Scientists theorize that collisions of astral bodies created the planets in our solar system.
After the sun formed, bits of space dust collided to form specks, then rocks, then boulders. As the space objects got bigger, their gravitational pull attracted smaller ones. A swarm of asteroids, about 18,000, were left in a belt between Mars and Jupiter. After the planets were formed, a process that may have taken almost 100 million years, asteroids continued to pelt the earth, with a violent collision occurring as often as once a month. Meteor Crater near Winslow, Arizona, was the first impact crater to be recognized as such.