Learn how scientists determine the ages of rocks and fossils. We’ll explore both relative and numerical dating on our quest to understand the process of geological dating. Along the way, we’ll learn how stratigraphic succession and radioactive decay contribute to the work of paleontologists.
Dating Dinosaur Fossils
Consider the following scenario: Paul the Paleontologist is a very famous scientist who has studied dinosaur bones all over the world.
Recently, he appeared on the evening news to talk about a new dinosaur he just discovered. The dinosaur is called superus awesomus. Paul says he can tell from the fossils that superus awesomus lived on Earth about 175 million years ago.
Paul is super awesome, so I’m going to take him at his word.But really, how do scientists figure out how old their dinosaur bones are? And, what about other findings like fossil fish, plants and insects? Scientists are always spouting information about the ages of rocks and fossils. How do they know these ages? Well, they figure it out using two different methods: relative dating and numerical dating.
Let’s find out more about these geological dating methods in order to understand how Paul the Paleontologist can be so sure about the age of his dinosaur fossils.
The first method that scientists use to determine the age of rocks is relative dating. In this method, scientists compare different layers of rock to determine an ordered sequence of events in geologic history.
That means they don’t really know how old their rocks actually are. The key in relative dating is to find an ordered sequence. Scientists piece together a story of how one event came before or after another. Relative dating cannot tell us the actual age of a rock; it can only tell us whether one rock is older or younger than another.The most common form of relative dating is called stratigraphic succession. This is just a fancy term for the way rock layers are built up and changed by geologic processes.
Scientists know that the layers they see in sedimentary rock were built up in a certain order, from bottom to top. When they find a section of rock that has a lot of different strata, they can assume that the bottom-most layer is the oldest and the top-most layer is the youngest. Again, this doesn’t tell them exactly how old the layers are, but it does give them an idea of the ordered sequence of events that occurred over the history of that geologic formation.
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