The now-famous Millerâ `` Urey experiment used a highly reduced mixture of gases â `` methane , ammonia and hydrogen â `` to form basic organic monomers , such as amino acids . The now-famous `` Millerâ `` Urey experiment '' used a highly reduced mixture of gasesâ `` methane , ammonia and hydrogenâ `` to form basic organic monomers , such as amino acids .