Fig. 2.

A diagrammatic representation of the time scale of life based on refs. 39–41, depicting the distribution of the three globin lineages in the three kingdoms of life. The origin of Cyanobacteria (Cy) is estimated at ≈2,600 Mya, and the divergence of plants (Pl), animals (An), and fungi (Fu) is estimated at ≈1,500 Mya. The red arrows indicate the two generally accepted endosymbiotic events: between an α-proteobacterium (Ap) and a eukaryote at ≈1,800 Mya, resulting in the emergence of mitochondria (M), and between a cyanobacterium and a eukaryote at ≈1,500 Mya, resulting in the formation of plastids (P). The dotted lines indicate uncertainty in dating the split. Aq, Aquificales; OB, other bacteria; Al, Algae; Em, Embryophytes (land plants); OEk, other eukaryotes; Cr, Crenarcheota; Eu, Euryacheota.