Why is radioactivity important?

Radioactivity is important for a number of reasons. It is the basis of both nuclear power and nuclear weapons. It allows for such things as medical X-ray examinations. Radioactive decay in the interior of the planet Earth is the source of the heat which causes the mantle to be liquid, and thereby causes continental drift, and earthquakes and volcanoes. None of those would exist without radioactivity. The study of radioactivity has provided scientists with many vital clues about the structure of atoms, and the behavior of subatomic particles.