Thermoluminescence: Silicate rocks, like quartz, are particularly good at trapping electrons.
Researchers who work with prehistoric tools made from flint — a hardened form of quartz — often use thermoluminescence (TL) to tell them not the age of the rock, but of the tool.
Egyptologists, for example, created a relative chronology of pre-pharaonic Egypt based on increasing complexity in ceramics found at burial sites.
Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.
Says Shea: “Beyond 40,000 years old, the sample is so small, and the contamination risk so great, that the margin of error is thousands of years.This includes factoring in many variables, such as the amount of radiation the object was exposed to each year.These techniques are accurate only for material ranging from a few thousand to 500,000 years old — some researchers argue the accuracy diminishes significantly after 100,000 years.Researchers can measure the amount of these trapped electrons to establish an age.But to use any trapped charge method, experts first need to calculate the rate at which the electrons were trapped.