Amino acids are likely to represent the first biochemical material present on Earth used for the emergence of living organisms. Experimental and analytical works suggest that amino acids could have been synthesized in the very primitive environment or/and brought by meteorites falling on Earth. Amino acids can assemble into small peptides with self-replicative and catalytic properties, making them candidates for initial biochemical reactions. The RNA world hypothesis proposes that small RNAs, as molecules carrying genetic information and possessing catalytic activities, may have been among the initial biomolecules with high level of structural complexity at the onset of life on Earth. The biosynthesis of small RNAs depends on a subset of amino acids used as precursors. A credible hypothesis is that peptides and small RNAs interacted giving rise to an ancestral elementary metabolic network surrounded by a layer of hydrophobic lipids. Presumably much later, the complex synthesis of DNA and the associated genetic code allowed to carry the information needed for the synthesis of proteins involved in more and more complex metabolic and physiological functions. It has been proposed that the theoretical Last Universal Common Ancestor (LUCA) would have given rise to the prokaryotic archaea and bacteria, and still much later of the eukaryotic organisms. According to comparative phylogenomic data, it is considered that amino acid metabolism in LUCA involved an ancestral elementary metabolic network allowing protein synthesis and amino acid utilization in relatively simple pathways.