Sunlight as an energetic driver in the synthesis of molecules necessary for life

Solar radiation was overwhelmingly the largest source of energy on the early Earth. Energy provided by the Sun has the potential to access different chemistries than energy provided by other sources, such as hydrothermal vents, because of the unique characteristics of photochemistry that differentiate it from conventional thermal chemistry. This review considers how sunlight-driven reactions can abiotically generate prebiotic molecules necessary for the evolution of life. We discuss briefly the characteristics of the early Sun and the likely environmental conditions on the early Earth because photochemistry is both environment- and molecule-specific. An overview of the fundamental principles of photophysics and photochemistry is followed by discussion of a selection of prebiotically-relevant examples of photochemical reactions, focusing on syntheses that lead to the production of cellular components (e.g. sugars, lipids, and biopolymer precursors). The role of photostability as an evolutionary driving force is also considered. These examples highlight the ability of simple organic molecules to harness solar energy and convert it into high-energy chemical bonds, generating molecular complexity.