Carbon dating was developed by Willard Libby in the late 1940s and has become a standard tool for archaeologists.
Radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide or Carbon 14, which is incorporated into plants by photosynthesis. Animals acquire Carbon 14 by eating the plants.
When the animal or plant dies, Carbon 14 undergoes radioactive decay. By measuring the amount of Carbon 14 in a sample from a dead plant or animal, such as piece of wood or a fragment of bone, scientists can determine when the animal or plant died.
First, the sample is visually inspected for any possible contaminants. The sample is then chemically cleaned so only the carbon in the sample remains.
The cleaned sample is loaded into a quartz combustion tube and is heated to turn the sample into carbon dioxide. The carbon dioxide is mixed with hydrogen in a graphite reaction vessel. The resulting reaction creates an elemental carbon or graphic sample.
The sample is placed in a vacuum chamber and is blasted with a cesium ion beam. The resulting stream of carbon ions goes through an accelerator where the Carbon 12 and Carbon 13 are separated from the Carbon 14 ions. A detector then measures the resulting stream of Carbon 14 ions.
The radiocarbon date is converted into a calendar date. While the rate of radioactive decay is theoretically constant, environmental factors such as above ground nuclear testing can impact the results. This, along with measurement uncertainty, is why radio carbon dating is expressed in a range of years.
The Chippewa River Canoe was built between 1436 and 1522 AD.
The Minnesota River Canoe was built between 1626 and 1679 AD.