Question

A bone needle was found in association with a burial. Using radiocarbon dating, the date for the needle was found to be 20,000 years old. Does this mean the person was buried 20,000 years ago? What does this date actually tell you?

Answer 1

Radiocarbon dating is a method used to determine approximate ages for carbon based (organic) materials. These materials are obtained from living organisms or their remains.

Radiocarbon (14C) is an isotope of carbon. It is unstable and weakly radioactive. Its stable isotopes are 12C and 13C. 14C is continually formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms. It is rapidly oxidized in air to form carbon dioxide and enters the earths's carbon cycle. It is then incorporated into plants by photosynthesis and animals then acquire 14C by eating the plants. This takes place throughout their lifetimes. When they die, they stop exchanging carbon with their environment and their 14C content then starts to decrease at a rate determined by the law of radioactive decay.

Radiocarbon dating is essentially a method designed to measure residual radioactivity of 14C. The amount of 14C in a sample is measured and used to calculate when the animal or plant had died (stop exchanging 14C). The older a sample is, less 14C is detected,

Thus, it does not mean the person was buried 20,000 years ago. It means the bone needle was made from a bone of an animal that had died about 20,000 years ago.

Altough it does not tell when the person was burried, a rough estimate can me made.