A Whiff of Oxygen Before the Great Oxidation Event

S values, which is comparable with uncertainties based on multiple standard measurements during each analytical session. For SF6 analyses, uncertainties are 0.14, 0.008, and 0.20‰ for d 34 S, D 33 S, and D 36 S, respectively. 19. Monte Carlo resampling of data suggests that the two intervals carry a unique isotopic mean. In the lower half, we calculated means of d 34