Fig. 1.

Temporal history of biomarker and fossil data. (A) Ratio of eukaryotic steranes over bacterial hopanes through time (details and references see text). Green circles, late Cryogenian to present data, including C₂₇ to C₂₉ steranes (cholestanes, ergostanes, and stigmastanes); red circles, Tonian to early Cryogenian steranes with a ∼100% cholestane predominance; and unfilled black circles, mid-Proterozoic biomarker assemblages, where hopanes are present but steranes are below detection limits. (B) First occurrences or radiations of organism groups and biomarkers (for data sources, see text). C, Cenozoic; Cr, Cryogenian; Ed, Ediacaran; M, Mesozoic; Neoprot., Neoproterozoic; P, Paleozoic; Tn, Tonian.