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.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.Fossils can't form in the igneous rock that usually does contain the isotopes.You can learn more about fossils, dinosaurs, radiometric dating and related topics by reading through the links on the next page.Radiometric dating isn't the only method of determining the age of rocks.In addition, the oldest known moon rocks are 4.5 billion years old.
Since the moon and the Earth probably formed at the same time, this supports the current idea of the Earth's age.
Using the basic ideas of bracketing and radiometric dating, researchers have determined the age of rock layers all over the world.
This information has also helped determine the age of the Earth itself.
These layers are like bookends -- they give a beginning and an end to the period of time when the sedimentary rock formed.
By using radiometric dating to determine the age of igneous brackets, researchers can accurately determine the age of the sedimentary layers between them.
As we mentioned above, the carbon-14 to carbon-12 ratio in the atmosphere remains nearly constant.