Name ________________________________________________________ Date _________________________
Relative Age of Rocks Review
Be able to answer and explain, in your own words, the following questions:
1) What is the Law of Superposition and what does it tell us about rocks?
Answer: The Law of Superposition tells us that in rock layers, the oldest layer is at
the bottom and each higher layer is younger than the layers below it.
2) When looking at a diagram, how to tell if the intrusion or extrusion is older
or younger than the surrounding layers.
Answer: For intrusion, the intrusion is younger than the rocks surrounding it. For
an extrusion, the extrusion is younger than the layers below it and older than the
layers above it.
3) What is an index fossil and how can geologists use them to explain the age
of another rock layer.
Answer: An index fossil is a fossil that is used to help geologist match rock layers. If
you find a fossil in one layer, and find a very similar fossil in other area, those rock
layers are from the same period.
Know and Understand the following vocabulary words:
Fault – A break in the Earth’s crust.
Extrusion – A hardened layer of lava on Earth’s surface
Intrusion – A hardened layer of lava below the Earth’s surface
Relative Age – The age of a rock compared with the age of other rocks.
Law of Superposition – The way to determine relative ages of rocks.
Unconformity – The surface where new rock layers meet a much older rock surface
beneath them.
Absolute Age – The number of years since a rock has been formed.
Index Fossil – Fossils used to help geologists match rock layers.