Nucleobases as Molecular Fossils of Prebiotic Photoselection

The molecular inventory on a prebiotic earth, some four billion years ago, would likely have included a large variety of heterocyclic compounds. Many chemical parameters may have affected the eventual selection of the canonical bases as the building blocks for life as we know it today. One of the aspects may have been photochemistry since prior to life the absence of an ozone layer in the atmosphere would have enabled more energetic photochemistry than today. This chapter discusses elements of nucleobase photochemistry that can contribute to an explanation of a possible role of photochemical selection in the origin of life.