Stellar nucleosynthesis is responsible for all of the other elements occurring naturally in the universe as stable isotopes and primordial nuclide, from carbon to uranium. These occurred after the Big Bang, during star formation. Some lighter elements from carbon to iron were formed in stars and released into space by asymptotic giant branch (AGB) stars. These are a type of red giant that "puffs" off its outer atmosphere, containing some elements from carbon to nickel and iron. Nuclides with mass number greater than 64 are predominantly produced by neutron capture processes—the s -process and r -process –in supernova explosions and neutron star mergers.