Geology 110: Earth and Space Science
Chapter 8 (Geologic Time) Homework
SELF-REFLECTION AND COMPREHENSION SURVEYS
Checkpoint 8.1, p. 216
#1: Place the following events that were described in the earlier chapters of the book in
the correct relative chronological order, from earliest to the most recent.
a. Tsunami struck Japan.
b. Ice sheet was present in India.
c. Asteroid collided with Yucatan Peninsula.
d. Mount Pinatubo erupted in the Philippines.
e. Wegener developed the continental drift hypothesis
Correct order is:
Checkpoint 8.2, p. 219
#2: Examine the following image of rock layers and answer Questions 1 and 2 about
relative time.
I. Which statement is most accurate?
a. D is older than B
b. E is older than A
c. F is older than C
II. 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
Checkpoint 8.3, p. 221
#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
following diagram.
a) Place the rock units in their order of formation, oldest to youngest.
Youngest
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Oldest
Checkpoint 8.5, p. 225
#4: Geologists look for similar rock types or fossils to tell them that geologic
environments were similar between two widely spaced locations. Can we do the same
kind of thing? What are some examples of modern (today) environments that have
characteristic assemblages of organisms?
Checkpoint 8.6, p. 225
#5: Outcrops of rock are examined in four different locations in a state. The rock types
and the fossils they contain are illustrated in the following diagram.
a. 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
b. Which fossil is least characteristic of a specific set of geological conditions?
a) Fossil 1 b) Fossil 2
c) Fossil 3
Checkpoint 8.7, p. 226
#6: Examine the following illustration and predict which rock unit in the Grand Canyon
is most likely to have formed in a depositional environment like the one pictured.
Checkpoint 8.14 and 15, p. 235
#7: a. 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 isotopes as parent
isotopes. What is the age of the rock?
a. 500 million years
c. 1,500 million years
b. 1,000 million years
d. 2,500 million years
#7:b. 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
Checkpoint 8.18, p. 239: Rates Timeline
#8: Events happen on Earth over periods of time that vary from seconds to millions of
years. Place 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?).
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
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
YOU CAN USE THE CHART BELOW TO ANSWER THE QUESTION ABOVE:
TIME
NUMBERED ANSWER(S)
ONE SECOND
to
ONE MINUTE
to
ONE DAY
to
ONE YEAR
to
ONE HUNDRED YEARS
to
ONE THOUSAND YEARS
to
ONE MILLION YEARS
to
ONE HUNDRED MILLION YEARS
to
ONE THOUSAND MILLION YEARS
(OR ONE BILLION YEARS)
Checkpoint 8.16, p. 236 (Optional extra credit)
#9: The following diagram represents three rock exposures containing fossils. Each
exposure contains a layer of volcanic ash (in red) that has been dated by the analysis of
238 206
U/ Pb isotopes.
a) Place the fossils in the correct order according to their relative ages, from oldest to
youngest:
b) Explain how you would estimate the potential age ranges of the C, G, and K fossils
based on the ages determined for the three volcanic ash layers.
(Question adapted from J. Dodick and N. Orion, “Measuring student understanding of
geological time,” Science Education, 2003, vol. 87, pp. 708-731.)
Checkpoint 8.11, p. 231: Ancient Leaves and Insect Extinctions
#10. When a 6-mile-wide asteroid slammed the Earth 65 million years ago, it wiped out
the dinosaurs, about 80 percent of the world’s plant species, and all animals bigger than
a cat. But what happened to the bugs?
It’s been tough for scientists to determine how the insects fared because they rarely leave
behind fossils, but a Denver paleontologist and his Smithsonian Institution colleagues
found a way around the problem. By studying insect damage etched into thousands of
fossil leaves, they determined that many plant-eating bugs perished in the big impact.
“These little insects are leaving their calling cards on the fossil leaves, and we have an
excellent fossil record of leaves,” said Kirk Johnson, curator of paleontology at the
Denver Museum of Nature & Science. “So by looking at the insect damage on the leaves
before and after the dinosaur extinctions, we can make a pretty good educated guess of
what happened to the insects.”
Johnson and his collaborators estimate that 55% to 60% of plant-eating insects were
exterminated. Over the past 20 years, Johnson has collected 13,441 plant fossils from
quarries in southwestern North Dakota. When the asteroid hit Mexico’s Yucatan
Peninsula, it threw up clouds of dust that traveled around the globe. Johnson pulled the
fossils from rock layers directly above and below those sediments. At the time,
southwestern North Dakota was a warm, forested plain with lots of broad-leafed trees.
Some leaves, now stored at the Denver museum and at Yale University, are up to a foot
long. Individual leaf veins are visible, as are the diagnostic chomp marks, tunnels, and
holes left by prehistoric beetles, grasshoppers, butterflies, and moths. Some insects are
specialists, rely on a single species of plant for sustenance; others are generalists that
feed on several plant types. By analyzing insect-damaged leaves before and after the
impact, the researchers determined that the generalists survived, while 70% of the
specialists did not.
Source: Rocky Mountain News (Denver, CO), February 22, 2002, Page 7A: Jim
Erickson.
Read the following abbreviated version of a newspaper article (above) and answer these
questions. Please designate sections of your answer as A., B. and C., so I know which
question you are answering:
a. What was the question being investigated by the scientists?
b. What observations did the scientists make during their investigations?
c.
What was the principal conclusion of their research?