So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.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.Also called absolute dating, scientists use the decay of radioactive elements within the fossils or the rocks around the fossils to determine the age of the organism that was preserved.

Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.

Half-life is defined as the time it takes for one half of a radioactive element to decay into a daughter isotope.

As radioactive isotopes of elements decay, they lose their radio activity and become a brand new element known as a daughter isotope.

The universe is full of naturally occurring radioactive elements.

Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.