NucleosynthesisNucleosynthesis is the process of creating new atomic nuclei either by nuclear fusion or nuclear fission. Big bang nucleosynthesis is responsible for most of the helium in the universe, and some heavier elements between carbon and iron are produced in stars via stellar nucleosynthesis. Most elements heavier than iron are produced as a result of supernova nucleosynthesis. Finally, some lighter elements are produced through cosmic ray spallation.
Theories of nucleosynthesis are tested by calculating elemental abundances and comparing with observed results.