Dating Artifacts

Radiocarbon dating is a process used to determine the age of an ancient object by measuring its radiocarbon content. Willard F. Libby, an American chemist, developed this technique in the late 1940s. Archaeologists and geologists have used this method to learn a lot about prehistoric human beings, animals and plants that have lived up to 50,000 years ago.

Radiocarbon in the tissues of living organisms decays extremely slowly. Half the radiocarbon in an object decays about every 5700 years. Newly cut wood retains most of its radiocarbon. After 5700 years, half the radiocarbon is left. After 11400 years, only a fourth remains.

There are two methods of radiocarbon dating. The traditional method is burning a piece of an object and converting it into carbon dioxide gas. Radiocarbon (carbon 14) atoms in the gas release electrons as radiocarbon changes into nitrogen 14. Radiation counters detect the number of electrons given off, which determines the objectís radiocarbon content. In the newer method, a particle accelerator fires charged atoms originally from a small piece of the object into a magnetic field. This field deflects and separates the various carbon atoms by their weight. Then a detector counts the individual carbon 14 atoms to determine the objectís radiocarbon content.

Dating Wood:

The best method known is dendrochronology. It involves the counting of yearly growth rings visible on cross sections of cut trees. Archaeologists match the pattern of tree rings with those of ancient wooden objects to determine the age of other objects. However, it can only be used with wooden objects up to about 8000 years old.