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2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 323-7
Presentation Time: 3:00 PM

REAPPRAISAL OF HYDROCARBON BIOMARKERS IN ARCHEAN ROCKS


FRENCH, Katherine L., Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, HALLMANN, Christian, Max Planck Institute for Biogeochemistry, Bremen, 28359, Germany, SCHOON, Petra L., Department of Earth Sciences, University of California Riverside, Riverside, CA 92521, ZUMBERGE, J. Alex, Department of Earth Sciences, UC Riverside, 900 University Avenue, Riverside, CA 92521, HOSHINO, Yosuke, Department of Earth and Planetary Science, Macquarie University, Sydney, 2109, Australia, GEORGE, Simon C, Department of Earth and Planetary Sciences, Macquarie University, Sydney, 2109, Australia, LOVE, G.D., Dept. of Earth Sciences, Univ. of California, Riverside, CA 92521-0423, BROCKS, Jochen J., Research School of Earth Sciences, Australian National University, 61 Mills Road, Acton, Canberra, 0200, Australia, BUICK, Roger, Dept. Earth & Space Sciences and Astrobiology Program, Univesity of Washington, Johnson Hall, 4000 15th Avenue NE, Seattle, WA 98195-1310 and SUMMONS, Roger E., Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, MIT, E25-633, 77 Massachusetts Ave, Cambridge, MA 02139, kfrench@whoi.edu

Hopanes and steranes found in Archean rocks have been presented as key evidence supporting the early rise of oxygenic photosynthesis and eukaryotes (e.g. 1), but it has been suggested that sample contamination could negate these results (e.g. 2). To resolve this debate, we performed a multilaboratory study of new cores from the Pilbara Craton, Australia, that were drilled and sampled using unprecedented hydrocarbon-clean protocols. We report that hopane and sterane concentrations measured in new ultraclean Archean drill cores from Australia are comparable to blank concentrations, yet their concentrations in the exteriors of conventionally collected cores of stratigraphic equivalence exceed blank concentrations by more than an order of magnitude due to surficial contamination. Polycyclic aromatic hydrocarbons and diamondoids in rock extracts and hydropyrolysates from the ultraclean cores exceeded blank concentrations and had high thermal maturity distribution patterns, comparable to those reported in previous Archean studies of conventionally collected samples. Together, these results demonstrate that previously studied Archean samples host mixtures of biomarker contaminants and indigenous overmature hydrocarbons. Therefore, existing lipid biomarker evidence no longer provides valid evidence for the emergence of oxygenic photosynthesis and eukaryotes by ∼2.7 billion years ago.

  1. Brocks et al. 1999. Archean Molecular Fossils and the Early Rise of Eukaryotes. Science 285: 1033-1036.
  2. Rasmussen et al. 2008. Reassessing the First Appearance of Eukaryotes and Cyanobacteria. Nature 455: 1101-1104.

Session No. 323

Geochemistry: Frontiers in Geochemistry
Wednesday, 4 November 2015: 1:30 PM-5:30 PM
Room 317 (Baltimore Convention Center)
Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p.817
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