Miller-Urey Amino Acids, circa 1953

When chemistry graduate student Stanley Miller first heard University of Chicago professor and Nobel laureate Harold Urey's idea that organic compounds, such as amino acids, arose in a reducing atmosphere, Miller was determined to find out. Together, they built the spark-charge apparatus—two glass flasks connected by glass tubing. Miller filled one flask with water to represent the ocean; to the other, he sucked out oxygen and pumped in methane, ammonium, and hydrogen—the chemicals then believed to comprise the early atmosphere. Miller used electrodes to generate a spark in the "atmosphere" flask, simulating early lightning. After one week, Miller detected the presence of five different amino acids, offering the first evidence that amino acids could be produced in the atmosphere of primitive Earth.