Figure 5.

Summary diagram showing relationship between timing of evolutionary events (Table 2) and that of Earth and atmospheric histories. Time estimates are shown with ± 1 standard error (thick line) and 95% confidence interval (narrow line). The phylogenetic tree illustrates the radiation of extant eubacterial lineages (blue), and dashed lines with arrows indicate the origin of eukaryotes (BK-o) and origin of mitochondria (BK-m). The earliest divergence (last common ancestor) was not estimated but is placed (arbitrarily) just prior to the AK divergence. The increasing thickness of the eukaryote lineage represents eubacterial genes added to the eukaryote genome through two major episodes of horizontal gene transfer. The rise in oxygen represents a change from <1% to >15% present atmospheric level [34,52], although the time of the transition period and levels have been disputed [19,53].