Name: ________________________
Due Date: _____________________
Per: ________
40 minutes
Correlating Rock Layers
Introduction: How do geologists determine whether the rocks or geologic
events occurring at one location are of the same age as those at another
location? The process of showing that rocks or geologic events occurring at
different locations are of the same age is called correlation.
Geologists have developed a system for correlating rocks by looking for
similarities in composition and rock layer sequences at different locations.
Certain fossils, called index fossils, existed for a very short time and were
distributed over a large geographic area. They aid geologists in correlating
sedimentary rock layers.
Purpose: At the end of this activity, you should be able to construct a geologic
history of a region by correlating rock layers from different locations.
Procedure:
1. Outcrop Set 1 and 2 have 3 outcrops from different locations.
2. Reconstruct the complete sequence of events. Assume that the oldest
rocks are on the bottom and the youngest are on the top.
3. Draw in the layers on the column to the right of the outcrop set. You do
not need to draw in the fault or igneous intrusion.
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Earth History
Correlating Rock Layers
Page 1 of 4
Outcrop Set 1:
Outcrop Set 2:
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Earth History
Correlating Rock Layers
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Outcrop Set 3:
1. Outcrop Set 3 has 4 outcrops from different locations.
2. Reconstruct the complete sequence of events. Assume that the oldest
rocks are on the bottom and the youngest are on the top.
3. Draw in the layers on the column to the right of the outcrop set. For
layers with an index fossil, write the age of the layer and the Geologic Period
that it comes from.
4. Write the approximate age of layers without fossils.
Ideal
column
Devonian
Ordovician
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Earth History
Jurassic
Date
mybp
Geologic
Period
Permian
Correlating Rock Layers
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Conclusions:
1. Explain why some rock layers can be missing from the sequence in some
outcrops.
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2. What does a field geologist look for in rock outcrops to help identify the
different rock layers?
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3. How could the Volcanic Ash layer in Outcrop Set 1 be useful in determining the
absolute age of the surrounding rock layers? _____________________________
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4. In Outcrop Set 2, how many years are represented between the top and
bottom fossil bearing layers? _________________________________________
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5. In Outcrop Set 1, which happened first, the fault or the igneous intrusion at
the bottom of Outcrop C? How can you tell? _____________________________
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6. In Outcrop Set 2, what do you think is a reason that the tan limestone in
Location X is thinner than in Location Z? ________________________________
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VVS Earth Science
Earth History
Correlating Rock Layers
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