4.2.6.2 Eukaryotic Biomarkers
The detection of steranes, fossil molecules formed from
sterols (Fig. 4.16), in ancient sediments, is considered a
proof of the existence of eukaryotic organisms. Their
occurrence in the sediments mentioned above suggests the
presence of such organisms 2.2 Ga ago. However, sterols
have been detected in a small number of contemporary
prokaryotes, weakening the argument coupling their
Fig. 4.14 Eukaryotic fossils from the Roper formation (northern
Australia). (a–c) Tappania plana b: detail of the protuberance indicated
by the arrow in a; (d) Valeria lophostriata; (e) Dictyosphaeria sp.; (f)
Satka favosa. In Satka favosa, the cell wall determines the fragmented
appearance. Scale: 35 μm for a and c, 10 μm for b, 100 μm for d, 15 μm
for e and 40 μm for f (Javaux et al. 2001) (Photographs: Copyright
courtesy of Nature Publishing Group)
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