The Miller and Urey experiment was carried out in 1952, whereby ammonia, hydrogen, methane and water were subjected to conditions believed to be similar to an early, prebiotic earth (although there were probably less reducing agents in the early environment). The water and gases were separated by two test tubes connected by a loop. A heat source was then placed under the liquid water to induce evaporation. The water vapor would then travel through a tube and into the elevated gaseous (atmospheric) test tube where in a pair of electrodes created sparks, simulating lighting. Everything would be allowed to cool and the cycle would begin again.
After a week long process, 2% of the mixture was composed of organic compounds (20 amino acids).