Chemical Evolution Can Be Simulated in the Laboratory

  The classic experiment on the abiotic (nonbiological) origin of organic biomolecules was carried out in 1953 by Stanley Miller in the laboratory of Harold Urey. Miller subjected gaseous mixtures of NH₃, CH₄, H₂O, and H₂ to electrical sparks produced across a pair of electrodes  (to simulate lightning) for periods of a week or more, then analyzed the contents of the closed reaction vessel  (Fig. 1–1). The gas phase of the resulting mixture contained CO and CO₂, as well as the starting materials. The water phase contained a variety of organic compounds, including some amino acids, hydroxy acids, aldehydes, and hydrogen cyanide (HCN). This experiment established the possibility of abiotic production of biomolecules in relatively short times under relatively mild conditions. More refined laboratory experiments have provided good evidence that many of the chemical components of living cells, including polypeptides and RNA-like molecules, can form under these conditions. Polymers of RNA can act as catalysts in biologically significant reactions and RNA probably played a crucial role in prebiotic evolution, both as catalyst and as information repository.

FIGURE 1–1 Abiotic production of biomolecules. Spark-discharge apparatus of the type used by Miller and Urey in experiments demonstrating abiotic formation of organic compounds under primitive atmospheric conditions. After subjection of the gaseous contents of the system to electrical sparks, products were collected by condensation. Biomolecules such as amino acids were among the products.