101-1 Archean life detection: Organic geochemical evidence for life in Archean rocks identified by pyrolysis-GC-MS and supervised machine learning

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns

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Abstract:

Throughout Earth’s history, organic molecules from both abiotic and biotic sources have been buried within sedimentary rocks. Most of these organic molecules have been altered by taphonomic, diagenetic, metasomatic, and/or metamorphic processes through deep time. Nonetheless, the nature and distribution of those ancient fragmentary remains may retain diagnostic biomolecular information for billions of years. We posit that biomolecules have been selected for their functions; therefore, fewer types of molecules are produced in greater abundances. This function-driven synthesis differs from abiotic molecular mixtures, for example those found in carbonaceous chondrite meteorites.

We combined analyses of 406 varied biotic and abiotic samples, including both ancient and modern specimens, using pyrolysis gas chromatography and mass spectrometry with machine learning methods to discriminate biotic versus abiotic, plant versus animal, and photosynthetic versus non-photosynthetic samples. Dividing 272 samples with known attributes into 9 categories, each further divided into 75% training and 25% testing sets, our models predict pairwise assignments of modern plants versus fossil organics or carbonaceous meteorites (100% correct assignments), fossil coals and woods versus carbonaceous meteorites (97%), modern plants versus fossil coals and woods (97%), and modern plants versus animals (95%). Pairwise comparisons between fossil biotic samples versus abiotic samples resulted in 93% correct assignments, while analysis of modern and ancient photosynthetic versus non-photosynthetic samples also resulted in 93% correct assignments.

Applying our well-validated machine learning methods to data from ancient samples yields quantitative predictions regarding their provenances. We find that some organic suites altered by temperatures greater than 400°C, such as those in coal slag and charcoal, have had most of their biotic/photosynthetic signatures obliterated. Nevertheless, we present evidence for biotic molecular assemblages in Paleoarchean sediments (3.33 Ga) and for photosynthetic life in Neoarchean sediments (2.52 Ga)—results consistent with morphological and isotopic data.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4870

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