4
$\begingroup$

Over the course of my worldbuilding, I have looked into many alternative substances from which oceans could be composed that would serve as a viable solvent for biochemistry, and I often run into the issue that most of the commonly suggested solvents contain hydrogen and that most hydrogen-containing liquids other than water react with oxygen, which would prevent an oxygen atmosphere and thereby aerobic metabolism.

The solution to this issue is to use a solvent which does not contain hydrogen in its molecules, since, while these often still react with oxygen, a far higher percentage of them do not.

Solvents which themselves have significant oxidising properties are also not practical.

With this in mind, liquid CO2 seems like the obvious solvent of choice, since it contains no hydrogen, does not react with oxygen, and has only minor oxidising properties itself. I am referring here to true liquid CO2, not to supercritical CO2.

Now, since I do not want the planet to be covered in water ice, it will be necessary for the planet overall to be very low in hydrogen, but this presents another issue: Earth's biochemistry is heavily reliant on hydrogen, so how do we have biochemistry without much of it?

I am looking for the basics of an alternative biochemistry which meets the following criteria:

  • Is no more than 5% hydrogen by number of atoms
  • Is primarily carbon-based
  • Allows aerobic metabolism
  • Can operate in a solvent which contains no hydrogen in its molecules, does not react with oxygen, and itself possesses no or only minor oxidising properties; this should preferably be liquid CO2, but any solvent which meets the requirements will do

I understand that I'm asking a lot here, but I do not think this question is beyond the capacity of the people here to answer.

Edit: Just to clarify, I am asking about the molecules in the solvent, not what the solvent should be.

$\endgroup$
5
  • 1
    $\begingroup$ You're going to need fairly high pressures to have liquid CO2 existing over a reasonable temperature range. Not a problem in itself, but it makes your environment somewhat more alien. $\endgroup$ Dec 10, 2022 at 14:09
  • $\begingroup$ I don't think it's possible with the limitations you've put in place. Bio (life)chemistry is about life and all life contains hydrogen. E.g. Protein is over 50% hydrogen.Even silicon-based lifeforms need hydrogen, but can "live" in an ocean of methane (carbon and hydrogen), etc. If you want life in your oceans, hydrogen will need to play a factor. If you want a liquid ocean without it being a solvent (a solvent for "what" is important, too; water is a "universal" solvent because it can dissolve more substances than any other solvent. $\endgroup$ Dec 10, 2022 at 14:11
  • $\begingroup$ Person with your username is ruling out fluorocarbons as the solvent? They sound perfect for your needs. $\endgroup$
    – Willk
    Dec 10, 2022 at 20:19
  • $\begingroup$ The problem with eliminating hydrogen is that your carbons' bond angles end up constrained, as we end up with lots of double and triple bonds. There may be a solution, though. $\endgroup$
    – user86462
    Dec 19, 2022 at 22:39

2 Answers 2

3
+100
$\begingroup$

Carbon tetrachloride

carbon tet

https://en.wikipedia.org/wiki/Carbon_tetrachloride

Is no more than 5% hydrogen by number of atoms

Yup

Is primarily carbon-based

Right in the middle there

Allows aerobic metabolism

It is poisonous to humans but because of hepatotoxicity. It is not a metabolic poison like cyanide.

Can operate in a solvent which contains no hydrogen in its molecules, does not react with oxygen, and itself possesses no or only minor oxidising properties; this should preferably be liquid CO2, but any solvent which meets the requirements will do

Carbon tetrachloride reacts with O2 only at high temperatures. The carbon is terminally oxidized by the chlorines and so is not on the market for more oxidants. Neither will it give up those chlorines willy nilly. CO2 is likewise terminally oxidized and so those 2 do not have much to say to each other.

Carbon tetrachloride is an excellent solvent. It is liquid over most terrestrial temperatures and so you should not need much tweaking of familiar biochemistry to assert stuff works in carbon tetrachloride.

$\endgroup$
5
  • $\begingroup$ I understand downvotes for my sassy attempts at humor. But I thought this was legit. If I have got the chemistry wrong or this is a poor fit for the question, please say why. I am a molecule groupie. I want to learn! $\endgroup$
    – Willk
    Dec 11, 2022 at 17:16
  • 2
    $\begingroup$ I'm not a downvoter but I think it's because the question wasn't about finding a solvent but about suggesting a life compatible class of solutes. I thought the same as you to begin with because of the first paragraph. I've never seen you with downvotes before. $\endgroup$
    – user86462
    Dec 19, 2022 at 22:37
  • $\begingroup$ This is a better answer than it looks like at first. There could be a huge diversity of carbon halide solutes. Swap out darned near every hydrogen for a chlorine or fluoride. I don't think you get life, but you might get comic book life. $\endgroup$
    – user86462
    Dec 20, 2022 at 4:25
  • $\begingroup$ Comic book life! The dream we all dream of! $\endgroup$
    – Willk
    Dec 20, 2022 at 4:29
  • $\begingroup$ Thanks for the bounty, Choro. And here I thought you were the downvoter! $\endgroup$
    – Willk
    Dec 27, 2022 at 21:48
2
$\begingroup$

That would be very weird. Carbon bonds to itself. It is hard to imagine chemical life working any other way. Hydrogen is smaller than carbon. Almost anything else you might attach would be heavier. But I guess the life could hoard its hydrogen. Or it may live near the interface between a carbon dioxide lake and some more hydrogen rich environment.

How about Brine pools?

There is some marvellous footage from Attenborough's Blue Planet 2. Showing what looks like a water surface but underwater. The brine can be five times the density of water with salts such as barium sulphate.

I know this is not what you asked for, but I doubt if anyone has an answer for that. This is still water of a sort, and there is hydrogen. But I feel this is weird enough to be answer adjacent.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .