Before revision: Sulfate was then reduced by microorganisms to produce hydrogen sulfide (H2S):
After revision: 2CH2O + SO4^2- -> H2S + 2HCO3^-By 1.8 Ga (billion years ago), sulfide (S2-) concentrations were high enough to precipitate iron out of the deep ocean by binding with iron to form pyrite (FeS2), effectively ending the formation of BIFs.Sulfate was then reduced by microorganisms to produce hydrogen sulfide (H2S):