The 1953 Miller–Urey experiment produced amino acids from simple gases exposed to electrical sparks.
Stanley Miller performed the experiment under the supervision of Harold Urey at the University of Chicago. Their apparatus circulated water and a gas mixture containing methane, ammonia, hydrogen, and water vapor, while electrodes supplied sparks intended to imitate lightning.
After about a week, the water contained several organic compounds, including amino acids. Amino acids are important because they are the building blocks of proteins, although the experiment did not create life or demonstrate the origin of living cells.
The precise composition of Earth's early atmosphere remains debated, and later versions using different gas mixtures produced different results. The experiment's enduring importance is that it showed some biologically relevant molecules can form naturally from simpler substances under plausible conditions.