Protons and neutrons formed – within seconds after the Big BangFormation of deuterium (heavy hydrogen)Fusion into helium-3 and helium-4Trace amounts of lithium and beryllium formedEnd of nucleosynthesis – as the universe cooled, fusion stoppedMain Light Elements FormedHydrogen (H)Helium (He)Lithium (Li)Trace Beryllium (Be)