Every day about 50 tonnes of rocky material from space lands on the Earth's surface. These rocks are called meteorites.
Nearly all meteorites come from the main asteroid belt between Jupiter and Mars. Although most asteroids are separated by thousands of kilometres of empty space, collisions are fairly common.
Sometimes an entire asteroid can break apart. Mostly a few small pieces are chipped off. These pieces travel through space for millions of years until they are caught by a planet's gravity.
If they survive the fiery journey through the air to land on the planet's surface, they become meteorites. Many thousands of meteorites have been found on Earth.
From studying these rocks, scientists have learned a lot about the age and birth of the Solar System. Some meteorites have been proved to come from the Moon or Mars.
The Hoba iron meteorite of southern Africa is the largest on Earth. It is 10 metres across and weighs 60 tonnes.
No one is known to have been killed by a falling meteorite, but several people have been bruised. Meteorites have also been known to kill a cow and damage houses and cars.