Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies

The timing of the evolution of non-photosynthetic sulphur (S)-oxidizing bacteria and changes in stable S isotopes indicates that these events were caused by a large increase in the atmospheric oxygen during late Proterozoic. The oxygen levels increased to more than 5 to 18% of the present atmospheric level and this permitted the development of an oxidative S cycle and bacterial evolution. Analysis of the 16S rRNA of gamma-proteobacteria shows that they evolved almost 0.76 billion years (Gyr) ago. A significant change in the S isotope composition took place between 0.64 to 1.05 Gyr ago.