Radioactive dating uses the decay rates of radioactive substances to measure absolute ages of rocks, minerals and carbon-based substances, according to How Stuff Works.
Scientists know how quickly radioactive isotopes decay into other elements over thousands, millions and even billions of years.
It may be used to date a wide range of natural and man-made materials.
Fossils may be dated by taking samples of rocks from above and below the fossil's original position.
A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will spontaneously change into a different nuclide by radioactive decay.
The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.
Anything which changes the relative amounts of the two isotopes (original and daughter) must be noted, and avoided if possible.
It's this resetting process that gives us the ability to date rocks that formed at different times in earth history.
A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.
For biological objects older than 50,000 years, scientists use radioactive dating to determine the age of rocks surrounding where the material was found.
By dating rocks, scientists can approximate ages of very old fossils, bones and teeth.
All rocks and minerals contain tiny amounts of these radioactive elements.