Dating

Dating of artifacts is called archaeometry. Archaeologists use different methods of archaeometry. Sometimes an artifact is easy to date because the date is on it, as we see on most coins. It is also easy to date an artifact if there are dates in written records mentioning the artifact. Unfortunately, most of the time dating is harder.

There are two major ways of dating objects. They are relative dating and absolute dating. Relative dating finds out the age of the object in relation to the age of another object. Relative dating only gives comparisons, not the actual dates. An example of relative dating is when archaeologists measure the fluorine content in bones. Fluorine is from underground water. Fluorine eventually replaces other things that are in bones, so the more fluorine the bones contain the older they are.
Another type of relative dating is stratigraphy. Stratigraphy determines the age of the object relative to other objects at the site. The deeper down the object is, the older it is, unless the layer of earth is pushed down in some places.

Absolute dating gives the age of the artifact in years. There are many examples of absolute dating. Radiocarbon dating is one of the most commonly used forms of archaeometry. Everything alive absorbs two types of carbon: carbon 12 and carbon 14. Carbon 14 atoms are radioactive and decay at the same rate no matter what. About half of the carbon 14 atoms disappear every 5,700 years. Carbon 12 atoms do not change. After a living thing dies, the ratio of carbon 14 to carbon 12 decreases at a rate known by archaeologists. Archaeologists can measure the amount of carbon 14 and carbon 12 in the formerly living artifact. From this, archaeologists can find out the age of the artifact. The problem with radiocarbon dating is that the only way to measure carbons 12 and 14 is to destroy part of the artifact.

Because radiocarbon dating only works on artifacts that were once alive, archaeologists use potassium-argon dating for some rock formations. These rock formations contain radioactive potassium. The potassium changes into argon at a constant rate. Archaeologists measure the amount of potassium and argon in the rock to find out the age of the formation.