[ItsTheMediaStupid]

If Earth collided with a Mars-sized planet, it's not clear to me how Earth could still have a near-circular orbit around the sun. I would think any such collision would seriously alter the orbit, perhaps even out of the plane of the ecliptic.

It doest have a near circular orbit. Also the earth's orbit is on a slightly different plane of most of the other planets. I think Pluto is the only other planet with a tilted orbit plane. Thank public schools for the dumbed down science books for thinking the orbit is circular.

The fact that the moon always faces the earth on one side and faces away on the other, should have been enough proof that it came from the earth, weather spit out from some huge explosion or a collision with a very large object.

[RadioAstronomer]

I think Pluto is the only other planet with a tilted orbit plane. Thank public schools for the dumbed down science books for thinking the orbit is circular.

Nope. The Earth orbit plane is defined by convention as at 0.00. All other planets are tilted, Mercury and Pluto being the most extreme.

[King Prout]

The fact that the moon always faces the earth on one side and faces away on the other, should have been enough proof that it came from the earth, weather spit out from some huge explosion or a collision with a very large object.

ah, no. that's just captured rotation. not at all uncommon in the solar system.