The nonenzymatic replication of ribonucleic acid (RNA) may have enabled the propagation of genetic information during the origin of life. RNA copying can be initiated in the laboratory with chemically activated nucleotides, but continued copying requires a source of chemical energy for in situ nucleotide activation. Recent work has illuminated a potentially prebiotic cyanosulfidic chemistry that activates nucleotides, but its application to nonenzymatic RNA copying had not been demonstrated. Here, we report a novel pathway that activates RNA nucleotides in a manner compatible with template-directed nonenzymatic copying. We show that this pathway, which we refer to as bridge-forming activation, selectively yields the reactive imidazolium-bridged dinucleotide intermediate required for copying. Our results will enable more realistic simulations of RNA propagation based on continuous in situ nucleotide activation.