zircon

Earth's age is not guessed from one rock. This guide explains radiometric dating, meteorites, zircon crystals, half-lives, and why 4.54 billion years is robust.

A grain of zircon mineral extracted from sandstone in the Jack Hills of Western Australia is 4.404 billion years old — older than most of Earth's crust, older than the oceans, nearly as old as the planet itself. Scientists identified its age by measuring the decay of uranium into lead trapped inside the crystal lattice. That single mineral grain, small enough to balance on a fingertip, is the oldest thing of terrestrial origin ever dated. Earth's age records span minerals, rocks, organisms, fossils, and ice — each type preserved by a different mechanism, each telling a different part of Earth's history.