# Given an initially high concentration of CO2 and H2O, how efficient can I conceivably make a photosynthetic reaction?

## I have been told that the high proportion of O2 and CH4 in my atmosphere are unsustainable unless constantly refreshed by an active process.

I would like to sustain the following atmospheric composition:

75.11% N2

22.04% O2

1.38% CH4

0.83% Ne

0.21% CO2

0.18% Xe

0.11% Ar

0.09% Kr

0.04% He

Molecular mass = 28.93

Rspecific = 287.38

Density at sea level = 1.08 kg/m3

Pressure at sea level = 0.81 atm

Scale height = 9717.35 m

## My question:

How efficient would my photosynthetic and other carbon sequestration processes need to be to maintain this equilibrium between O2, CH4, CO2 and H2O? Keep in mind that it doesn't need to be perfect; My planet is highly geologically active and I can provide methane via volcanism (I think).

I'm trying to find examples of photosynthetic bacteria that produce a lot of methane as a byproduct of their metabolism, but nothing comes to mind right away. I'll edit it in if I find anything! I know at least if I can't find a cyanobacterium that does this, I can find a chemotrophic bacterium that does.

• Gas with 75% $H_2O$ at 1.8 atm? Is it an ocean world? What temperature are we talking about? Commented Feb 22, 2018 at 16:43
• Yes: my oceans cover 95.45% of my surface. I need to re-work this obviously, because as somebody pointed out, my temperature and pressure would condense my water vapor out of the atmosphere. (I'm a tunnel-visioned idiot) Commented Feb 22, 2018 at 16:46
• Are you still looking for this question to be answered? Commented Feb 22, 2018 at 16:59
• Suggestion: save link to this question, delete it and then when you will get back from your drawing board edit it and undelete. Commented Feb 22, 2018 at 17:02
• Where all h2o went? On Earth it is 0.25% and that's a reasonable start for planet with ocean. Commented Feb 22, 2018 at 19:13