Roughly 65 million years ago, a large asteroid smashed into Mexico's Yucatan Peninsula. The crater left by the asteroid was estimated at 105 miles across and almost a mile deep. The energy released by the impact was billion of times as powerful as an atomic bomb.

This powerful collision kicked up tons of dust and debris that would have remained in the atmosphere for many months, blocking sunlight and lowering temperatures around the world. A layer of clay formed from the dust includes high levels of the element iridium from the asteroid, and is found in the geologic record worldwide. This layer is sometimes called the K-T boundary, since it marks the end of one time period (Cretaceous) and the beginning of another (Tertiary).

The drop in temperature, together with global fires, volcanic activity, tidal waves, severe storms and high arisdo resulting from the impact could have significant changed living condition for animals and plants around the world. Those living things which could not adapt to their new environment died.

Many scientists believe this asteroid impact was the main cause for the mass extinction that marked the end of the Cretaceous period. Physicist Luis Alvarez and his son Walter first proposed the asteroid impact theory in 1980.