By comparison with the tree rings in the extremely old bristle-cone pines, however, a corrected carbon date can be found for objects over about 1500 years old.
The trees are themselves dated by the carbon-14 method using dead parts in the bark.
Radiometric dating, often called radioactive dating, is a technique used to determine the age of materials such as rocks.
It is based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.
For example if you consider the uranium series that the final stable isotope is lead-206, and if we assume that there was no lead in the rock when it was formed the ratio of the number of atoms of lead 206 (N The carbon 14 is then absorbed by plants; these in turn are eaten by animals which may then be eaten by other animals.
The different methods of radiometric dating are accurate over different timescales, and they are useful for different materials.
Different nuclides, which have the same proton number (but different nucleon numbers) are called isotopes (isotopic nuclides).
The first radioisotope was an unstable isotope of phosphorus.
The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.
For geological purposes, this is taken as one year.