Raman and ion microscopic imagery of graphitic inclusions in apatite from older than 3830 Ma Akilia supracrustal rocks, west Greenland
Three-dimensional molecular-structural images of apatite grains and associated minerals embedded in a banded quartz-pyroxene-magnetite supracrustal rock from Akilia, southern west Greenland, were constructed by using Raman confocal spectroscopy. The rock sample is the same as that from which apatite-hosted isotopically light graphitic inclusions were reported by Mojzsis and colleagues in 1996; the results were challenged in 2005 by Lepland and colleagues who failed to find carbon-bearing inclusions in this and other Akilia samples. Here we demonstrate that inclusions of graphite wholly contained within apatite occur in this rock. The carbon isotopic composition of one such inclusion, its graphitic composition established by Raman spectroscopy, was measured by secondary ion mass spectrometry to be isotopically light (δ13C = -29‰ ± 4‰), in agreement with earlier analyses. Our results are thus consistent with the hypothesis that graphite-containing apatite grains of the older than 3830 Ma Akilia metasediments may represent chemical fossils of early life.