Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.To determine the ages of these specimens, scientists need an isotope with a very long half-life.Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.These are released as radioactive particles (there are many types).
Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock.
The most widely known form of radiometric dating is carbon-14 dating.
This is what archaeologists use to determine the age of human-made artifacts. The half-life of carbon-14 is only 5,730 years, so carbon-14 dating is only effective on samples that are less than 50,000 years old.
Some of these atomic arrangements are stable, and some are not.
The unstable isotopes change over time into more stable isotopes, in a process called radioactive decay.