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Chapter 8

Multiple Choice
Identify the choice that best completes the statement or answers the question.
 

 1. 
A series of processes on Earth’s surface and in the crust and mantle that slowly changes rocks from one kind to another is called
a.
erosion.
b.
crystallization.
c.
the rock cycle.
d.
evaporation.
 

 2. 
Which of the following is NOT one of the possible stages in the rock cycle?
a.
volcanic activity
b.
erosion
c.
smelting
d.
melting
 

 3. 
What step in the rock cycle would be required to change granite into sandstone?
a.
Granite particles settle on the ocean floor.
b.
Lava flows melt the granite sediment.
c.
Pieces of the granite melt when they return to the mantle by subduction.
d.
Magma hardens into granite sediment.
 

 4. 
Erosion on a mountain range that was pushed up as a result of two continental plates colliding will lead to the formation of
a.
igneous rock.
b.
metamorphic rock.
c.
magma.
d.
sedimentary rock.
 

 5. 
During the rock cycle, a collision between two continental plates could force one plate down toward the heat of the mantle, producing
a.
coarse-grained rock.
b.
metamorphic rock.
c.
igneous rock.
d.
sedimentary rock.
 

 6. 
The relative age of a rock is
a.
its age compared to the ages of other rocks.
b.
less than the age of the fossils the rock contains.
c.
the number of years since the rock formed.
d.
its age based on how much carbon-14 the rock contains.
 

 7. 
The law of superposition states that, in horizontal layers of sedimentary rock, each layer is
a.
younger than the layer above it and older than the layer below it.
b.
neither older nor younger than the other layers.
c.
older than the layer above it and younger than the layer below it.
d.
always older than any vertical layers.
 

 8. 
What is the age of an intrusion of igneous rock in relation to the sedimentary rock layers through which it passes?
a.
sometimes younger, sometimes older
b.
always older
c.
the same age as the other rock layers
d.
always younger
 

 9. 
The fossils of organisms that were widely distributed but only lived during a short period of time are called
a.
trace fossils.
b.
petrified fossils.
c.
index fossils.
d.
carbon film fossils.
 

 10. 
Why are index fossils useful to geologists?
a.
They tell the absolute age of the rock in which they occur.
b.
They tell the ages of many different rock layers.
c.
They tell the age of the rock at one location only.
d.
They tell the relative age of the rock in which they occur.
 

 11. 
Radioactive decay occurs when atoms of an unstable element
a.
become part of a fossil.
b.
join with atoms of another element.
c.
break down to form atoms of another element.
d.
are exposed to chemical weathering.
 

 12. 
The time it takes for half of the radioactive atoms in a sample of a radioactive element to decay is the element’s
a.
relative age.
b.
potassium-argon date.
c.
absolute age.
d.
half-life.
 

 13. 
Radioactive dating enables geologists to determine
a.
the age of the atoms in a rock.
b.
the half-life of a fossil organism.
c.
the relative ages of rocks.
d.
the absolute ages of rocks.
 

 14. 
Radioactive dating works best with what type of rocks?
a.
igneous rocks
b.
sedimentary rocks
c.
metamorphic rocks
d.
fossilized rocks
 

 15. 
Precambrian Time, which includes most of Earth’s history, began with
a.
an ice age.
b.
Earth forming from a mass of dust and gas.
c.
an asteroid impact.
d.
the formation of thick deposits of sediment.
 

 16. 
The geological theory that states that pieces of Earth’s outer layer are in constant, slow motion is the theory of
a.
subduction.
b.
plate tectonics.
c.
deep-ocean trenches.
d.
sea-floor spreading.
 

 17. 
If one of Earth’s plates moves 5 centimeters every year, how far will it move in 500 years?
a.
25 kilometers
b.
25 centimeters
c.
25 meters
d.
250 meters
 

 18. 
Earth’s plates move a few millimeters to several centimeters each
a.
day.
b.
week.
c.
month.
d.
year.
 

 19. 
Knowing the average speed of Earth’s plates helps scientists
a.
avoid collisions between the plates.
b.
feel the plates moving.
c.
predict future changes.
d.
prevent earthquakes.
 

 20. 
The geologic time scale is a record of
a.
the thickness of sedimentary rock layers.
b.
the rate of fossil formation.
c.
the life forms and geologic events in Earth’s history.
d.
the time since the evolution of dinosaurs.
 

 21. 
How did Earth change about 2.5 billion years ago when many organisms began using photosynthesis to make food?
a.
The amount of oxygen in the atmosphere increased.
b.
Mass extinctions occurred.
c.
The oceans became larger.
d.
Rainfall increased.
 

 22. 
About 260 million years ago, Earth’s continents moved together to form the supercontinent called
a.
Antarctica.
b.
Cambria.
c.
North America.
d.
Pangaea.
 

 23. 
During the Cambrian Explosion that began the Paleozoic Era, the many new forms of life that evolved
a.
lived on land.
b.
were invertebrates that lived in the sea.
c.
were vertebrates covered with scales or fur.
d.
were single-celled.
 

 24. 
During the Devonian Period, animals that could live on land began to evolve. These animals still spent part of their lives in the water. What were these animals called?
a.
trilobites
b.
reptiles
c.
amphibians
d.
dinosaurs
 

 25. 
What do most scientists think caused the mass extinction of dinosaurs and other organisms at the end of the Cretaceous Period?
a.
Volcanic eruptions covered large areas with lava.
b.
An object from space struck Earth.
c.
An ice age covered most of Earth with ice.
d.
The dinosaurs ate too many other organisms and then starved.
 

 26. 
Hutton’s observations of the geologic forces around him allowed him to infer that these same geologic processes had operated in the past. This idea is now referred to as
a.
the rock cycle.
b.
the law of superposition.
c.
the principle of uncomformity.
d.
the principle of uniformitarianism.
 

 27. 
The continents have changed location over time because of
a.
the rock cycle.
b.
volcanoes.
c.
earthquakes along fault lines.
d.
the movement of Earth’s plates.
 

 28. 
You are looking at a fossil of a Precambrian organism that is 3.5 billion years old fossil. What were the organism’s distinguishing characteristics? It was a(n)
a.
single-celled organism.
b.
vertebrate jawless fish.
c.
invertebrate jellyfish.
d.
land-dwelling reptile.
 

 29. 
Australia’s unique communities of marsupials may be explained by
a.
human activities that have killed off marsupials everywhere else.
b.
Australia’s former location in northern latitudes.
c.
the Permian extinction, which wiped out marsupials in other parts of the world.
d.
 isolated evolution due to continental drift.
 

 30. 
Two ways in which continental drift might affect evolution are
a.
isolation of populations and climate change with change of latitude.
b.
isolation of populations and an increase in floods.
c.
an increase in floods and climate change with change of latitude.
d.
isolation of marsupials and a decrease in floods.
 

Modified True/False
Indicate whether the statement is true or false.  If false, change the identified word or phrase to make the statement true.
 

 31. 
Plate movements drive the process of erosion by pushing rock back into the mantle, where it melts and becomes magma again. _________________________

 

 32. 
Each major group of rocks follows only one pathway in the rock cycle. _________________________

 

 33. 
The law of superposition helps geologists determine the absolute age of a rock layer. _________________________

 

 34. 
Rock layers are always younger than the faults that cut across them. _________________________

 

 35. 
Geologists divide Earth’s long history into smaller units that make up the geologic time scale. _________________________

 

 36. 
Life on Earth first appeared during the Cambrian Period. _________________________

 

 37. 
At the beginning of the Paleozoic Era, a great number of different types of organisms evolved in an event called the Cambrian Explosion. _________________________

 

 38. 
The ozone layer was necessary to protect life from ultraviolet rays when organisms first moved onto land. __________________

 

 39. 
Scientists believe that the sun is 4.6 billion years old, approximately the same age as Earth. _________________

 

 40. 
The continenets resemble a jigsaw puzzle because they were once part of a supercontinent called Pangaea, according to the law of superposition.   ___________________

 

Completion
Complete each statement.
 

 41. 
A series of processes known as the ____________________ slowly changes rocks from one kind to another kind.
 

 

 42. 
The uplift, folding, and faulting that move rocks through the rock cycle are caused by movements of Earth’s tectonic ____________________.
 

 

 43. 
A rock layer’s ____________________ age is its age compared to the ages of other rock layers.
 

 

 44. 
A(n) ____________________ is a gap in the geologic record where some rock layers have been lost because of erosion.
 

 

 45. 
Certain ammonites are used as ____________________ fossils because they lived in many different areas but for only a brief time.
 

 

 46. 
The breakdown of unstable carbon-14 to form stable nitrogen-14 is an example of ____________________ decay.
 

 

 47. 
The time it takes for one half of the atoms in a sample of a radioactive element to decay is called the element’s ____________________.
 

 

 48. 
Potassium-40 is useful for dating very old rocks because it has a(n) ____________________ of 1.3 billion years.
 

 

 49. 
Geologists use the radioactive element ____________________ to determine the age of organic remains, such as bone.
 

 

 50. 
Scientists hypothesize that Earth formed at the same time as the other planets and the sun, roughly ____________________ years ago.
 

 

 51. 
Jawless fish were Earth’s first ____________________, or animals with backbones.
 

 

 52. 
The mass extinction at the end of the Paleozoic Era may have occurred because Earth’s ____________________ moved together into one large landmass, changing Earth’s climate.
 

 

 53. 
Reptiles, such as dinosaurs, were so successful during the ____________________ Era that this time is often called the Age of Reptiles.
 

 

 54. 
Life first appeared around 3.5 billion years ago, about _________________ years after the formation of Earth.
 

 

 55. 
The idea that all geological formations are the result of unique, sudden, catastrophic events was popular until the principle of _________________ showed that geological processes operating today are the same as geological processes in the past.
 

 

 56. 
You know that saber-toothed cats went extinct during the most recent Quaternary ice age. To determine the age of a saber-toothed cat fossil you would use ________________ dating.
 

 

 57. 
Fossilized sand dunes similar to active sand dunes in the Gobi desert provide support for the principle of ______________.
 

 

 58. 
A fossil organism that is widely distributed and that existed only briefly may serve as a(n) _____________ that helps geologists date rock layers.
 

 

 59. 
Historians consider time in terms of millenia that are subdivided into centuries; geologists consider time in terms of ____________________ that are subdivided into periods.
 

 

 60. 
You find fossils of a dinosaur on the east coast of South America. Your colleague finds fossils of the same species on the west coast of Africa. You are not surprised, because the theory of __________________ explains how these two areas were once joined.
 

 

Short Answer
 
 
Use the diagram to answer each question.

nar001-1.jpg
 

 61. 
Which sedimentary rock layer is older, A or B? Explain your answer and name the scientific law that you applied to reach your conclusion.
 

 62. 
List layers E, D, and C in order from oldest to youngest.
 

 63. 
How do layers B and D compare in age? If rock layers between B and D have eroded away, what is the boundary between B and D called?
 

 64. 
Layer F is an igneous extrusion. How could a geologist use layer F to infer the age of layer A.
 

 65. 
G began as magma that hardened underground to form igneous rock. What is the age of G in relation to C? What term applies to bodies of rock such as G?
 

 66. 
If layer C is sedimentary rock and layer G is igneous rock, which would be more likely to contain fossils? Explain your answer.
 
 
Strontium-90 is a radioactive form of the element strontium that undergoes radioactive decay. The graph shows the decay of strontium-90 over time.

Use the diagram to answer each question.

nar002-1.jpg
Time in Years
 

 67. 
What is the half-life of strontium-90? Explain your answer.
 

 68. 
How long will it take until only 25 percent of the strontium-90 remains?
 

 69. 
If the graph represents the decay of strontium-90 in an igneous rock, what event occurred at 0 years on the horizontal axis?
 

 70. 
Based on the graph, what can you say about the amount of time it will take for the strontium-90 to decay completely?
 

 71. 
In general, how does the amount of strontium-90 change over time?
 

 72. 
Would strontium-90 be useful for determining the age of fossils? Explain your answer.
 

Essay
 

 73. 
Explain how a grain of sand that washes up on a beach could end up some day as lava pouring from a volcano.
 

 74. 
Contrast the relative and absolute age of a rock.
 

 75. 
Define index fossils and state what geologists learn from them.
 

 76. 
Two satellite tracking stations are on two of Earth’s plates that are moving toward each other. One plate is moving east at a rate of 5 cm/yr. The other plate is moving west at a rate of 5 cm/yr. If the stations are now separated by 200 km, in how many years will the stations be 198 km apart? Explain.
 

 77. 
Define the geologic time scale and explain why geologists use it to show Earth’s history.
 

 78. 
Name one or more common organisms that lived or lives during each of the three eras of geologic time.
 

 79. 
Describe a scientific theory that explains the mass extinction of dinosaurs and many other organisms at the end of the Cretaceous Period.
 

 80. 
Explain how the theory of plate tectonics relates to geologic time, the rock cycle and the theory of evolution.
 



 
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