This NotebookLM Deep Dive details how scientists determined that the Earth is approximately 4.54 billion years old, moving beyond historical and religious estimates that suggested a much younger planet. The modern scientific consensus is built upon multiple independent, converging lines of evidence, most notably radiometric dating of meteorites and terrestrial rocks. While carbon-14 dating is useful for recent organic samples, researchers rely on long-lived radioactive isotopes like uranium-lead, potassium-argon, and rubidium-strontium to measure deep geological time. Beyond chemistry, this ancient age is corroborated by diverse fields including helio-seismology, the study of sedimentary rock layers, evolutionary biology, and the mechanics of plate tectonics. Together, these independent disciplines provide a robust and consistent quantitative framework for understanding the immense history of our planet.