Brief-Constructed Response
Relative Dating
Relative Dating
Teacher Guide
Students will need about 45 minutes to complete these constructed response tasks.
Objectives assessed:
 State the underlying assumptions that scientists use to explain Earth’s history.
1. Compare and contrast catastrophism and uniformitarianism. Be sure to correctly define
each term and explain how these views may be integrated.
Correct response(s):
Sample Correct Response: The principle of catastrophism states that Earth has been
shaped by sudden, violent events such as floods or volcanic eruptions. The principle
of uniformitarianism states that processes that occurred in the past operate in the
same way as they do in the present—many changes occur gradually over millions of
years. An integrated view might hold that although Earth changes gradually over
millions of years, it is also sometimes reshaped by sudden, violent events.
Response scoring tool:
Score
Content
3
Correctly defines catastrophism and uniformitarianism and explains how
both views may reasonably be integrated.
2
Correctly defines catastrophism and uniformitarianism but does not
explain how both views may reasonably be integrated.
1
Correctly defines either catastrophism or uniformitarianism but not both.
Does not explain how both views may reasonably be integrated.
0
No response, or response not appropriate to the question.
Objectives assessed:
 Identify relative dating techniques and explain how scientists use them.
2. The following diagram shows a simple rock sequence:
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Relative Dating
Identify the relative dating principle that supports each of the following conclusions.
Explain your answers.
 Layer C is older than layer B.
 Intrusion D is younger than layers A, B, and C.
 The bits of rock embedded in layer A are older than layer A.
 The sections of layer B on either side of fault E were once completely connected.
 Fault E is younger than intrusion D.
Correct response(s):
Sample Correct Response: The principle of superposition, which states that
sedimentary rock formations are deposited such that the oldest layer is on the bottom
and the youngest layer is on top, supports the conclusion that layer C is older than
layer B. The principle of cross-cutting relationships, which states that any geologic
feature that cuts partially through or completely across another geologic feature is
the younger of the two features, supports the conclusion that intrusion D is younger
than layers A, B, and C. The principle of inclusions, which states that any rock that is
enveloped by another rock must be older than the surrounding rock, supports the
conclusion that the bits of rock embedded in layer A are older than layer A. The
principle of lateral continuity, which states that rock formations that have been
subdivided since their formation can be assumed to have originally been laterally
continuous, supports the conclusion that the several sections of layer B were once
completely connected. The principle of cross-cutting relationships, which states that
any geologic feature that cuts partially through or completely across another geologic
feature is the younger of the two features, supports the conclusion that fault E is
younger than intrusion D.
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Relative Dating
Response scoring tool:
Score
Content
5
Correctly identifies each of the relative dating principles (in order:
superposition, cross-cutting relationships, inclusions, lateral continuity,
and cross-cutting relationships), and explains how each principle
supports its conclusion.
4
Correctly identifies four of the five relative dating principles, and explains
how each correctly identified principle supports its conclusion.
3
Correctly identifies three of the five relative dating principles, and
explains how each correctly identified principle supports its conclusion.
2
Correctly identifies two of the five relative dating principles, and explains
how each correctly identified principle supports its conclusion.
1
Correctly identifies one of the five relative dating principles, and explains
how that principle supports its conclusion.
0
No response, or response not appropriate to the question.
Objectives assessed:
 Explain how scientists describe gaps in the rock record.
3. Gaps in the rock record are called unconformities.
 Identify and define the three main types of unconformity.
 Explain how unconformities form.
Correct response(s):
Sample Correct Response: The three main types of unconformity are angular
unconformities, disconformities, and nonconformities. An angular unconformity is an
erosion surface in which the sedimentary rock layers below the surface form an angle
with the sedimentary rock layers above the surface. A disconformity is an
unconformity between parallel layers of sedimentary rock. A nonconformity is an
unconformity between sedimentary rock and metamorphic or igneous rock.
Unconformities form when weathering and erosion wear away rock material in a rock
layer. Over time, new material is deposited on the old, eroded surface, creating a gap
in the rock sequence.
Score
5
4
Content
Meets all of the following criteria:
 Correctly defines angular unconformity.
 Correctly defines disconformity.
 Correctly defines nonconformity.
 Identifies the two main steps in the formation of unconformities: 1)
weathering and erosion create an erosion surface; 2) new material
is deposited on the erosion surface.
Meets four of the criteria listed above.
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Relative Dating
3
Meets three of the criteria listed above.
2
Meets two of the criteria listed above.
1
Meets one of the criteria listed above.
0
No response, or response not appropriate to the question.
Objectives assessed:
 Identify relative dating techniques and explain how scientists use them.
4. Describe each of the following geologic laws and explain their limitations in determining
the age of rocks.
 original horizontality
 superposition
 lateral continuity
 cross cutting relationships
 unconformities
 fossil succession and biozones
Correct response(s):
Sample Correct Response: The law of original horizontality states that sediments
were deposited in horizontal layers; therefore, any folding or tilting of the rock
beds must have occurred after the rock was formed. Superposition explains that
the rocks on the top of a geologic column are the youngest, while the rocks on the
bottom of a geologic column are the oldest. Lateral continuity explains that layers
in the rock can be considered continuous, even if they are carved out by rivers or
disrupted by other geologic events. These three laws have limitations in helping
scientists determine the age of the rock beds. First of all, these three laws can only
be applied to sedimentary rock beds. In addition, these methods can only tell the
relative age of the rock, or which rock bed is older and which is younger. These
laws cannot tell scientists exactly when the rocks formed.
The law of cross-cutting relations states that an igneous intrusion or a fault that
cuts across a layer of rock is younger than the rock it cuts across. The limitation is
that this law cannot tell scientists exactly when faulting or intrusion event
occurred; it can only tell scientists when it happened in relation to the formation of
the youngest of the rock beds.
Unconformities are gaps in the rock record usually caused by erosion. They limit
scientists in determining the age of rock beds because it is hard to tell exactly how
much “time” has been washed away from the rock record.
Finally, fossil succession and biozones tell scientists that the animals and plant life
has changed over time. Scientists are able to determine that two rock layers are of
similar age, even if they are separated by great distance, if the rock layers contain
the same fossils. However, scientists are limited in discovering the exact age of the
rock based on the fossils alone.
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Relative Dating
Score
5
4
3
2
1
0
Content
Meets all of the following criteria:
 Correctly explains the law of original horizontality,
superposition, lateral continuity, cross cutting relationships,
unconformities, fossil succession and biozones.
 Identifies the limitations of each of the geologic laws listed
above.
Explains at least four of the laws listed above and provides limitations of
each of these laws in determining the age of the rock beds.
Explains at least three of the laws listed above and provides limitations
of each of these laws in determining the age of the rock beds.
Explains at least two of the laws listed above and provides limitations of
each of these laws in determining the age of the rock beds.
Explains at least one of the laws listed above and provides limitations of
each of these laws in determining the age of the rock beds.
No response, or response not appropriate to the question.
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