Chemistry Reference
In-Depth Information
TABLE 13
Radiometric Methods of Dating Used in Archaeology
Method
Measurement
Applicability
Reference
Methods Based on Measurement of Radioactive Radiation or Amount of
Radioactive Isotope or Daughter Isotope in Materials
Radiocarbon
Counting of beta radiation
Organic matter
Textbox 52
or amount of carbon-14
Potassium argon
Relative amounts of parent-
Volcanic rocks
Textbox 15
and daughter-isotope
Uranium series
Relative amounts of parent-
Calcareous rocks, Textbox 16
and daughter-isotope
shell
Methods Based on Measurement of Cumulative Changes Caused by
Radiation on Materials
Fission track
Number of fission tracks in
Obsidian, glass,
Textbox 26
a solid
slag
Thermoluminescence
Amount of light emitted
Pottery, burned
Textbox 24
at high temperature
flint
Optically stimulated
Amount of light emitted
Sediments and
Textbox 24
luminescence
when sample is
soil
illuminated with laser
light
Comparing the relative amount of a particular radioactive isotope of
known half-life remaining in a sample of material with that of its decay prod-
ucts, or measuring the effects of the radiation of such an isotope on sur-
rounding matter, for example, enables one to estimate the time that the
material has existed. The most convenient isotopes for archaeological dating
are those that are relatively common in nature and whose half-lives are com-
patible with archaeological dates. Table 13 lists radiometric methods of
dating that are widely used in archaeological studies.
Potassium-Argon Dating
Potassium-argon dating is the only feasible technique for dating very old
rocks that include potassium in their composition. It is based on the fact that
one of the radioactive isotopes of potassium, potassium-40 (K-40), decays to
an isotope of the gas argon, argon-40 (Ar-40). Since the half-life of potassium-
40 is known, by comparing the relative amount of potassium-40 to that of
argon-40 in a sample of rock, the date the rock was formed can be deter-
mined (see Textbox 15). Unlike the case in other radiometric dating tech-
niques used in archaeology, the materials dated with the potassium-argon
