The asteroid that ended the dinosaurs

What happened

About 66 million years ago, at the very end of the Cretaceous, an asteroid several kilometres wide struck what is now the coast of Mexico, leaving the huge, buried Chicxulub crater. The Natural History Museum calls the result one of the most dramatic mass extinctions Earth has ever seen: the impact hurled so much material into the atmosphere that soot and dust darkened the sky worldwide and cut off sunlight, and all non-bird dinosaurs, along with many other groups, died out. The first clue to the cause was a thin worldwide layer of iridium, a metal rare in Earth's rocks but common in asteroids, found in end-Cretaceous rocks by Luis and Walter Alvarez in the late 1970s.

How we know

The Natural History Museum describes the 66-million-year-old impact, the buried Chicxulub crater off Mexico, the worldwide blackout of sunlight, and the iridium evidence behind the Alvarez hypothesis, now the most widely accepted explanation.

Sources

• Natural History Museum, London. What killed the dinosaurs? (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
• Reduced contribution of sulfur to the mass extinction associated with the Chicxulub impact event (peer-reviewed, via PubMed Central) (2025) · Peer-reviewed (author-declared)pmc.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)