Carbon dating at

23 Jan

Carbon-14, or radiocarbon—which is now widely used to date organic material—was discovered 75 years ago on February 27 by Martin Kamen and Sam Rubin at the UC-Berkeley Radiation Lab.

Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms. Our Living Language : In the late 1940s, American chemist Willard Libby developed a method for determining when the death of an organism had occurred.

He first noted that the cells of all living things contain atoms taken in from the organism's environment, including carbon; all organic compounds contain carbon.

An expert on radiation, Libby gets to the heart of the matter in this article on radiocarbon dating: “(1) Cosmic rays make living things radioactive to a certain level fixed by the environment through the food eaten. Taylor, who calls radiocarbon dating revolutionary, summarized a half-century of advances made in radiocarbon dating.

(2) At death the intake of food stops so no replenishment of the immutable radioactive decay of C can occur and the degree to which decay is observed to have occurred gives the time lapse since death (radiocarbon age.)” The dating of archaeological evidence before radiocarbon was based on historical records, stratigraphy (the study of layers of rock), and educated guesswork. Taylor wrote, “It is difficult for many people to appreciate just how dramatically the advent of radiocarbon dating transformed archaeology.

Bone, wood (including charcoal), and other plant remains could be dated to approximately 50,000 years ago.