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Comment by ramshanker | Hacker News Reader

If life could exist 10km below the ocean, I have strong gut feeling, we will find life deep inside the Jupiter thick atmosphere. Whatever depth that may be. It is like there is a FISH WITH WORKING EYE at 10km depth, so for much simplified multicellular organisms, limit could be even more extreme.

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The problem I see with that line of thinking is that there's a long chain of evolution underpinning that fish living at 10km depth, it didn't pop into existence being able to live in that environment.

I do think finding extremophiles in the solar system is a distinct possibility (Titan seems like a good bet) but I'm doubtful any of it will be multicellular.

It's my understanding unicellular life popped up on Earth pretty much as soon as it had a non-lava surface. While Earth seems super friendly today it was incredibly hostile when life formed. Early life on Earth were all what we'd consider extremophiles or at least extreme-adjacent.

I'd bet (at least a small amount of money) that life, at least the most basic unicellular life, will pop up wherever the requisite materials exist in environments where they're not immediately destroyed but have enough external energy to facilitate some more energy intensive chemical reactions.

Jupiter's atmosphere (to me) seems just as likely a place for life to form as the surface of Titan. It would be harder for us to find that life since the environment is so demanding compared to our level of technology. The surface of Titan or Europa are much easier exploration targets relative to Jupiter's atmosphere.

I broadly agree on the timeline, but "as soon as it had a non-lava surface" is still plus/minus a couple hundred Mya. I do believe temperate conditions were a requirement. I doubt the first cell membranes, for instance, were terribly robust.

Life in the deepest ocean requires considerable adaptation. For example, the proteins in your body would cease to function at that pressure, denatured to uselessness. The proteins the life has there are adapted to resist this. The organisms also have solutes, like trimethylamine, that help proteins maintain their structure. Many deep sea organisms are unpalatable because they contain such chemicals.

Go to high enough pressure and the very polymers of life begin to break. It becomes energetically favorable for proteins to be decomposed to individual amino acids, due to their now exposed charged ends assisting in compressing water.

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