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.
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.
As no Argon was present in the rock when it first solidified, all Argon in the rock is due to the radioactive decay of Potassium.
By measuring the amounts of Potassium and Argon present we can date volcanic rocks that are millions of years old.