Enduring Understanding 1D

The origin of living systems is explained by natural processes.

The process of evolution explains the diversity and unity of life. A number of experimental investigations have provided evidence that the conditions early in the Earth’s history provided an environment capable of generating complex organic molecules and simple cell-like structures. For example, in the “organic soup” model, the hypothesized primitive atmosphere contained inorganic precursors from which organic molecules could have been synthesized through natural chemical reactions catalyzed by the input of energy. In turn, these molecules served as monomers (building blocks) for the formation of more complex molecules, including amino acids and nucleotides. Some models suggest that primitive life developed on biogenic surfaces, such as clay, that served as templates and catalysts for assembly of macromolecules. Under laboratory conditions, complex polymers and self-replicating molecules can spontaneously assemble. It remains an open question whether the first genetic and self-replicating material was DNA or RNA.