Subject: Gases in primordial atmospheres

I know that the anicent atmosphere of the Earth is thought to contain gases 
such as CO2, CH4 and NH3. But it seems to me quite strange. CO2 is oxidized 
compound, and it has acidic properties. Ammonia is reduced, and basic.
So, these two should react, forming ammonium bicarbonate, or the ammonia could 
be oxidized into nitrogen, I think. Also methane and carbon dioxide (fully 
redeuced+fully oxidized Carbon) shouldnt exist together. 
BUT these three compounds were all imporatant for the origin of life, so they 
must have been there for a long time. Maybe the mixture was not so unstable, 
but why?

Re: Gases in primordial atmospheres