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Name: ____________________________
Date: ______________
Lab#: ______
Lab: Determining Relative Ages
Objective: Use the key principles of relative dating techniques to determine the geologic history
of an area.
Background: A number of prominent geologists contributed to the study of Earth’s history
including Major John Wesley Powell who while leading an expedition down the Colorado River
and through the Grand Canyon in 1869, realized that the evidence for an ancient Earth was
concealed in the rocks.
In the late 1700s, James Hutton put forth the fundamental principle of uniformitarianism,
which meant that Earth was much older than previously thought. Finally, Nicolaus Steno, a
Danish anatomist, geologist and priest, is credited with describing a set of geologic observations
that provide the basis for relative dating.
Procedure:
1 Using Figure A and Figure B provided, answer the analysis questions that follow.
2 Cut and paste each figure into your lab notebook.
Figure A
1 Were any layers of rock deposited after the igneous intrusion formed? Explain.
2 What type of unconformity is shown? Is it possible that there were originally more layers
of rock than are shown here? Explain.
3 What type of fault is shown?
4 Based on the figure alone, do you know whether the shale was deposited before or after
the fault occurred? Assume that the layers have not been overturned.
5 Is it possible to determine if the igneous intrusion formed before or after the fault
occurred? Explain.
Figure B
1 What type of fault is shown?
2 Is the igneous intrusion on the left older or younger than the unconformity nearest the
surface? Explain.
3 Are the two igneous intrusions shown the same age? How do you know?
4 Which two layers of rock may have been much thicker at one time than they are now?
Conclusions
1
2
Make a sketch in your lab notebook of Figure A. Indicated on it the relative age of each
rock layer, igneous intrusion, fault and unconformity. For example, the shale layer is the
oldest, so mark it with a “1”. Mark the next oldest feature with a “2” and so on.
Repeat the procedure in question 1 above for Figure B.