Primordial nuclide
Oxygen is one of the primordial nuclides. Onviously, it is found on Earth in rocks and in the atmosphere. The molecules have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed. They were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and perhaps by other processes.