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Nature. 2002 Aug 8;418(6898):627-30.

Reassessing the evidence for the earliest traces of life.

Author information

1
Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0236, USA. mvanzuil@ucsd.edu

Erratum in

  • Nature 2002 Nov 14;420(6912):202.

Abstract

The isotopic composition of graphite is commonly used as a biomarker in the oldest (>3.5 Gyr ago) highly metamorphosed terrestrial rocks. Earlier studies on isotopic characteristics of graphite occurring in rocks of the approximately 3.8-Gyr-old Isua supracrustal belt (ISB) in southern West Greenland have suggested the presence of a vast microbial ecosystem in the early Archean. This interpretation, however, has to be approached with extreme care. Here we show that graphite occurs abundantly in secondary carbonate veins in the ISB that are formed at depth in the crust by injection of hot fluids reacting with older crustal rocks (metasomatism). During these reactions, graphite forms from the disproportionation of Fe(II)-bearing carbonates at high temperature. These metasomatic rocks, which clearly lack biological relevance, were earlier thought to be of sedimentary origin and their graphite association provided the basis for inferences about early life. The new observations thus call for a reassessment of previously presented evidence for ancient traces of life in the highly metamorphosed Early Archaean rock record.

PMID:
12167858
DOI:
10.1038/nature00934
[Indexed for MEDLINE]

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