The Day the Dinosaurs Died: On
The end-Cretaceous mass extinction, also known as the Cretaceous/Paleogene (K/Pg) boundary, occurred 66 million years ago and is one of the ?Big Five? mass extinctions in Earth history. The two leading hypotheses to account for the rapid and widespread loss of many terrestrial and marine organisms are: 1) impact by an asteroid, and/or 2) massive volcanism. An impact crater dating to the K/Pg event is preserved at the northernmost tip of the Yucatan Peninsula and fallout deposits from the impact are global and coincide with mass extinction.