Radioactive dating

A useful application of half-lives is radioactive dating. Carbon- 14 (C-14), a radioactive isotope of carbon, is produced in the upper atmosphere by cosmic radiation. The primary carboncontaining compound in the atmosphere is carbon dioxide, and a very small amount of carbon dioxide contains C-14.  Plants absorb C-14 during photosynthesis, so C-14 is incorporated into the cellular structure of plants. Plants are then eaten by animals, making C-14 a part of the cellular structure of all living things.

As long as an organism is alive, the amount of C-14 in its cellular structure remains constant. But when the organism dies, the amount of C-14 begins to decrease. Scientists know the  half-life of C-14 (5,730 years), so they can figure out how long ago the organism died.

Radioactive dating using C-14 has been used to determine the age of skeletons found at archeological sites. It was also used to date the Shroud of Turin, a piece of linen in the shape of a burial cloth that contains an image of a man. Many thought that it was the burial cloth of Jesus, but in 1988, radiocarbon dating determined that the cloth dated from around 1200–1300 CE.

Carbon-14 dating can only determine the age of something that was once alive. It can’t determine the age of a moon rock or a meteorite. For nonliving substances, scientists use other isotopes, such as potassium-40.