Definition of radioactive dating radiometric dating system
any method of determining the age of earth materials or objects of organic origin based on measurement of either short-lived radioactive elements or the amount of a long-lived radioactive element plus its decay product.
The object's approximate age can then be figured out using the known rate of decay of the isotope.
Other forms of radioactive dating are more broadly applicable.
All living things have carbon in them; but a small amount of that carbon is radioactive. The law of conservation and mass states that matter can not be destroyed nor created.
Assuming that the parent radioisotope was present at the time of formation of the rock, etc., then the number of daughter isotopes produced by radioactive decay of the parent depends only on the half-life of the parent and the age of the sample.
Half-lives must therefore be known with great accuracy for precise dating and should range from about 10 years.
So that is why carbon-14 is used for radioactive dating.