How does radioactivity allow us to estimate the Earth?

Radioactive or radiometric dating allows us to estimate the Earth's age by giving us the actual age of rock within a range of several million years. Radiometric dating is based on the scientific law of radioactive decay and the half-life of radioactive elements. Uranium and some other elements decay into lead over time at a specific rate. Knowing the content of these elements in the makeup of a rock allows its age to be calculated. Currently, the oldest rocks of Earth origin are estimated to be over 4 billion years old.