Who is THIS guy at Europa? Options

[Bill Harris]

Life may or may not have started around hydrothermal vents, we don't know yet. But the provide nutrients and energy without resorting to photosynthesis and the ocean does provide a great buffer against temperature extremes as well as protection from UV and other radiation. In a hostile world, they can provide a safe haven.

--Bill

[centsworth_II]

...hydrothermal vents.... provide nutrients and energy without resorting to photosynthesis...

I think that whether life began deep in the ocean or in shallow surface waters, photosynthesis had nothing to do with it. Solar UV energy may have produced (or destroyed) compounds necessary to life, but life had probably been around a long time before photosynthesis evolved. I think the question is which environment was sufficient for life's origin: shallow water with lightning, geothermal, and solar (but not photosynthetic) energy, or deep geothermal vents. Or both.

[ljk4-1]

And wasn't the Sun *less* luminous in the really old days than
it is now? And wasn't there more cloud cover way back then
(I am thinking of the long time period where rains helped to fill
the oceans, or has that been surplanted by numerous comet strikes?
Either way, a lot of clouds would be blocking the sunlight), that's
another strike against the idea of needing the Sun only to survive
and thrive.