Stock Photo - Extinction of the dinosaurs, artwork. Asteroids impacting around a T rex dinosaur ... . It is thought that an asteroid that impacted Earth around 65 million years ago caused the extinction of the dinosaurs. The impact, known as the K-T event, took place at sea and sent tsunamis around the globe. Water vapour thrown into the atmosphere lowered global temperatures. Plant and then animal life began to die off. The dinosaurs never recovered, and mammals rose to become the dominant form of life.