If the earth is millions and millions of years old, why hasn’t all the radioactive stuff died out?
Good question!
The Institute for Creation Research has undertaken studies on this kind of thing. Check this out:
The half-life of uranium-238 is about 4.5 billion years, uranium-235 about 700 million years, and uranium-234 about 25 thousand years.
The half-life of U238 is 4.45 billion years. And as U238 decays, other radioactive isotopes are formed. Plus, other isotopes such as Carbon-14 are created in the upper atmosphere as solar radiation and cosmic rays interact with molecules there.