The stable C12 and C13, and the unstable or radioactive Carbon 14. Only one C14 atom exists for every one trillion C12 atoms.
The halflife of carbon 14 is 5730 ± 30 years, and the method of dating lies in trying to determine how much carbon 14 (the radioactive isotope of carbon) is present in the artifact and comparing it to levels currently present in the atmosphere.
Above is a graph that illustrates the relationship between how much Carbon 14 is left in a sample and how old it is.
Radiocarbon dating can easily establish that humans have been on the earth for over twenty thousand years, at least twice as long as creationists are willing to allow.
Therefore it should come as no surprise that creationists at the Institute for Creation Research (ICR) have been trying desperately to discredit this method for years.
Radiocarbon or C14 dating employs complex systems of measuring the unstable isotopes in once living matter.