In the Miller–Urey experiment of 1953, amino acids formed from a simulated early-Earth atmosphere.
Stanley Miller, working with Harold Urey at the University of Chicago, sealed water, methane, ammonia, and hydrogen in a glass apparatus. The mixture was heated to create water vapor, while electrical sparks simulated lightning. After about a week, the water had accumulated several organic compounds, including amino acids.
Amino acids are important because they are building blocks of proteins, but the experiment did not create life, proteins, or DNA. It showed that some biologically relevant molecules could arise from simpler chemicals under particular laboratory conditions.
The original atmospheric mixture is not now regarded as the only or necessarily most accurate model of early Earth. Later experiments using different gases, volcanic conditions, ultraviolet light, or impact energy also produced organic compounds. The enduring significance of Miller–Urey is therefore chemical: it demonstrated a plausible route to organic molecules, not a complete explanation of the origin of life.