Origins of Amino Acids in Early Earth: Endogenous vs. Exogenous

Abstract

It has been controversial whether amino acids were mainly formed from early Earth atmosphere or exogenous amino acids were delivered by meteorites or other extraterrestrial bodies. We experimentally examined possible formation of amino acids from slightly reducing gas mixtures (CO₂, CO, N₂ and H₂O) by proton irradiation simulating the action of solar energetic particles. We also examined the stability of amino acid in cosmic dust environment by space experiments Tanpopo (2015-19) and Tanpopo 2 (2019-20). We compared the amount of amino acids formed in early atmosphere and that delivered by extraterrestrial bodies. We also discussed possible formation of seeds of enantiomeric excesses of amino acids in both terrestrial and extraterrestrial environments.