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Abstract:
Raman spectroscopy is widely used to evaluate the nature and potential origins of carbonaceous matter
in Earth's oldest rocks and minerals. It is also the tool that will be used for organic detection on the next
vehicles to remotely explore the surface of Mars. Here we present, for the first time, a novel quantitative
method in which previously neglected Raman spectral features are correlated directly, linearly, and with
excellent accuracy, to the microchemistry of carbonaceous materials through the elemental H:C ratio,
regardless of contamination. We show applicability and predictive capabilities of this methodology in
evaluating H:C ratios between 0.01 and 0.65 in Archean and type III kerogens. We demonstrate its
application to chemical microRaman mapping by statistical analysis of a 750Ma microfossil and its
encompassing sediments. Raman-derived H:C data can also be used to estimate the degree to which
kerogen C-isotopic data has been shifted from its original values due to the effects of metamorphism. The
new methodology directly and non-invasively affords spatially resolved assessments of organic matter
preservation and microscale chemical diversity within any geologically preserved terrestrial or extraterrestrial
sample, including in the use of organic matter in technological applications.
