Half life and carbon 14 dating
Desmond Clark (1979) wrote that were it not for radiocarbon dating, "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation" (Clark, 1979:7).Writing of the European Upper Palaeolithic, Movius (1960) concluded that "time alone is the lens that can throw it into focus".14C also enters the Earth's oceans in an atmospheric exchange and as dissolved carbonate (the entire 14C inventory is termed the carbon exchange reservoir (Aitken, 1990)).Plants and animals which utilise carbon in biological foodchains take up 14C during their lifetimes.The halflife of carbon 14 is 5730 ± 30 years, and the method of dating lies in trying to determine how much carbon 14 (the radioactive isotope of carbon) is present in the artifact and comparing it to levels currently present in the atmosphere.Above is a graph that illustrates the relationship between how much Carbon 14 is left in a sample and how old it is.
Included below is an impressive list of some of the types of carbonaceous samples that have been commonly radiocarbon dated in the years since the inception of the method: The historical perspective on the development of radiocarbon dating is well outlined in Taylor's (1987) book "Radiocarbon Dating: An archaeological perspective".
The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14.
The reaction is: (Where n is a neutron and p is a proton).
Libby later received the Nobel Prize in Chemistry in 1960: (From Taylor, 1987).
Today, there are over 130 radiocarbon dating laboratories around the world producing radiocarbon assays for the scientific community.
By measuring the C14 concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the countrate or number of decay events per gram of Carbon.