<p>Life is composed of genetic and functional polymers, such as nucleic acids. For life to have emerged, a prebiotic mechanism for assembling these polymers is essential. In a prebiotic environment teeming with diverse organic molecules, selecting, concentrating and bringing together only relevant building blocks poses a significant challenge. G-quadruplexes, a secondary structure of DNA and RNA, are known to self-assemble from nucleotide monomers, creating an ideal preassembly for nucleotide polymerization. We investigate the detailed structure of self-assembled G-quadruplexes using high-resolution atomic force microscopy (AFM) measurements in solution. We show that G-quadruplexes of nucleotide monomers are stable on surfaces in aqueous solution at concentrations orders of magnitude below their solubility limit. When subjected to cycles of evaporation and rehydration at elevated temperatures, the G-quadruplexes partially transform into extended, RNA-like structures, also stable on surfaces in solution, consistent with a polymeric nature. G-quadruplexes self-assembled from nucleotide monomers could have served as persistent prepolymer scaffolds, providing genuine molecular selectivity in prebiotic environments.</p>