IN CONTEXT

KEY FIGURE

Luis Alvarez (1911–88)

BEFORE

1953 American geologists Allan O. Kelly and Frank Dachille suggest in their book Target: Earth that a meteor impact may have been responsible for the extinction of the dinosaurs.

AFTER

1991 The Chicxulub Crater in the north of the Yucatan Peninsula in southeastern Mexico is proposed as the site of a massive comet or meteor impact at the end of the Cretaceous period.

2010 An international panel of scientists agrees that the Chicxulub impact led to the Cretaceous–Paleogene mass extinction, around 65 million years ago.

There have been five periods in Earth’s history when abnormally large numbers ...

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