What is primordial nucleosynthesis?
Primordial nucleosynthesis was the production of elements heavier than Hydrogen soon after the Big Bang.
Soon after the Big Bang the Universe was filled with mainly Hydrogen in the form of protons and neutrons. The conditions were then right for fusion reactions to occur. These produced the Hydrogen isotopes Deuterium and Tritium and Helium 3 and helium 4.
As Helium 4 is the most stable nucleus after Hydrogen vast quantities of it were produced.
Due to the fact that there are no stable nuclei with 5 or 8 nucleons The process came to an end with only small quantities of Lithium 7 being produced.
The production of heavier elements requires the triple alpha process which only occurs in large stars.