Where did all the water on earth come from?
It did not come from hydrogen and oxygen reacting. The earth has never had sufficient gravity to hold the mass of hydrogen that would be required to create the oceans (1/9 the mass of the oceans themselves). It was not part of the original creation unless the moon was created at the same time, and the oceans that might have existed before the moon was formed by impact cannot believably have survived a molten earth process that ejected the moon. So comets seem the logical choice. On the other hand, the biggest “dirt-magnet” in the solar system is Jupiter, whose gravity well has drawn in a lot of debris, which ought to include comets. Yet it has almost no water at all. If we can get past Jupiter…and it would be sheer speculation on my part, but one way is if Jupiter is a relatively late comer to the solar system…then comets again become viable as the source of water. The inner planets might all have had their comet-encounters, but Mercury and Venus were far too close to the Sun to ke
