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Both plants and animals exchange carbon with their environment until they die.
Afterward, the amount of the radioactive isotope carbon-14 in their remains decreases.
Certain unstable isotopes of trace radioactive elements in both organic and inorganic materials decay into stable isotopes. By measuring the proportion of different isotopes present, researchers can figure out how old the material is.
Here are some of the most common radiometric methods: Radiocarbon dating: Sometimes called carbon-14 dating, this method works on organic material.
Egyptologists, for example, created a relative chronology of pre-pharaonic Egypt based on increasing complexity in ceramics found at burial sites.
Methods fall into one of two categories: relative or absolute.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.Paleomagnetism: Earth’s magnetic polarity flip-flops about every 100,000 to 600,000 years.
The polarity is recorded by the orientation of magnetic crystals in specific kinds of rock, and researchers have established a timeline of normal and reversed periods of polarity.
Paleomagnetism is often used as a rough check of results from another dating method.