© Wikimedia Commons, Public Domain. Author: Lokal_Profil, 5 August 2008.
The nuclei of the light elements hydrogen, helium, lithium, and their various isotopes were produced when nucleosynthesis took place in the first three minutes after the birth of the universe. Starting with a primordial mixture of protons (p+), neutrons (n0), and photons (), the above reactions successfully predict the abundances of these light elements in the universe. Nucleosynthesis halted as the universe cooled to a temperature too low to support the nuclear reactions required to produce elements heavier than lithium. (Unit: 10)