Suntrack2 seemed to be trying to say something I've thought about for a while. I might be wrongly projecting, though, since it is an idea I've had for a while which suntrack2 reminded me of. Anyway, my question, and possibly suntrack2's if I understood him/her correctly, is this:

Could the same event that resulted in the formation of the moon also have resulted in the Earth's uneven crust thickness, which is what gives us separate seas and continents now? After all, we know that the crust is that way, with a handful of higher areas (continents) and a handful of lower areas (oceans), so there's got to be some reason why.

I've seen an animation of what the lunagenic impact would have looked like from space. The strike is a bit off-center, so it opens up one side of the planet like an expanding clamshell but leaves the other mostly intact. It stands to reason that the later-reconstituted planet could have had two sides that were, even if only slightly, different in composition (such as with one side incorporating more of the foreign object's mass than the other side) and/or structure (such as with one side more thoroughly vertically sorted according to material densities than the other is, due to having been stirred and mixed more thoroughly and recently). And just a two-sided arrangement, with a giant continent on one side and a giant ocean on the other, could have then broken apart into what we've got now.