Rapid, direct and non-destructive assessment of fossil organic matter via microRaman spectroscopy

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 2 preserved terrestrial or extraterrestrial sample, including in the use of organic matter in technological applications.

Paleoproterozoic sterol biosynthesis and the rise of oxygen

“…Other biomarker studies of Archean, Paleoproterozoic and Mesoproterozoic sedimentary rocks, conducted in the era of heightened contamination awareness, reveal a similar picture of non-detection of eukaryote-specific 24-alkylated steranes (Blumenberg et al, 2012;Flannery and George, 2014;Hoshino et al, 2015) or their detection at levels than cannot be reliably distinguished from contamination (Luo et al, 2015;Zhang et al, 2016). Finally, new methodologies for evaluating the thermal regime experienced by sedimentary organic matter (Ferralis et al, 2016), the cleaning of contaminated rock samples prior to analysis (Jarrett et al, 2013) and a focus on directed identification and sampling of pockets of well-preserved Proterozoic and Archean sediments (Bruisten et al, 2013) suggest that the pre-Cambrian biomarker record can be elaborated and imbued with greater confidence.…”

Raman Spectroscopy Detects Amorphous Carbon in an Enigmatic Egg From the Upper Cretaceous Wido Volcanics of South Korea

“…By using the parameters derived from the Raman spectra of thermally matured carbonaceous materials, the preserved carbonaceous matter in metasedimentary rock samples (Beyssac et al, 2002;Rahl et al, 2005;Lahfid et al, 2010) or fossil fuels (Schito et al, 2017;Henry et al, 2019a) could be used as a 'thermometer' because the parameters are affected mainly by heat, but little affected by other variables such as pressure at least in higher metamorphic grade (T > 350 • C) (Lahfid et al, 2010). The Raman spectroscopy, therefore, has been widely used by micropaleontologists and applied to diverse fossils including, but not limited to, acritarch (Marshall et al, 2005;Schiffbauer et al, 2012), conodont (Marshall et al, 2001;McMillan and Golding, 2019), foraminifera (McNeil et al, 2015), kerogenous microfossils (Schopf et al, 2005), plant spores (Bernard et al, 2007), and protist (Ferralis et al, 2016) to investigate the thermal maturity of those fossils. Although Raman spectroscopy does not fully prove the biogenicity of preserved carbonaceous matter in fossil and needs further confirmation by independent approaches (Pasteris and Wopenka, 2003;Marshall et al, 2010), Raman spectroscopy is the simplest tool to detect carbonaceous material in fossils, thus make further biogenicity test possible (Marshall et al, 2010).…”

Previously unknown class of metalorganic compounds revealed in meteorites

“…Meteorites contain Mg-rich minerals (Fig. S1) (17) and complex organic compounds (1, 5), which are thought to evolve chemically, not simultaneously, in the early solar system (18, 19). For example, Fischer–Tropsch-type (FTT) reactions are believed to play an important role in providing pathways to form (complex) organic molecules.…”