What cosmological model for the universe took place approximately 13.8 Billion years ago and is generally understood to be nucleosynthesis in stars followed by mass ejection?
Primordial nuclide:  Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. Big Bang:  Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe.
Big Bang