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Accretion in astrophysics is when particles accumulate into a large object by gravity. It is mostly gaseous matter that is attracted together, and it forms an accretion disk. Combined with dust to create more of a solid, this was how many planets were formed.
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The moon formed about 30-50 million years after the formation of the Solar System. It formed out of debris that was thrown into orbit after another planet around the size of Mars collided with Earth. It stayed in orbit around Earth because of Earth's gravitational attraction.
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Before, Earth was scorching hot, magma was everywhere, and no life was sustainable. There were great movements and activities on and in the interior of planets, creating heat. As planets cooled, those movements declined until there was none.
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Heavy bombardment happened when small asteroids and planets that failed to form slammed into planets, which scarred their surfaces. Collisions were much more frequent in the Solar System during this tame.
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Earth's core was formed by accretion when metal from impactors sank through the then magma surface of early Earth and to the center. The core is also mostly metal, as those materials could gravitate to the center of the Earth.
