Name and Period
Chapter 17 – The Rock Record
INTRODUCTION: Rocks contain clues to the earth’s past, including evidence of ancient life-forms. Information found in
the rock record helps us understand the geologic processes that have shaped the earth’s crust. In this chapter, you will
learn about the methods earth scientists use to uncover the geologic history of the earth.
Section 17.1 – Determining Relative Age (pages 323 -326)
A. Section Objective #1: State the principle of uniformitarianism.
1. (Page 323 paragraph 2) The principle of uniformitarianism states that __________________________________
___________________________________________________________________________________________
2. (same paragraph) The Scottish physician and gentleman farmer who proposed this principle is named:
_____________________________________
3. (same paragraph) This principle is one of the basic ___________________________________ of the science of
geology.
4. (same paragraph) Geologists later refined Hutton’s ideas how? _______________________________________
___________________________________________________________________________________________
B. Section Objective #2: Explain how the law of superposition can be used to determine the relative age
of rocks.
1. (page 324 paragraph 3) When sediments accumulate and are compressed and solidified into rock layers, these
layers are then called beds. What is a bedding plane? ______________________________________________
__________________________________________________________________________________________
2. (page 324 paragraph 4) Scientists make use of the law of superposition to determine the relative age of a layer
of sedimentary rock. The principle states ________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
3. (page 324) Refer yourself to figure 17-2 and read what the caption says. This is also sketched on the board. Try
your own sketch below:
C. Section Objective #3: Compare three types of unconformity.
1. (page 325 paragraph 2) An unconformity is a break in the geologic record. How does an unconformity happen?
To answer this properly, you want to copy down the first 3 sentences from the paragraph:
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__________________________________________________________________________________________
__________________________________________________________________________________________
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2. (page 325 paragraph 3) The first type of unconformity is called the NONCONFORMITY.
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Write out the definition of nonconformity: ____________________________________________________
_________________________________________________________________________________________________
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An example is the boundary between sandstone that was deposited over a layer of eroded granite. The
boundary between them is a nonconformity and it represents an unknown _______________________ of
_____________________ during which the granite was eroded.
3. (page 325 paragraph 4) The second type of unconformity is called the ANGULAR UNCONFORMITY.
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Write out the definition of angular unconformity: ______________________________________________
________________________________________________________________________________________________
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This type of unconformity results when rocks deposited in _____________________________________
layers are folded or ___________________________ and then ______________________________.
4. (page 325 paragraph 5) The third type of unconformity is called the DISCONFORMITY.
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Write out the definition of disconformity:_____________________________________________________
_________________________________________________________________________________________________
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This can happen to seafloor that is uplifted, eroded, and submerged again to have new deposition occur.
Although the rock layers look as if they were deposited continuously, a _____________________________
__________________ __________ exists where the upper and lower layers meet at the unconformity.
D. Section Objective #4: Apply the law of crosscutting relationships to determine the relative age of
rocks.
1. (page 326 paragraph 1) State the law of crosscutting relationships: __________________________________
_________________________________________________________________________________________________
2. This law is used when there is tectonic activity, such as a fault, that has disturbed the rock layers. If a fault has
occurred, the law of superposition may not be adequate to determine relative ages. The geologist may need to
use the law of crosscutting relationships instead.
3. Define FAULT: _____________________________________________________________________________
4. Define INTRUSION: _________________________________________________________________________
5. This law can be complex. In figure 17-4, the INTRUSION is younger than layers A, B, and C. Why not D?
The reason why the intrusion is younger than A, B, and C is because __________________________________________.
It is older than D because ____________________________________________________________________________ .
6. In figure 17-4, the FAULT is younger than all four layers. Why? The fault is relatively younger than layers A, B, C,
& D because ______________________________________________________________________ .
Next up is a worksheet to review the concepts we have learned in 17.1. After that, we will be heading to section 17.2.