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, archaeologists could usually make a general estimate as to 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 proposed that rocks containing radioactive uranium could be dated by measuring the amount of lead in the sample. This was because uranium, as it underwent radioactive decay, would transmute into lead over a long span of time. Thus, the greater the amount of lead, the older the rock. Boltwood used this method, called radioactive dating...