Geog 106LRS - Prof. Fischer
Chapter 8
Checkpoint 8.1 Place the following events
that were described in the earlier chapters of the
book in the correct relative chronological order,
number them 1-5 from earliest to most recent.
__A tsunami struck Japan.
__An ice sheet was present in India.
__An asteroid collided with Yucatan Peninsula.
__Mount Pinatubo erupted in the Philippines.
__Wegener developed the continental drift hypothesis.
Checkpoint 8.2 Examine the image of rock
layers in your text, and answer Questions 1 and
2 about relative time.
1. Which statement is most accurate?
a) D is older than B
b) E is older than A
c) F is older than C
2. When did the tilting of the layers occur?
a) After A was deposited
b) Between deposition of layers E and A
c) Before B was deposited
d) Between deposition of layers C and E
Examine the following image of layers in your
text and answer Questions 3 and 4 about relative
time.
3. Which sequence of letters best represents the
order in which the layers were formed (from
oldest to youngest)?
a) C, D, B, A
b) C, B, D, A
c) B, C, D, A
d) A, B, D, C
4. An unconformity is present between layers
a) C and D.
b) B and D.
c) C and B.
d) A and B.
Checkpoint 8.3 Use the principles of original
horizontality, superposition, cross-cutting
relationships, and inclusions to determine the
order of events for the idealized location shown
in the diagram in your text.
a) Place the rock units in their order of
formation, from oldest to youngest.
Youngest 1. _____ 2. _____ 3. _____ 4. _____
5. _____ 6. _____ 7. _____ 8. _____ 9. _____
10. _____ Oldest
b) Examine the rock types identified by the
symbols in the diagram, and determine which
rock units best match the following descriptions.
Letter Characteristic
Name ________________________
_____ Interbedded layers of rocks that indicate
alternating shallow marine environments
and coastal swamps in tropical
conditions
_____ Coarse-grained clastic sedimentary rocks
overlying an erosional surface
(unconformity surface)
_____ Granite
_____ A rock containing a foliation
_____ The most recently deposited sedimentary
rock
_____ Sedimentary bed that has undergone
contact metamorphism on its uppermost
surface
_____ Basalt
Checkpoint 8.6 Examine the diagram in your
book. Which fossil would be the best choice to
use as an index fossil for these rocks?
a) Fossil 1
b) Fossil 2
c) Fossil 3
Which fossil is least characteristic of a specific
set of geologic conditions?
a) Fossil 1
b) Fossil 2
c) Fossil 3
Checkpoint 8.9 Read the article and then
answer the questions at the end concerning the
difference among observations, hypotheses, and
predictions.
1. What were the key observations in this
article?
a) Trackways of footprints are present in
Cambrian age rocks.
b) Trackways are common in sandstone that
represented a beach environment.
c) Euthycarcinoids had eight legs and segmented
bodies.
d) Fossil remains of insectlike arthropods were
found in the rocks.
2. What hypothesis was developed from the
observations?
a) Rocks dated as Silurian in age were really
Cambrian.
b) Euthycarcinoids are associated with
sandstone quarries.
c) Organisms may have colonized the land much
earlier than previously thought.
d) Life evolved earlier in Canada than
elsewhere.
3. What prediction did scientists intend to test in
an attempt to support the hypothesis?
a) Fossils of insectlike arthropods were found in
the rocks.
b) Rocks previously identified as Silurian can be
dated to discover if they are actually Cambrian
in age.
c) Trackways of footprints may be found in
similar Cambrian-age rocks in New York.
Checkpoint 8.10 Carefully examine the
diagram in your text.
Which letter corresponds most closely to the
first appearance in the rock record of abundant
fossils? ____
Which letter corresponds most closely to the
extinction of the dinosaurs? ____
Checkpoint 8.13 Between 1860 and 1920,
geologists attempted to estimate Earth’s age by
how long it would take for the thickest
sequences of sedimentary rocks to form.
Geologists examined sequences of rocks for
each geologic period. From the estimated rates
for the formation of these units, different
scientists estimated ages for Earth ranging from
3 million years to 15 billion years. Explain why
these estimates varied over such a wide range.
Checkpoint 8.11 Read the article and answer
these questions.
a) What was the question being investigated by
the scientists?
b) What observations did the scientists make
during their investigations?
Checkpoint 8.14 Radioactive isotopes in
clastic sedimentary rocks always predict an age
that is
a) older than the sedimentary rock.
b) younger than the sedimentary rock.
c) correct for the sedimentary rock.
The isotope of element X has 15 protons, 17
neutrons, and 15 electrons. The element has an
atomic number of _____ and a mass number of
_____.
a) 15; 32 b) 17; 15 c) 17; 47 d) 15; 30
If radioactive decay began with 400,000 parent
isotopes, how many would be left after three
half-lives?
a) 200,000 b) 100,000 c) 50,000 d) 25,000
c) What was the principal conclusion of their
research?
Checkpoint 8.15 The half-life of a radioactive
isotope is 500 million years. Scientists testing a
rock sample discover that the sample contains
three times as many daughter atoms as parent
isotopes. What is the age of the rock?
a) 500 million years
b) 1,500 million years
c) 1,000 million years
d) 2,500 million years
Checkpoint 8.16 The diagram represents
three rock exposures containing fossils. Place
the fossils in the correct order according to their
relative ages, from oldest to youngest.
Oldest ____, ____, ____, ____, ____, ____,
____, ____, ____, ____ Youngest
Explain how you would estimate the potential age
ranges of the C, G, and K fossils on the basis of the ages
determined for the three volcanic ash layers.
4. Period required to form the Atlantic Ocean
5. Formation and decay of a tornado
6. Earth’s orbit around the sun
7. Length of orbit for a long-period comet
8. Time between mass extinctions
9. Time required to carve the Grand Canyon
10. Growth of major U.S. cities
11. Formation and decay of a hurricane
Checkpoint 8.19
We have just provided some examples of rare,
high-magnitude events and common, lowmagnitude events. Review the previous
chapters, and identify other examples of highand low-magnitude events.
Checkpoint 8.17 Identify three examples of
everyday objects that change over time but at
different rates. For example, something that is
used up or worn out in a matter of days (e.g.,
chalk), or months (e.g., jeans), or years.
Checkpoint 8.18
Write the number for each of the following
events in the appropriate location on the
timeline provided here, according to either its
frequency (how often?) or the length of time
over which it occurs (how long?). (Use arrows
to indicate where on the timeline a number
belongs if you don’t have sufficient room to
write.)
1. The time between large eruptions of the same
volcano
2. A season (e.g., spring)
3. Time between great earthquakes on the San
Andreas fault
Geog 106LRS - Prof. Fischer
Name ________________________
Checkpoint 8.20
We have presented an Earth history stretching back 4.6 billion years. Has the history of life on Earth been
more affected by rare, high-magnitude events or frequent, low-magnitude processes? Justify your choice.
Geologic Time Concept Map, p. 241
Complete the following concept map to evaluate your understanding of the interactions between the Earth
system and geologic time. Label as many interactions as you can, using information from this chapter.
A
B
C
D
E
F
G
H
I
J
K
L
M
N