20h 16min, jan 1, 0 y - Nucleosynthesis, from 3 minutes to 20 minutes

Description:

The temperature of the universe falls to about a billion degrees which allows protons and neutrons combine through nuclear fusion to form the nuclei of the simple elements of hydrogen, helium and lithium. After about 20 minutes, the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue.