Illustration of Pteranodon sp. flying reptiles watching a massive asteroid approaching Earth's surface. A similar impact is believed to have led to the death of the dinosaurs some 65 million years ago. The impact would have thrown trillions of tons of dust into the atmosphere, cooling the Earth's climate significantly, which may have been responsible for the mass extinction. A layer of iridium-rich rock, known as the K-pg boundary, is thought to be the remnants of the impact debris.