Chemistry Reference
In-Depth Information
Taylor et al. 1994). After over half a century of further developments and
use, there are many significant uses of radiocarbon dating not only in
archaeology but also in a variety of different fields, including environmen-
tal studies, ecology, geology, climatology, hydrology, meteorology, and
oceanography. Radiocarbon dating provides the most consistent technique
for dating materials and events that occurred during the last 50,000 years on
the surface of the earth. At the end of the twentieth century there were,
around the world, well over 100 laboratories that determined radiocarbon
dates on a vast range of materials (Lowe 1997; Bowman 1990).
Radiocarbon Dating
Radiocarbon dating
is a
radiometric
technique based on measuring the relative
amount of radiocarbon (
carbon-14
), a
radioactive isotope
of carbon in matter
containing carbon as a component. The method, which is most useful for
dating organic materials, provides reliable absolute dates not only of organic
and biological materials but also of carbonate sediments and other inorganic
carbon-containing materials.
Carbon, and therefore also radiocarbon, is a natural component of the
earth's atmosphere, where it occurs combined with oxygen in the form of
carbon dioxide. All living organisms acquire radiocarbon, as well as all the
other isotopes of carbon, in the same way: plants, acquire it in the form of
carbon dioxide, through the process of photosynthesis; animals acquire it
when feeding from plants. When vegetable or animal organisms die, their
intake of carbon, and therefore also of radiocarbon, ceases. Since radiocar-
bon undergoes radioactive decay, the dead remains begin to lose radiocar-
bon. This loss, which is regulated only by the
half-life
of the isotope, results
in a continuous reduction in the total number of atoms of radiocarbon, as
well as in the relative amount of atoms of radiocarbon to those of stable
carbon-12 in the dead tissues. Therefore, the age of dead remains, or of any
carbon-containing matter, can be determined by measuring the relative
amount of radiocarbon they contain.
TEXTBOX
52
RADIOCARBON DATING
Carbon, a common element in the outer crust of the earth, and the main
component of all biological and organic substances, occurs in three isotopic
forms: carbon-12 or C-12 for short (whose chemical symbol is
12
C), carbon-
13 or C-13 (
13
C), and carbon-14 or C-14 (
14
C) (see Fig. 8 and Table 66).
