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I imagine that in my fictional solar system there is a gas giant which has bacteria-like life in it. Could plants eventually evolve in this gas giant? If so, what would they be like?

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    $\begingroup$ We don't have enough details. What kinds of gas? What size planet? How far from its star? What bacteria are you imagining? Please keep in mind that you're basically asking us to to invent an entire biome. It's a bit of a tall order for Stack Exchange, where questions are expected to be specific, practical, and reasonably objective - especially when the one and only data point we have for life of any kind is Earth. $\endgroup$
    – JBH
    Commented Nov 3, 2021 at 3:29
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    $\begingroup$ It's an interesting question, does need more precision. VTC-ing for the time being until more details are added. Also, official policy is to refrain answering poor questions, even if you have a good answer - but I will happily submit options once you help us help you, OP. $\endgroup$
    – Nyakouai
    Commented Nov 3, 2021 at 15:30
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    $\begingroup$ Could you clarify whether you want to know if complex organisms can potentially evolve in this environment or if you are looking for something more specific? Please edit your question to include the clarifications. A question including technical details related to your system and the gas giant will be received better. I will vote to close as Needs details of clarity, but I will happily retract my vote or vote to reopen once you make your edits. Please ping me. I am looking forward to reading the answers to your question. $\endgroup$
    – Otkin
    Commented Nov 3, 2021 at 16:07

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Could plants eventually evolve in this gas giant?

Very unlikely.

The basic building blocks (organic substances, even may be easier than for Earth's case, the pretty energetic weather of a gas giant to mix the gasses and availability of the "raw materials" to get those organic substances may be enough.

But the same high level of churning will prevent the accumulation of those substances in concentrations high enough for the following two things that need to happen for the emergence of life:

  • the self-assembly of the building blocks in protein chains
  • the replication of the protein chains

The most compelling (to my mind) hypotheses on what made the life appear on Earth are:

  • underwater volcanic vents for the production of the building blocks (other factors, like lightning, may have contributed, but they aren't localized enough to explain higher concentration in small places and I can't imagine entire oceans with a concentrated soup of organic materials)
  • tidal pools for places where the self-assembly in replication could take place (thanks, Moon, highly grateful for you being around when needed).

In regards with the role of the tidal pools in the emergence of protein based life on Earth

The evaporation taking place at low tides would have increased the concentration of salt. Now, higher concentration of salt is used even today to precipitate the proteins in a solution - the technique is called salting out. In a tidal pool, precipitation would have resulted in the perfect conditions for the organic substances to come very close together and start to self-assemble. An gentle UV exposure or active radicals from lighning would have helped too, but the "coming together" is essential for self-assembly.

If the things would have stopped with high concentration, it is likely that life wouldn't have emerged either. But here comes the high tide, which deliver less salty water and the proto-proteins can "hydrate" back and unfurl and be ready to favor other more complex chemical reactions (the way the sophisticated enzyme system do in the body of all living creatures on Earth).

The nice thing about tides, the concentration of salt and the speed of reaction in tidal pools would go up and down gently, adding variability in the environment the chemistry takes place.
What is essential in the tidal pool case is the repeatable variability of the conditions over long period of times. This in contrast with a gas giant, where the variability is chaotic, with little to no conditions for a gradual evolution.

If the things that I tried to put together are a bit unclear, I found this article in the Scientific American, Without the Moon, Would There Be Life on Earth?

Both DNA and RNA—the messengers of life as we know it—almost certainly were selected and evolved from a large diverse group of protonucleic acid molecules. But for DNA and RNA to evolve from this group of protonucleic acid structures, first they had to be able to replicate. That involved organizing their copying via cyclic assembly and dissociation.

"A lot of origin-of-life reactions involve getting rid of water," says Kevin Zahnle, a planetary scientist at the NASA Ames Research Center at Moffett Field, Calif. "So you look for means to concentrate your solutions. One way to do that is to throw water up on a hot rock, then have the waters recede and evaporate."

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In the early Earth environment, Lathe notes that such fast lunar tidal oscillations would result in the highly saline low-tide environment that protonucleic acid fragments would have needed to associate and assemble complementary molecular strands.

Having bonded in pairs at low tide, these newly formed molecular strands would then dissociate at high tide, when salt concentrations were reduced, providing what Lathe terms a self-replicating system. Lathe believes that DNA would ultimately have arisen from such protonucleic acids.

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