Dinosaurs and Fossils Determining the age of dinosaur

Dinosaurs and Fossils Determining the age of dinosaur fossils

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

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

Dating Techniques • Relative Dating – Dating using rock layers, doesn’t determine an exact age • Radiometric Dating – ages can be determined using radioactive decay of elements

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

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

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