Terrestrial Abiotic Synthesis of Simple Precursor Molecules Starting from Two Approaches: The Universality of Carbon Reduction

To address the chemistry responsible for life's emergence, we examine the simple chemicals accessible on early Earth and the processes that could have transformed them. We focus on carbon reduction as a process central to the direct precursors of life. Two main approaches for the emergence of life's building blocks and their associated functions are discussed. One approach investigates chemical routes for forming life's building blocks via processes that worked differently from those of extant life, referred to as "unrestricted" prebiotic chemistries. The other approach establishes a direct mechanistic connection between prebiotic building blocks and extant biochemistry, referred to as "lifelike" prebiotic chemistries. Significant gaps remain in our understanding of early Earth's conditions, which makes it difficult to constrain the possible locations and mechanisms of life's emergence and the sources of precursors. Although numerous differences remain between the main origin-of-life hypotheses, consideration of the geochemistry of carbon reduction is a common denominator of these historically divided hypotheses.