Are the oldest 'fossils' fossils? Two significant but opposing papers on the same (supposed) Precambrian fossils recently appeared in the same issue of Nature. In the first, Schopf and colleagues from the Universities of California and Alabama reported (v.416, p.73, 2002) that they had used laser-Raman spectroscopic imagery of individual microbe-like objects, including the oldest such specimens yet known, to demonstrate that the objects did indeed have a biological origin. Hitherto, it has been difficult to prove the biogenicity of such Precambrian (including Archean) specimens even when they are indigenous and syngenetic with the formation of rocks of known provenance and well-defined age, although some, but far from all, workers have been convinced by the results of carbon-isotope analysis. Even more convincing, claim Schopf and his colleagues, not only here but earlier (Proceedings of the Notional Academy of Sciences, v.98, p.823, 2001) is Raman spectroscopy, a non-intrusive, non-destructive technique for imaging material at a molecular level. The spectra from filaments in rocks suspected to be mineralized fossils (Fig. 1) have peaks typical of kerogenous material, which appears to establish the biogenic origin of the filaments.
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