Dating by radioactive materials has solved numerous problems in the Chihuahuan Desert, from the ages of lava flows to the spread of agriculture. Radiometry, though, has a drawback: proper radioactive materials must be present. Scientists have searched for, and found, methods of dating prehistoric objects and events by other means.
Most soils have low levels of radioactivity useless for dating by
classical methods. However, such common minerals as quartz and feldspar capture energy
when buried in soil that has even low levels of radioactivity—and the longer they are
buried, the more energy is captured. This bound energy is measured by the technique of
luminescence dating. Heating or exposing the material to light releases the captured
energy in the form of light—thus the term luminescence. The clock is set to zero when
the material is heated, as in the firing of pottery, or when exposed to light on the
surface of the ground. Measurement of the energy released in the lab together with the
level of soil radioactivity gives a date by simple calculation.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.