Re: Oxygen content of the atmosphere over the last 10,000 years

Doug Jones (
Fri, 06 Aug 1999 20:30:18 -0700

I think there are two different but linked feedback loops involved here. The O2 partial pressure is limited by flammability- above 23%, even green wood burns enthusiastically, so the oxygen level won't rise higher, instead, more biomass will get oxidized. There is a *lot* of carbon available for this equilibrium, peat bogs and tropical forests should suffice.

The second loop is the CO2 temperature feedback- warmer climate encourages more coral reefbuilding which sequesters CO2 in carbonate reefs. IIRC, there are other temperature feedback mechanisms that would remove the CO2.

Where these two run into trouble is the increasing luminosity of the sun, which is driving CO2 toward zero. C4 plants arose relatively recently in response to the stress of lower CO2, and when this crucial component goes too low in about 200 million years, *that* could be a problem.

Since the next few decades are the real issue, all the above is only of scientific interest...

James R. Andrix wrote:
> At 12:51 PM 8/6/99 -0700, Peter McCluskey wrote:
> > See Barrow and Tipler's The Anthropic Cosmological Principle, pages 567-569.
> >They show a long-term trend of rising oxygen levels which threatens to cause
> >most vegetation exposed to the atmosphere to burn 200 million years from now.
> What do you mean 'to burn' exactly? I'll assume that includes the death of
> all terrestrial plant life. 200 million years seems like an awfully short
> time, geologicaly.
> I'm thinking of this in terms of a 'Great Filter' i.e. If intelligent life
> has to evolve before oxygen destroys plants (and then just about all life)
> and WE made it with only 200 million years to spare...
> Of course marine plants aren't exposed to the atmoshpere.