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Chapter 12 Geologic Time Chapter Test
Multiple Choice
Write the letter that best answers the question or completes the statement on
the line provided.
1. Rocks record geological events and
a. life forms of the present.
b. life forms of the past.
c. astronomical milestones of the past.
d. Earth’s circumference and diameter in the past.
2. The geologic processes that shape Earth’s features today
a. are much different from those of thousands of years ago.
b. did not operate in the distant past.
c. are basically the same today as they were in the
geologic past.
d. became important only several hundred years ago.
3. For what purpose do geologists use relative dating?
a. to determine which rock layer in a canyon wall
formed first
b. to find the age of a rock layer
c. to determine how a rock’s composition has changed
over time
d. to identify past life forms that once lived in a rock layer
4. In general, the law of superposition states that in an
undeformed sequence of sedimentary rocks, each layer is
a. about the same age.
b. older than the one below it.
c. older than the one above it.
d. thicker than the one above it.
5. According to the principle of cross-cutting relationships, an
intrusive rock body is
a. deposited as sedimentary layers.
b. younger than the rocks it intrudes into.
c. always made of the same materials as rock around it.
d. older than the rocks it intrudes into.
6. Which type of geologic event has to occur to create an
angular unconformity?
a. uninterrupted deposition of sediment
b. igneous intrusion into layered rock
c. sediment deposited on older, eroded igneous rock
d. folding or tilting of rock layers
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7. The laws of superposition and original horizontality are
best applied to
a. all rock types.
b. igneous rocks.
c. sedimentary rocks.
d. metamorphic rocks
8. What are fossils?
a. the oldest layers of rock in a region
b. the remains or traces of an organism preserved from the
geologic past
c. living creatures with habitats in or around rock
d. objects that people of long ago left behind as artifacts
9. Which of the following environments would NOT
contain fossils?
a. sediment deposited in a riverbed
b. intrusive rock formed from cooled magma
c. a thick deposit of dried mud
d. layers of sand that accumulated over thousands of years
10. Which of the following is important if an organism is to
become a fossil?
a. soft parts and slow burial
b. rapid burial and hard parts
c. rapid burial and soft parts
d. hard parts and slow burial
11. Index fossils allow geologists to
a. match rocks of the same age in different regions.
b. determine the exact age of rocks.
c. identify organisms that did not leave fossil
evidence behind.
d. determine why some organisms became extinct
12. The principle of fossil succession states that different types
of fossil organisms
a. generally leave behind hard parts.
b. occur most often in sedimentary rock.
c. succeed one another in a definite order.
d. are older in the deepest layers of rock.
13. Radioactivity is produced when unstable nuclei
a. bond.
b. break apart.
c. become cooler.
d. expand.
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14. If the half-life of an unstable isotope is 10,000 years and only
1/8 of the radioactive parent remains, how old is the sample?
a. 10,000 years old
b. 20,000 years old
c. 30,000 years old
d. 40,000 years old
15. Radiocarbon dating is used to date
a. geologic events up to 75,000 years ago.
b. geologic events up to 10,000 years ago.
c. geologic events more than 1 million years ago.
d. all geologic events of the past.
16. Which two substances are involved in carbon-14 dating?
a. carbon-12 and carbon-10
b. carbon-14 and uranium-238
c. lead-206 and carbon-14
d. carbon-14 and carbon-12
17. Why is radiometric dating on sedimentary rocks usually
unsuccessful?
a. Sedimentary rocks are too young.
b. Sedimentary rocks form from many older rock particles.
c. Sedimentary rocks never have particles that contain
radioactive isotopes.
d. Sedimentary rocks form too quickly to be accurately dated.
18. When did the Phanerozoic eon begin?
a. about 2.0 million years ago
b. about 540 million years ago
c. about 10.1 million years ago
d. about 20.5 billion years ago
19. The largest expanse of time on the geologic time scale is the
a. eon.
b. epoch.
c. era.
d. period.
20. About 88 percent of Earth’s history is within the time period
before the Phanerozoic eon, called the
a. Cambrian.
b. Paleozoic.
c. Cenozoic.
d. Precambrian.
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Completion
Complete each statement on the line provided.
1. Geologist John Wesley Powell was impressed with the record
of Earth’s history in the exposed rock walls of the
.
2. The principle of states that physical,
biological, and chemical processes we observe today have also
operated in the geologic past.
3. Relative dating tells geologists the in which
events occurred.
4. The principle of original horizontality states that layers of sediment
are usually deposited in a(n) position.
5. Pieces of one rock unit that are contained within another are
.
Use Figure 1 to answer the following three questions.
6. Interpreting Graphics The type of
unconformity shown in Diagram A
is a(n) .
7. The type of unconformity shown in
Diagram B is a(n) .
8. The type of unconformity shown in
Diagram C is a(n) .
9. The process in which rock layers in different
regions are matched is .
10. Fossils rarely preserve unburied
parts of animals
because scavengers often eat them and
bacteria decompose them.
11. A half-life is the amount of time needed for
one half of the in a
sample to decay to form its stable isotope.
12. Radiometric dating allows geologists to
determine the of some
rocks and minerals.
13. It is hard to use radiometric dating to tell the age of
rocks because the age of the minerals in
them may not represent when the rocks actually formed.
14. The three within the Phanerozoic eon are the
(ancient life),
(middle life), and the (recent life).
15. Great worldwide changes in geology or forms of
on Earth mark the boundaries of eras.
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Short Answer
In complete sentences, write the answers to the questions on the lines provided.
1. Briefly describe each of Steno’s principles.
2. What is an unconformity?
Use Figure 2 to answer the following two questions.
3. Interpreting Graphics Which
is older—the sandstone layer or
Dike A? Explain your answer.
4. Applying Concepts Did Fault Aoccur before or after the deposition
of the layer of conglomerate? Explain your answer.
5. Describe the formation of two types of fossils.
6. Drawing Conclusions Ageologist finds the fossils of tropical sea
organisms in rock that is now in a temperate desert. What does this
tell the geologist about the way the area has changed over
thousands or millions of years?
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7. How does radiometric dating work?
8. Applying Concepts Can scientists use radiocarbon dating to find
the age of a very tall, living redwood tree? Explain your answer.
9. Describe the divisions of the geologic time scale, using the terms
eon, era, epoch, and period.
10. Why is Precambrian time divided into fewer time units than other
divisions on the geologic time scale?
Essay
In complete sentences, write the answers to the questions on the lines provided.
1. Earth as a System A given tree changes over many thousands of
years into a petrified log. Describe the transition of this tree from
being a part of the biosphere to being a part of the geosphere.
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