Measurements have shown that in recent history, radiocarbon levels have remained relatively constant in most of the biosphere due to the metabolic processes in living organisms and the relatively rapid turnover of carbonates in surface ocean waters.
Radiation counters are used to detect the electrons given off by decaying C-14 as it turns into nitrogen.
Carbon-14 dating can be used on objects ranging from a few hundred years old to 50,000 years old.
Libby and others (University of Chicago) devised a method of estimating the age of organic material based on the decay rate of carbon-14.
However, the principle of carbon-14 dating applies to other isotopes as well.
Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years.