Chicxulub impact crater, Yucatan, Mexico. This impact crater (circle, upper left) is more than 180 kilometres across and is located on land and underwater off the coast of the Yucatan Peninsula. It is thought to have been formed around 65 million years ago by the impact of an asteroid or comet core which was at least 10 kilometres across. This massive impact is thought to have caused the extinction of the dinosaurs and many other species as dust thrown into the atmosphere led to the lowering of global temperatures. The crater was discovered in the 1970s and 1980s. It is one of the largest confirmed impact structures in the world.