Radiocarbon dating

Quick Facts: Who was Radiocarbon dating?

Subject:

Radiocarbon dating

Known for:

A scientific method using radioactive carbon-14 to determine the age of organic materials.

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2Day Chrono-Wiki & Primary Historical Archives

Origins & Early Life

Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s at the University of Chicago by Willard Libby. It is based on the fact that radiocarbon (14C) is constantly being created in the Earth's atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay.

Pivotal Works & Achievements

Measuring the amount of 14C in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14C there is to be detected. The half-life of 14C (the period of time after which half of a given sample will have decayed) is about 5,730 years, so the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago, although special preparation methods occasionally make an accurate analysis of older samples possible. Libby received the Nobel Prize in Chemistry for his work in 1960. Research has been ongoing since the 1960s to determine the proportion of 14C in the atmosphere over the past 50,000 years.

Enduring Legacy & Impact

The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of 14C in different types of organisms (fractionation), and the varying levels of 14C throughout the biosphere (reservoir effects). Additional complications come from the burning of fossil fuels, such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s. Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for their 14C to decay below detectable levels, fossil fuels contain almost no 14C. As a result, beginning in the late 19th century, there was a noticeable drop in the proportion of 14C as the carbon dioxide generated from burning fossil fuels began to accumulate in the atmosphere.

Chronological Milestones & Life Events

1. 1960: 1960 Milestone — Libby received the Nobel Prize in Chemistry for his work in 1960.

Historical Fact-Check Quiz: Radiocarbon dating

True or False: “The initial measurement technique for radiocarbon dating relied exclusively on modern accelerator mass spectrometry (AMS).”

Answer (FALSE ❌): Radiocarbon dating was originally measured using beta-counting devices before the adoption of AMS.

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Frequently Asked Questions about Radiocarbon dating