Meteors are small bits of interplanetary debris broken off from asteroids or comets. When the Earth plows through the stream emitted by a comet, we get a meteor shower. Meteors burn up about 100 km above the Earth, but some survive to hit the ground. Most of these meteorites that reach Earth are rocky, some are metallic, and a few are a mix of the two. Very big meteorites can be a very big problem, but there are plans in the works to prevent us from going the way of the dinosaurs.