Download GG 101, Spring 2006 Name_________________________ Exam 2

GG 101, Spring 2006
Exam 2, March 9, 2006
Name_________________________
A. Fill in the blank (2 points each)
1.
The velocity of an S-wave is ______lower_________ than the velocity of a P-wave.
2.
What type of seismic wave is being recorded by the above diagram? A __P__ wave.
3.
The most voluminous layer of Earth is the ___mantle_________.
4.
The rigid layer of Earth which consists of the crust and uppermost mantle is called
the __ lithosphere__________.
5.
Which of the major subdivisions of Earth's interior is thought to be liquid?
____outer core________.
6.
When the giant ice sheets in the northern hemisphere melted after the last ice age, the
Earth's crust ____rebounded____ because a large weight was removed.
Name _______________________________
GG 101 Exam 2
Page 2
7.
The process described in question 6 is an example of ___isostasy____.
8.
Earth's dense core is thought to consist predominantly of ____iron________.
9.
The island of Hawaii experiences volcanism because it is located above a(n) ___hot
spot_________.
10. The Himalaya Mountains were caused by ___collision__ between
___India__________ and Asia.
11. ___Folds____ are the most common ductile response to stress on rocks in the earth’s
crust.
12. ___Faults___ are the most common brittle response to stress on rocks in the earth’s
crust.
13. What types of faults are depicted in the cross section shown above?
___thrust_______ faults.
Name _______________________________
GG 101 Exam 2
Page 3
14. The structure shown in the above diagram is a(n) ____anticline_____.
15. The name of a fold that occurs in an area of intense deformation where one limb of
the fold has been tilted beyond the vertical is called a(n) ____overturned____ fold.
B. Short Answer. Briefly answer the following questions. Use the back of the page if
necessary.
1. How do we know that iron and nickel are important components of the Earth’s core?
(5 points)
Iron’s density and abundance on earth makes it a good candidate for core material, and the
fact that it could conduct electricity to create a magnetic field strengthens this belief.
Meteorites are thought to be good analogs of early earth materials. Iron meteorites are
composed of mainly iron and nickel. Experiments performed at high pressures are
consistent with an iron and nickel metal core.
2. How could you use P and S seismic waves to find a chamber of molten magma in the
earth’s crust? (5 points)
Because P-waves travel more slowly through liquids than through solids and S-waves are
absorbed by liquids, one could generate seismic waves of both types and search for
areas below the surface where the P-waves slowed and the S-waves disappeared.
Name _______________________________
GG 101 Exam 2
Page 4
3. According to the video "Winds of Change", the Himalaya mountains and Tibetan
Plateau were uplifted ~2,000 m about 10 million years ago. What caused this sudden
uplift? (5 points)
Mountains are pushed up when the continental lithosphere is compressed – in the process,
both the crustal and mantle parts of the lithosphere are thickened, creating a deep root
beneath the mountains. The mantle portion of the root is denser than the underlying
asthenosphere and eventually drops off, and this is what allowed the mountains to
suddenly rise higher.
4. How do fossil plants help us understand the history of uplift of the Himalayan
Mountains? (5 points)
The shape of leaves can be used in the Himalayan Mountains to infer elevation. The
climate of central Asia is strongly influenced by the presence of the Himalayan
Mountain range and the Tibetan Plateau. During summer monsoon, the high plateau
warms up and the overlying air is heated. As the hot air rises, water-laden winds from
the Indian Ocean are sucked in dropping their moisture. However, most of the moisture
falls as fain over the Himalayas before reaching Tibet. This is why the Tibetian Plateau
is a desert, while much of the Himalayas are cloaked with thick vegetation. Plant leaves
and the type of vegetation changes with temperature and rainfall and thus in the
Himalayas vegetation changes with altitude. The variety of leaf shapes have been used
to create a “leaf thermometer”. This thermometer can be used to estimate altitude.
Using fossil plants, geologists can estimate the altitude of the mountains in the past.
5. Why is there a "bend" in the Hawaii Island-Emperor Seamount chain? (5 points)
The Pacific plate originally was moving north-northwest over the Hawaiian “hot spot”
resulting in the chain of volcanic islands known as the Emperor Seamounts. A sharp
change to a more westerly plate movement occurred (about 45 million years ago)
resulted in the Hawaiian Islands Ridge. The “bend” occurs because of this change in
direction of movement of the Pacific Plate.
Name _______________________________
GG 101 Exam 2
Page 5
6. What four factors predominantly affect deformation of rocks? (5 points)
1.
2.
3.
4.
Temperature
(Confining) Pressure
Strain Rate
Rock Type
7. What causes the P wave shadow zone? (5 points)
The P-wave shadow zone extends from 105° to 142°. P waves cannot reach the surface
within this zone because of the way they are bent (refracted) when they enter and leave
the core. At the core-mantle boundary, the P-wave speed drops by almost a factor of
two. Therefore, the waves are refracted downward into the core and emerge at greater
distances after the delay caused by their detour through the core. This refraction effect
forms a P-wave shadow zone at angular distances between 105° and 142°.
8. Why can geologists infer features of mantle convection, such as rising and descending
convection currents, from seismic tomography? (5 points)
Using numerous seismic data and small changes in the speed of S-waves, geologists are
able to interpret the data revealed by the speed of the S-waves to identify features such
as mantle convection and convection currents. Faster wave motion can correspond to
denser or colder regions and slower wave motion can correspond to buoyant or warmer
regions.
Name _______________________________
GG 101 Exam 2
Page 6
9. Identify the layers of the earth on the diagram below: (5 points)
EXTRA CREDIT – 5 points!!!!
A rock formed initially with 1,000 atoms of a radioactive parent element, but only contains
250 radioactive parent atoms today. If the half-life for the radioactive element is one
million years, how old is the rock?
A)
B)
C)
D)
250,000 years old
500,000 years old
1,000,000 years old
2,000,000 years old