Low 13C-13C abundances in abiotic ethane

Abstract

Distinguishing biotic compounds from abiotic ones is important in resource geology, biogeochemistry, and the search for life in the universe. Stable isotopes have traditionally been used to discriminate the origins of organic materials, with particular focus on hydrocarbons. However, despite extensive efforts, unequivocal distinction of abiotic hydrocarbons remains challenging. Recent development of clumped-isotope analysis provides more robust information because it is independent of the stable isotopic composition of the starting material. Here, we report data from a 13C-13C clumped-isotope analysis of ethane and demonstrate that the abiotically-synthesized ethane shows distinctively low 13C-13C abundances compared to thermogenic ethane. A collision frequency model predicts the observed low 13C-13C abundances (anti-clumping) in ethane produced from methyl radical recombination. In contrast, thermogenic ethane presumably exhibits near stochastic 13C-13C distribution inherited from the biological precursor, which undergoes C-C bond cleavage/recombination during metabolism. Further, we find an exceptionally high 13C-13C signature in ethane remaining after microbial oxidation. In summary, the approach distinguishes between thermogenic, microbially altered, and abiotic hydrocarbons. The 13C-13C signature can provide an important step forward for discrimination of the origin of organic molecules on Earth and in extra-terrestrial environments.

Isotopic evidence of acetate turnover in the Precambrian continental crust

“…In contrast, acetate in Kidd Creek is 13 C-enriched relative to TOC. 36 If microbial activity is similarly responsible for acetate turnover in Kidd Creek fracture fluids, the reactions(s) consuming acetate must have larger (normal) carbon isotope effects than those in Birchtree.…”

“…38 When fermentation of organic matter to acetate is coupled with methanogenic consumption, acetate can indeed be 13 C-enriched relative to TOC; however, this enrichment is not consistent across environments and the mechanisms behind it are still unclear. 24,30,32,37 Furthermore, the isotopic composition of methane and low ratio of methane-to-higher-alkanes in Kidd Creek fluids are not consistent with the significant rates of acetoclastic methanogenesis required to generate the observed 13 C enrichment in acetate. 11,38 As such, other mechanisms should be considered to explain acetate turnover in this system.…”

“…This is commonly attributed to minimal isotope effects associated with the production of acetate by microbial fermentation and consumption by anaerobic respiration. [31][32][33] Acetate in Birchtree fracture fluids has d 13 C values that match this expectation, but it does not have the characteristic 13 C and 2 H depletion associated with chemolithoautotrophic acetogenesis. 21,[33][34][35] This suggests that acetate turnover in Birchtree fluids is driven by heterotrophic microbial metabolisms.…”

“…[5][6][7][8][9] At sufficiently high concentrations, H 2 can reduce inorganic carbon to generate methane and higher hydrocarbons through abiotic Sabatier and polymerization reactions. [10][11][12][13] . It was recently suggested, based on laboratory experiments, that radiolysis in Kidd Creek may also generate simple organic acids such as acetate, formate and oxalate from water and dissolved inorganic carbon.…”

The use of lntramolecular carbon isotope distributions (13c/12c) of biomolecules to study temporal organization of post-photosynthetic metabolism in a plant cell

“…DOI: https://dx.doi.org/10.17352/ab.000006 and physiological tasks, which arise when it is necessary to investigate the metabolism of an unexplored organism or to identify the pathway of synthesis of an unknown compound [5,6]. The applications of the 13 C distribution technique to various geochemical tasks, including distinguishing biogenic or abiogenic life [7] the investigations of organic compounds associated with extraterrestrial life or with life in extreme conditions and other studies in related fi elds of knowledge [8,9]. Below we will consider a method for determining the spatial and temporal organization of metabolism in organisms based on the analysis of the relationship between the metabolic pathway and carbon isotope distribution in biomolecules.…”