Download Earth`s Interior

Base your answers to questions 24 through 28 on the following map, The map shows the time of arrival of
seism-ic sea waves (tsunamis) from locations throughout the Pacific Ocean to the Hawaiian lslands.
For example, an earthquake at any loGtion on the line labeled '6 h' could prcduce a tsunami that would
arrive in Honolulu 5 hour later.
‐ ヽ
Reporting Stations
.
a
0 5∞ 1000
1
Tide stations
Seismograph
stations
2000
1
:
Distance (miles)
From which location would a tsunami arrive at
Honolulu in the shortest time?
１
２
Kodiak
(3)Tahiti
La Jo‖ a
(41 Wake iS:and
(3)Honolu!u
27. The most likely reason for collecting this Pacific
Ocean data is that Honolulu is
(l)
the site of frequent maior eruptions
(2) an equal distance from manY
seismic stations
26. Approximately how fast do seismic sea waves
travel from Midway to Honolulu, Hawaii?
(3)1500to 2000 mph
(1)31to 51 mph
14)3000 to 5000 mph
(2)300to 500 mph
AM● del
(3) surrounded by earthquake-prone zones
(4) the site of a major tide station
28.
O Tahti
h = hours
:
Which reporting station is NOT located on the
Pacific plate?
(1)HOng Kong
(2)Midway
ぃ 。
Locations in this region where major
earthquakes occur are most closely
associated with areas of
(1) volcanic eruptions
(2) P-wave absorption
(3) magnetic field reversal
(4) mid-continental folding
Start Here
of■ artht h“ erl●
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:ヨ :T∬1:田 語
影議RI油出塁讐:馴鼠嘗僣雷轟議期よ」
the study of earthquake waves.
Topic
l2:
Earth3 Dynamic Crust and
lnterior 255
Methods of Studying Earth,s lnterior
The deepest mines are little more than 3.5 kilometers deep, and the deepest
drill hole (in Russia) is approximately 12 kilometers deep. ffri, f Z
kilometers represents less than 0.2 pircent of the distance to the center of
Earth.
properties of Earth,s interior through the study
T"ibT (earthquake) the
of seismic S"r.^ost.of
waves. This is much the same as stud/ing truman
interiors with methods such as X-rays, ultrasounds, and CAT scais, By
comparing thousands of seismograms from hundreds of locations,
scientists have determined the times the different types of seismic
waves
arrive and when they don't arrive at numerous lociiions around Earth. By
comparing these records with tests done using explosives in the oil
industry and tests with nuclear bombs, scienti-sts discovered that seismic
*"y"r fj".j1Tflect, change velocity, and become absorbed by various
parts of Earth's interior. Figures 12-10 and 12-11 show the most corunon
model of Earth's interior that has resulted from these seismic wave studies.
Zones
of Earth
Our analysis of seismic waves indicates that Earth is composed of a
number of zones, as shown in Figures 12-10 and 12-11, The crust is the
outermost part of Earth below the atmosphere or hydrosphere. Though
mostly solid rock, the crust includes the ioil and eroded and weatheid
rock deposits. Below the crust is the mostly solid part called the mantle,
Earth's thickest zone that contains approximatellg0 percent of Earth,s
The mantle is separated from the crust by a ttLln interface caled
1olurn9.
the Moho. Below the Moho, the rocks become denser. The whole crust and
F" "9V "f-g"11ost portion of the mantle (called the rigid mantle) are
together
called the lithosphere. (See Figure 12-11.) The lithosphere is
Earthquake focus O.
60°
lo2° 120。 143°
Distance in degrees
102°
……>Refracted
――) Rttected
waves
waves
寵
変
訥 ざ
F1911ぃ ●■2・ ■0.Arr:v● :ti_and Paths Of seismic waves moving thrOugh Earthヽ
:nterion Ana:ysis of the■ mes seismic waves
ar"ve has resulted in interpetat10ns of ref:ecuons and refractions ofthtt waves in Eartht inte"or This analysis has resu:ted
in the
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standad
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256
■^_^_^_^=‐ __‐ ●￨
model
of the
zone! ot Earth! lnterior ihown herE“ ^.I_1^`●
fopt tz:
Eanhb Dynamrc C.usr and tnteflor
divided into sections called "plates," which you
will study in the next section.
襦
Below the lithosphere is another portion of the
upper rnantle called the asthenosphere. This zone
was discovered because it was found that seismic
waves decreased in velocity from approximately
100 to 700 kilometers below Earth's surface. The
asthenosphere is believed to be a plasticJike
portion of the upper mantle that is at least Partly
２
center
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differences in composition and density.
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The two crusts are also distinguished by
127131
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coastal regions.
Andes
Trench
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Earth's Crust Earth's crust, or upper lithosphere, is
divided into two major divisions. The continental
crust makes up the continents and larger islands,
and the oceanic crust makes up most of the crust
beneath the oceans. The continental crust is
usually much thicker than the oceanic crust. The
contential crust is thickest where highest-in
mountain regions-and usually thinnest beneath
h°
99‐ 122
● ｏｂ ‘０いｏＥ に いｏ ∽ｃｐ 〓 Ｅ ︶
Figure 12-10 shows the outermost dimension-by
area---of the shadow zone of the outer core that,
due to refraction, does not receive any refracted
seismic waves. The bottom of the outer core is
indicated by the waves reflected off the outside
edge of the inner core. Figure 12-10 also provides
evidence that the outer core is liquid: Because no
9waves pass through the zone, it can't be a solid,
and because the zone has too much pressure, it
cannot be a gas. The 9waves are absorbed as they
enter the outer core. The liquid nature of the outer
core is also indicated by the major drop in P-wave
velocity, as shown in Figure 12-11. Beneath the
outer core is the inner core extending down
to Earth's center. Due to the great pressures and
the increase in P-wave velocity at the inner core
(as shown in Figure l2-11), the inner core is
believed to be a solid.
3.0 oceanic
４
Beneath the mantle Earth's core is divided into
two parts-the inner core and the outel core.
III
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molten. Much of the magma and lava of the crust
and lithosphere is thought to originate in
this zone. Note on the temPerature graph in
Figure 12-11 that the melting Point and
temperature curve intersect, indicating this partial
melting. The asthenosphere allows the plates of
the lithosphere to move around Earth's surface
and to move up and down. Below the
asthenosphere is the maiority of the mantle, called
the stiffer mantle.
:潟
υ
7 continental
1000
0
0
10002000 3000400050006000
Depth(km)
FIgurG
l2-ll.
Properties and zonet of Earth's interior:
Analysis of the seismic wave! and other studies have resulted
in the inlejen(e about Earth! interior illurtrated here. Note that
most ot Earthb interior i5 solid except for the outer <ore and
portions of the asthenosphere, both ot which are liquid' (See
algo the lnferred Properties of Earth3 lnterior in the Earth scr'ence
Befetence lablet.,
Topic 12: Earth's Dynamic Crustand
lnterior 257
The continental crust is made largely of granitic
^
(p
rocks-rocks with
a
mineral or chemical composition similar to granite. The oceanic crust is
composed mostly of basaltic rocks-rocks similar in mineral or chemical
composition to basalt. The granite is less dense than the basalt; thus, the
granitic continental crust is less dense than the basaltic oceanic crust. See
the average value of the density of the continental crust and oceanic crust
on the Ir:rferred Properties of Earth,s Interior in the Earth Science Reference
Tables.
Composition of Earth's lnterior Many scientists think Earth,s inner and
outer core are composed largely of iron and nickel. There is much evidence
to support this hypothesis, including the iron and nickel composition of
many meteorites and Earth's magnetism-iron and nickel are two of a few
magnetic elements. In addition, a combination of iron and nickel at the
temperafures and pressures believed to be in Earth,s core can account for
the observed properties of the seismic waves that pass tfuough the core.
The high-density iron-nicke-l composition of the core and the low-density
composition of the crust indicate that the mantle must have a composition
different from the crust and the core and an interrnediate density.
:
(!)
29.
Earth's crust is composed mostly of rocks and minerals, as illustrated on
the various charts in the Edrth Science Reference Tables depicting minerals,
sedimentary rocks, metamorphic rocks, and ign"ors .o"-ks. Geierally, the
crust is composed of low-density rocks with a mixture of granitic and
basaltic cornpositions.
ln developing a model of Earth,s deep interior,
most of the evidence was derived from
(1) deep wells
(2) mining operations
(3) observation of other planets
(4) seismic data
30. Through which
zones
(P-waves) travel?
of Earth do primary waves
(1) only the crust and mantle
(2) only the mantle and outer core
(3) onlythe outer and inner core
(4) the crust, mantle, outer core, and inner core
31. According to the Earth
Science Reference TableT
in which group are the zones of Earth,s interior
correctly arranged in order of increasing averい０ ●“
age density?
258
crust, mantle, outer core, inner core
crust, mantle, inner core, outer core
inner core, outer core, mantle, crust
outer core. inner core, mantle, crust
fopic t U: Earth's Dynamic Crust and tnterior
32. What evidence
has been obtained concerning
the existence of the Moho and Earth,s mantla?
(1) satellite images
(2) well drillings
(3) exposures in deep canyons like the Grand
Canyon
(4) refraction of earthquake waves
33. What
is the relationship among density,
temperature, and pressure inside Earth?
(1) As depth increases, density, temperature,
and pressure decrease.
(2) As depth increases, density and temperature
increase, but pressure decreases.
(3) As depth increases, density increases, but
temperature and pressure decrease.
(4) As depth increases, density, temperature,
and pressure increase.
!14. ln which parts of Earth's interior would melted
or partially melted material be found?
(1) stiffer mantle and inner core
(2) stiffer mantle and outer core
(3) crust and inner core
(4) asthenosphere and outer core
How does thickness and density of the continental crust compare to that of the oceanic crust?
(l) The continental crust is thicker and less
dense than the oceanic crust.
(2) The continental crust is thicker and denser
than the oceanic crust.
(3) The continental crust is thinner and less
dense than the oceanic crust.
(4) The continental crust is thinner and denser
than the oceanic crust.
An earthquake occurs in city A. Recordings on a
seismograph in city B show only the presence of
P-waves. City A and B are on opposite sides of
Earth-180' apart. what does this information
allow you to infer about the structure of Earth's
interior?
How does the composition oJ the oceanic crust
compare with the composition of the continen-
tal crust?
(1) The oceanic crust is mainly limestone, while
the continental crust i5 mainly sandstone.
(2) The oceanic crust is mainly limestone, while
the continental crust is mainly granitic.
(3) The oceanic crust is mainly basaltic, while the
continental crust is mainly sandstone.
(4) The oceanic crust is mainly basaltic, while the
continental crust is mainly granitic.
39.
The overall density of Earth is approximately
5.5 9/cm3. The average density of Earth's crust
is between 2.5 gtcm3 and 3.0 g/cmr. What does
this suggest about the density of Earth's core?
40.
The composition of some meteorites supports
the inference that Earth's core is corlposed of
(l)
Stop Here
41.
The temperature of rock located 1000 kilometers
below Earth's surface is approximately
１
２
００
つυ 助
crust generally
decreases
increases
remains the same
aluminum and calcium
(2) iron and nickel
(3) silicon and oxYgen
(4) magnesium and potassium
37. As one travels from an ocean shore to the
interior of a continent, the thickness of Earth's
1000° C
2600° C
3300° C
4300° C
Plate lbctonics
People have always wondered about the origin of continents, mountain
ranles, volcanoes, earthquakes, and the multitudes of other features and
err"its. In the pust, many legends, religious beliefs, and scientific theories
have hied to explain Earth's features and events. Some of the older
scientific theories include cooling and contraction of Earth, expansion
of Earth, and continental drift. None of these earlier theories seems
satisfactory for most of the scientific community today. Since the 1960s
many new discoveries from the studies of ocean drilling, Earth's
magnetism, satellite observations, and detailed analysis of rocks and fossils
hav-e led to *re plate tectonic theory. This theory has done for the earth
sciences what evolution and genetics have done for the biological sciences'
It has provided a unifying model to explain most, if not all, rnajor features
and events of Earth's lithosphere.
The Plate Tectonic TheorY
The basic concept of the plate tectonic theory is that Earth's lithosphere
is broken up into sections or pieces called plate*also called lithospheric
plates and iectonic plates-and their movement and interaction produce major changes in Earth's surface. In this book the term "plates" will mosdy
be used.
These plates move about Earth's surface at a rate of a few centimeters per
year (ipproximately the rate of fingemail growth)' These plates can also
move up and down-usually at rates of only millimeters per y€ar--due to
uplifting and sinking. The plates can move around and up and down
because"they are floitlng on the asthenosphere--a plasticJike layer of the
mantle'
Topic 12: Earths Dynamic crusl and lnterior
259
!e{er to fjqle t2-12 and the lbctonic plates map in the Earth Scimce (D
familiar with the namis and locations of the
various plates. You will observe that the plates usually don,t follow
continent or ocean boundaries. Note tnaitfre North Rmerican plate
includes parts of Asia and North America; the pacific, Arctic, and the
Atlantic Oceans; and Greenland and part of lceland. Westemmost
Refermce Tablw to become
Califomia and Mexico are part of the pacific plate. Most plates have
continmta_l and oceanic cnrst at their tops. Almail number of plates are
oceanic-that is, they have only oceaniC cmst at their tops, like the Nazca
and Philippine plates.
At least three times, if not more, most of the large landmasses (continents
and larger islands) have come together, formin! supercontinents.
Figure 12-12 shows how the supercontinent Rdin; formed approximately
800 million years ago and how the continmts have split and formed
since'
then. Note that diagrams G and H indicate the proiected positions of
landmasses in the future, based on the rates ana dfuections the plates
are
moving in now
The Three
flpes of plate Boundaries
As tfie plates move, they interact in three ways-they can separate,
collide,
and slide by each other. Most of the major evints involving Earth,s
such as mountain building, earthquakes, and volcanic eruptions_occur
at
Uo.un$a1a yhere the plates interact. Each of the three-types of plate
$e
boundaries has its own set of unique events and features, whicfr are
crusj
illustrated in Figure 12-13.
Diuergent Platc Eoundaries Wherc two plates sqrarate, or diverge,
the
boundary is catled a divergent ptate Uounaary.
tfr"s"
to"utio.E
tt
pt"t""
^dt
move apart and magma rises from below to fill in the separation, resulting
"
in igneous intrusions and extrusions, such as lava flows^urrd volca.roes.
(See Figure 12-138.) This divergmce is sometimes
called sea-floor
spreading.
"
Thig magm? and resulting lava form igneous rock that creates new crust
and lithosphere, which are then sptit and divided in two by the divefueice.
The magma that forms in these regions is the result of divJrgence
thai
lowers the- confiningpressure and-melts rocks of the lower li-thosphere and
asthenosphere. The divetgence also results in many earthquakes,
most of
which are shallow in depth. If the divergmce is wiihin thJcontinental
crust, the result is a continental rift valley of mountains created by faulting
and much volcanic activity. (See Figure iZ-taa.;
Whm the divergmce is within oceanic crust,.the faulting and volcanic
activity result in a mid-ocean ridge, a mountain range atihe bottom of
theocean that is composed moslly of volcanoes ani lava flows. The
mid-ocean-ridges often have a central depression, or rift valley, as
shown
in Figure 12-138.
Convergent Plate Boundaries When two plates collide, or
converge, the
result is a convergent plate bounaary, Much of the dramatic events
and
feafures of Earth's crust are deated it these convergent boundaries.
There
are three varieties of convergent plate boundaries:
o both plates with oceanic crust on top
260
Topic 12: Earthi Dynamic Crust and tnterior