The rise of atmospheric oxygen fundamentally changed the chemistry of surficial environments and the nature of Earth’s habitability¹. Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations^2,3, with the initial rise of oxygen concentration to above 10⁻⁵ of the present atmospheric level constrained to about 2.43 billion years ago^4,5. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago⁴, which represents the estimated timing of irreversible oxygenation of the atmosphere^6,7. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10⁻⁵ of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

大气中氧气的增加从根本上改变了地表环境的化学成分和地球宜居性的性质¹。早期的大气氧化发生在以多次全球冰川作用为标志的极端气候不稳定的长期时期^2,3，氧气浓度最初上升到目前大气水平的 10 ^-5以上被限制在大约 24.3 亿年前^4,5。然而，据报道大气中氧气水平的后续波动一直发生到大约 23.2 亿年前⁴，这代表了大气不可逆氧化作用的估计时间^6,7. 在这里，我们报告了古元古代早期最后两次冰川期大气和当地海洋氧化还原条件的高分辨率重建，正如南非德兰士瓦超群的海洋沉积物所记录的那样。使用多种硫同位素和铁-硫-碳系统学，我们证明了大约 23.2 亿年前大气中氧气水平的持续振荡，这与海洋氧化还原化学和气候的主要扰动有关。^{因此，氧气水平在当前大气水平的 10 -5}阈值范围内波动了大约 2 亿年，随着 Lomagundi 碳同位素漂移，永久性大气氧合最终在大约 22.2 亿年前到达，比目前估计晚了大约 1 亿年。