Lyle L. Nelson

Abstract The accumulation of free oxygen in the atmosphere ≈2.45 billion years ago was one of the most transformative events in Earth’s past. Since its identification, this interval termed the ‘Great Oxidation Event’ (GOE), has garnered a large amount of attention from a wide array of perspectives, with some suggesting it should define its own geologic era or period.

1 Introduction The Ediacaran–Cambrian transition (ca. 550–533 Ma) was a period marked by significant evolutionary and ecological changes (e.g., Darroch et al. 2018, 2023; Mángano and Buatois 2016; Seilacher et al. 2005; Wood et al. 2019; Zhu et al. 2017; Zhuravlev and Wood 2018).

Abstract Understanding causal relationships between evolution and ocean oxygenation hinges on reliable reconstructions of marine oxygen levels, typically from redox-sensitive geochemical proxies. Here, we develop a proxy, using dolomite U–Pb geochronology, to reconstruct seawater U/Pb ratios. Dolomite samples consistently give U–Pb dates and initial 207Pb/206Pb ratios lower than expected from their stratigraphic ages.