Source: cirosantilli/argon-is-abundant-on-earth-s-atmosphere-because-it-comes-from-the-decay-of-potassium-40
= Argon is abundant on Earth's atmosphere because it comes from the decay of Potassium-40
And notably, it is almost all <Argon-40>, which is stable, but not the most common one to come from natural <#nucleosynthesis>.