Calcium Carbonate as a Potential Template for the Origin of Life: Coupled Inorganic–Organic Geochemistry of Travertine Deposit from Puga Hot Spring

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Unraveling life’s origin involves finding environments that can form and preserve organic molecules, with hydrothermal systems offering a likely setting. Terrestrial mineral deposits in the form of silicates and carbonates may have functioned as natural reactors that facilitated early prebiotic chemical reactions. At lab scale, calcium carbonate (CaCO 3 ) surfaces accelerate key prebiotic reactions, yet natural sites focusing on organic preservation associated with CaCO 3 remain limited. This study shows that CaCO 3 can actively concentrate and stabilize organic molecules under extreme conditions. In this work, we present the first empirical demonstration that Puga, Ladakh’s hot-spring travertine, hosts prebiotic molecules, serving as a natural template for mineral-driven organic reactions. X-ray diffraction showed C–O lattice distortions in calcite linked to biogenic input, while molecular analysis identified carbonate bands with organic groups. Biomarker analysis detected trapped biomarkers including traces of β-alanine derivatives (amino propanoic acid), pyran-2-thione, TMS-derivatized formamide, cyclooctasulfur (S 8 ), and hexadecenoic methyl ester (fatty acid). Stable-isotopic signatures of travertine yielded δ 18 O carb ∼ −24‰ VPDB and δ 13 C carb ∼ −5‰ VPDB. Elemental geochemistry indicated low-temperature hydrothermal enrichment in large-ion lithophiles and depletion of high-field-strength elements. We hypothesized a four-step conceptual model emphasizing travertine’s dual role in preserving inorganic tracers and organic precursors. Findings reveal that cold ambient conditions synergize with hydrothermal processes to host and concentrate prebiotic molecules within calcic matrices. Rapid CO 2 degassing and cooling of vent fluids in a colder external environment trigger low-Mg calcite precipitation, encapsulating diatoms and organic moieties, offering new insights into mineral scaffolds that could have triggered early-life reactions.