How did radiometric dating help determine that Earth is about 4.6 billion years old?

Radiometric dating determines the age of geologic materials by measuring the ratio of radioactive parent isotopes to their stable daughter products. Because these isotopes decay at a constant, known rate—expressed as a half-life—scientists can calculate the time elapsed since a mineral or rock formed.12

To determine Earth's age, geochronologists apply these methods to meteorites, which formed at the same time as the rest of the solar system. By analyzing the lead isotope histories of these meteorites and comparing them with terrestrial lead samples, scientists have established that Earth and other solar system bodies accreted approximately 4.6 billion years ago.3

This process relies on the principle that radioactive decay is immutable, remaining unaffected by external conditions like heat or pressure. By using uranium-lead and rubidium-strontium dating, researchers can provide numerical estimates that anchor the geologic time scale, allowing us to understand the history of our planet far beyond the reach of the oldest surviving rock record.2453