Considering these redox potential constraints, Mn oxidation is an attractive photosynthetic donor on a trajectory to oxidizing water (16–18).
An initial manganese-oxidizing photosystem also explains both why the only known biological system that can oxidize water originally procures electrons from Mn and why WOC assembly begins with Mn oxidation.
The timing of cyanobacterial origins remains controversial because of the absence of a robust Archean fossil record.
The use of molecular fossils was explored with much apparent potential (21).
Early ideas suggested a Mn-bearing protein was evolutionarily coopted to become the WOC.