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.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 the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.Unfortunately, these elements don't exist in dinosaur fossils themselves.(This is consistent with the geologic ‘age’ assigned to the granites in which these zircons are found.) There is a significant amount of helium from that ‘1.5 billion years of decay’ still inside the zircons.
Scientists have also made improvements to the standard radiometric measurements.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.In this particular case, it takes 4,460,000,000 years for half of a sample of U238 to decay into Pb206.It takes another 4,460,000,000 years for half of the remaining sample to decay into Pb206 and then another 4,460,000,000 years for half of what’s then left to decay, and so on.