Abiotic synthesis of graphitic carbons in the Eoarchean Saglek-Hebron metasedimentary rocks.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38971883.
- Also identified by DOI 10.1038/s41467-024-50134-1 and PMC identifier 11227522.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Graphite in metasedimentary rocks of the Eoarchean Saglek-Hebron Gneiss Complex (Canada) is depleted in <sup>13</sup>C and has been interpreted as one of the oldest traces of life on Earth. The variation in crystallinity of this oldest graphitic carbon could possibly confirm the effect of metamorphism on original biomass, but this is still unexplored. Here, we report specific mineral associations with graphitic carbons that also have a range of crystallinity in the Saglek-Hebron metasedimentary rocks. Petrographic, geochemical and spectroscopic analyses in the Saglek-Hebron banded iron formations suggest that poorly crystalline graphite is likely deposited from C-H-O fluids derived from thermal decomposition of syngenetic organic matter, which is preserved as crystalline graphite during prograde metamorphism. In comparison, in the Saglek-Hebron marble, disseminations of graphite co-occur with carbonate and magnetite disseminations, pointing to abiotic synthesis of graphitic carbons via decarbonation. Our results thus highlight that variably crystalline graphitic carbons in the Saglek-Hebron metasedimentary rocks are potential abiotic products on early Earth, which lay the groundwork for identifying the preservation of prebiotic organic matter through metamorphism on Earth and beyond.