Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons an neutrons). The primordial nucleons themselves were formed from the quark-gluon plasma of the Big Bang as it cooled below ten million degrees. A few minutes afterward, starting with only protons and neutrons, nuclei up to lithium and beryllium (both with mass number 7) were formed but only in relatively small amounts. This first process of primordial nucleosynthesis may also be called nucleogenesis. The subsequent nucleosynthesis of the elements (including all carbon, all oxygen, etc.) occurs primarily in stars either by nuclear fusion or nuclear fission.