This is completely ignoring the fact that lifeforms that aren’t based on carbon are entirely hypothetical. Could these lifeforms breathe oxygen like us, or would they need to use some sort of technology to live in oxygen rich environments? How would a planet have to be if these were to be the main denizens of it?

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    $\begingroup$ It's unlikely that sulphur based lifeforms could exist. But assuming they did it is indeterminate whether they would breathe oxygen or not it would depend upon the detailed biochemistry of the aliens. $\endgroup$
    – Slarty
    Nov 23, 2019 at 23:13

1 Answer 1


Sulfur-based life is pretty unlikely, for the same reason that life on Earth isn't oxygen-based. Sulfur, like oxygen, usually only likes to form two covalent chemical bonds. Thus, you can in principle have chains of sulfur atoms of varying lengths with with different atoms attached to either end, but that really isn't enough variety of structure to permit the complex interactions that in turn give rise to life. Also, the S-S single bond isn't particularly strong. Stronger than O-O, but not as strong as C-C. And while carbon-based polymers can have several parallel bonds linking each monomer (or a multitude of cross-linked strands), S-S chains would be limited to only a single strand.

Could an alien biochemistry use sulfur as a replacement for carbon? I doubt it. Could an alien biochemistry use sulfur or sulfur compounds as a replacement for other parts of Earth-typical biochemistry? Absolutely.

For an example, look no further than Earth's own hydrothermal vents. These vents deep in the oceans spew forth water loaded with a variety of chemicals not found in significant quantities in the rest of the ocean, including hydrogen sulfide (H2S). Some bacteria in the vents can produce energy by reacting the sulfide with other chemicals, such as oxygen and carbon dioxide, producing elemental sulfur or sulfate (SO4). They use sulfur like plants use sunlight.

Alternatively, sulfur could replace the role of water. Or, more precisely, sulfuric acid (H2SO4). In Earth's biochemistry, water's primary role is as a solvent. It dissolves things, and lets them interact with each other in solution. Acids, of course, are also quite good at dissolving things. Although since sulfuric acid has a tendency to tear apart organic compounds, lifeforms that evolve in lakes of sulfuric acid might have to use silicon-oxygen chains (aka silicones) as the backbone of their biochemistry instead of carbon.


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