The Miller-Urey experiment was a groundbreaking study conducted by chemists Stanley L. Miller and Harold C. Urey in 1952. It was one of the first experiments to investigate the possibility of organic compounds important to life spontaneously forming from inorganic precursors under conditions thought to resemble those of the early Earth.

In the experiment, Miller and Urey simulated a primitive Earth atmosphere by using a mixture of gases: methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). They chose these gases based on the scientific understanding of Earth's early atmosphere at the time.

This mixture was put into a closed system with two connected flasks. One flask was heated to simulate the Earth's ocean, causing water to evaporate. The other flask had electrodes to simulate lightning. The water vapor mixed with the gases, and then sparks were fired between the electrodes to simulate lightning storms thought to be common on the early Earth.

After running the experiment for a week, Miller and Urey found that several organic compounds had formed in the mixture, most notably including amino acids, the building blocks of proteins, which are critical for life. This demonstrated that simple organic compounds could be made from inorganic precursors under conditions hypothesized to have been present on the early Earth.