Answer:
The planets grew from the impact of innumerable smaller bodies early in the history of the solar system. This process is called planetary accretion. The early history of the terrestrial planets is marked by continuous collisions with larger and larger planetary bodies. Accretion was essentially complete by 4.56 billion years ago. Meteorites and asteroids are materials left over from the formation of the solar system that have not yet accreted to a planet. Accretion continues even today at a very slow rate whenever a meteor falls to Earth.