Fig. 4

Comparative reconstruction of the temporal evolution of atmospheric pO₂ and estimated age of emergences of major eukaryotic assemblages (MEAs). In the upper diagram, the blue band shows the estimated range of Earth’s atmospheric oxygen content for the last three billion years (Gyr), modified from Lyons et al. [2]. The yellow and green lines delineate the upper and lower limits, respectively, of the estimated range based on geochemical proxies [3]. Red arrow on the top indicates the time point (0.80–0.64 Gyr ago) when pO₂ exceeded the Pasteur point (the presumed level of oxygen required for mitochondrial respiration). In the lower diagram, the estimated divergence times (95% highest probability density) of selected MEAs and the estimated age of LECA are shown, according to Parfrey et al. [37]. This illustrates a conspicuous discrepancy between the timing of the final oxygenation of the atmosphere and the appearance of extant eukaryotic lineages with notable affinity for molecular oxygen. PAL present atmospheric level, MEAs major eukaryotic assemblages, LECA last eukaryotic common ancestor, SAR the supergroup Stramenopiles–Alveolata–Rhizaria