Carbon dating is a technique used to determine the approximate age of once-living materials. It is based on the decay rate of the radioactive carbon isotope C-14, a form of carbon taken in by all living organisms while they are alive.

Before the twentieth century, determining the age of ancient artifacts was considered the job of archaeologists, not nuclear physicists. By comparing the placement of objects with the age of the rock and silt layers in which they were found, archeologists could usually make a general estimate of their age. However, many objects were found in caves, frozen in ice, or in other areas whose ages were not known; in these cases, it was clear that a method for dating the actual object was necessary.

In 1907, the American chemist Bertram Boltwood (1870- 1927) proposed that rocks containing radioactive uranium could be dated by measuring the amount of...