In 1952, Stanley Miller and Harold Urey conducted an experiment to test the primordial soup hypothesis by simulating the early Earth's atmosphere. They combined water ($\text{H}_2\text{O}$), methane ($\text{CH}_4$), hydrogen ($\text{H}_2$), and ammonia ($\text{NH}_3$) in a sealed, sterile flask, heated the mixture to generate water vapor, and introduced electrical sparks to simulate lightning. After one week, they analyzed the contents and discovered amino acids, which are the structural units of proteins.