The asteroid that ended the dinosaurs
A single impact clears the way for mammals
Quick facts
- When
- 66 million years ago, end of the Cretaceous
- Impact site
- The buried Chicxulub crater, off Mexico
- Mechanism
- Sky darkened worldwide, sunlight cut off
- First clue
- A layer of iridium (Alvarez, late 1970s)
What happened
About 66 million years ago, at the end of the Cretaceous Period, an asteroid several kilometers wide slammed into 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 threw 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 of animals, died out. The first clue to the cause was a thin layer of iridium, a metal common in asteroids but rare in Earth's rocks, found in rocks from exactly the end of the Cretaceous by Luis and Walter Alvarez in the late 1970s.
Why it matters
This single event ended the 180-million-year age of dinosaurs and cleared the world for mammals, the group that had lived in the dinosaurs' shadow and now expanded into the empty space they left behind. That group eventually produced primates and, much later, us. If the asteroid had missed, our branch might never have had room to rise.
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 for the extinction.
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) · 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)
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Related timelines
- Age of Dinosaurs → · Zoom in: the impact, the extinction, and what survived