RNA with iron(II) as a cofactor catalyses electron transfer

Removing Mg2+ from RNA and replacing it with Fe2+ confers on some RNAs the ability to catalyse single-electron transfer. Here, it is hypothesized that Fe2+ was an RNA cofactor on the early Earth, when iron was benign and abundant, and was replaced by Mg2+ during a period known as the great oxidation, brought on by photosynthesis.