One-carbon moieties such as methyl groups (CH3-R) are found throughout the solar system including in titan's atmosphere the enceladus' plumes and martian soils

Methyl groups can be synthesized by multiple abiotic processes but are also made by biology. Life as we know IT can synthesize methyl groups DE novo many organisms can assimilate them from the environment and the last universal common ancestor may have been a methylotroph. Given the centrality and primacy of biologic methyl shuffling (i.e. onecarbon assimilation reassembly and export) on earth IT is possible that life on other solar system bodies would need to make or modify methyl groups too. Given the ubiquity of methyl groups in the solar system a generalizable biosignature of methyl shuffling would be widely applicable. Stable isotopes can help constrain formation mechanisms. However conventional tracers like carbon-13 are insufficient for distinguishing methyl group origins because carbon-13 fractionation factors of biologic and abiotic processes often overlap. To overcome this limitation we will 1) add a novel isotopic dimension and 2) develop an isotopic framework that explicitly links methyl group reactants and products. Clumped isotopic compositions of one-carbon moieties have a "built-in" reference frame are preserved during simple methyl transfer reactions and change in predictable ways during simple reactions that create or destroy C-H bonds. When existing data are viewed in this framework biology VS. Abiotic methyl groups are resolved. While encouraging all existing biogenic data come from plants or methanogens and so are limited in scope.