Big Bang Nucleosynthesis

This stage of the Universe lasted 17 minutes from 3 to 20 minutes after the Big Bang.  It occurred over the entire Universe.  The process started one second after the Big Bang when the temperature and density dropped enough to support stable protons and neutrons.  The temperature stayed high for nuclear fusion only enough time for atom nuclei (note 2) lighter than Beryllium to form.  After this period was over no more atoms fused until stellar formation  This material was the beginning of the formation of stars and galaxies millions of years later.