In simple terms

Radiocarbon dating estimates how long ago something that was once alive stopped taking in carbon. Living plants and animals absorb carbon that includes a trace of carbon-14, a radioactive form of the element. When the organism dies the intake stops, the carbon-14 decays at a fixed rate, and the amount left behind works as a clock. [1][2]

Because the clock depends on once-living carbon, the method dates organic material such as wood, charcoal, bone, seeds and textiles, not stone or metal.

How it works

A laboratory measures either the radioactivity still coming from a sample or the number of carbon-14 atoms in it. [2] Turning that into an age needs the half-life, the time in which half the carbon-14 decays. Here the field carries an oddity. The value recommended by the Decay Data Evaluation Project, an international group of measurement scientists, is 5,700 years give or take 30, while conventional radiocarbon ages still use the older Libby half-life of 5,568 years. [2] Other published work describes carbon-14 as a 5,730 year radionuclide. [1] The disagreement matters less than it sounds, because conventional ages are calibrated against independently dated records such as tree rings, sediment layers and corals. [2]

Willard Libby’s group reported in 1947 that methane from a sewage plant contained carbon-14 while fossil fuel methane did not: living carbon is radioactive, old carbon is not. [2] Early dating consumed about 8 grams of carbon; accelerator mass spectrometry, which spread in the 1980s, brought that down to tiny samples and opened the method to precious objects. [1][2]

Why it matters

Radiocarbon dating is what allows an organic find to be given an age in years rather than a place in a sequence, so archaeological chronologies rest on it. Calibration produced a second result: Libby’s assumption of a steady supply of carbon-14 does not hold. Earth’s magnetic field wanders, the ocean takes up carbon unevenly, cosmic ray bombardment rises and falls, fossil fuel burning added carbon free of carbon-14, and weapons testing in the 1950s and 1960s left a sizable spike. [2] Those deviations are now evidence in their own right.

Where you’ll see it

• Museum labels and excavation reports, where dates appear with a plus or minus range
• Authentication of manuscripts and relics, the Shroud of Turin among the best known [2]
• Climate and environmental records built from sediment, coral and tree ring sequences
• Work on recent organic material, where the weapons testing spike acts as a time marker

Example

Charcoal from a hearth at an excavation goes to a laboratory, which reports a conventional radiocarbon age that is then calibrated into a calendar date range.

Often confused with

Radiocarbon dating is one of several radiometric methods. Others use isotopes with longer half-lives to date rock and far older material.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed October 7, 2026Researched and drafted with AI assistanceReport an issue