Miller-Urey Experiment

In 1952, the graduate student Stanley Miller, working under the chemist Harold Urey at the University of Chicago, built a sealed laboratory apparatus that circulated a mixture of gases thought to resemble the early Earth's atmosphere, including methane, ammonia and hydrogen, over water and subjected it to repeated electrical sparks meant to simulate lightning. After running for about a week, the apparatus was found to have produced several amino acids, the building blocks of proteins, from simple inorganic starting materials, offering the first experimental evidence that the organic molecules necessary for life could plausibly have formed spontaneously under early Earth conditions. The experiment became a foundational touchstone for the scientific study of the origin of life, though later research revised the assumed composition of the early atmosphere and the exact relevance of Miller and Urey's original gas mixture remains debated.