Photosynthesis carbon fractionation

A small fraction (less than 1%) of the fixed carbon produced by photosynthesis is buried and physically removed from any potential reaction with oxygen (until the buried material is brought to the surface - at a much later time). Thus, the oxygen in our contemporary atmosphere is the consequence of many millions of years of fixed carbon burial. More details on this topic can be found in Chapters 8 and 11. 

If the global oxygen production caused by the small fraction of carbon fixed by photosynthesis that is buried were not balanced by an oxygen consumption term, and other processes remained the same, the O2 content of the atmosphere would roughly double in about 2 million years. This is a short time geologically, particularly because it is believed there has been... 

Vogel, J.C. 1980 Fractionation of the Carbon Isotopes During Photosynthesis. New York, Springer. 

Early reviews by O Leary (1981) and Farquhar et al. (1989) have provided the biochemical background of carbon isotope fractionations during photosynthesis, with more recent accounts by Hayes (2001) and Freeman (2001). 

Park R, Epstein S (1960) Carbon isotope fractionation during photosynthesis, Geochim Cosmochim Acta 21 110-126... 

---