Some evidence suggests that this extinction was caused by a large extraterrestrial object or objects impacting with what is now the Yucatan Peninsula, where there is a large crater of the right age. This crater is named Chicxulub after the town at its centre.

The object was probably a meteor. These are large balls of rock abundant in the solar system and frequently impact with other celestial bodies. They are rich in elements unusual on the earth, such as Iridium. A thin layer of Iridium can be found in terrestrial rocks worldwide of an age corresponding to the K-T Boundary - further evidence that the impact was powerful enough to cause a mass extinction.

There are a number of smaller craters of the same age that could have been produced by fragments of the larger meteor.

The main impact would have killed all life within a large radius. Devastating tsunamis travelled in all directions and an enormous amount of dust and dirt was thrown into the atmosphere. This may have blocked out the sun and plunged the earth into darkness and extreme cold. It may also have increased volcanic activity around the world, resulting in the contamination of the atmosphere with noxious gases.