Pub. date: 2006 | Online Pub. Date: September 15, 2007 | DOI: 10.4135/9781412952453 | Print ISBN: 9780761930297 | Online ISBN: 9781412952453| Publisher:SAGE Publications, Inc.About this encyclopedia
L. A. Pavlish
Radiocarbon is the best-known radiometric dating technique due to its successful application to problems in human history and prehistory for over 50 years. Willard Libby's development of the technique in the late 1940s permitted relative time to be sorted radiometrically in archaeological contexts in a manner that eclipsed the more traditional relative dating methods that had developed over the previous century. Carbon-14 is a radioactive isotope produced in the upper atmosphere when cosmic rays generate neutrons as they bombard that outer atmosphere. These neutrons can enter abundant nitrogen-14 nuclei (78% of the atmosphere), converting some of them to carbon-14. The carbon-14 combines with oxygen to form carbon-14 dioxide, which is assimilated by plants and the animals that consume those plants. The carbon-14 production is relatively constant over short periods of time and is in equilibrium with the carbon sinks in the environment (see figure). The Libby radiometric clock is started ...