Hello, Adam!
Robin Canup, PhD is a she. :)
The above is from 1999, still the basic theory is same. Now, I'm no expert :), but it says there that: Another planetary body with roughly the mass of Mars had formed nearby with an orbit that had, by chance, placed it on a collision course with Earth. Why did it have to be another 'planetary' body? Why not a comet? A huge, young, fast and very icy comet that, quite possibly had given birth to our moon but whose hot core melded with that of Earth's. That would also explain the abundance of water earth had/has. Also, that Earth-moon separation may also explain why most of Earth's land mass was concentrated in one area for much of Earth's young history (Pre-Cambrian and even before). Of course, all of that is debatable. *g* Marcia Marcia
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