Arla Johnson writes:
> No one that I know of has ever questioned the impact of both human and
> natural activities on the world's OXYGEN supply. After all 6 billion or
> so can
> live in a primordial swamp with oodles of co2 but we haven't any
> personal
> oxygen generators handy if the Oxygen begins to drop off.
Actually, there is a known abiogenic mechanism (water photolysis, with the hydrogen escaping into space) which constantly replenishes the oxygen pool, and some not well characterized mechanisms which removes the oxygen from the atmosphere (probably mostly oxidation of volcanic material).