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How does carbon-14 dating determine the age of once-living materials?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Carbon-14 dating determines the age of once-living materials by measuring the decay of the radioactive isotope carbon-14.12

While an organism is alive, it maintains a stable ratio of carbon isotopes by consuming food or air that contains carbon-14, which is continuously formed in the atmosphere by cosmic rays. Upon death, the organism ceases to intake carbon, and the carbon-14 in its tissues begins to undergo beta decay into nitrogen-14 at a constant rate.132

Because carbon-14 has a known half-life of 5,730 ± 40 years, scientists can estimate the time elapsed since death by measuring the residual amount of the isotope in the sample, typically using an accelerator mass spectrometer. To account for historical fluctuations in atmospheric carbon levels, these raw dates are calibrated using data from sources like dendrochronology (tree-ring analysis) to provide a more precise age. This method is effective for organic remains approximately 500 to 50,000 years old.1432