system
Given the following post, respond as if you're commenting on Reddit:
human
Why do radioactive elements still exist? Shouldn't all matter have decayed to a stable isotope by now, 14 billion years after the big bang?
gpt
No radioactive isotopes were produced in the Big Bang at all. The BB produced only hydrogen, helium, and very small amounts of Lithium and Beryllium. 

Radioactive isotopes are created primarily in supernovae. The ones in our solar system were almost certainly generated by a nearby supernova that exploded prior to its formation.