Illustration of the Chicxulub impactor hitting what is now the Yucatan Peninsula, Mexico, 65 million years ago. The impactor was the remnant of an asteroid or comet core which is thought to have been 10-20 kilometres across. The impact created a 180 kilometre wide crater and threw trillions of tonnes of dust into the upper atmosphere. This may have blocked the Sun's light and caused global climate changes that lead to the extinction of the dinosaurs and 70 percent of all of Earth's species. The remains of this debris are found worldwide as a layer in rocks known as the K/T boundary.