Earth may have underground 'ocean' three times that on surface

[Anomalocaris]

Do you have any idea how many comets it would have taken to bring all of the water to Earth? You guys are insane! The Earth makes its own damn water as well as its own gases and petroleum.

I don't think anyone is arguing that it either has to be one or the other (well, apart from you, obviously). It could be and most likely was both. Considering that hydrogen is far and away the most abundant element in the Universe, with the next most abundant reactive element, oxygen, coming in third (the second most abundant, helium, is chemically inert), it would be more surprising if proto-Earth didn't produce the stuff. Comets (ie the boring, bog-standard variety as distinct from the magic ones) still played their part. The Solar System is a shooting gallery; the formative one consideraly and quite insanely so. Cometary colliisions can and do happen - we've actually seen it.

You seem to be under the impression that we're saying first there was the Earth, and then the comets came with their water delivery. If so, you're neglecting the very real fact that protoplanetary collisions are how planets are actually formed. It's not that these comets slammed into the Earth - for the most part, they became the Earth.

There is one school of thinking which postulates rapid and energetic formation of earth, which left the earth almost completely molten after initial formation. In this scenario, most of the water the earth acquired during its formation was either boiled off into space with the heat of formation, or only stayed by remaining chemically locked up in its mantle. Surface water actually mostly came from a later period of impacts which occurred after the surface of the earth cooled and crusted over.

Violent formation of the moon scenario by giant impact between earth and a mars sized protoplanet also argues that earth must have lost much of its initial inventory of water to evaporation after its formation, and water in its ocean came later in an episode of cometary collisions distinct from the original formation of earth. In this scenario if the earth wasn't molten right after it formed, it was after it got wacked by the mars sized protoplanet.

I think recent evidence argues for a less energetic mode of formation, in which earth was always comparatively cool and had a solid surface more or less from beginning and retained much more of the water that came with its original formation.

There is also evidence the more water than previously thought could have survived the moon forming collision without being boiled off into space. If the moon forming impact was energetic enough to boiled off most of the water from the earth's mantle, it would be energetic enough to boil off all the water in rocks actually blasted into orbit to later form the moon, and moon rocks should be bone dry.

But moon rocks seem to have a lot more water than previously thought.