Asteroid impact. Illustration of a large asteroid colliding with Earth on the Yucatan Peninsula in Mexico. This impact is believed to have led to the death of the dinosaurs some 65 million years ago. The impact formed the Chicxulub crater, which is around 200 kilometres wide. The impact would have thrown trillions of tons of dust into the atmosphere, cooling the Earth's climate significantly, which may have been responsible for the mass extinction. A layer of iridium- rich rock, known as the K-Pg boundary, is thought to be the remnants of the impact debris.