How Carbon Dating Works
During the lifetime of an organism, carbon is brought into the cell from the environment in the dating relationship of either carbon dioxide or carbon-based food molecules such as glucose; then used to build biologically important molecules such as sugars, proteins, fats, and nucleic acids. Therefore, organisms from a single-celled bacteria to the largest of the dinosaurs leave behind carbon-based remains.
Carbon dating is based upon the decay of 14C, a radioactive isotope of carbon with a relatively long half-life years. While 12C is the most abundant carbon isotope, there is a close to constant ratio of 12C to 14C in the environment, and hence in the molecules, cells, and tissues of living organisms. Decay of radioactive isotopes Radioactive isotopes, such as 14C, decay exponentially.
Returning to our example of carbon, knowing that the half-life of 14C is years, we can use this to find the constant, k. Other radioactive isotopes are also used to date fossils.
The half-life for 14C is approximately years, therefore the 14C isotope is only useful for dating fossils up to about 50, years old.