I still haven't found a good article dating the ejection of the moon from the earth, after a collision which would have liquified any rock on the surface and sterilized any life.
But I did find this, dated just this January!
http://phys.org/news/2025-01-moon-chunk-ejected-earth-formation.html
"New measurements indicate that the moon formed from material ejected from the Earth's mantle with little contribution from Theia.
In addition, the findings support the idea that water could have reached Earth early in its development and may not have been added by late impacts. The results are published in the Proceedings of the National Academy of Sciences."
Apparently there is a long way yet to go in coming up with a reasonable story. They still apparently aren't sure if the earth had most of its water before, or only formed that after?
FWIW, the theory I heard said THAT collision is what gave the earth its spin! So, if there had been no collision, there likely wouldn't have been the day night cycle which keeps the earth's oceans from super-heating?
The whole thing seems a lot more improbably fortunate than the "mere" continental drift, which supposedly enabled all the mountain formation relatively recently! And without the mantle turning like that, the evolution of life would have gone way differently -- if at all.
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Ok. Well I guess all the theories say it would have been (relatively) shortly after the formation of the solar system itself "around 4.5 BILLION years ago". http://science.nasa.gov/moon/formation/
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