Preview Extract
Chapter 23 Geologic Time–Reading the Rock Record
23.1 The Rock Record–Relative Dating
1) When comparing geologic time to a calendar year, the time of the dinosaurs is in the
A) middle of October.
B) first half of December.
C) second half of December.
D) first half of February.
Answer: C
2) Deposition of sediment with each new layer younger than the layer below illustrates the
principle of
A) original horizontality.
B) superposition.
C) nonconformity.
D) horizontality and nonconformity.
Answer: B
3) In a thick bed of sedimentary rocks we find an igneous dike. The order of formation is
A) together.
B) igneous before sedimentary.
C) sedimentary before igneous.
D) unknown.
Answer: C
4) In a sequence of rock layers we find trilobite and dinosaur fossils. The dinosaur fossils are at
the bottom of the rock sequence and the trilobites are at the top. This sequence tells us that
A) dinosaurs are older than trilobites.
B) the beds are overturned.
C) trilobites survived the age of the dinosaurs.
D) the beds are folded.
Answer: B
5) In a sequence of rock layers we find trilobite fossils at the bottom of the rock sequence and
dinosaur fossils directly above the trilobite fossils. We conclude that
A) trilobites survived up to the time of the dinosaurs.
B) the beds are overturned.
C) the processes of erosion created a gap between the age of trilobites and the age of dinosaurs.
D) dinosaurs fed on trilobites.
Answer: C
6) Fossils are found in
A) sedimentary rocks.
B) metamorphic rock.
C) igneous rocks.
D) sedimentary and some metamorphic rocks.
Answer: D
7) In a sequence of rock layers we find trilobite fossils at the bottom of rock layer 1 and dinosaur
fossils directly above the fossil trilobites in layer 2. There are inclusions of trilobites in layer 2.
We conclude that
A) dinosaurs were extinct long before trilobites came into existence.
B) dinosaurs are from the Cambrian Period.
C) by inclusion and faunal succession, layer 1 is older than layer 2.
D) there is no time gap between the rocks.
Answer: C
8) The principle of superposition states that the top layer of rock is
A) igneous.
B) the youngest.
C) sedimentary.
D) the oldest.
Answer: B
9) An assumption that Earth processes occurring today have always occurred is called
A) the principle of superposition.
B) uniformitarianism.
C) the principle of original horizontality.
D) theory of unconformity.
Answer: B
10) A surface of erosion between rocks that represents a gap in Earth history is
A) called a dike.
B) an unconformity.
C) a faunal conformity.
D) none of the above
Answer: B
11) The theory that different forms of animals throughout Earth's past occurred in a definite
order is called the principle of
A) fossil assemblage.
B) faunal succession.
C) conformable fossils.
D) fossil determination.
Answer: B
12) An eroded surface of metamorphic rocks on which a horizontal bed rests is called a
A) strata.
B) dike.
C) nonuniform surface.
D) nonconformity.
Answer: D
13) An unconformity can be interpreted as
A) an occurrence of radioactive decay.
B) repeated intrusions of igneous rock.
C) a buried surface of erosion.
D) the result of repeated volcanic action.
Answer: C
14) Conditions for the preservation of fossils are best achieved
A) in desert environments.
B) in glaciated environments.
C) in shallow river beds.
D) on the floors of shallow seas.
Answer: D
15) In any sequence of sedimentary rock layers that have not been subjected to stress, you would
expect to find
A) horizontal layers.
B) older layers at the bottom and younger layers at the top.
C) fossils in the bottom layers and inclusions in the upper layers.
D) older horizontal layers at the bottom with younger horizontal layers at the top.
Answer: D
16) Sediments deposited in an even, horizontal manner illustrate the principle of
A) superposition.
B) original horizontality.
C) succession.
D) conformity.
Answer: B
17) The principle of faunal succession states that
A) fossil organisms follow one another in a definite, irreversible time sequence.
B) rock cycling may dislodge and relocate fossils, making their age difficult to determine.
C) fossils are always older than the rock in which they are found.
D) fossils are ordained.
Answer: A
18) Which relative dating principle states that in an undeformed sequence of sedimentary rocks,
each layer is older than the one above and younger than the one below?
A) Original horizontality.
B) Superposition.
C) Cross-cutting.
D) Inclusion.
Answer: B
19) The principle of original horizontality states that each
A) sedimentary layer is older than the layer above.
B) sedimentary layer is younger than the layer above.
C) new layer of sediment is laid down nearly horizontally over older sediment.
D) new layer of sediment is laid down accordingly.
Answer: C
20) An unconformity is
A) a scientific debate between Earth scientists.
B) when younger igneous plutonic rock s are above older sediments.
C) a continuous sequence of sedimentary layers.
D) a gap in an otherwise continuous time-sequence of rock layers.
Answer: D
21) Fossils can be used to determine the relative age of rock layers because they are
A) found in a definite order.
B) deposited horizontally, one fossil at time.
C) radioactive.
D) found in sedimentary rocks.
Answer: A
22) Relative dating tells us the
A) time gaps that occur during deposition.
B) age of rock layers.
C) sequence of rock layers–which formed first, second, and last.
D) actual date of formation for a rock layer.
Answer: C
23) To help determine the age of rock layers over a large area we can use the principle of
A) original horizontality.
B) lateral continuity.
C) superposition.
D) fossil assemblage.
Answer: B
24) The laws of physics, chemistry, and geology have operated unchanged through time to shape
Earth as we know it today can be summed up by the idea of
A) evolution.
B) everlasting change.
C) uniformitarianism.
D) natural history.
Answer: C
25) The rather simple idea that, unless disturbed, younger sedimentary layers overlie older
layers, is referred to as the principle of
A) original horizontality.
B) uniformitarianism.
C) faunal succession.
D) superposition.
Answer: D
26) According to most estimates, Earth is approximately
A) 4.5 thousand years old.
B) 4.5 million years old.
C) 4.5 billion years old.
D) 45 billion years old.
Answer: C
27) In a sedimentary rock that contains inclusions of metamorphic rock, the inclusions must be
A) older than the sedimentary rock.
B) younger than the sedimentary rock.
C) on top of the sedimentary rock.
D) below the sedimentary rock.
Answer: A
28) In a sequence of sedimentary rocks, the bottom layer is the youngest and the top layer is the
oldest. This type of sequence suggests that the
A) principles of original horizontality and superposition are flawed.
B) beds must have been overturned by some structural disturbance.
C) dates for these rocks must be in error.
D) principles of original horizontality and superposition hold true.
Answer: B
29) The idea of uniformitarianism suggests that
A) the natural laws that operate today are different than those that have operated in the past.
B) sediments are laid down layer upon layer with younger layers always on the top.
C) the processes and natural laws that operate today have been valid throughout geologic time.
D) all rocks layers are originally uniform.
Answer: C
30) When tilted or folded sedimentary layers are covered by younger, horizontal rock layers it is
called
A) an intrusion.
B) an angular unconformity.
C) a syncline.
D) conformable.
Answer: B
31) The five principles used to determine the relative ages of rock include original
A) horizontality, superposition, cross cutting, inclusion, and faunal succession.
B) horizontality, nonconformity, cross cutting, inclusion, and faunal succession.
C) inclusion, superposition, uniformitarianism, horizontality, and fossil succession.
D) horizontality, uniformitariansism, cross cutting, stromatolite, and faunal succession.
Answer: A
32) What types of rocks are representative of the principle of original horizontality? Why?
Answer: Sedimentary rocks formed by sediments deposited in horizontal layers, one on top of
the other by either wind or water.
33) On what four assumptions is the principle of faunal succession based?
Answer: 1) The general sequence of fossils is similar worldwide. 2) Rock layers of different ages
will contain different groups of fossils. 3) The principle of original horizontality is valid. 4) The
principle of superposition is valid.
34) How do geologists determine the relative ages of different rocks?
Answer: Geologists use the six common sense relative dating principles: original horizontality,
superposition, cross-cutting, inclusions, faunal succession, and lateral continuity..
35) What does the principle of superposition say about the ages of rocks?
Answer: The oldest rock in any undeformed sequence of rocks will be the rock on the bottom.
36) What type of igneous formation would agree with the principle of superposition?
Answer: Lava flows. When volcanoes or fissures erupt, lava flows outward; with each eruption
new lava flows on top of older lava flows. Although magma also flows, magma can intrude
between existing layers.
23.2 Radiometric Dating
1) Radiometric dating is based on
A) decay of uranium-238 to lead-206.
B) sequence of rocks and the relative position of one layer to another.
C) proportions of radioactive isotopes and their decay products.
D) the half-life of radioactive atoms.
Answer: C
2) To date relatively young rocks and materials, we use the decay of
A) uranium-238 to lead-206.
B) potassium-40 to argon-40.
C) carbon-14 to nitrogen-14.
D) uranium-235 to lead-207.
Answer: C
3) The time required for one-half of a radioactive material to decay is called the
A) absolute age.
B) half-life.
C) date age.
D) true-life.
Answer: B
4) To date the age of Earth, we look for rocks with a high percentage of
A) uranium-235 to lead-207.
B) uranium-238 to lead-206.
C) potassium-40 to argon-40.
Answer: B
5) Radiometric dating assumes that, once a mineral has crystallized, any daughter product results
only from the decay of the original unstable parent. Some complications are
A) variations in temperature.
B) failure to take samples too close together.
C) "time clock resetting" due to metamorphism, and product leakage that yields false age
estimation.
D) a poorly maintained teleometer.
Answer: C
6) The ultimate truth of any radiometric date depends on the
A) size of the given sample.
B) chemical composition of the sample being tested.
C) precision and accuracy of the lab techniques.
D) reset date of the sample.
Answer: C
7) The process where an element spontaneously changes into a different element (transmutation)
by a change in the nucleus of an atom is called
A) radiometric dating.
B) radioactive decay.
C) radiometric decay.
D) none of these
Answer: B
8) The oldest rocks that have been dated by radioactivity are approximately
A) 2 million years old.
B) 200 million years old.
C) 4 billion years old.
D) 10 billion years old.
Answer: C
9) Radiocarbon dating is limited to the remains of plants and animals that died no longer than
about
A) 100 years ago.
B) 5700 years ago.
C) 40,000 years ago.
D) 1,000,000 years ago.
Answer: B
10) To date a rock thought to be many millions of years old, you should NOT use the decay of
A) uranium to lead.
B) potassium to argon.
C) carbon-14.
Answer: C
11) If a radioactive element has a half-life of 704 million years, and the amount of parent
material remaining is one-eighth of the original amount, the specimen is about
A) 2,112,000,000 years old.
B) 1,408,000,000 years old.
C) 2,816,000,000 years old.
D) 3,520,000,000 years old.
Answer: A
12) If the half-life of some radioactive element is 1 billion years, and a mass of rock originally
contained 100 g of that element, how many grams of the radioactive element would be left after
three billion years had passed?
A) 6.25 g
B) 12.5 g
C) 25 g
D) 50 g
E) none
Answer: E
13) The numerical dates associated with events on the geologic time scale were determined by
A) relative dating.
B) superposition.
C) radiometric dating.
D) fossil assemblages through time.
Answer: C
14) The isotope most useful for dating rocks from the late Pleistocene is
A) uranium-238.
B) uranium-235.
C) potassium-40.
D) carbon-14.
Answer: D
15) Granitic pebbles with a radiometric age of 300 million years are embedded in a sedimentary
rock. A dike, dated at 200 million years, intrudes into the sedimentary rock. With all this
information we can estimate the age of the sedimentary rock to be
A) older than 300 million years.
B) younger than 200 million years.
C) between 200 and 300 million years old.
D) precisely 300 million years old.
Answer: C
16) The resetting of a mineral's time clock means that
A) a mineral can be formed and reformed again and again.
B) the date obtained will be the date of the metamorphic event, not the date of the rock's
formation.
C) the date obtained will be the date of the rock's formation, not the date of the metamorphic
event.
D) minerals can tell time just like a clock can tell time.
Answer: B
17) By radiometric dating, the oldest mineral in a sedimentary rock was found to be 1.4 million
years old. What is the age of the sedimentary rock?
A) Radiometric dating does not work for sedimentary rocks.
B) 1.4 million years.
C) No older than 1.4 million years.
D) No younger than 1.4 million years.
Answer: C
18) What are the limitations in obtaining radiometric dates?
Answer: When using the half-life method, scientists assume a closed system where there has
been no addition or loss of parent or daughter products. If this assumption is not true, age
determination will be wrong–the age will be either too old or too young. Another limitation
exists for rocks subjected to metamorphism in which the rock's age has been reset. Making sure
that a good sample is used, and careful cross checking between samples increases accuracy.
19) What are some of the uncertainties in obtaining radiometric carbon dates?
Answer: The largest uncertainties related to carbon dating are due to the fluctuation of carbon-14
production in the atmosphere and the amount of carbon dioxide present in the atmosphere.
20) Which isotopes are most appropriate for dating formations from the following ages: (a) the
early Precambrian; (b) the Mesozoic; (c) the late Pleistocene?
Answer: For the early Precambrian, use uranium-238. For the Mesozoic, use uranium-235
(uranium-238 will also work but is not as precise). For the late Pleistocene, carbon-14 is the only
reasonable isotope to use.
21) In dating a mineral, what is meant by "resetting of the mineral's time clock"?
Answer: The "time clock" can be reset if the mineral is heated during a metamorphic event. The
date obtained from that mineral may be the date of the metamorphic event, not the original age of
the mineral.
22) A radiometric date is determined from mica that has been removed from a rock. What does
the date signify if the mica is found in granite? What does the date signify if the mica is found in
schist?
Answer: If the mica is found in granite, the date signifies the time of the granites crystallization.
If the mica is found in schist, the date signifies the time of the last metamorphic event to affect
that rock.
23.3 Geologic Time
1) The geologic time scale is broken up into time units of different sizes based on
A) eons, eras, periods, and epochs.
B) changes in fossilization.
C) visible and nonvisible life forms.
D) major changes in life forms.
Answer: D
2) The fundamental time unit representing a major change in life forms is the
A) eon subdivision.
B) era subdivision.
C) period subdivision.
D) epoch subdivision.
Answer: C
3) Why are periods the most fundamental time unit?
Answer: Periods are small enough time units to chronicle major changes in life forms. Eras are
for too big, and epochs are too small.
23.4 Precambrian Time (4500 to 543 Million Years Ago)
1) The Precambrian witnessed the development of
A) the first atmosphere.
B) the ozone layer.
C) photosynthesis.
D) photosynthesis, an oxygenated atmosphere, and the ozone layer.
Answer: D
2) Life forms in the Precambrian included
A) trilobites.
B) brachiopods.
C) coelacanths.
D) cyanobacteria.
Answer: D
3) Life forms in the Precambrian include
A) trilobites, brachiopods and stromatolites.
B) cyanobacteria and trilobites.
C) the agnatha and the coelacanths.
D) stromatolites and certain primitive blue-green algae.
Answer: D
4) Which of the following is NOT true of the fossil record?
A) The fossil record spans 3 billion years of Earth's 4.6 billion year age.
B) The most common fossils are from organisms that had hard parts like shells and bones.
C) Similar to present day stromatolites, the first fossils were simple, anaerobic algal plants.
D) The Paleozoic era is credited with the emergence of life.
Answer: D
5) The banded iron formations began to form when
A) carbon dioxide dissolved in seawater.
B) varying oxygen levels allowed the precipitation of alternating layers of iron oxide.
C) oxide minerals were deposited on the ocean bottom.
D) iron from lava flows settled into layered formations.
Answer: B
6) The oldest known fossils are
A) trilobites and brachiopods.
B) algae and bacteria.
C) fungi and algae.
D) worms and jellyfish.
Answer: B
7) The oldest known fossils of single-celled organisms are
A) 4.6 billion years old.
B) 3.9 billion years old.
C) 3.3-3.5 billion years old.
D) 1.3-1.5 billion years old.
Answer: D
8) During the Precambrian, the development of the ozone layer helped
A) primitive organisms on Earth's surface to nucleate.
B) shield Earth's surface from harmful ultraviolet radiation.
C) promote the emergence of stromatolites.
D) promote the development of anaerobic organisms.
Answer: B
9) Development of Earth's early oceans was likely due to
A) water-rich meteors bombarding Earth's surface.
B) volcanic outgassing in Precambrian time.
C) intense convection in the mantle, and severe heat dissipation from Earth's interior.
D) cooler temperatures that promoted the condensation of water vapor in the atmosphere.
Answer: D
10) Earth's first atmosphere was rich in water vapor but poor in free oxygen. The atmosphere
became more oxygenated with the
A) development of the ozone layer.
B) emergence of stromatolites that developed a simple version of photosynthesis.
C) emergence of gases from volcanic eruptions.
D) both A and B.
Answer: B
11) What was the one most important event in the Precambrian?
Answer: The accumulation of free oxygen in the atmosphere. This allowed the ozone layer to
form and allowed life to emerge.
12) Describe the conditions of Earth during the Precambrian.
Answer: Hadean: intense volcanic activity, meteorite bombardment, precontinents in a state of
constant change from internal and external forces.
Archean: gases from volcanic eruptions led to creation of a primitive atmosphere (rich in water,
poor in oxygen) and the oceans. Blue-green algae, bacteria, and stromatolites were the first signs
of life, organisms evolved a primitive form of photosynthesis, which later led to the development
of the ozone layer.
Proterozoic: with the ozone layer in place, Earth was shielded from harmful UV radiation and
new life emerged.
23.5 The Paleozoic Era (543 to 248 Million Years Ago)
1) Sea level fluctuated several times during the Paleozoic. Which of the following is NOT a
representative factor for sea level rise in the Paleozoic?
A) Melting of continental glaciers.
B) Ocean basins stood high on the asthenosphere due to active seafloor spreading.
C) Ocean basins stood high on the asthenosphere due to slow but continuous seafloor
convergence.
D) The breakup of the Precambrian supercontinent
Answer: C
2) The Paleozoic era begins with the Cambrian and concludes with the
A) Ordovician period.
B) Silurian period.
C) Permian period.
D) Triassic period.
Answer: C
3) The most important event during the Cambrian period was the
A) emergence of the fishes.
B) ability of organisms to form an outer skeleton.
C) emergence of the trilobite.
D) ability of organisms to develop lungs.
Answer: B
4) Large deposits of gypsum and other evaporite minerals are evidence of
A) volcanic activity during the Cambrian period.
B) dried up shallow seas from the Silurian period.
C) seafloor spreading during the Permian period.
D) glaciation during the Triassic period.
Answer: B
5) The Devonian period is most noted for the
A) ability of certain fishes to breath air.
B) ability of certain fishes to move onto land.
C) first amphibians.
D) great diversification of fishes–some developed lungs, some moved to land, and some became
amphibians.
Answer: D
6) Rocks from the Carboniferous period are significant because they
A) contain diamonds.
B) provide gold and silver deposits.
C) have large deposits of coal and oil.
D) are a source of cement.
Answer: C
7) The Carboniferous period is well noted for the
A) emergence of the insect.
B) evolution of the amniotic egg.
C) age of the reptiles.
D) extinction of shallow water organisms.
Answer: B
8) The formation of the supercontinent of Pangaea
A) resulted from the collision of all major land masses.
B) produced widespread mountain building in the Himalayas.
C) resulted in extensive volcanic activity and flood basalts.
D) all of these
Answer: A
9) The Permian period experienced major extinctions, which may have been due to
A) global warming.
B) the emergence of the reptile.
C) the breakup of Pangaea.
D) the formation of Pangaea.
Answer: D
10) The formation of the early Appalachian Mountains began as a result of tectonic activity
during the
A) Paleozoic era.
B) Triassic era.
C) Mesozoic era.
D) Cenozoic era.
Answer: A
11) The formation of the supercontinent of Pangaea caused
A) a worldwide rise in sea level.
B) a worldwide drop in sea level.
C) no change in sea level.
D) none of these
Answer: B
12) The climatic zones of Pangaea ranged from
A) glaciation in the south, and a mild temperate climate in the north.
B) cold, dry temperatures in the north, and warm, tropical temperatures in the south.
C) humid uplands in the north, and drier, desert like conditions in the south.
D) widespread glaciation in the north, and a warm, tropical climate in the south.
Answer: A
13) The beginning of the Paleozoic is marked by the emergence of
A) organisms with hard parts.
B) fish and fungi.
C) extensive glaciated deposits.
D) none of these
Answer: A
14) The first reptiles occurred during the
A) Tertiary.
B) Ordovician.
C) Triassic.
D) Carboniferous.
Answer: D
15) At the end of the Paleozoic era, all
A) dinosaurs became extinct.
B) flowering plants grew to great heights.
C) fish species became extinct.
D) trilobites became extinct.
Answer: D
16) Ancient geologic processes as revealed in Paleozoic rock layers were
A) predominantly volcanic in origin.
B) primarily glacial.
C) predominantly processes of erosion and sedimentation.
D) very similar to processes seen today.
Answer: D
17) Coal is composed of
A) petrified wood.
B) buried plant material that has partially decayed.
C) buried animal material that has partially decayed.
D) a combination of oil-rich sediments and calcareous ooze.
Answer: B
18) Most coal deposits were formed in the
A) Cenozoic era.
B) Mesozoic era.
C) Paleozoic era.
D) Precambrian era.
Answer: C
19) The emergence of terrestrial life–for example, land plants, came about during the
A) Triassic.
B) Silurian.
C) Ordovician.
D) Carboniferous era.
Answer: B
20) Organisms with the ability to be easily preserved as fossils began to flourish about
A) 4.6 billion years ago.
B) 3.8 billion years ago.
C) 543 million years ago.
D) 65 million years ago.
Answer: C
21) The first time period for which abundant fossils have been found is the
A) Precambrian.
B) Silurian.
C) Pliocene.
D) Cambrian.
Answer: D
22) The "Cambrian explosion" refers to the
A) great many meteorite bombardments that occurred during that time.
B) great diversity of life that blossomed during that time.
C) evolution and great diversity of blastoids during that time period.
D) numerous volcanic eruptions that took place during that time.
Answer: B
23) Ancient coal beds can be found in Antarctica because
A) at one time the climate of Antarctica was mild enough to support swamplands.
B) ancient coal beds were frozen in the Antarctic ice.
C) it used to be located in the northern hemisphere.
D) it was located at the equator during the Carboniferous period.
Answer: A
24) Possible ways that sea level could lower include a decrease in
A) worldwide temperatures and an increase in the rate of seafloor spreading.
B) worldwide temperatures and a decrease in the rate of seafloor spreading.
C) tectonic activity and an increase in worldwide temperatures.
D) the rate of seafloor spreading and an increase in worldwide temperatures.
Answer: B
25) The high concentration of iridium at the Cretaceous Tertiary boundary is most likely
attributed to
A) a worldwide rise in sea level.
B) meteorite bombardment.
C) an out flux of iridium from Earth's interior.
D) none of the above.
Answer: B
26) Earth's early life forms were marine organisms. Life moved to the land during the
A) Cambrian period.
B) Ordovician period.
C) Silurian period.
D) Triassic period.
Answer: C
27) The supercontinent of Pangaea formed during the
A) Cenozoic.
B) Paleozoic.
C) Mesozoic.
D) Precambrian.
Answer: B
28) The Permian extinction predominantly affected
A) reptiles.
B) marine life.
C) insects life.
D) terrestrial life.
Answer: B
29) All continental landmasses joined together as Pangaea resulted in
A) a reduction in shallow marine habitats.
B) a long duration of high sea level.
C) an increase of seafloor spreading.
D) increased species diversification.
Answer: A
30) Why is it believed that large parts of the United States were once covered by shallow seas?
Answer: Marine fossils found in the interior of the continent.
31) What spectacular development in organisms marks the beginning of the Paleozoic era?
Answer: Organisms developed ability to secrete calcium-carbonate and calcium-phosphate for
the formation of hard shells and skeletons. Hard shells provided protection from predators and
UV radiation, and made organisms better able to be preserved as fossils.
32) What types of events ended the Paleozoic era?
Answer: The formation of Pangaea–which affected Earth's climate and hence the evolution of
life. Greatest extinction of animals–95% of all marine species and 70% of all land species.
33) Coal beds are formed from the accumulation of plant material that becomes trapped in
swamp floors. Yet coal deposits are present in the continent of Antarctica, where no swamps or
vegetation exists. How can this be?
Answer: During the Paleozoic, the present-day continents of Africa, Australia, Antarctica, South
America, New Zealand, India, and southeastern Asia moved across the South Pole. In late
Paleozoic time, these continents collided with North America and Eurasia to form Pangaea.
Throughout this time the southern continents experienced cyclic episodes of glaciation. During
warmer interglacial stages, Glossopteris and other plants tolerant of the cool, damp climate,
flourished and provided the materials for thick seams of coal.
34) Why does sea level rise when spreading rate increases?
Answer: Sea level rises because a faster spreading rate means warmer ocean crust (same cooling
rate as during periods of slower spreading), which is less dense than colder ocean crust. Since it
is less dense, the ocean crust "rides" higher on the asthenosphere, forcing seawater onto the
continents.
35) Paleozoic sedimentary rocks derived from marine deposits are widely distributed in all of the
continents. What does this indicate about the height of the continents relative to sea level during
the Paleozoic?
Answer: During the Paleozoic, periodic active and rapid seafloor spreading allowed the oceanic
lithosphere to stand high on the asthenosphere. This resulted in shallower ocean basins, a
condition that forced seawater onto low portions of the continents. The ultimate result was a rise
in sea level and the formation of shallow seas on top of continental crust.
23.6 The Mesozoic Era (248 Million Years Ago)
1) The Mesozoic era is known as the age of the
A) dinosaur.
B) reptile.
C) fishes.
D) synapsids.
Answer: B
2) During the Cretaceous period, Earth experienced a worldwide rise in sea level caused by
A) melting of glacial ice.
B) the thermal expansion of the crustal surface and the breakup of Pangaea.
C) subduction of the seafloor.
D) subduction of continental land masses.
Answer: B
3) The breakup of Pangaea began in the Mesozoic era
A) during the Jurassic.
B) during the Triassic.
C) at the end of the Triassic.
D) at the end of the Ordovician.
Answer: B
4) The breakup of Pangaea resulted in
A) a worldwide rise in sea level.
B) a worldwide drop in sea level.
C) no significant change in sea level.
D) alternating sea level changes.
Answer: A
5) The break-up of Pangaea had worldwide consequences with the exception of
A) the lowering of sea level.
B) a rise in sea level.
C) the divergence and evolution of new species.
D) climate change.
Answer: A
6) Iridium is an element that is relatively
A) abundant on Earth, but very rare in meteorites.
B) rare on Earth, but very common in meteorites.
C) abundant on both the Earth and the Moon.
D) rare on both Earth and in meteorites.
Answer: B
7) Dinosaurs were abundant during the
A) Paleozoic era.
B) Devonian era.
C) Mesozoic era.
D) Cenozoic era.
Answer: C
8) Going from oldest to youngest, the three periods of the Mesozoic are
A) Triassic, Jurassic ,and Permian.
B) Jurassic, Triassic, and Cretaceous.
C) Triassic, Jurassic, and Cretaceous.
D) Cretaceous, Permian, and Jurassic.
Answer: C
9) The breakup of Pangaea began in the Mesozoic era
A) with the rifting apart of North America and Africa.
B) with the collision of North America with Africa..
C) with the formation of the Himalayan Mountains.
D) at the end of the Ordovician.
Answer: A
10) The breakup of Pangaea resulted in the separation of
A) habitats.
B) landmasses.
C) plant and animal life.
D) landmasses, and plants and animals and their habitats.
Answer: D
11) The Andes and the Sierra Nevada Mountains began to form during the Mesozoic due to
A) the formation of the Atlantic Ocean.
B) subduction of Pacific oceanic crust beneath North and South American continental crust.
C) rifting between North America and Africa.
D) meteorite bombardment in Mexico.
Answer: B
12) What is the evidence that a meteorite impact caused the great extinction at the end of the
Mesozoic?
Answer: The concentration of iridium at the Cretaceous/Tertiary boundary. Most of Earth's
iridium is deep within its interior. The concentration of iridium in a meteorite is higher than the
iridium concentration in Earth's crust.
13) What types of changes occurred in land-dwelling animals during the Mesozoic?
Answer: Land animals began to greatly diversify. Many of the reptiles that survived the
Paleozoic extinction evolved to become the dinosaurs; some reptiles evolved to become
mammals.
14) What is the most widely accepted hypothesis for the dinosaur extinction at the end of the
Cretaceous period?
Answer: The Alvarez hypothesis that Earth was hit by a very large meteorite. The abundance of
iridium at the Cretaceous—Tertiary boundary (65 million years ago–the time of the great
dinosaur extinction) supports this hypothesis.
23.7 The Cenozoic Era (65 Million Years Ago to the Present)
1) The Cenozoic Era is known as the
A) age of the mammals.
B) age of man.
C) age of the reptile.
D) ice age.
Answer: A
2) The most noteworthy event that occurred during the Pleistocene was the
A) emergence of the early humans.
B) ice age.
C) appearance of the grasslands.
D) divergence of horses.
Answer: A
3) During the Cenozoic era animals grew to great sizes and proportions. The wooly mammoth
and the saber tooth tiger were much larger than animals we see today. Some of the causes for
their extinction may be
A) the emergence of man and competition for food.
B) burning of the grasslands, severe climatic change, and man's emergence.
C) dwindling food supplies, extreme climatic variation, and man's emergence.
D) the extensive ice sheets that covered the land surface.
Answer: C
4) Uplift of the Rocky Mountains was a result of
A) compressional forces.
B) tensional forces.
C) crustal extension.
D) none of these
Answer: A
5) The Cenozoic era represents a period of
A) almost continuous tectonic activity.
B) relative tectonic stability.
C) worldwide tropical climates.
D) great diversification of fish species.
Answer: A
6) During the Pleistocene ice age
A) there was one large episode of glacial advance.
B) there were several episodes of glacial advance and retreat.
C) Earth's entire surface was covered with ice.
D) Earth's oceans were completely frozen.
Answer: B
7) In general, when we refer to the time of the "Ice Age" we are referring to the
A) Jurassic.
B) Tertiary era.
C) Pleistocene epoch.
D) Pliocene era.
Answer: C
8) The extensive glaciation of the Pleistocene caused sea level to
A) drop because a great deal of water was bound in glaciers.
B) rise because a great deal of water was tied up in glaciers.
C) drop because of increased ablation and reduced accumulation.
D) rise because of increased accumulation and reduced ablation.
Answer: A
9) Pangaea formed during the Paleozoic and broke up in the Mesozoic. Of all the former
continental unions that existed in Paleozoic time, only that of
A) Australia and Antarctica has survived to the present time.
B) Africa and India has survived to the present time.
C) North and South America has survived to the present time.
D) Europe and Asia has survived to the present time.
Answer: D
10) The birth of the San Andreas Fault corresponds to the collision of
A) the Pacific Plate and the Hawaiian islands.
B) the Pacific ridge system and North America.
C) the movement of the Pacific Plate over a turbulent zone.
D) India and Eurasia.
Answer: B
11) Which of the following is not a presumed cause of ice ages?
A) The arrangement of continents around the globe.
B) The amount of sunlight being reflected back into space .
C) The geometry of Earth's rotation on its axis and revolution around the Sun.
D) Volcanic eruptions blocking the sunlight with clouds.
Answer: B
12) The San Andreas Fault was created
A) during the Cenozoic.
B) by the collision of the westward moving North American Plate and the Pacific ridge.
C) by the same tectonic activity that formed the Gulf of California.
D) by Cenozoic tectonic activity that also formed the Gulf of California as the North American
Plate collided with the Pacific ridge.
Answer: D
13) Glacial striations on the continental landmasses provide evidence
A) that Hawaii was once joined to Alaska.
B) of the direction of Pleistocene ice flow.
C) that the Cenozoic was a very cool time.
D) that Baja California was once joined to Mexico.
Answer: B
14) The great height of the Himalayas is due to
A) continental-continental convergence where neither plate undergoes subduction.
B) the continuing after affect of the collision between the Alps and the Urals.
C) convergence of the Farallon Plate with India.
D) the subduction of India beneath Asia.
Answer: A
15) The San Andreas fault is still active today as the northwest moving
A) North American Plate grinds against the southwest moving Pacific Plate.
B) Pacific Plate grinds against the southwest moving North American Plate.
Answer: B
16) Similar reptiles were present on all continents during the Mesozoic era, but mammals of the
Cenozoic era are often different on the different continents. Explain.
Answer: Tectonics. At the beginning of the Mesozoic, the various continents were assembled
into one large landmass (Pangaea). With one large landmass, animals could roam from one
"continent" to another. The break up of Pangaea occurred throughout the Mesozoic. By the
Cenozoic the landmass of Pangaea ceased to exist. The various continents were separated, as
such, so were the various mammals of the Cenozoic.
17) In what way could sea level be lowered? How might this affect existing life forms?
Answer: Sea level could be lowered if the climate turned colder, causing more water to be tied
up in glacial ice. This could drastically affect shallow water creatures (habitat destruction) and
cause many extinctions. The colder climate could also cause the demise of some species through
habitat destruction and scarcity of food. Sea level could also be lowered if seafloor spreading
were to slow down.
18) In what way could sea level rise? Is this likely to happen in the future? Why or why not?
Answer: A rise in sea level could be caused by an increase in spreading rates, such as what
occurred during the Paleozoic, or if the polar ice caps were to melt. Although the Mid-Atlantic
ridge continues to spread, it is unlikely that our generation, or the one after ours, will witness a
rise in sea level due to a high stand of the asthenosphere (as such changes are slow to manifest).
A more probable cause could come about if the grim predictions of global warming due to
greenhouse gasses were to occur. In either case, it is difficult to predict the future.
23.8 Earth History in a Capsule
1) Changes in Earth's history are recorded
A) in the rock record.
B) in magnetic tape at the bottom of the oceans.
C) by rocks at the Library of Congress.
D) Moon rocks.
Answer: A
2) You would expect to find the least number of fossils in rocks from the
A) Cenozoic era.
B) Mesozoic era.
C) Paleozoic era.
D) Precambrian era.
Answer: D
3) The most important highlight of Precambrian Time was the
A) explosion of life.
B) asteroid impact that resulted in the formation of our Moon.
C) accumulation of free oxygen in the atmosphere.
D) emergence of reptiles.
Answer: C
4) The most noteworthy highlight of the Mesozoic era was the
A) break-up of Pangaea.
B) emergence of humans.
C) Pleistocene extinction.
D) ice age.
Answer: A
5) The most noteworthy highlight of the Cenozoic era was the
A) break-up of Pangaea.
B) emergence of humans.
C) Pleistocene extinction.
D) ice age.
Answer: B
Test Bank for Conceptual Physical Science
Paul Hewitt, John Suchocki, Leslie Hewitt
9780321752932, 9780134060491
