Radiocarbon dating measures the decay of carbon-14 to determine the age of organic remains. Living things absorb carbon from the atmosphere, including a tiny amount of radioactive carbon-14. When they die, that carbon begins to decay at a known rate. By measuring how much remains, scientists can calculate how long ago the organism died. Willard Libby developed the method in the late 1940s and won a Nobel Prize for it in 1960.

The technique works on materials up to about 50,000 years old. Bone, wood, charcoal, shell, and peat are common samples. Contamination is a constant problem. A single fingerprint or a drop of preservative can skew results. Calibration is also necessary because atmospheric carbon-14 levels have varied over time. Tree-ring sequences and other data are used to correct raw dates.

What it can and cannot do

• Dates organic materials, not stone or metal.
• Effective up to roughly 50,000 years.
• Requires calibration against known standards.
• Contamination is a major source of error.

Radiocarbon dating transformed archaeology. It turned relative sequences into absolute chronologies and forced researchers to abandon many earlier assumptions about the pace of prehistory.