Beyond the Prebiotic Soup: Solid Organic Films and Protocell-Like Formation in Prebiotic Discharge Experiments

The original Miller-Urey experiment demonstrated the abiotic synthesis of organic compounds under early Earth conditions, yet the physicochemical properties and internal organization of the associated insoluble solid organic films (SOFs) remain poorly constrained. Here we present a spatially resolved characterization of SOFs formed in prebiotic discharge experiments, focusing on their chemical heterogeneity, structural organization, and role in the emergence of hollow organic biomorphs. Using a combination of electron microscopy and spectroscopic techniques, we show that the insoluble SOF is a continuous but chemically heterogeneous matrix whose molecular composition varies systematically across the reactor as a function of local gas-liquid-solid interactions. Distinct regions of the SOF are enriched in aliphatic amine-rich polymers, aromatic carbon domains, cyanide-derived intermediates, and amorphous carbon, indicating that hydrogen cyanide (HCN)-derived chemistry evolves differently within specific microenvironments rather than proceeding uniformly throughout the system. We further demonstrate that spherical, caterpillar-like, and polyp-like hollow biomorphs preferentially emerge at hydrated interfacial regions of the SOF, thereby directly linking their morphogenesis to spatial chemical heterogeneity and phase-boundary chemistry in spark-driven systems. The SOF's capacity to shield chemically fragile solutes and emerging biopolymers through near-ultraviolet chromophore absorption, combined with its abiotic compartmentalization properties, suggests a potentially important role in abiogenesis.