- Researchers use nanoscale IR spectroscopy to identify, for the first time, remains of elements of life bound to carbonaceous material in 3.7 billion year old metasedimentary rocks
- The findings of Eoarchean organic residue preservation supports claims for biogenic origins of carbon in Isua metasediments
T. Hassenkam, M.P. Andersson, K. N. Dalby, D. M. A. Mackenzie and M. T. Rosing
Metasedimentary rocks from Isua, West Greenland (over 3,700 million years old) contain 13C-depleted carbonaceous compounds, with isotopic ratios that are compatible with a biogenic origin1–3. Metamorphic garnet crystals in these rocks contain trails of carbonaceous inclusions that are contiguous with carbon-rich sedimentary beds in the host rock, where carbon is fully graphitized. Previous studies4,5 have not been able to document other elements of life (mainly hydrogen, oxygen, nitrogen and phosphorus) structurally bound to this carbonaceous material. Here we study carbonaceous inclusions armoured within garnet porphyroblasts, by in situ infrared absorption on approximately 10−21 m3 domains within these inclusions. We show that the absorption spectra are consistent with carbon bonded to nitrogen and oxygen, and probably also to phosphate. The levels of C–H or O–H bonds were found to be low. These results are consistent with biogenic organic material isolated for billions of years and thermally matured at temperatures of around 500 oC. They therefore provide spatial characterization for potentially the oldest biogenic carbon relics in Earth’s geological record. The preservation of Eoarchean organic residues within sedimentary material corroborates earlier claims2,6 for the biogenic origins of carbon in Isua metasediments. doi:10.1038/nature23261
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