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.Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.If one knows how much of this radioactive material was present initially in the object (by determining how much of the material has decayed), and one knows the half-life of the material, one can deduce the age of the object. The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s.
The most widely known form of radiometric dating is carbon-14 dating.
The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.
Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.