In the study of life's origins, a key challenge is understanding how RNA could have polymerized and subsequently replicated in early Earth. We present a theoretical and computational framework to model the non-enzymatic polymerization of ribonucleotides and the template-dependent replication of primordial RNA molecules, at the interfaces between the aqueous solution and a clay mineral. Our results demonstrate that systematic polymerization and replication of single-stranded RNA polymers, sufficiently long to fold and acquire basic functions (>15 nt), were feasible under these conditions. Crucially, this process required a physico-chemical environment characterized by large-amplitude oscillations with periodicity compatible with spring tide dynamics, suggesting that large moons may have played a role in the emergence of RNA-based life on planetary bodies. Interestingly, the theoretical analysis presents rigorous evidence that RNA replication efficiency increases in oscillating environments compared to constant ones. Moreover, the versatility of our framework enables comparisons between different genetic alphabets, showing that a four-letter alphabet -particularly when allowing non-canonical base pairs, as in current RNA- represents an optimal balance of replication speed and sequence diversity in the pathway to life.