<<  There would be a significant period of time, at least a few hundred
million years, before non-thermophile life could survive.  The
thermophiles would have the place all to themselves, and on the ocean
floor, indeed in 99% of the ocean, UV radiation is not an issue.
 >>


IMO the environment was very hot for sure.

When the rains began, that formed the sea
 - they took a lot of the
CO2 (a greenhouse gas) out of the environment.
This may have led to a cooler atmosphere.
It also may well have led to the sun's rays
shining through the clouds for the first time.
I tend to think with no ozone layer etc. these
first rains, and that first sun , and that first
real reduction of CO2, and the beginning of
the first oceans, was the best window of
opportunity for the origin. I'm guessing
as early as 4.1 or 4.0.

Just some points - UV damages T the most.
Note that in RNA there is no T but U instead.

I tend to think that UV may have been a boon
in more ways than it was destructive.
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