CO Chondrite Identified as the Meteorite That Triggered the Dinosaur Extinction

The Cretaceous‑Paleogene boundary marks one of Earth’s most dramatic turning points, when a cosmic impact erased the non‑avian dinosaurs. A new study has identified the culprit as a rare carbonaceous‑chondrite of the CO class, based on a distinctive nickel‑isotope fingerprint preserved in the global impact clay. By linking this isotopic signature to the impactor, scientists have refined the picture of what slammed into Earth 66 million years ago. The finding reshapes how we think about the chemical drivers of the mass extinction. It also demonstrates the power of high‑precision isotope geochemistry for unraveling ancient catastrophes.

What happened

Researchers from UBC, Paris, Brussels and Vienna measured nickel isotopes in samples taken from the thin worldwide clay layer that settled after the impact. The isotopic ratios differ from those of most known meteorite classes but match the signature of CO chondrites, a rare type of carbonaceous meteorite.

CO chondrites contain markedly less sulfur, zinc, carbon and water than other classes. This low‑sulfur composition suggests that the massive release of fine debris, rather than sulfur vapor, dominated the atmospheric perturbations that followed the impact.

The team published the results in Science Advances, emphasizing that only a minute fraction of the original projectile survived the vaporizing blast, making the isotopic evidence the most reliable clue to its identity.

Why it matters

Identifying a low‑sulfur CO chondrite narrows the range of chemical processes that could have driven the rapid, global crisis after the impact, shifting focus from sulfur‑induced acid rain to the climatic effects of fine particulate injection. This refinement improves climate‑impact models used to simulate the extinction event and informs the search for similar signatures in other ancient impact layers. Moreover, the study showcases how precise isotope geochemistry can resolve long‑standing debates about Earth’s most famous catastrophe, guiding future investigations of impactors and their environmental footprints.

How to think about it

When evaluating ancient impact events, start by asking what isotopic fingerprints survive in the post‑impact deposits. Compare those signatures against the known spectrum of meteorite classes to narrow possibilities. Consider both the chemical makeup of the impactor and the physical consequences of the impact—such as ejecta volume and atmospheric loading—because composition alone may not dictate the severity of the aftermath. Finally, treat any single line of evidence as part of a broader, multidisciplinary reconstruction that includes geology, paleontology, and climate modeling.

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