The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century.No other scientific method has managed to revolutionize man’s understanding not only of his present but also of events that already happened thousands of years ago.Archaeology and other human sciences use radiocarbon dating to prove or disprove theories.
American physical chemist Willard Libby led a team of scientists in the post World War II era to develop a method that measures radiocarbon activity.He is credited to be the first scientist to suggest that the unstable carbon isotope called radiocarbon or carbon 14 might exist in living matter. Libby and his team of scientists were able to publish a paper summarizing the first detection of radiocarbon in an organic sample. Libby who first measured radiocarbon’s rate of decay and established 5568 years ± 30 years as the half-life. Libby was awarded the Nobel Prize in Chemistry in recognition of his efforts to develop radiocarbon dating.Radiocarbon, or carbon 14, is an isotope of the element carbon that is unstable and weakly radioactive. Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms.It is rapidly oxidized in air to form carbon dioxide and enters the global carbon cycle.Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes.
When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay.
Radiocarbon dating is essentially a method designed to measure residual radioactivity.
By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known. Some inorganic matter, like a shell’s aragonite component, can also be dated as long as the mineral’s formation involved assimilation of carbon 14 in equilibrium with the atmosphere.
It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used. Samples that have been radiocarbon dated since the inception of the method include charcoal, wood, twigs, seeds, bones, shells, leather, peat, lake mud, soil, hair, pottery, pollen, wall paintings, corals, blood residues, fabrics, paper or parchment, resins, and water, among others.
Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content.
There are three principal techniques used to measure carbon 14 content of any given sample— gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry.