1. Department of Earth Sciences, University of California, Riverside, California 92521, USA
2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239, USA
3. Petroleum and Marine Division, Geoscience Australia, Canberra, Australian Capital Territory 2601, Australia
4. School of Civil Engineering and Geosciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK
5. Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
6. School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK
7. Present address: NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, UK.

Correspondence to: Gordon D. Love^1,2 Correspondence and requests for materials should be addressed to G.D.L. (Email: glove@ucr.edu).

Abstract

The Neoproterozoic era (1,000–542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems¹. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C₃₀ sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation (635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology², constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, 713 Myr ago in Oman²).

1. Department of Earth Sciences, University of California, Riverside, California 92521, USA
2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239, USA
3. Petroleum and Marine Division, Geoscience Australia, Canberra, Australian Capital Territory 2601, Australia
4. School of Civil Engineering and Geosciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK
5. Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
6. School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK
7. Present address: NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, UK.

Correspondence to: Gordon D. Love^1,2 Correspondence and requests for materials should be addressed to G.D.L. (Email: glove@ucr.edu).

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