1. Dinosaurs and Fossils Determining the age of dinosaur fossils

2. Dino Domination Dinosaurs ruled the earth for 165 million years Mass extinction at the end of the Cretaceous period, 65 million years ago

3. How do we know? Fossils of every shape and size have been found on 6 continents Limited fossil record but we continue to discover more We can tell the age of fossils using 2 dating techniques

4. Dating Techniques Relative Dating – Dating using rock layers, doesnt determine an exact age Radiometric Dating – ages can be determined using radioactive decay of elements

5. Relative Dating Only technique available in the 18 th and 19 th century Relative ages of fossils can be found based on the rock layers they are found in Principle of Superposition: Younger sedimentary rocks are deposited on top of older sedimentary rocks

7. Radiometric Dating Ages of rocks and fossils can be more closely determined Some elements have isotopes that are unstable (parent isotope) These isotopes have a natural tendency to change, or decay (form daughter isotope) If we know the proportion of parent and daughter isotope present, and its half life, we can find the age of the fossil

8. Half Life The time it takes for an element to go to a 50:50 proportion of parent and daughter isotopes With measurements on very large numbers of elements we can determine their half lives