There have been large extinctions throughout Earth’s history. The most famous of these caused the end of the dinosaurs about 65 million years ago. At that time, about seventy percent of all the species on earth died out. Although dinosaurs had been in a period of decline before the extinction, it is thought that they could have recovered if something terrible had not prevented it. The most accepted theory about the cause of this extinction is the asteroid theory.
It is believed that an asteroid about 10 kilometers in diameter hit the Earth. It is suggested that the asteroid destroyed everything within about 500 kilometers of where it landed. It would also have caused fires, increased volcanic activity, and sent huge clouds of dust, gases, and water vapor into the atmosphere. Because of this, there would have been months of darkness, cooler temperatures, and acid rain. There is a huge crater off the northwest tip of the Yucatan Peninsula in Mexico. The crater has been dated as 65 million years old and is believed to be evidence of a large asteroid impact.