Fig. 1.

Summary of oxygen accumulation of earth history. Data for oxygen levels from Ref. [17], for the emergence of autotrophy from Ref. [1], of methanogens from Ref. [3], of cyanobacteria from Ref. [20], of animals from Ref. [24], of eukaryote anaerobes from Refs. [47,95], of eukaryote algae from Ref. [21], of algal anaerobic enzymes from Ref. [61], of land plants from Ref. [13], and for the eukaryote age from Refs. [8,30]. PAL: percent of present atmospheric level. GOE: great oxidation event. The GOE marks the appearance of continuous atmospheric O₂ in the geochemical record [17,26,27,[30], [31], [32], [33]].