Rachel Wood does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. Radiocarbon dating has transformed our understanding of the past 50, years. Professor Willard Libby produced the first radiocarbon dates in and was later awarded the Nobel Prize for his efforts.
Carbon is one of the chemical elements. Along with hydrogen, nitrogen, oxygen, phosphorus, and sulfur, carbon is a building block of biochemical molecules ranging from fats, proteins, and carbohydrates to active substances such as hormones. All carbon atoms have a nucleus containing six protons.
Ninety-nine percent of these also contain six neutrons. They have masses of 13 and 14 respectively and are referred to as "carbon" and "carbon If two atoms have equal s of protons but differing s of neutrons, one is said to be an "isotope" of the other.
Carbon and carbon are thus isotopes of carbon Isotopes participate in the same chemical reactions but often at differing rates. When isotopes are to be deated specifically, the chemical symbol is expanded to identify the mass for example, 13 C. Both 13 C and 14 C are present in nature. The abundance of 14 C varies from 0.
The highest abundances of 14 C are found in atmospheric carbon dioxide and in products made from atmospheric carbon dioxide for example, plants. Unlike 12 C and 13 C, 14 C is not stable.
As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged. Carbon is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere. The rate at which 14 C decays is absolutely constant. Given any set of 14 C atoms, half of them will decay in years.
The carbon 14 (c) dating method
Since this rate is slow relative to the movement of carbon through food chains from plants to animals to bacteria all carbon in biomass at earth's surface contains atmospheric levels of 14 C. However, as soon as any carbon drops out of the cycle of biological processes - for example, through burial in mud or soil - the abundance of 14 C begins to decline.
After years only half remains.
After another years only a quarter remains. This process, which continues until no 14 C remains, is the basis of carbon dating. A sample in which 14 C is no longer detectable is said to be "radiocarbon dead.
They are derived from biomass that initially contained atmospheric levels of 14 C. But the transformation of sedimentary organic debris into oil or woody plants into coal is so slow that even the youngest deposits are radiocarbon dead. The abundance of 14 C in an organic molecule thus provides information about the source of its carbon.
If 14 C is present at atmospheric levels, the molecule must derive from a recent plant product.
How carbon dating works
The pathway from the plant to the molecule may have been indirect or lengthy, involving multiple physical, chemical, and biological processes. Levels of 14 C are affected ificantly only by the passage of time. If a molecule contains no detectable 14 C it must derive from a petrochemical feedstock or from some other ancient source.
Intermediate levels of 14 C can represent either mixtures of modern and dead carbon or carbon that was fixed from the atmosphere less than 50, years ago. als of this kind are often used by chemists studying natural environments.
A hydrocarbon found in beach sediments, for example, might derive from an oil spill or from waxes produced by plants.
If isotopic analyses show that the hydrocarbon contains 14 C at atmospheric levels, it's from a plant. If it contains no 14 C, it's from an oil spill. If it contains some intermediate level, it's from a mixture of both sources. What is Carbon Dating?
How does Radiocarbon work? Scientific American Editor Michael Moyer explains the process of radiocarbon dating. The Radiocarbon Collaborative.