Thread:Wormulon/@comment-3309941-20121208194836/@comment-1073312-20121209001555

Although we live on the surface of the Earth where we are are used photosynthetic - and photosynthetic-dependant organisms, on Earth in other environments there are a great diversity of Chemoautotrophs. Most of them live in anoxic environments because the first photosynthesizing organisms created the "oxygen catastrophy", this happened somewhere between 3 and 2.5 billion years ago.

The point I'm getting to is that this occured before the development of sexual reproduction, which by then was dominated by Eukaryotes, most of which were probably capable of photosynthesis. This was an important stage for diversification. Chemoautotrophs on the other hand never got a chance to get this complex, hugging around the last vestiges of their primordial environments.

If allowed life on this world of yours didn't have an oxygen catastrophy, then I think yes, there is no problem with them evolving sexual reproduction and thus evolving far more quickly.

If they are using methane and sulfur, then the primary sources would be from volcanic activity. I would imagine the best places for this might be Mid-Ocean ridges, they are "wounds that never heal" in the sense that they are stable enough to develop complex communities. I doubt hydrogen would be a good source though, most would escape the atmosphere, and organisms which use hydrogen compunds on the Earth react them with oxygen.

Could ocean life become sentient? Of course! Could it create its own society, civilisation and technology? Perhaps! So life on the world you describe could become as complex as ourselves.