Abstract

Although the Phanerozoic history of atmospheric oxygen can be reconstructed by mass balance models and proxies such as sedimentary pyrogenic carbon, these strategies have not yielded coherent solutions, leaving unresolved the true history of this key parameter. Building upon prior efforts using the stable carbon isotopic ratios of plant resins to infer atmospheric pO2, we extend the record to 450 million years (Ma) by including terrestrial organic matter sourced by C3 metabolism. Unlike prior efforts, we fail to retrieve a hyper-oxic Late Paleozoic atmosphere, and instead suggest that pO2 has unlikely been significantly higher than present in the Phanerozoic. These results have implications for evolutionary models that link atmospheric pO2 to phenomena such as gigantism in arthropods and tetrapods.