The origin of life in the Hadean eon required the formation of amino acids and nucleosides among the key molecules of life. In an often postulated strongly reducing atmosphere, HCN and its derivatives are robustly formed as plausible starting molecules. But HCN does not form in a Hadean, weakly reducing atmosphere. Instead, aldehydes and NO are produced, which react to produce oxime, amidoxime, and nitrile-based feedstock molecules as precursors.

Abstract

The origin of life in the Hadean eon required the formation of amino acids and nucleosides among the key molecules of life. It is assumed that highly unsaturated carbon and nitrogen containing feedstock molecules, which form in a strongly reducing H₂-atmosphere were the reactive starting materials. The Hadean Earth was, however, surrounded by a CO₂-dominated atmosphere and the question of how under such inert conditions the biomolecules could have formed is unsolved. Here, we report that HNO and formaldehyde, which form robustly in a weakly reducing atmosphere by lightning and UV-irradiation, react with SO₂ to produce oxime, amidoxime, and nitrile-containing molecules, which react to give precursors to amino acids and all four canonical nucleosides. The small number of feedstock molecules required suggests that the molecules of life can robustly form on all types of rock planets with volcanic activity and a CO₂-dominated atmosphere.