Well, I guess my Astro kids can call me a liar! I've been preaching for years about the "Big Crash" moon theory where a Mars-sized planet(oid) did a demolition derby thing with the earth long ago and the ejecta formed the moon. Well, there's a slightly new theory in town.
In Nature Magazine this month, comes an explanation on why the two "sides" of the moon are so different. The near-side, the one we see from earth, is mostly smooth while the far-side, the daunted "dark" side, is rough and mountainous and cratered and icky.
Following are images of near and far sides:
So, according to these guys, a Mars-sized panetoid did hit the earth, but formed TWO moons; one larger than the other. After a long time of gravity tugs at Lagrange points, the little guy smashed into the big guy and formed the back side. Also explains, differently than conventional theory, the tidal lock and why it faces us all the time. The little guy hit the big guy "slowly" so not much rock melted and no huge crater was formed. Just sorta covered one side with a thick layer of rock. This agrees with observation that the moon's crust is thicker on the back side.
Something to ponder.