The Chicxulub impact structure

A buried crater around 180 km across, identified in 1991 as the impact site linked to the end-Cretaceous extinction.

Yucatán Peninsula, Mexico · End-Cretaceous (66 million years ago)

In 1980, Luis and Walter Alvarez and colleagues reported an iridium-rich clay layer at the Cretaceous–Paleogene boundary and proposed an asteroid impact. In 1991 the buried Chicxulub structure in Mexico was identified as a candidate crater of the right age and size.

The impact is documented. How much of the extinction was caused by the impact, and how much by contemporaneous Deccan volcanism in India, is discussed in our Journal.