Reply to post: What I've never understood about this comets and water business is...

Did rock-hard aliens turn young Earth MOIST? New probe data emerges


What I've never understood about this comets and water business is...

...the assumption that just because the earth was "too hot for water to exist in a liquid state", that all the water would therefore disappear completely from the planetary aggregation, and need replacing from some other source like comets. Assuming that the original matter from which the earth accreted did contain water (would that be the case?), then as the planet was (or became) too hot for that water to be liquid, the water would vapourise - but if the earth's mass was roughly the same as it is now, surely the vapour would simply have hung around in an atmosphere within the planet's gravity well, rather than disappearing off into space - just as water vapour stays within the gravity well now, because only hydrogen and helium are light enough to disappear off into the great black yonder.

And then when the planet cooled down again, the water vapour in the extended atmosphere would have condensed into liquid on the surface, and formed the oceans.

Any astro-boffins out there care to explain why this shoudn't be the case? Genuinely interested...

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