Dinosaurs became extinct about 65 million years ago. This extinction event occurred between the Cretaceous and Tertiary periods and wiped out about 50 percent of all other organisms then living on the planet.
Because the dinosaurs died out in a relatively short period of time, scientists surmise that some sort of global disaster had caused this massive extinction event. Some extinction theories include an increase in volcanism, a change in the climate, the movement of continents and the consumption of dinosaur eggs by evolving mammalian species.
In the 1980s, Luis Alvarez proposed one of the most probable theories for the extinction. He believed that an extraterrestrial object such as an asteroid or meteorite crashed on Earth, throwing up debris into the atmosphere. This debris effectively blocked out much of the sun's light, causing plants to die worldwide, which led to the extinction of many species unable to cope with this climate change.