Help for FTL

I'm currently writing on my FTL (Secret of Life) and I'm looking for a gas which could replace oxygen in an alien organism.

For this specific race I've already thought up a homeworld with more landmass than earth, but far higher sea levels. This resulst in a world with 85% watermass, looking a bit like a whole-world indonesia (archipelagos, yay!).

So, what I'll need now is any gas which could be used for respiration and still allows this world to occur.

PS: I do want them not to use gills, mainly because they still are a land-walking species. They have better water adaption than humans already have, but they shouldn't be fish altogether.
 
The only gas(ses) I can think of off the top of my head would be sulphur-based...

But I'm no expert...

Paging Thande! Will Thande please report to the thread...
 
Well, if I remember right, plants release oxygen because they take the hydrogen atoms from water to form sugar, releasing the oxygen in the process. So theoretically, there should be alternatives to water. All alternatives that I can think of have obvious disadvantages:

H2S for example has a drastically lower boiling point than water. Obviously, H2S could also be readily available in the atmosphere or the water (having said that, I don't remember how solutable H2S is actually, we should ask Thande!). The question that I have is where the H2S would come from.

And alas, one final issue is that sulphur is much rarer than oxygen in the universe. The problem with chlorine is similar btw.
 
You could maybe have a race from a world where photosynthesis never developed; the basic chemistry might be similar to that of the Earth, but the atmosphere would be very different, with no free oxygen etc. and the base of the food chain being chemsynthetic rather than photosynthetic organisms...
 
You could maybe have a race from a world where photosynthesis never developed; the basic chemistry might be similar to that of the Earth, but the atmosphere would be very different, with no free oxygen etc. and the base of the food chain being chemsynthetic rather than photosynthetic organisms...

Mh - could you explain that a little bit further? With such a planet, the rest of the alien race could've developed as I thought them up.

So a water planet with no photosyntethis .. and the aliens would use chemsynthetic as well? So no breathing? It wouldn't matter, I only need an explanation on how the race could've developed in a water world, while Earth's atmosphere is deadly for them.
 
Mh - could you explain that a little bit further? With such a planet, the rest of the alien race could've developed as I thought them up.

So a water planet with no photosyntethis .. and the aliens would use chemsynthetic as well? So no breathing? It wouldn't matter, I only need an explanation on how the race could've developed in a water world, while Earth's atmosphere is deadly for them.

If I'm not mistaken though, chemosynthetis (not really sure how to spell it) performs precisely the same as photosyntheis, it just gets its energy from an underground heat vent as opposed to the sun. So the chemical process is exactly the same, its just the source of the energy that is different.

I would say nitrogen would be an interesting gas to base life on, though I don't know how well that would work . . . nitrogen-fixing bacteria rule the world?
 
Wouldn't CO2 work as an oxygen substitute? It could be a planet ruled by sentient plants or fungi.

Well, but that warm the planet to such an extend that the temperatures would be too high to form humanoid like lifeforms.

And that's what this alien form is based on - A more aquatic "human", if you like to say so. Does anybody know on which gas a multicellular life form could work then?
 
Methane is another option, although I would think any biochemistry involving methane would be on a cooler planet than Earth.
 
Top