Formation of moon is also known as The big splash theory
The big splash theory suggests that the moon is formed from debris ejected after a collision of earth and mars sized body/object named theia
The impact of the collision resulted in the material eventually coming together to form the moon
The first evidence is evidence from rocks:
The composition of rocks on the moon and earth are identical. Moon rock samples show evidence of being molten at one point, which would happen in a collision
The second evidence is the evidence of movement:
The spin of the earth and they way the moon orbits the earth suggests that there is a close relationship between them.