2002), through at least two great oxidation events (e.g., Campbell and Allen, 2008;Farquhar et al., 2014), probably caused by photosynthesising microorganisms (e.g., Campbell and Squire, 2010). The first great oxidation event occurred at about 2.4-2.3 Ga, and is best evidenced by a distinct change in the S isotope signature of sedimentary sulfide and sulfate minerals (Farquhar et al., 2014). Prior to this first great oxidation event these minerals record distinct signatures of massindependently fractionated sulfur isotopes, whereas afterwards this signature disappears completely (Farquhar et al., 2014).