Quote:
Originally Posted by CraigS
It seems that Earth may have captured most of the water within 1AU of G2V ... but that's about all we presently really know.
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That's still open to debate. Given that the earth differentiated very early on in the piece means that there must've been a substantial amount of water present within the body of the planet. Despite all the bits and pieces that went into forming the body of the planet, it was never hot enough to melt right through, initially. Much of the heat which melted the planet came from the radioactive elements that were present in the materials which made it up. But even then, if the Earth were completely dry, it would take a tremendous amount of heat to melt it through and it would take a long time. The presence of water would lower the solidus temperature of the rocks, so they'd melt more easily and the process would be accelerated along because of this. The presence of water would aid in melting the planet and allowing it to differentiate.
Of course, some water would come in via comets etc, but it's how much that was initially present which is the subject of the question. Despite the Earth being where it is in the solar system and the temp here having been higher than the b.p. of water in this region of the solar nebula, that doesn't mean that water wasn't present. Being locked up in dust grains and rocky materials can, in fact, shield the water from the heat and radiation that was present. Plus, the speed at which it was incorporated into planetesimals and then the planets themselves would also become a factor in the survivability of the water.