[Buttons12]

meteorites, asteroids, and to a lesser degree, comets, over the eons brought in lots of H2O and precursors.

Must have been quite a lot, seeing as most incoming these days burns up on the way in. You would think any water would dry up pretty fast...Instead we have many quintillions of gallons. Hmmm.

Thanks for the link! Thick reading often has the most protein. :)

[Paul R.]

Water vapor is a combustion product in many cases. More water vapor* eventually leads (usually) to more precipitation.

*Granted that individual water molecules at great altitude likely escape to space. But other stuff gets through. And, yes, in the past there was a lot more clutter in the neighborhood.