Stagewise oxygenation of the Earth's atmosphere and oceans

Earth's surface oxygenation was a protracted, multi-step process. It is widely accepted that atmospheric O₂ rose through three major steps, each closely linked to key evolutionary innovations. Recent advances, particularly in sulfate triple-oxygen isotope records, now provide new constraints on the timing, tempo, and magnitude of atmospheric oxygenation. These data reveal a positive coupling between atmospheric and oceanic oxygenation on billion-year timescales, with stagewise rises in atmospheric O₂ consistently preceding oceanic responses, whereas on shorter, million-year timescales, their redox states could diverge, exhibiting negative coupling. Oceanic redox evolution was also spatially and temporally heterogeneous, progressing from localized Archean oxygen oases (>3.0 Ga) to a globally oxygenated state by the Paleozoic (<0.41 Ga). Here, we synthesize geochemical, sedimentological, and palaeobiological evidence to reconstruct this coupled and dynamic atmosphere-ocean oxygenation history and to reassess its timing, mechanisms, and ecological consequences. These deep-time perspectives illuminate the co-evolution of life and Earth's surface environments and provide a conceptual framework for evaluating planetary habitability.