Ocean oxygenation in the wake of the Marinoan glaciation

Data are presented that support the idea of an oxygenation event in the immediate aftermath of the Marinoan glaciation, pre-dating previous estimates for post-Marinoan oxygenation by more than 50 million years. A breath of oxygen for the early metazoans Macroscopic metazoans first appeared in the fossil record shortly after the termination of the late Cryogenian (Marinoan) glaciation about 635 million years ago. It has been suggested that an oxygenation event at about this time was the driving factor behind the rise of the metazoans, but current estimates suggest that oxygenation occurred between 580 million and 550 million years ago, well after initial animal diversification. New geochemical data from early Ediacaran organic-rich black shales of the basal Doushantuo Formation in South China now suggest that the oxidation event occurred more than 50 million years earlier, in the immediate aftermath of the Marinoan glaciation. The data provide evidence for a significant postglacial oxygenation and support a link between the most severe glaciations in Earth's history, the oxygenation of Earth's surface and the earliest emergence of complex animals. Metazoans are likely to have their roots in the Cryogenian period 1 , 2 , 3 , but there is a marked increase in the appearance of novel animal and algae fossils shortly after the termination of the late Cryogenian (Marinoan) glaciation about 635 million years ago 4 , 5 , 6 . It has been suggested that an oxygenation event in the wake of the severe Marinoan glaciation was the driving factor behind this early diversification of metazoans and the shift in ecosystem complexity 7 , 8 . But there is little evidence for an increase in oceanic or atmospheric oxygen following the Marinoan glaciation, or for a direct link between early animal evolution and redox conditions in general 9 . Models linking trends in early biological evolution to shifts in Earth system processes thus remain controversial 10 . Here we report geochemical data from early Ediacaran organic-rich black shales (∼635–630 million years old) of the basal Doushantuo Formation in South China. High enrichments of molybdenum and vanadium and low pyrite sulphur isotope values (Δ 34 S values ≥65 per mil) in these shales record expansion of the oceanic inventory of redox-sensitive metals and the growth of the marine sulphate reservoir in response to a widely oxygenated ocean. The data provide evidence for an early Ediacaran oxygenation event, which pre-dates the