A wide variety of experiments have been conducted to synthesize bioorganic compounds such as amino acids since Miller's historical discharge experiments in 1953. Amino acids were easily obtained from strongly reducing gas mixtures. Even if the primitive Earth atmosphere was less reducing, amino acid precursors could be formed by using high-energy radiations. Extraterrestrial organics were another plausible sources of amino acids, and were contained possible seeds of homochirality of bioorganic molecules. There have been controversies concerning the first catalytic molecules in primordial soup. Some of the hypotheses are reviewed, including the RNA world, the Fe-S world and the garbage-bag world.
