Much of our understanding about asteroids comes from examining pieces of space debris that fall to the surface of Earth. Asteroids that are on a collision course with Earth are called meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite. One of the best places to look for meteorites is the ice cap of Antarctica.
Stony meteorites are the hardest to identify since they look very much like terrestrial rocks.
Since asteroids are material from the very early solar system, scientists are interested in their composition. Spacecraft that have flown through the asteroid belt have found that the belt is really quite empty and that asteroids are separated by very large distances. The impact of a large asteroid can be truly catastrophic. For example some believe that the object that smashed into the Yukatan Peninsula 65 million years ago was the event that wiped out the dinosaurs. The Gulf of Mexico may mark the crater that it left behind.