I have so many questions about this, I hardly know where to begin. First of all, considering the sheer amount of water on earth — oceans, seas, lakes, rivers, the atmosphere, organic beings, underground, etc. — it just seems incredible to me that comets from the Oort Cloud supplied earth with this much water while supplying practically none by comparison to any other solar system body.
Second, attributions to early solar system chaos don’t seem relevant, given the early state of earth as a scorching hot ball of surface magma on which one would think water might be atomized. And that gives rise to the third problem, which is, if cometary hypotheses are true, then what happened to all the deuterium? Shouldn’t there be proportional amounts in both the source (comets) and the destination (earth)?
Finally, if earth didn’t begin collecting comet water until after it cooled, does that give enough time to collect that much? How many frigging comets would it take of any appreciable size? Especially given that each comet that was miles in diameter would have hit with tens of megatons of force, creating temps upwards of God knows how many degrees Kelvin, effectively atomizing the water anyway just as if the earth had still been molten.
So I guess I’ll just ask one question: what am I missing?
I’m not familiar with the details of the theory, but it seems to me that it’s just that other bodies don’t have water now. There’s certainly been evidence that Mars once had significant water. Any water that Mercury might get would get boiled, then kicked off into space. The moon likewise would lose its water, eve though farther away, because of its much lower gravity than the earth. The gas giants would just swallow it – presumably it’s still there under all that. There’s water on some of the gas giant moons – it’s too far from the sun to vaporize, and has frozen on the surface.
So it seems quite likely that water ended up on all the planets, but it either boiled and get expelled into space because gravity couldn’t hold it, or disappeared beneath a lot of gas layers, or it’s frozen on the surface. Only Earth has the right combination of distance from the sun and sufficient gravity to retain large amounts of liquid water for so long. A happy chance for us, although, had it not been the case, we wouldn’t have evolved as we did to ponder the matter. Yay, Anthropic Principle.
I don’t know why Mars’ water went away. I’d imaine that over long periods of time its lower gravity would allow it to get kicked off the top of the atmosphere. I doubt if Beanstalk Trees were involved, but you can never tell.