459
G I V E I T S O M E T H O U G H T
Refer to Figure 18.5 and answer the following questions. Briefly
explain each answer.
a. Is fault A older or younger than the sandstone layer?
b. Is dike A older or younger than the sandstone layer?
c. Was the conglomerate deposited before or after fault A?
d. Was the conglomerate deposited before or after fault B?
e. Which fault is older, A or B?
f. Is dike A older or younger than the batholith?
A mass of granite is in contact with a layer of sandstone. Using a
principle described in this chapter, explain how you might determine whether the sandstone was deposited on top of the granite,
or whether the magma that formed the granite was intruded after
the sandstone was deposited.
Refer to Figure 18.9 and consider the angular unconformity at
Scotland’s Siccar Point for the following exercises.
a. Describe in general what occurred to produce this feature.
b. Suggest ways in which all four spheres of the Earth system could
have been involved.
c. The Earth system is powered by energy from two sources.
How are both sources represented in the Siccar Point
unconformity?
If a radioactive isotope of thorium (atomic number 90, mass number
232) emits 6 alpha particles and 4 beta particles during the course
of radioactive decay, what is the atomic number and mass number
of the stable daughter product?
A hypothetical radioactive isotope has a half-life of 10,000 years.
If the ratio of radioactive parent to stable daughter product is 1:3,
how old is the rock containing the radioactive material?
5
4
3
2
1
Key Terms
Archean (p. 455)
angular unconformity (p. 442)
Cenozoic (p. 455)
conformable (p. 442)
correlation (p. 444)
cross-cutting relationships,
principle of (p. 441)
disconformities (p. 443)
eons (p. 455)
epochs (p. 455)
eras (p. 455)
fossils (p. 446)
fossil succession,
principle of (p. 448)
geologic time scale (p. 455)
hadean (p. 455)
half-life (p. 451)
inclusions (p. 441)
index fossils (p. 448)
Mesozoic (p. 455)
nonconformity (p. 443)
numerical date (p. 439)
original horizontality,
principle of (p. 440)
paleontology (p. 446)
Paleozoic (p. 455)
periods (p. 455)
Phanerozoic (p. 455)
Precambrian (p. 455)
Proterozoic (p. 455)
radioactivity (p. 450)
radiocarbon dating (p. 452)
radiometric dating (p. 450)
relative dating (p. 440)
superposition, law of (p. 440)
unconformity (p. 442)
Solve the problems below that relate to the magnitude of Earth
history. To make calculations easier, round Earth’s age to
5 billion years.
a. What percentage of geologic time is represented by
recorded history? (Assume 5000 years for the length
of recorded history)
b. Humanlike ancestors (hominids) have been around for roughly
5 million years. What percentage of geologic time is represented
by the existence of these ancestors?
c. The first abundant fossil evidence does not appear until the
beginning of the Cambrian period, about 540 million years ago.
What percentage of geologic time is represented by abundant
fossil evidence?
The accompanying diagram is a cross-section of a hypothetical area.
Place the lettered features in the proper sequence, from oldest to
youngest. Where in the sequence of events can you identify an
unconformity?
7
6
Companion Website
www.mygeoscienceplace.com
The Essentials of Geology, 11e companion Website contains numerous multimedia resources accompanied by assessments
to aid in your study of the topics in this chapter. The use of this site's learning tools will help improve your understanding
of geology. Utilizing the access code that accompanies this text, visit www.mygeoscienceplace.com in order to:
• Review key chapter concepts.
• Read with links to the Pearson eText and to chapter-specific web resources.
• Visualize and comprehend challenging topics using the learning activities in GEODe: Essentials of Geology and the
Geoscience Animations Library.
• Test yourself with online quizzes.
G I V E I T S O M E T H O U G H T
Refer to Figure 18.5 and answer the following questions. Briefly
explain each answer.
a. Is fault A older or younger than the sandstone layer?
b. Is dike A older or younger than the sandstone layer?
c. Was the conglomerate deposited before or after fault A?
d. Was the conglomerate deposited before or after fault B?
e. Which fault is older, A or B?
f. Is dike A older or younger than the batholith?
A mass of granite is in contact with a layer of sandstone. Using a
principle described in this chapter, explain how you might determine whether the sandstone was deposited on top of the granite,
or whether the magma that formed the granite was intruded after
the sandstone was deposited.
Refer to Figure 18.9 and consider the angular unconformity at
Scotland’s Siccar Point for the following exercises.
a. Describe in general what occurred to produce this feature.
b. Suggest ways in which all four spheres of the Earth system could
have been involved.
c. The Earth system is powered by energy from two sources.
How are both sources represented in the Siccar Point
unconformity?
If a radioactive isotope of thorium (atomic number 90, mass number
232) emits 6 alpha particles and 4 beta particles during the course
of radioactive decay, what is the atomic number and mass number
of the stable daughter product?
A hypothetical radioactive isotope has a half-life of 10,000 years.
If the ratio of radioactive parent to stable daughter product is 1:3,
how old is the rock containing the radioactive material?
5
4
3
2
1
Key Terms
Archean (p. 455)
angular unconformity (p. 442)
Cenozoic (p. 455)
conformable (p. 442)
correlation (p. 444)
cross-cutting relationships,
principle of (p. 441)
disconformities (p. 443)
eons (p. 455)
epochs (p. 455)
eras (p. 455)
fossils (p. 446)
fossil succession,
principle of (p. 448)
geologic time scale (p. 455)
hadean (p. 455)
half-life (p. 451)
inclusions (p. 441)
index fossils (p. 448)
Mesozoic (p. 455)
nonconformity (p. 443)
numerical date (p. 439)
original horizontality,
principle of (p. 440)
paleontology (p. 446)
Paleozoic (p. 455)
periods (p. 455)
Phanerozoic (p. 455)
Precambrian (p. 455)
Proterozoic (p. 455)
radioactivity (p. 450)
radiocarbon dating (p. 452)
radiometric dating (p. 450)
relative dating (p. 440)
superposition, law of (p. 440)
unconformity (p. 442)
Solve the problems below that relate to the magnitude of Earth
history. To make calculations easier, round Earth’s age to
5 billion years.
a. What percentage of geologic time is represented by
recorded history? (Assume 5000 years for the length
of recorded history)
b. Humanlike ancestors (hominids) have been around for roughly
5 million years. What percentage of geologic time is represented
by the existence of these ancestors?
c. The first abundant fossil evidence does not appear until the
beginning of the Cambrian period, about 540 million years ago.
What percentage of geologic time is represented by abundant
fossil evidence?
The accompanying diagram is a cross-section of a hypothetical area.
Place the lettered features in the proper sequence, from oldest to
youngest. Where in the sequence of events can you identify an
unconformity?
7
6
Companion Website
www.mygeoscienceplace.com
The Essentials of Geology, 11e companion Website contains numerous multimedia resources accompanied by assessments
to aid in your study of the topics in this chapter. The use of this site's learning tools will help improve your understanding
of geology. Utilizing the access code that accompanies this text, visit www.mygeoscienceplace.com in order to:
• Review key chapter concepts.
• Read with links to the Pearson eText and to chapter-specific web resources.
• Visualize and comprehend challenging topics using the learning activities in GEODe: Essentials of Geology and the
Geoscience Animations Library.
• Test yourself with online quizzes.