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Originally published in Science Express on 29 September 2005
Science 21 October 2005:
Vol. 310. no. 5747, pp. 471 - 474
DOI: 10.1126/science.1115769
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Reports

Biomarker Evidence for Photosynthesis During Neoproterozoic Glaciation

Alison N. Olcott,1* Alex L. Sessions,2 Frank A. Corsetti,1 Alan J. Kaufman,3 Tolentino Flavio de Oliviera4

Laterally extensive black shales were deposited on the São Francisco craton in southeastern Brazil during low-latitude Neoproterozoic glaciation ~740 to 700 million years ago. These rocks contain up to 3.0 weight % organic carbon, which we interpret as representing the preserved record of abundant marine primary productivity from glacial times. Extractable biomarkers reflect a complex and productive microbial ecosystem, including both phototrophic bacteria and eukaryotes, living in a stratified ocean with thin or absent sea ice, oxic surface waters, and euxinic conditions within the photic zone. Such an environment provides important constraints for parts of the "Snowball Earth" hypothesis.

1 Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA.
2 California Institute of Technology, Pasadena, CA 91125, USA.
3 University of Maryland, College Park, MD 20742, USA.
4 Companhia Mineira de Metais, Brazil.

* To whom correspondence should be addressed. E-mail: olcott{at}usc.edu

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