Mesoproterozoic sulphidic ocean, delayed oxygenation and evolution of early life; sulphur isotope clues from Indian Proterozoic basins

Analyses of sulphur isotope compositions in sedimentary pyrites from the Vindhyan, Chattisgarh and Cuddapah basins show heavy delta (super 34) S (> +25 per mil) values during the Mesoproterozoic. The data provide evidence in support of a hypothesized global Proterozoic sulphidic anoxic ocean where very low concentrations of marine sulphate, bacterially reduced in closed systems, produced delta (super 34) S values in pyrites similar to or even heavier than marine sulphate. The extreme environmental conditions induced by these anoxic oceans could have been responsible for the delayed oxygenation of the biosphere and retarded evolution of multicellular life.