain after the impact.

In other words, if the asteroid was low‑sulfur to begin with, the real villain may have been the enormous plume of fine dust and ash that the impact threw high into the atmosphere. That cloud would have blocked sunlight for months, choking photosynthesis and upping global temperatures in a chaotic, “impact winter” scenario.

The isotope work was no small feat. The researchers at the Institut de Physique du Globe and the Université de Paris used ultra‑precise mass spectrometry to tease out the nickel fingerprint from a handful of clay samples collected over decades. “Only a minute fraction of the projectile survives in the KT clay layer because the whole thing vaporized on impact,” says Dr. Claeys, who now splits his time between Brussels and the Pacific Centre for Isotopic and Geochemical Research at UBC.

Where did this rare rock come from? The answer is still fuzzy. It could have originated in the distant, icy outskirts of the solar system, or perhaps from the outer reaches of the main asteroid belt near Jupiter. CO chondrites are among the most primitive material left from the solar system’s birth, so their journey to Earth would have been a long, unlucky one for the dinosaurs.

We already know the impactor was huge—roughly 10‑15 km across, traveling at about 64 000 km/h, and creating the massive Chicxulub crater that lies hidden beneath Mexico’s Yucatán Peninsula. What’s new now is a finer picture of its composition, and with it, a subtle shift in how we think the extinction unfolded.

“Being hit by such a rare, distant projectile really underscores how unlucky the dinosaurs were,” reflects Dr. Claeys. It also reminds us that Earth’s history is shaped not just by the size of an impactor, but by its chemistry, the dust it spits out, and where it comes from.