Figure 2.

Evidence for microbial life in Proterozoic rocks. (a) Stromatolites accreting on top of limestone cobbles, ca 800 Ma Limestone-Dolomite Series, central East Greenland; (b) colonies of cyanobacteria-like coccoidal cells, ca 750 Ma Draken Conglomerate, Svalbard; (c) short cyanobacterial trichome, 1400–1500 Ma Billyakh Group, northern Siberia; and (d) filamentous and coccoidal microfossils in iron-rich rocks of the 1860 Ma Gunflint Formation, Ontario. Scale bars: 3 cm in (a), 25 µm in (b,d) and 15 µm in (c). (Online version in colour.)