These use radioactive minerals in rocks as geological clocks.The atoms of some chemical elements have different forms, called isotopes.They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.
Sometimes, scientists already know the age of the fossil because fossils of the same species have been found elsewhere and it has been possible to establish accurately from those when the dinosaur lived.Scientists use two kinds of dating techniques to work out the age of rocks and fossils. This considers the positions of the different rocks in sequence (in relation to each other) and the different types of fossil that are found in them.The second method is called absolute dating and is done by analysing the amount of radioactive decay in the minerals of the rocks.The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out. The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle.