The RNA World Hypothesis: A Critical Reassessment of Prebiotic Plausibility

The RNA world hypothesis (RWH) proposes that life originated from self-replicating RNA molecules, yet its prebiotic plausibility remains poorly quantified. This study applies equilibrium thermodynamics to evaluate maximum achievable concentrations of abiotic RNA oligomers in aqueous solution. The free energy of phosphodiester hydrolysis (ΔG°_hyd = −22.2 kJ/mol) indicates an equilibrium constant K ≈ 1.3 × 10⁻⁴ for nucleotide condensation at 25°C and pH 7. Analysis of prebiotic nucleotide synthesis reveals significant chemical constraints: (1) ribose from formose reactions requires contradictory conditions (pH ~10–12, 60°C–80°C) incompatible with nucleobase formation from HCN polymerization (pH < 7, <0°C); (2) prebiotic phosphate availability was <10⁻⁷ M due to mineral sequestration; (3) N-glycosidic bond formation exhibits prohibitively high activation energy; (4) successfully formed molecules and bonds are too unstable on a prebiotic timescale to permit accumulation: ribose t_½ ≈ 300 days at 25°C; RNA phosphodiester t_½ ≈ 4 years/bond (a 1000-nt RNA has t_½, strand ≈ 4 years/999 ≈ 1.5 days). Assuming unrealistically high nucleotide concentrations of 10⁻¹⁰ M—comparable to amino acid estimates—yields tetranucleotide (N₄) concentration [N₄] ≈ 10⁻⁵² M, seven orders of magnitude below the concentration corresponding to one molecule in Earth's total water (10⁻⁴⁵ M). Strategies to increase local oligomer concentration through wet-dry cycles or montmorillonite catalysis require experimentally optimized conditions (e.g. pure 10–15 mM activated nucleotides, precise pH 2.5–3, 80°C–90°C) that are prebiotically implausible. Additionally, D-ribose exists as five equilibrating isomers with four potential glycosidic bond sites per isomer, generating ~180–300 mononucleotide isomers and >10⁷ dinucleotide variants, diluting functional sequences exponentially with chain length. These thermodynamic and kinetic constraints indicate that even short RNA oligomers (>3 nucleotides) most probably did not accumulate prebiotically at detectable concentrations, challenging the hypothesis that an RNA World bridged prebiotic chemistry to deoxyribonucleotide hydrolysis (DNA)-basedlife.