Which isotope is used to date artifacts or things that were once living?

• A. Carbon-14
• B. Carbon-12
• C. Oxygen-18
• D. Nitrogen-14

Answer: (A)

Radiocarbon dating uses carbon-14, a radioactive isotope of carbon, to determine the age of artifacts from once-living material. While an organism is alive, it maintains a constant ratio of carbon-14 to carbon-12 by exchanging carbon with the atmosphere. After death, this exchange stops, and carbon-14 decays to nitrogen-14 at a known rate (half-life about 5,730 years). Measuring how much carbon-14 remains lets scientists estimate how long it has been since death, so the age of the artifact can be determined. This method works well for organic materials up to roughly 50,000 years old. The other isotopes are either stable (carbon-12 and nitrogen-14) or used for different purposes (oxygen-18 in paleoclimate studies), so they don’t serve as a clock for dating artifacts.