Illustration of the Chicxulub crater, shortly after its formation. This crater was formed 66 million years ago, off the coast of present-day Mexico, following the impact of an asteroid 10-14 kilometres across. The asteroid is widely believed to have provoked the extinction of the dinosaurs and other species at this time. The crater measures some 150 kilometres in diameter. Since its formation it has been buried in silt and covered by the sea, and is now only detectable using gravity measurements of the immediate area.