Old arguments that free O 2 must have been available at Earth's surface prior to the origin of photosynthesis have been revived by a new study that shows that aerobic respiration can occur at dissolved oxygen concentrations much lower than had previously been thought, perhaps as low as 0.05 nM, which corresponds to a partial pressure for O 2 of about 4 ×10 -8 bar. We used numerical models to study whether such O 2 concentrations might have been provided by atmospheric photochemistry. Results show that disproportionation of H 2O 2 near the surface might have yielded enough O 2 to satisfy this constraint. Alternatively, poleward transport of O 2 from the equatorial stratosphere into the polar night region, followed by downward transport in the polar vortex, may have brought O 2 directly to the surface. Thus, our calculations indicate that this "early respiration" hypothesis might be physically reasonable.
All Science Journal Classification (ASJC) codes
- Agricultural and Biological Sciences (miscellaneous)
- Space and Planetary Science