Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating.
Scientists find out the age of a dinosaur fossil by dating not only the rocks in which it lies, but those below and above it.
Elements occur naturally in the earth, and they can tell us a lot about our Earth's past.
Carbon, uranium and potassium are just a few examples of elements used in radioactive dating.
The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.
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.