Fig. 3|. A revised Neoproterozoic-Cambrian timeline showing co-occurrences of 26-mes and 24-ipc sterane biomarkers.
The South Oman record commences in the Cryogenian period (>635 Ma) after the Sturtian glaciation (terminating at around 660 Ma6) and continues throughout the Ediacaran period into the Early Cambrian for Huqf Supergroup rocks (Supplementary Tables 1–2). Other Ediacaran oils also contain the C30 steranes series (Supplementary Table 3), but some Ediacaran rocks are devoid of the C30 sterane series, although they contain predominantly algal steranes with a C29 dominance40. The distribution and abundance patterns of the C30 sterane 26-mes have yet to be fully established for the Phanerozoic rock record; however, it can be detected in some Phanerozoic rocks and oils (see Supplementary Table 3). Cryostane is a potentially older biomarker for sponges or unicellular protists, and it has been detected in pre-Sturtian rocks in the 800–717 Myr age range29 but not in older samples. Cryostane is a C28 sterane analogue of 26-mes, but corresponding sterol precursors for cryostane have never been reported from any extant taxa despite the identification of 26-mes demosponge sterols many decades ago20,21,23,38,39. ‘M’ signifies the Marinoan glaciation; cryostane temporal range is represented by red shading although possible ocurrences in younger rocks and oils require further investigation; 26-mes and 24-ipc range is represented by the black bar.