Chemical identification of microfossils from the 1.88‐Ga Gunflint chert: Towards empirical biosignatures using laser ablation ionization mass spectrometer

In this contribution, we investigated the chemical composition of Precambrianmicrofossils from the Gunflint chert (1.88 Ga) using a miniature laser ablationionization mass spectrometer (LIMS) developed for in situ space applications.Spatially resolved mass spectrometric imaging (MSI) and depth profilingresulted in the acquisition of 68,500 mass spectra. Using single mass unit spec-tral decomposition and multivariate data analysis techniques, we identified thelocation of aggregations of microfossils and surrounding inorganic host min-eral. Our results show that microfossils have unique chemical compositionsthat can be distinguished from the inorganic chert with high fidelity. Chemicaldepth profiling results also show that with LIMS microprobe data, it is possibleto identify chemical differences between individual microfossils, thereby pro-viding new insights about nature of early life. Analysis of LIMS spectraacquired from the individual microfossils revea ls complex mineralization,which can reflect the metabolic diversity of the Gunflint microbiome. Anintensity-based machine learning model trained on LIMS Gunflint data mightbe applied for the future investigations of putative microfossils from silicifiedmatrices, where morphological integrity of investigated structures is lost, andpotentially in the investigation of rocks acquired from the Martian surface