LAUSR

Significance Understanding the rise of atmospheric oxygen on Earth is important for assessing precursors to complex life and for evaluating potential future detections of oxygen on exoplanets as signs of extraterrestrial biospheres. However, it is unclear whether Earth’s initial rise of O2 was monotonic or oscillatory, and geologic evidence poorly constrains O2 afterward, during the mid-Proterozoic (1.8 billion to 0.8 billion years ago). Here, we used a time-dependent photochemical model to simulate oxygen’s rise and the stability of subsequent O2 levels to perturbations in supply and loss. Results show that large oxygen fluctuations are possible during the initial rise of O2 and that Mesoproterozoic O2 had to exceed 0.01% volume concentration for atmospheric stability.