Evolution of Oxygen Biogeochemical Cycle

Evolution of photosynthesis was one of the most important biological events of the early Earth s history. Anaerobic pbotosyntbetic bacteria, like tbe modem green and purple sulfur bacteria, would have been tbe first pbotosyntbetic organisms. There is no remarkable evidence of tbe development of these organisms before 3.0-3.5 billion years ago, however, the process of anaerobic photosynthesis is thought to have occurred before this time. The following speculations can prove this hypothesis. 

The anaerobic photosynthetic bacteria can not produce oxygen in an aerobic atmosphere. They would have produced oxygen carrying out the anaerobic oxidation of the reduced sulfur compounds H2S and S, with the formation of S and SOa , correspondingly  

Organic matter produced by this photosynthetic process was represented by CH2O. 

Oxygenic photosynthesis has been dated to before 2.0 billion years ago by some distinctive geological records. The extensive banded iron formation (BIEs) dated 2.0-2.5 billion years ago, can serve as an evidence of the development of this type of photosynthesis. The iron occurs in the form of almost pure ferric oxide and silica, and the formation of BIFs can be explained by the oxidation of ferrous iron in solution with oxygen, produced in large quantities in photosynthesis. The only pre-Cambrian photosynthetic organisms that could carry this out were cyanobacteria. There are extensive fossil records of similar organisms in geological formations of that age. 

Here we have to say a few additional words about the role of oxygen in the evolution of Earth s biogeochemical cycling. The paramount importance of oxygen has to be commented on specifically. The chemistry of oxygen suits it uniquely for its biogeochemical role. 

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