Even in this prebiotic world, RNA molecules have certain
shapes and hold certain "information."
Because of the way information is stored in bases
(A, G, C, U), copies of RNA molecules
can be made by similarly complicated molecules.
RNA molecules have shapes and in general are more affected by their environments than DNA molecules. This is both good and bad for survival: Bad because they are more easily destroyed, good because they more easily can mutate and produce more successful offspring.
RNA can self-catalyze -- help make more copies of itself to be made -- and slightly more robust mutated offspring could be created.