Multiple Choice
Identify the
letter of the choice that best completes the statement or answers the question.
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1.
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On
the geologic time scale, the smallest unit of time is called a(n) ____. a. | era | c. | period | b. | eon | d. | epoch | | | | |
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2.
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When
part of the rock record is destroyed, the erosional gap that forms is a(n) ____. a. | inclusion | c. | unconformity | b. | key bed | d. | superposition | | | | |
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3.
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Which
of the following is used to determine the absolute age of a rock? a. | relative-age
dating | c. | permineralization | b. | correlation | d. | radiometric dating | | | | |
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4.
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Index
fossils are useful to geologists if the fossils ____. a. | have lived over
a short period of time | b. | are not easily recognized | c. | are not widely
distributed geographically | d. | are scarce | | |
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5.
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What
are fossil insects preserved in hardened tree sap called? a. | trace
fossils | c. | coprolites | b. | gastroliths | d. | amber | | | | |
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6.
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Molds, casts, coprolites, and petrified wood are all example of ____. a. | fossils | c. | unconformities | b. | radioactive isotopes | d. | disconformities | | | | |
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7.
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The
Phanerozoic Eon includes the Paleozoic, Mesozoic, and ____. a. | Cenozoic
Periods | c. | Tertiary
Epochs | b. | Jurassic Periods | d. | Cenozoic Eras | | | | |
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8.
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The
Archean and Proterozoic are examples of ____. a. | eons | c. | epochs | b. | periods | d. | eras | | | | |
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9.
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Which
of the following lists the units of geologic time in order from shortest to longest? a. | era, eon,
period, epoch | c. | eon, era,
period, epoch | b. | epoch, eon, period, era | d. | epoch, period, era, eon | | | | |
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10.
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An
example of a trace fossil includes a ____. a. | cast of a clam | c. | mud crack | b. | worm
trail | d. | raindrop
impression | | | | |
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Short Answer
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11.
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Much
of northern New Jersey was covered with glaciers during the last ice age. While digging in this
region, a geologists discovers bands of light- and dark-colored clays just below the surface. What
are these sediments and how is the geologist most likely to determine their age?
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12.
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Identify the type of unconformity shown in the diagram below and describe how it
formed.
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13.
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Identify the two types of unconformities in the diagram below and describe how they
formed.
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14.
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Contrast relative-age dating and absolute-age dating.
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15.
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Describe how geologists use index fossils. List the characteristics that make an index
fossil.
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Radiometric dating has proved invaluable to scientists in the attempt to determine how
long ago Earth formed. A granite intrusion found in South Africa that contains inclusions of the
metamorphic rock quartzite is believed to be one of the oldest rocks on Earth. Using radiometric
dating, scientists determined the age of the rock to be approximately 3.2 billion
years.
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16.
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From
this data, what conclusion can you draw about the age of Earth? Explain your answer.
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17.
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Use
the data above to state a hypothesis about the age of Earth. Describe how you would go about testing
your hypothesis.
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In a
laboratory, you produce a quantity of the radioactive isotope thorium-234. Over the course of several
weeks, the unstable isotope decays, and you measure the amount of thorium-234 remaining in the
sample. You obtain the following data.
Days Elapsed | Grams of Thorium-234 Remaining | 0 | 16 | 12 | 11 | 24 | 8 | 36 | 6 | | |
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18.
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Use
the data to determine the half-life of thorium-234. Explain your answer.
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19.
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Use
the data to complete the graph below.
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20.
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How
long will it take for 15 grams of the original thorium-234 to decay?
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Problem
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The
table lists commonly used radioactive isotopes and their half-lives. Study the table and answer the
following questions.
Half-Lives of
Selected Radioactive Isotopes | Radioactive Isotope | Approximate
Half-Life | Decay
Product | Rubidium-87 | 48.6 billion
years | Strontium-87 | Thorium-232 | 14.0 billion years | Lead-208 | Potassium-40 | 8.4 billion
years | Argon-40 | Uranium-238 | 4.5 billion years | Lead-206 | Uranium-235 | 0.7 billion
years | Lead-207 | Carbon-14 | 5730 years | Nitrogen-14 | | | |
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21.
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Which
isotope has the longest half-life?
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22.
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Which
stable element does Uranium-238 decay into?
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23.
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Which
isotope would be most helpful in dating bones thought to be about 6000 years old?
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24.
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After
28 billion years, what percentage of an original sample of Thorium-232 will remain
undecayed?
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