Graphite, Isua

A 13C/12C ratio about 3% above that of a standard value (the so-called VPDB standard) had been found in western Australian rock samples from the Pilbara Formation similar values were found for the Isua rock. However, since this no longer had its original morphology, the yeast-like relicts found by Pflug (1978) may not be real, and doubts have been cast, in particular by the American scientists J. W. Schopf andE. Roedder (Breuer, 1981,1982). Neither the Isua microfossils nor their 13C/12C isotope ratio could convince Bill Schopf that 3.8-billion-year-old samples were really involved. The Isua graphite flakes could also be a charred residuum from the... 

Fig. 14a-dL UV-visible absorption spectra of fossil organic particles after demineralization a) Alginite from Permian Boghead coal, b) Huronispora (Gun-flint), c) Isuasphaera (Isua), d) Graphite (Pflug, 1985) 18>... 

Naraoka H., Ohtake M., Maruyama S., and Ohmoto H. (1996) Non-biogenic graphite in 3.8-Ga metamorphic rocks from the Isua district, Greenland. Chem. Geol. 133, 251-260. 

Considerable light has recently been shed on this dilemma by two very detailed petrographic studies of the graphitic rocks at Isua. Lepland et al. (2002) examined the mineral apatite, host to the graphite grains studied by Mojzsis et al. (1996). They found that there were two types of apatite in the Isua sediments, distinguished on the basis of their rare... 

Lepland, A., Arrhenius, G., and Cornell, D., 2002. Apatite in early Archaean Isua supracrustal rocks, southern west Greenland its origin, association with graphite and potential as a biomarker. Precambrian Res., 118, 221-41. 

Graphite and carbonates in the 3.8 Ga-old Isua supracrustal belt, southern west Greenland. Precambrian Res., 126, 331 18. 

Van Zuilen, M.A., Mathew, K., Wopenka, B., Lepland, A., Marti, K., and Arrhenius, G., 2005. Nitrogen and argon isotopic signatures in graphite from the 3.8 Ga-old Isua supracrustal belt, southern west Greenland. Geochim. Cosmochim. Acta, 69, 1241-52. 

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