Re: Earth's water. Where does it come from?
Interesting recent PBS show, "H2O, the Molecule that Made Us," gives this origin story from geologist Stephen Mojzsis:
"We long held this idea… A belief really that water was delivered by comets and asteroids and so on… But instead what we found is that water was already here. And we know this from the investigation of the very oldest minerals of all.
Stephen says that water first showed up on the surface about 4.3 billion years ago.
So much of the surface was molten rock that we call this time the Hadean, which means “hell.”
This is very much like what we might imagine the Hadean Earth was like. A bright red sky. That atmosphere is dominantly carbon dioxide…Soon after it had finished its cooling, rocks and minerals released water as steam. It goes into the atmosphere – expands—and cools and as clouds then result in rain.
So began the first water cycle…And it rained so much that two thirds of our planet was submerged under water. This water has special powers. Well water is, is like the superhero of molecules. Water is a really great solvent…We call it ‘the universal solvent’ because it dissolves more substances than any other liquid.
And that meant, our ancient oceans were this primordial soup of chemicals...That is the crucible of life’s origin. We don’t know for sure but scientists think there was a spark... And then... A water molecule is the link between the non-living and the living world. Stephen says the development of life could not have happened at a more crucial moment. Because at this time, Earth’s atmosphere was mostly carbon dioxide, which acted like a blanket hugging the Earth. That heated things up and threatened to vaporize all of our water.
Earth’s fate would have been a super-hothouse with a dense carbon dioxide atmosphere. No water, no life… hellish surface. But then, Stephen told me, early life evolved to rescue Earth from this scorching apocalypse. Because a kind of bacteria photosynthesized the carbon dioxide out of the atmosphere…"https://www.pbs.org/wgbh/molecule-that- ... e-1-pulse/