There are millions of small bodies in the asteroid belt and in the oort's cloud. which is orbiting the Sun.
There are few objects called near earth asteroids.There is a Chance that a huge asteroid or comet may hit the earth once in million years..Such an object is supposed to have hit south America about 65 million years and caused the extinction of dinosaurs
IN Arizona uSA there is a huge crater called Baringer crater.It is about half kilometer wide and having deph.t.This was v caused by a meteorite about 50,000 years back..
Many other such craters were filled up with water or l due to wind, floods a etc.
picture credit thunderbolt information.