Illustrated representation of chicxulub crater. An asteroid impact at Chicxulub on the Yucatan Peninsula, Mexico, may have caused the extinction of the dinosaurs and 70% of all Earth's species 65 million years ago. The impact was caused by an asteroid or comet core which is thought to have been 10-20 km across. The impact created a 180-km wide crater and threw trillions of tonnes of dust into the atmosphere. This may have blocked the Sun's light and caused global climate changes. The remains of this debris are found worldwide as a layer in rocks known as the "K/T boundary."