Stock Photo - Death of the dinosaurs. Computer illustration of Velociraptor sp. dinosaurs watching an asteroid or comet core as it rushes towards the Earth ... . This impact, which occurred about 65 million years ago at the end of the Cretaceous geological period, may have caused the extinction of the dinosaurs and 70% of all species on Earth. The object, thought to be 10-20 km across, struck the Earth at Chicxulub on the Yucatan Peninsula, Mexico. It threw huge amounts of debris into the upper atmosphere, blocking sunlight and causing global climate changes. The remains of this debris are found as a layer in rocks called the K/T boundary.