How did the dinosaurs die out?

Well we're not entirely sure, but it wasn't just the dinosaurs that died out. The dinosaurs died out at the end of the Cretaceous period of history along with lots of plant life, things in the sea like ammonites and sea reptiles. Only the amphibians and mammals survived mostly untouched.

Why is a tricky question. Several theories have been put forward and I doubt if we'll ever know completely one way or the other. One theory that's popular at the moment is the Asteroid Theory. Two American scientists, Walter and Lus Alvarez, suggested that the impact of an asteroid (or meteorite) on the Earth sent up huge quantities of rock debris into the atmosphere. The cloaked the Earth in darkness for several months or longer. With no sunlight able to penetrate this cloud layer, photosynthesis ceased so plants died out which disrupted the food chain. With no plants to eat, some of the animals died out, and with no animals to eat, some of the larger animals died out.

This theory isn't necessarily correct. Some people think the dinosaurs died out over a long period of time and this theory wouldn't necessarily explain that. Some people think the rearrangement of the Earth's continents that was happening at the time was to blame. This could have caused environmental changes over a longer period of time that could have made the difference. There is also the idea that lots of volcanic eruptions, or one large one, could have had the same environmental effects as an asteroid impact.

Before we can decide between theories, we must decide between the theories of gradual extinction of dinosaurs, and the more catastrophic, instantaneous extinction that might have occurred as the result of an asteroid impact. This is difficult as looking back in history is fraught with problems. Even an event large enough to cause the extinction of vast numbers of animals needn't have left that big a mark in the Earth's crust that we can trace now.

So how, when and why the dinosaurs and other animals became extinct doesn't have an answer, just lots of theories.