What Is Carbon-14 Dating?
Carbon-14 (a carbon atom with six protons and eight neutrons) is an isotope of normal carbon, which is also known as carbon-12 (a carbon atom with six protons and six neutrons). An isotope is an atom of an element that has a different number of neutrons than the common, stable form of the element.
Carbon-14 is radioactive and is produced naturally in the atmosphere when cosmic rays collide with nitrogen atoms. When carbon-14 atoms subsequently combine with oxygen, they form carbon dioxide that gets absorbed by plants. When humans and animals eat plants, they take in carbon-14 atoms.
Carbon-14 atoms decay at a constant rate, because they are radioactive. The rate of radioactive decay of a substance is defined by its half-life, that is, the time it takes for half the atoms in a radioactive isotope to decay. Scientists have measured the half-life of carbon-14 atoms to be approximately 5,700 years. At the same time, the environment constantly produces new carbon-14, so that the percentage of carbon-14 in all living plants and animals remains fairly constant.
When an animal dies, it stops taking in new carbon. The carbon-14 it contains, though, continues to decay, while the amount of normal carbon-12 remains the same. Scientists can then compare the ratio of normal carbon (carbon-12) to radioactive carbon-14 to determine an approximate age of the creature by testing and analyzing its ancient, fossilized bones.
Since the half-life of carbon-14 is about 5,700 years, carbon-14 can only be used reliably to date objects up to around 60,000 years old. You’ve probably heard scientists talk about things that they claim are millions, if not billions, of years old, though.
Carbon-14 is not the only radioactive isotope scientists can measure and use to date an artifact. Other radioactive isotopes, such as potassium-40, uranium-235, uranium-238, thorium-232, and rubidium-87, have half-lives that extend from millions to billions of years.