Abstract
A hypothesized rise in oxygen levels in the Neoproterozoic, dubbed the Neoproterozoic Oxygenation Event, has been repeatedly linked to the origin and rise of animal life. However, a new body of work has emerged over the past decade that questions this narrative. We explore available proxy records of atmospheric and marine oxygenation and, considering the unique systematics of each geochemical system, attempt to reconcile the data. We also present new results from a comprehensive COPSE biogeochemical model that combines several recent additions, to create a continuous model record from 850 to 250 Ma. We conclude that oxygen levels were intermediate across the Ediacaran and early Palaeozoic, and highly dynamic. Stable, modern-like conditions were not reached until the Late Palaeozoic. We therefore propose that the terms Neoproterozoic Oxygenation Window and Palaeozoic Oxygenation Event are more appropriate descriptors of the rise of oxygen in Earth's atmosphere and oceans.