What was the solar system like when the moon form?

Answer 1

Busy, lots of things were crashing into each other. A planetesimal about the size of mars is believed to have formed at a Lagrange point along Earth's orbit and was pulled out of it possibly by Jupiter inevitably crashing into Earth putting debris into orbit around the Earth that might had formed the moon. After that, something is known to have crashed into the moon creating the Aiken basin which is over 1,300 kilometers across. The Borealis basin on Mars was the location of a hit too at 8,500 kilometers across. And we can't forget Mercury's Caloris basin also at about 1,300 kilometers.

Answer 2

When the moon formed around 4.5 billion years ago, the solar system was a chaotic place with many collisions and impacts happening among the young planets and celestial bodies. The moon is believed to have formed from the debris left over from a collision between Earth and a Mars-sized body, which eventually coalesced into the moon.