Nucleosynthesis

Process of creating new atomic nuclei from existing nucleons

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium, traces of other elements, such as lithium, and the hydrogen isotope deuterium.

From Wikipedia, under CC BY-SA. More on occurri.