Sadly, photosynthesis is impossible for now. Just like ebbor said, the simple cells cannot deal with the free radicals and other waste products from the chloroplasts would destroy the cell, without advanced mechanisms to defend it. No photosynthesis... For now.
Certainly not oxygen. That stuff is pure poison.
We have a shortage of carbon dioxide for that anyway. So yeah, more volcanism.
((The life near the blacksmokers is quite isolated. The water around the smokers is often too cold to support life, preventing alien life from leaving it. Occasionally the warm water escaping from the smoker might last long enough for the bacteria to survive the trip to the bottom of the sea, but that's about it. The beings at the bottom of the sea will be anaerobic, feeding on the chemicals that escape the smokers))
Yeah, so overrated anyway. Especially its byproduct, ozone. Overrated. Anyways, you can never have enough carbon dioxide, can ya?
I feel somehow inadequate against the creative minds of this forum all of a sudden. This, while I can understand it, is beyond my ability to create...
Don't worry, it won't stay this complicated if that's your problem. Once we get from the cell level, it'll get simpler.
The water around the smokers is often too cold to support life
I was first shocked to read that, knowing water can reach 180°C there, but then realized you meant the water between there and the surface. Which is completely untrue IRL, but probably true for our fragile, tiny specks of life.
I support the rest of your post. No oxygen for now (it's a waste product we got used to, nothing more), more CO2 (it being food source) and black smokers life being anaerobic and chemiotrophic.
I will now steal this tree of life and add my favourites. *excited mode ON*
EDIT: The Cometborns, having suffered through a thousand lightyears before getting to a relative rest on this planet, earned the ability to harvest deadly radiations, and turn it into useable energy. This marvel of survival is done by them having lots of redundant RNA strings that shield the useful bits, and get broken down by the radiation, then repaired. This endless cycle produce an energy output that keep the cell alive. Cometborns turned deathly rays into feeding light.
Interesting way of life you have there. I like your originality.
((Repairs cost energy, they don't produce it. Besides, radiation levels will be far to low for that to be feasible anyway))
Well, there is no ozone and basically almost no other protective layers in the atmosphere. Well, there's the magnetic field, but it can't block all of it.
"Say, the sun is firey right? Screw it, we don't have any gods of light; I'll take up that burden."
Grant one of the comet-borne prokaryotes photosynthesis.
Once that prokaryote becomes established, fiddle with some of the soupy prokaryotes to help them engulf smaller cells in a symbiotic fashion.
"Could be patient. Don't feel like it."
For reasons I stated before, that won't work until the cells get more advanced ways of dealing with the dangerous stuff coming with photosynthesis.
Wait, we aren't?
Well, we are still at the prokaryotic level. These simple cells are basically just a storage for RNA (a simple nucleus) and a membrane. Not much more, yet.
Planet: Genesis
Mass: 0.95 Earth masses
Diameter: 11858 km
SMA: 2.4 AU
Atmosphere: Nitrogen (95.2%), Carbon Dioxide (4%), Other gases (Argon, water vapor etc.) (0.8%), 1.0 ATM
Axis: 58°
Water covering: 60% of the surface, quite unstable climate
Geology: Active, Earth-like
Moons:
Unnamed moon 1:
Mass: 0.012 Earth masses
Diameter: 3446 km
SMA: 403 000 km
Orbital inclination: 28°
Atmosphere: None
Geology: Dead
Unnamed moon 2:
Mass: 0.007 Earth masses
Diameter: 3177 km
SMA: 151 000 km
Orbital inclination: 87°
Atmosphere: None
Geology: Volatile, Io-like