Volcanic ash used dating fossils
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.
Using the basic ideas of bracketing and radiometric dating, researchers have determined the age of rock layers all over the world.
There are several different methods for estimating the ages of fossils, including: Paleontologists rely on stratigraphy to date fossils.
You can learn more about fossils, dinosaurs, radiometric dating and related topics by reading through the links below.
Radiometric dating isn't the only method of determining the age of rocks.
Family-tree relationships can help to narrow down the date when lineages first appeared.
For example, if fossils of B date to X million years ago and the calculated “family tree” says A was an ancestor of B, then A must have evolved earlier.
These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top.