Radiocarbon dating

Abstract

The cosmic ray production of new atoms in m atter is the basis of radiocarbon dating. In this case the atom is carbon of mass fourteen made from the most abundant atom in air—nitrogen of mass fourteen. Radiocarbon— carbon-14, 14 C—lasts 8300 years on the average (see note on radioactive decay on p. 10 for explanation of ‘half life’ and ‘average life’) before reverting in radioactive decay to nitrogen-14 and during this time it enters all living things as well as sea water and air. Chemically carbon dioxide (the product of the combustion of carbon with air—which is 20% oxygen) is the food of life and presumably the freshly produced 14 C atom burns sooner or later (probably in a few days, although this time is not at all well known) to 14 CO 2 a which is mixed with the ordinary carbon dioxide (0.03% in air) which contains mainly non-radioactive carbon atoms of masses 12 and 13 in abundances of 99% and 1%, respectively. The process which converts CO 2 a into plants—photosynthesis—is the way in which the radio­ carbon is introduced into living beings, for all life on Earth so far as is known either is a plant or lives off plants. In principle and in theory one could understand if organisms were to live off fossil (or primeval, if there be any) organic matter and that radiocarbon dating would not work for them. They would not be in touch with the cosmic rays through recent photosynthesis and the long time that coal or oil has been underground would have required that the original radiocarbon (assuming the cosmic rays were working when the coal and oil deposits were made) would long since have disappeared.