Relative Dating and Superposition
Learning Objective
I can explain how the law of superposition helps determine the relative ages of rocks and fossils.
Key Concepts
The geologic time scale divides Earth's history into units called eons and eras, which are mapped out using clues found in rocks.
The law of superposition states that in undisturbed rock layers, the layers at the bottom are older than the layers at the top.
The law of cross-cutting relationships helps determine relative ages when an igneous intrusion or fault cuts through existing rock layers.
Practice Questions
This lesson includes 10 practice questions to reinforce learning.
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1. What does the law of superposition help scientists figure out?
2. Imagine you have a stack of books. The bottom book has a copyright date of 1990, and the top book has a copyright date of 2020. Which book is older?
3. What is relative dating?
...and 7 more questions
Educational Video
Fossils and rock layers | The geosphere | Middle school Earth and space science | Khan Academy
Khan Academy