The K-t boundary or the Cretaceous-Tertiary boundary signifies the beginning of the Tertiary and the end of the Cretaceous; sixty-five million years ago. The boundary can be observed in various locations across the globe and is a relatively thin layer of dust sediments with an abnormally high amount of iridium. Iridium is a rare earth element and is only found in large amounts in asteroids. This knowledge led scientists to conclude that the debris deposited was caused by a massive asteroid impact. The impact crater was eventually located and was found just of the coast of the Yucatan peninsula. The asteroid was over ten miles in diameter and this impact was thought to be instrumental in the extinction of the dinosaurs.
