Earth’s surface underwent stepwise oxygenation before persistently reaching modern levels late in its history1–5, but the details of this transition remain unclear5–16. Here we present a high-resolution 2.5-Gyr record of mass-independent oxygen isotopes in sedimentary sulfate (Δ′17Osulfate), a proxy linked to the atmospheric partial pressure of O2 ( \({p}_{{{\rm{O}}}_{2}}\) )17–19. This record, together with existing sedimentary Δ33S data20–22, demonstrates a 2-Gyr transition characterized by generally low, fluctuating \({p}_{{{\rm{O}}}_{2}}\) between an O2-free state before 2.4 billion years ago (Ga) and a modern \({p}_{{{\rm{O}}}_{2}}\) state after 0.41 Ga, with relatively elevated levels after 1.0 Ga. Our data also show coupled declines in Δ′17Osulfate and sulfate-δ34S during major negative carbonate-δ13C excursions in the Neoproterozoic. Quantitative biogeochemical modelling indicates that these isotopic couplings reflect the increasing \({p}_{{{\rm{O}}}_{2}}\) , which may have driven episodic ocean oxygenation through an increased atmospheric O2 influx. This process intensified the oxidation of marine organics and reduced-sulfur species, while triggering temporary \({p}_{{{\rm{O}}}_{2}}\) drawdowns as negative feedback15. These findings support a dynamic, lengthy co-oxygenation history for the atmosphere and oceans—marked by long-term positive coupling and short-term negative feedbacks—offering a coherent explanation for the anomalous Neoproterozoic carbon cycles23,24 and the protracted, episodic rise of complex life25–27.
