How does radioactivity make it possible to understand how earth can be so old and still have a hot interior?

Radioactivity contributes to our understanding of Earth's age and its hot interior through the process of nuclear decay, which generates heat over billions of years. Radioactive isotopes, such as uranium and thorium, release energy as they decay, contributing to the planet's geothermal gradient and maintaining a molten core. This heat production, combined with the slow cooling of the Earth since its formation, supports the theory that the planet has been geologically active for about 4.5 billion years, allowing for both its age and ongoing heat. Thus, radioactivity serves as a crucial mechanism for sustaining Earth's internal heat while providing evidence for its extensive geological history.