Questions Regarding Precambrian Sulfur Isotope Fractionation

This is the authors' abstract. We don't add key points for this paper.

The discovery by Farquhar et al. (1) of mass-independent isotope fractionation of33S and 36S in rocks formed more than ∼2 billion years ago (Ga), but not in younger rocks, has boosted the theory postulating a dramatic change from an anoxic to an oxygen-rich atmosphere about 2 Ga. That is because the only known natural process that may cause mass-independent fractionation of both 33S and 36S involves atmospheric photochemical reactions by ultraviolet light in the absence of an ozone shield (1). Here, we suggest the strong possibility that the fractionation observed by Farquhar et al. (1) may have been created by analytical rather than natural processes.