Production of molecular oxygen was a turning point in the Earth’s history. The geological record indicates the Great Oxidation Event, which marked a permanent transition to an oxidizing atmosphere around 2.4 Ga. However, the degree to which oxygen was available to life before oxygenation of the atmosphere remains unknown. Here, phylogenetic analysis of all known oxygen-utilizing and -producing enzymes (O₂-enzymes) indicates that oxygen became widely available to living organisms well before the Great Oxidation Event. About 60% of the O₂-enzyme families whose birth can be dated appear to have emerged at the separation of terrestrial and marine bacteria (22 families, compared to two families assigned to the last universal common ancestor). This node, dubbed the last universal oxygen ancestor, coincides with a burst of emergence of both oxygenases and other oxidoreductases, thus suggesting a wider availability of oxygen around 3.1 Ga.

分子氧的产生是地球历史上的一个转折点。地质记录表明发生了大氧化事件，这标志着在 2.4 Ga 左右向氧化性大气层的永久转变。然而，在大气层氧化之前氧气对生命可用的程度仍然未知。在这里，对所有已知的氧气利用和产氧酶（O ₂酶）的系统发育分析表明，氧气在大氧化事件之前就已广泛用于生物体。约 60% 的 O ₂- 可以确定出生日期的酶家族似乎是在陆地和海洋细菌分离时出现的（22 个家族，与分配给最后一个普遍共同祖先的两个家族相比）。这个节点，被称为最后一个普遍的氧气祖先，与加氧酶和其他氧化还原酶的突然出现同时发生，因此表明在 3.1 Ga 附近有更广泛的氧气供应。