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Primordial Earth was buried in carbon dioxide. When life started, it was with algae using energy from the sun to crack the carbon out of carbon dioxide, with the byproduct of releasing the corrosive and toxic oxygen gas into the air. From there we get animals that use said oxygen, and so on with increasing complexity.

So, to get sapient species that breathe fluorine gas in a similar manner as we do oxygen, we must begin at the beginning, with plants. What compounds would need to exist in abundance on a primordial planet in order for a photosynthetic reaction that results in fluorine as a waste product to occur?

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    $\begingroup$ Might be a better question for Chemistry.SE $\endgroup$
    – Machavity
    May 9 '17 at 19:44
  • $\begingroup$ Not gonna happen. Would you like an answer that would explain why? $\endgroup$
    – Mołot
    May 9 '17 at 19:47
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    $\begingroup$ Purely by analogy that would be CF4, carbon tetrafluoride; but, unfortunately, the entire idea is doomed, because fluorine is very very very much more reactive than oxygen. It's way too reactive. For example, it forms compounds with noble gases and it "reacts violently with water forming hydrogen fluoride, and liberates oxygen"... Think about it: water burns in fluorine. $\endgroup$
    – AlexP
    May 9 '17 at 20:18
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    $\begingroup$ Needs to assume an ocean of Hydrogen Fluoride and an atmosphere of Florine.. Even the rocks would dissolve. $\endgroup$
    – Andrew Dodds
    May 9 '17 at 20:30
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    $\begingroup$ Generally you should wait 24 hours before Accepting an answer. Accepting the first post immediatly does not give others a chance to contribute $\endgroup$
    – JDługosz
    May 9 '17 at 22:43
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Fluorine gas burns the ashes that other reactions leave behind

Given the absurd reactivity of fluorine, anything it comes in contact with will ignite. Attempting to develop a system of biochemistry, which requires long chains of stable links, on an element that burns everything it touches is an exercise in futility.

While it's true that oxygen is very reactive, it's unreactive enough at the temperatures that life currently lives that it's a useful oxidizer. Fluorine is too reactive. Fluorine gas reacts with carbon at room temperatures. Fluorine reacts with hydrogen very energetically (assumed at room temperature). Hydrogen plus fluorine plus water is hydrofluoric acid, an especially nasty chemical. At elevated temperatures, fluorine will react with noble gases and metals which ordinarily don't react with anything!

On Earth, fluorine is only found in minerals. What did appear in the atmosphere reacted with water or carbon di/mon-oxide almost immediately.

While there are some fluoride metals, these metals don't appear to offer the complexity that carbon-oxygen-nitrogen-hydrogen chemistry does. As such, I'm highly skeptical that you could base biochemistry in an atmosphere with any substantial amount of fluorine.

Fun Reading

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    $\begingroup$ This isn't an answer to the question. $\endgroup$
    – sphennings
    May 9 '17 at 19:54
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    $\begingroup$ Assuming this is an attempt to challenge the premise, it seems like it might be valid. Having an extremely reactive byproduct to any chemical reaction without any good way to dispose of it is not good for life continuing to use that reaction. $\endgroup$
    – HDE 226868 ♦
    May 9 '17 at 19:56
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    $\begingroup$ @sphennings, challenge accepted :) $\endgroup$
    – Green
    May 9 '17 at 20:03
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    $\begingroup$ @sphennings but it does! Fluorine burns everything. Even water. It can't be byproduct, unless organism is doing it once and dies, but that's kinda bad. And you can't have it free in atmosphere unless everything on the surface is fluorine compound - because anything exposed would get burnt. $\endgroup$
    – Mołot
    May 9 '17 at 20:06
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    $\begingroup$ @Green Thanks for completing your answer. :) $\endgroup$
    – sphennings
    May 9 '17 at 20:13
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So..

How does our planet look like, first?

For some reason - and I really can't think of a good one, perhaps some extreme fractionation in a nebula - we have no oxygen around. Oxygen messes things up in this case. Instead we have Fluorine, which is always more fun.

So instead of rocks, we have Silicon fluoride rocks (Si(n)F(2n)F2). Instead of oceans of water, we have oceans of HF. And instead of an oxygen atmosphere, we have a Fluorine atmosphere. The surface temperature would be something like -100 degrees centigrade - this does help by lowering reaction rates.

Organic chemistry is hard in this environment. It would have to be based around Carbon-Fluorine polymers, which would be stable, as opposed to our Carbon-Hydrogen-Oxygen polymers, which would react violently. Presumably some trace oxygen and nitrogen would have to be available to allow more diverse chemistry; the interior of cells would have to do a lot of work to avoid the HF destroying everything.

The equivalent of CO2 in this world would be CF4 gas, which would be reacted through photosynthesis into C(n)F(2n) polymers with F2 being released. This is one of the more straightforward parts, although you'd want very high energy wavelengths of light to drive it, so perhaps our plants would look red rather than green.

One thing I would not want to do is try and land on this planet..

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  • $\begingroup$ Your answer is more in line with my original intent and I thank you profusely! $\endgroup$
    – Gio
    May 11 '17 at 17:04

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