Stone arrowheads can be dated using relative or absolute methods.
When an archaeologist is collecting artifacts from a site, knowing how old they are is important. The age of the artifacts contained within a site can tell you a lot about how a site was used by the people who occupied it. Layers of artifacts can show use of a site by different groups at different times, and dating the artifacts within the layers is useful for differentiating among occupations.
Relative dating is the estimation of the age of an artifact and is based on many factors. The most important factor for relative dating is an artifact’s position in the soil layers at a site. Generally, deeper layers will contain older artifacts while layers closer to the surface will contain more recent ones. While relative dating is inexact, it is useful because it allows the artifacts at a site to be placed in a chronological sequence. The two main techniques used in relative dating are stratigraphy and seriation.
Stratigraphy refers to the layering of soil at a site, and relies on the general “rules” known as “terminus post quem” and “‘terminus ante quem.” Terminus post quem is the notion that an artifact of known age (for example, a coin dated 1850) provides the date on or after which all the artifacts on that layer were deposited. Terminus post quem is the concept that all of the layers below an artifact of known age must have been deposited first, and are therefore older.
Seriation is a relative dating technique where artifacts are placed in a chronological sequence in order to provide an estimate of age. Seriation is based on the theory that objects are slowly introduced into a culture and gradually increase in popularity, before eventually declining and disappearing from use. The styles of these objects often change over time, allowing earlier versions can be differentiated from later ones, and age to be inferred by where an artifact fits in the sequence.
Absolute dating uses scientific techniques to date an object to a specific time. These techniques are much more accurate than relative dating techniques, and are generally used in conjunction with them to get a complete picture of the ages of artifacts within a site, as well as the age of the site as a whole. The main absolute dating technique calculates the age of an artifact by measuring its concentration of the radioactive isotope carbon-14.
Radiocarbon dating is used to determine the age of organic materials like bone, and, for artifacts less than 40,000 years old, it is accurate to within 150 years. All living organisms contain carbon-14 at the the same level as that of the atmosphere, and when they die it begins to decay. Because this rate of decay is known and measurable, archaeologists are able to measure how much carbon-14 in an artifact has been lost in order to calculate when the organism died.