Curious artist, not a chemist, kinda dumb boi looking for some kind galaxy brains here.

Okay. So. I have this planet. Its atmospheric composition is fairly earthlike: 21.6% O2, 77% N2, 0.2% CO2, 0.4% Ar, and 0.7% SO2, with the remaining 0.1% being other gases. The surface of the planet is mostly covered in oceans, so I imagine that there's gonna be some dilute sulfuric acid in them cuz of the SO2 interacting with water and oxygen.

What I'm really interested in knowing is how the little sulfur dioxide could affect biochemistry. I already kinda feel like most life is gonna stick to the ocean, since I know for a fact that it's gonna rain H2SO4 and surviving on land would be the opposite of fun (even tho I have plans to make land organisms that maybe have a shell of some sort? I was thinking SiC but, like, again, I have no idea if it would even work).

What would these organisms use in place of our biomolecules? And what kind of protection would they use against the sulfuric acid rains? These are pretty much my main questions.

Thank y'all in advance <3 <3

  • $\begingroup$ Where is all this sulfur dioxide coming from? It would dissolve into you oceans and get eventually converted to sulfur compounds. There would be a mass-extinction event, then it would be gone. But if it were always being renewed somehow, life would function at a different pH set-point, but otherwise be similar. $\endgroup$
    – DWKraus
    May 21, 2021 at 13:36
  • $\begingroup$ If we assume constant high levels of vulcanism, the seas will be very acidified by constantly absorbing all the sulfuric acid. Something would need to either fix/liberate all that sulfur, or the seas would be sulfuric acid baths. Rock and mineral composition of the planet would be very influenced by the action of all that concentrated acid. I can't quite see how you can have all that SO2 together stably with all that O2, since SO2 is a reducing agent. Venus has 150 ppm of sulfuric acid and it completely changes the atmosphere (that and CO2). $\endgroup$
    – DWKraus
    May 21, 2021 at 13:58

1 Answer 1


0.7% atmospheric Sulfur dioxide would not be stable in an aqueous environment. Unless it was replaced at a prodigious rate, it would be washed out of the atmosphere and dissolve in the ocean. In the presence of an oxygen atmosphere it would also be oxidized over time to sulfur trioxide forming sulfuric acid.

Some life can survive in very acidic solutions down to Ph 0 and have adapted to either efficiently pump out hydrogen ions or to evolve more acid resistant biochemistry. In the case of Ferroplasma acidiphilum Up to 86% of cellular proteins are iron-metalloproteins




  • $\begingroup$ Thank you! This is the answer I wanted to give, but I've been too busy to give more than a couple comments this AM. $\endgroup$
    – DWKraus
    May 21, 2021 at 14:16
  • $\begingroup$ Tbh I applied a bunch of handwaving in all of this. I really wanted to toy around with an earthlike atmosphere and do weird stuff with the organisms. Didn't seem to work out well. I don't know much about chemistry, main reason why I'm doing this. Learning thru trial and error and all that. Thank you both for the replies <3 $\endgroup$
    – They
    May 21, 2021 at 14:39
  • $\begingroup$ NP - You could easily have a very acidic ocean, just difficult to have that much SO2 in the atmosphere with the oxygen and water. $\endgroup$
    – Slarty
    May 21, 2021 at 14:46

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