Radiocarbon dating
Radiocarbon dating estimates the age of once-living materials by measuring carbon-14, a radioactive isotope that decays after an organism stops exchanging carbon with the environment. It transformed archaeology, geology, climate science, and the study of recent Earth history.
What radiocarbon dating is
Radiocarbon dating, also called carbon-14 dating, is a method for estimating when a once-living material stopped exchanging carbon with its environment. A plant takes in carbon while it grows. An animal takes in carbon by eating plants or other organisms. After death, new carbon is no longer added in the same way, and radioactive carbon-14 begins to decline in the material.
How carbon-14 forms
Carbon-14 forms when cosmic rays create neutrons that interact with nitrogen in the upper atmosphere. The new radiocarbon becomes part of atmospheric carbon dioxide and enters the carbon cycle. Living organisms contain a small amount of carbon-14 along with stable carbon isotopes. Once the organism dies, carbon-14 decays toward nitrogen-14 at a predictable rate.
Half-life and age
A half-life is the time it takes for half of a radioactive isotope in a sample to decay. Carbon-14 has a physical half-life of about 5,730 years, although radiocarbon reporting also preserves an older conventional half-life for consistency in calculated radiocarbon ages. Measuring how much carbon-14 remains gives an estimate in radiocarbon years, not automatically a calendar date.
Why calibration is required
Atmospheric carbon-14 has not been perfectly constant. Solar activity, Earth's magnetic field, ocean circulation, fossil fuel emissions, nuclear testing, and other processes can change the amount of radiocarbon available to living things. Calibration curves built from known-age records, especially tree rings and other archives, translate radiocarbon measurements into calendar-age ranges.
What can be dated
Radiocarbon dating works best on carbon-bearing material that once belonged to living organisms. Charcoal from a hearth, seeds from a storage pit, bone collagen, textile fibers, wood, peat, and shell can be candidates. It is not a general method for dating most rocks, metals, pottery, or dinosaur fossils. The material must contain original carbon from the event being studied and enough measurable carbon-14.
Sampling and contamination
A radiocarbon date is only as good as the sample and context. Soil carbon, conservation chemicals, rootlets, handling, groundwater, smoke, marine reservoir effects, and reused old wood can shift results. Laboratories use pretreatment methods to isolate the most reliable fraction of a sample, and archaeologists interpret the date alongside stratigraphy, artifacts, site formation, and other evidence.
AMS and measurement
Early radiocarbon dating measured radioactive decay events, which required larger samples and longer counting times. Accelerator mass spectrometry, or AMS, counts carbon isotopes more directly and can work with much smaller samples. AMS widened the method's usefulness, but it did not remove the need for calibration, pretreatment, context, and statistical reporting.
Limits and time range
Radiocarbon dating is strongest for relatively recent geological and archaeological time. Very young samples can be affected by recent atmospheric changes, while very old samples contain so little carbon-14 that background contamination becomes difficult to separate from signal. Many practical applications focus on the last tens of thousands of years rather than the full age of Earth.
Why it matters
Radiocarbon dating gave researchers an independent clock for many questions about people, ecosystems, climate, and landscapes. It helped build chronologies for prehistoric archaeology, agriculture, migration, climate shifts, volcanic events, lake sediments, peat deposits, and marine records. Its power comes not from a single number, but from careful measurement joined to calibration and context.