text: Theories about the origin of life require knowledge of chemical pathways that permit formation of lifes key building blocks under plausible prebiotic conditions.  The RNA world hypothesis holds that in the primordial soup there existed free-floating ribonucleotides, the fundamental molecules that combine in series to form RNA.  Complex molecules like RNA must have arisen from small molecules whose reactivity was governed by physico-chemical processes.  RNA is composed of purine and pyrimidine nucleotides, both of which are necessary for reliable information transfer, and thus Darwinian evolution.  Becker et al. showed how pyrimidine nucleosides can be synthesized from small molecules and ribose, driven solely by wet-dry cycles.  Purine nucleosides can be synthesized by a similar pathway.  5-mono- and di-phosphates also form selectively from phosphate-containing minerals, allowing concurrent formation of polyribonucleotides with both the purine and pyrimidine bases.  Thus a reaction network towards the purine and pyrimidine RNA building blocks can be established starting from simple atmospheric or volcanic molecules.