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

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Grand Canyon rock layering — geochronology The steep walls of the Grand Canyon contain a number of layers of sedimentary rock laid down over millions of years. The lower formations belong to the early Precambrian age, while the upper layers are of the Paleozoic age. The line between the two sets of formations is called the Great Unconformity.

Radiometric dating allows scientists to determine the age of Earth by measuring the decay of long-lived radioactive isotopes into 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 by analyzing the ratio of parent to daughter atoms within a sample.213

Determining Earth's age of approximately 4.6 billion years relies on uranium-lead dating and similar isotopic analyses. Since Earth is geologically active, its oldest rocks have been recycled, making it difficult to find samples from the planet's inception. To overcome this, scientists analyze meteorites, which are remnants from the formation of the solar system. By comparing the lead isotopic composition of these meteorites—which represent primordial material—with the evolution of lead isotopes found in terrestrial samples, researchers have established that Earth and other solar system bodies accreted from the same solar nebula about 4.6 billion years ago.456