Moon is slowly receeding from Earth (a couple inches a year as verified by laser and radar probing). Thus, the Moon was closer to Earth(likely 2-3 times closer) when it was born (time of which is estimated to be about 4 billion years ago, shortly after Earth clumped out of space protoplanetary dust/rock ring).

Because Moon's composition is of double origin (there are Earth minerals there, and completely foreign to Earth ones), it is believed to originate in a collision of Earth with another planet, after which Earth was surrounded by equatorial rings of debrie from both. With time rings coalesce into what we now call Moon. This collision also believed to give Earth the 23 degree tilt which gives us seasons, and probably some ellipticity of orbit. Magnitude of collision erazed any life forms existing before it (if any) and probably melted young Earth's crust again completely.

Computer simulations also support this "catastrophic creation of Moon" hypothesis.