Meteorites are pieces of rock and metal that fall to the Earth. Almost all are fragments broken from asteroids during collisions, taking between around 0.2 and 100 million years to journey from the asteroid belt to the Earth. There are also currently about 30 meteorites that come from the Moon, and a similar number from Mars. Meteorites are the only physical materials available on the Earth that allow direct study of the original dust from which the Solar System formed. Meteorites are named from their place of find or fall. Wherever possible, the name is taken from the nearest inhabited place to the actual site. In practice, the recovery of meteorites from desert regions has resulted in a name-number nomenclature that combines geographic and date information.