The availability of molecular oxygen shapes the size and structure of Earth’s biosphere. Geological and geochemical records imply that, for most of the Precambrian (the entirety of Earth’s history with the exception of the most recent 540 million years), atmospheric oxygen concentrations were only a fraction of that of the present. A notable exception occurred in the wake of the first major rise in atmospheric oxygen between ∼2.3 and 2.0 billion years ago. This interval is characterized by the largest and longest-lived marine carbon isotope excursion in Earth’s history, the Lomagundi, which was accompanied by a major reorganization of global biogeochemical cycles. Despite this prominent change in the Earth system, the cause(s) of this remarkable inferred rise and subsequent fall in atmospheric oxygen levels and the consequences—for both marine biogeochemical cycling and the emergence and radiation of eukaryotic life—remain underexplored. Importantly, there is no robust evidence for increased biological complexity or the emergence of organisms with high oxygen demands despite strong indications of a stable and well-oxygenated Earth system over the 100–300 million-year Lomagundi interval. This decoupling is in sharp contrast to oxygenation during the later Neoproterozoic and early Paleozoic Eras, which temporally coincided with the expansion of eukaryote-rich ecosystems, including the appearance and radiation of animals. Emerging evidence for strong and stable, albeit ultimately impermanent oxygenation in the Paleoproterozoic that was divorced from increases in evolutionary complexity substantially broadens our framework for reconciling environmental and biotic co-evolution through Earth’s history. The lack of an obvious temporal link between this prominent Paleoproterozoic episode of long-lived and likely substantial oxygenation and physiological and ecological diversification suggests that the former does not always foster the latter.

分子氧的可用性决定了地球生物圈的大小和结构。地质和地球化学记录表明，对于前寒武纪的大部分时间（地球的整个历史，最近的 5.4 亿年除外），大气中的氧气浓度仅为现在的一小部分。一个值得注意的例外发生在大约 2.3 到 20 亿年前大气中氧气的第一次大幅上升之后。该间隔的特点是地球历史上最大和最长寿的海洋碳同位素漂移，Lomagundi，伴随着全球生物地球化学循环的重大重组。尽管地球系统发生了这种显着变化，大气中氧气水平的这种显着的推断上升和随后下降的原因以及海洋生物地球化学循环和真核生命的出现和辐射的后果仍未得到充分探索。重要的是，尽管有强烈迹象表明在 100-3 亿年的 Lomagundi 间隔期间地球系统稳定且充氧良好，但没有强有力的证据表明生物复杂性增加或出现高氧需求的生物。这种脱钩与新元古代晚期和古生代早期的氧合作用形成鲜明对比，后者在时间上与富含真核生物的生态系统的扩张同时发生，包括动物的出现和辐射。强有力和稳定的新证据，尽管古元古代的最终非永久性氧合作用与进化复杂性的增加脱节，但它大大拓宽了我们在地球历史上调和环境和生物共同进化的框架。古元古代显着的长寿且可能大量充氧事件与生理和生态多样化之间缺乏明显的时间联系，这表明前者并不总是促进后者。