Chemistry Reference
In-Depth Information
CHRONOMETRIC
DATING METHODS
SELECTION CRITERIA
APPENDIX II
Dating methods are used for placing ancient materials, objects or events,
within a timescale. Two basically different types of dating methods are rec-
ognized:
relative
and
absolute dating
.
Relative dating
methods reveal the tem-
poral order of a sequence of materials, objects or events, disclosing whether
these occurred before, contemporarily or after other materials, objects or
events.
Absolute
, or
chronometric dating
methods reveal the age, measured in
calendar years, of materials, objects or events. Chronometric dating methods
(see Fig. 88) make use of a variety of physical or chemical measurements to
ascertain the time when events occurred or when materials and objects were
made, used, or altered. Chronometric dates are not exact dates, but numer-
ical age estimations and are generally expressed as a range of dates quali-
fied by an indication of the uncertainty of the dates.
When selecting a method of dating, the nature of of the material to be
dated and the estimated age to be determined must be considered. Only
wood, for example, can be dated by dendrochronology; all organic materi-
als, can be dated with the radiocarbon and many with the amino acid racem-
ization methods. Coral, bones, teeth, and shell can also be dated using the
electron spin resonance method. Pottery and other burned-clay materials
that contain crystalline solids are usually dated using the thermolumines-
cence technique. Glassy minerals, such as mica and obsidian, can be dated
by employing the fission track method. The potassium-argon method is
used to date volcanic rock and ash and the uranium series method, for dating
such materials as travertine, marl, coral, mollusc shells, bone, and teeth,
which are formed through precipitation processes (Schwarcz 2002; Smart
and Frances 1992).
As for the estimated age: two chronometric methods, radiocarbon and
dendrochronological dating, enable the accurate dating of materials or/and
events in the timespan between the present and 10,000 years ago. The
