Aproximately 65 million years ago, the age of the dinosaurs ended suddenly when a mass extinction terminated the dinosaurs, ammonites and some other kinds of animals. The survivors of this extinction included the ancestors of all the modern animals and plants. The extinction coincided iwth a collision between the earth and a comet or asteroid off the coast of Mexico.
Very rarely, perhaps only once every 100 million years or so, a mountain-sized rock collides with the Earth, causing drastic global climate change and extinctions. A little more than 100 miles (160 km) in diameter, the Chicxulub impact crater off the coast of Yukatan, Mexico, is believed to record the impact that ended the Cretaceous Period. The object that struk the Earth to create this craterwas probably about 6 miles (10 km) in diameter and traveling at speeds between 15 and 20 km per second. A small asteroid may have created Chicxulub. When the asteroid hit, it released energy equivalent to more than five billion Hiroshima atom bombs (100 million to 10 trillion megatons or about 10,000 times today's total nuclear arsenal).