~66 million years agoPeer-reviewed · 2 sourcesWell documented
End-Cretaceous mass extinction
On the timeline · around ~66 million years ago · Geologic
What happened
An asteroid roughly 10 km wide struck near Chicxulub, Mexico; about three-quarters of species, including the non-avian dinosaurs, went extinct.
Why it matters
Cleared ecological space for the rise of mammals — and, eventually, humans.
How we know
A global iridium-rich clay layer, shocked quartz, and the buried Chicxulub crater date the impact to ~66 million years ago.