The dust particles were brought together by the forces of drag to form clumps of rock that grew into what scientists call “planetesimals,” which are tens to hundreds of miles across, and then to Mars-sized “protoplanets” by colliding with each other.Įarth grew to its final size through one last major collision with another Mars-sized object. The Earth, like all the other planets in the solar system, started out its life as a disc of dust and gas orbiting the young sun.
