Well, half of it will. The half life of potassium-40 is ~1.25 billion years. It decays to calcium-40 about 89% of the time and argon-40 11%. When using potassiu

Well, half of it will. The half life of potassium-40 is ~1.25 billion years. It decays to calcium-40 about 89% of the time and argon-40 11%. When using potassium-40 decay for dating, the usual method is determining the ratio of K-40 to radiogenic Ar-40 [1]. This is not easy and involves irradiating samples in a nuclear reactor. [1] https://en.wikipedia.org/wiki/Argon%E2%80%93argon_dating https://en.wikipedia.org/wiki/Argon%E2%80%93argon_dating