Radiocarbon dating reads a built-in clock that starts ticking at death

Every living thing is mildly radioactive. The atmosphere constantly makes carbon-14, a heavy form of carbon that plants take in and animals eat, so all life carries a steady trace of it. The moment an organism dies, it stops taking up fresh carbon — and its carbon-14 begins to decay at a fixed, predictable rate.

That decay is the clock. Carbon-14 has a half-life of about 5,730 years, meaning half of it vanishes every 5,730 years. By measuring how little remains in a bone, seed or scrap of charcoal, scientists can calculate how long ago the thing died — usefully back to roughly 50,000 years.

Chemist Willard Libby developed the method at the University of Chicago in the late 1940s, and it earned him the 1960 Nobel Prize in Chemistry. Radiocarbon dating transformed archaeology, replacing guesswork with numbers and anchoring everything from cave paintings to mummies to a real timeline.