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Carbon-14 and Carbon-14 Dating


Carbon-14 is an isotope of the element carbon. All carbon atoms have 6 protons in their nucleus. Most carbon atoms also have 6 neutrons, giving them an atomic mass of 12 ( = 6 protons + 6 neutrons). Carbon-14 atoms have two extra neutrons, giving them a total of 8 neutrons. Carbon-14 has an atomic mass of 14 ( = 6 protons + 8 neutrons). The extra neutrons make the nucleus of carbon-14 unstable. Carbon-14 is radioactive!Radioactive carbon-14 (also written as 14C) has a half-life of 5,730 years. 14C is used to determine the ages of artifacts that were once living (such as pieces of wood, teeth or bones, coral skeletons, etc.) via a technique called “carbon-14 dating” or “radiocarbon dating”.Some of the carbon dioxide gas in Earth’s atmosphere contains 14C atoms. The supply of CO2 molecules which contain carbon-14 is continuously replenished in our atmosphere. Cosmic rays from space sporadically strike nitrogen atoms, converting some common nitrogen-14 atoms into radioactive carbon-14 atoms.

Carbon-14 Dating

This picture shows:
1: Formation of Carbon-14
2: Decay of Carbon-14
3: The “equal” equation is for living organisms, and the unequal one is for non-living ones, in which the C-14 then decays (hence the 2).
( source: C14_methode_physikalische_grundlagen.svg)

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.

source:windows to the universe


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