How do we know? A few things we've learned from science.

[HarryT]

Originally Posted by kennyc

News today that analysis of the Apollo Moon rock samples support the massive impact theory of the Moon's origin: http://news.nationalgeographic.com/n...space-science/

Interesting, although there's been very little doubt about it for many years. There's no other explanation that fits the evidence.

[kennyc]

Thanks Harry, yep, the convincing evidence for me are more the computer simulations of potential impact conditions (impactor size, angle, etc.) It is thought that this same impact is responsible for the 23 degree tilt of Earth, giving us our seasons.

[HarryT]

Originally Posted by kennyc

Thanks Harry, yep, the convincing evidence for me are more the computer simulations of potential impact conditions (impactor size, angle, etc.) It is thought that this same impact is responsible for the 23 degree tilt of Earth, giving us our seasons.

The real clincher is the fact that the moon has no metallic core, as it would have had if it had been formed in situ. It is entirely composed of rock similar to that of the Earth's crust.