Radiocarbon Dating

Radiocarbon dating estimates the age of organic material by measuring its residual carbon-14, the radioactive isotope that decays at a known rate after an organism dies.

Definition

A chronometric dating method that determines the age of carbon-bearing materials up to roughly 50,000 years old by measuring the decay of the radioactive isotope carbon-14 relative to stable carbon.

Scope

This topic covers the principles of carbon-14 production and decay, the assumptions and limits of the method, sample selection and contamination, measurement by conventional and accelerator mass spectrometry (AMS), and the calibration of radiocarbon ages to calendar years using internationally agreed curves and Bayesian modeling.

Core questions

• How does carbon-14 form, enter organisms, and decay after death?
• What materials can be dated and how does contamination affect results?
• How does AMS differ from conventional counting?
• How are radiocarbon ages calibrated and modeled into calendar dates?

Key theories

Carbon-14 decay clock

Libby's insight that living things equilibrate with atmospheric carbon-14 and, once dead, lose it through radioactive decay at a fixed half-life, providing a clock for organic remains.

Calibration and Bayesian chronological modeling

The combination of measured radiocarbon ages with calibration curves and prior stratigraphic information, using Bayesian statistics to produce more precise calendar date estimates.

History

Willard Libby developed radiocarbon dating in the late 1940s, earning the 1960 Nobel Prize in Chemistry. The method was refined by the discovery that radiocarbon years diverge from calendar years, prompting tree-ring calibration, and was transformed again by accelerator mass spectrometry, which allowed dating of milligram samples and the spread of Bayesian chronological modeling.

Debates

Reservoir effects and sample reliability

Marine, freshwater, and other reservoir effects, along with contamination and the 'old wood' problem, complicate radiocarbon results and drive debate over which materials and pretreatments give reliable dates.

Key figures

• Willard Libby
• R. E. Taylor
• Christopher Bronk Ramsey

Seminal works

• libby1955
• taylorbar2014
• bronkramsey2009

Frequently asked questions

What can radiocarbon dating be used on?

It works on materials that once contained living carbon, such as charcoal, wood, bone, shell, and plant remains, generally up to about 50,000 years old.

Why are radiocarbon dates given with a plus-or-minus range?

The measurement has statistical uncertainty and calibration adds further spread, so dates are reported as a probability range of calendar years rather than a single year.