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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.