Origin and Significance of Archean Quartzose Rocks at Akilia, Greenland

doi:10.1126/science.298.5595.919q

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Fedo and Whitehouse (Reports, 24 May 2002, p. 1448) reinterpreted 3.8 billion year old quartzose rocks in Greenland--previously thought, based on carbon isotope signatures, to harbor evidence for Earth's oldest life--as metasomatized ultramafic igneous rocks, an origin that, they maintained, invalidates claims that the rocks record early biological activity. In separate comments, Mojzsis and Harrison and Friend et al. argue that rare earth element signatures and other geochemical patterns of these rocks are more similar to those of ancient sedimentary banded iron formations than to those of ultramafic igneous rocks, and that field relations suggest that Fedo and Whitehouse did not analyze a key unit sampled in earlier studies. Fedo and Whitehouse respond that these earlier studies, and the current comments, have relied heavily on a single sample that has not been adequately described in the literature, and that a more comprehensive evaluation of field and geochemical data from the Akilia locality supports the interpretation of these rocks as metasomatized ultramafics.

The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/298/5595/917a