This picture shows radioactive decay of a carbon-14 atom. The carbon atom gives off a beta particle of radiation. The carbon atom turns into a nitrogen atom.
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Original artwork by Windows to the Universe staff (Randy Russell).
Carbon-14 dating (also called "radiocarbon dating") is used to determine the age of materials that contain carbon that was originally in living things. It is often used in archeology and some types of biology. Living creatures ingest carbon. Plants (and other autotrophs) take in carbon dioxide gas from the atmosphere during photosynthesis. Animals (and other heterotrophs) get their carbon by eating plants or other animals, from decaying organic matter, or from other similar sources.
Some of the carbon is a radioactive isotope called carbon-14 (14C). When the creature dies, it stops ingesting carbon. The radioactive 14C gradually undergoes radioactive decay, transforming it into nitrogen, and therefore gradually "disappears". Scientists can study samples from the once-live creatures' remains to see how much radioactive 14C, as compared to the normal isotope of carbon (carbon-12 or 12C), is still around. This tells the scientists how long ago the organism died.
14C has a half-life of 5,730 years, meaning that after about five thousand years about half of the 14C will decay and turn into nitrogen. After several half-lives, too little 14C will remain in a sample for it to be useful for dating. Radiocarbon dating is therefore only useful for samples with ages of less than about 65,000 to 80,000 years.
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