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EESA06H3 (240)
Nick Eyles (207)
Chapter 4

Chapter 4 Notes

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Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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Chapter 4
The Earths Interior
the earths crust is a thin skin of rock
earth is divided into three major layers
othe crust
othe mantle
othe core
seismic reflection and refraction suggest that the continents are largely igneous and
metamorphic rock, such as granite and gneiss, overlain by a veneer of sedimentary rocks
geophysics the application of physical laws and principles to a study of the earth
seismic reflection the return of some of the energy of seismic waves to the earths
surface after the waves bounce off a rock boundary
othese reflected waves are recorded on a seismogram, which shows the amount of
time the waves took to travel down to the boundary, reflect off it, and return to the
surface
seismic refraction the bending of seismic waves as they pass from one material to
another
oas a seismic wave strikes a rock boundary, much of the energy of the wave passes
across the boundary
oas the wave crosses from one rock layer to another, it changes direction
occurs only if the velocity of seismic waves is different in each layer
What is Inside the Earth?
it was the study of seismic refraction and seismic reflection that enabled scientists to plot
the three main zones of the earth
the crust
othe outer layer of rock, which forms a thin skin on earths surface
oit is thinner beneath the oceans than beneath the continents
oseismic waves travel faster in oceanic crust than in continental crust
othe two types of crust are made up of different kinds of rock
oseismic P waves travel through oceanic crust at about 7 km per second, which is
also the speed at which they travel through basalt and gabbro
othe upper part of the oceanic crust is basalt, and the lower part is gabbro
oseismic P waves travel more slowly through continental crust
ocontinental crust is often called granitic
othe continental crust is highly variable and complex, consisting of a crystalline
basement composed of granite, other plutonic rocks, gneiss, and schists, all
capped by a layer of sedimentary rocks
ofelsic (rocks high in feldspar and silicon) is used for continental crust
omafic (rocks high in magnesium and iron) is used for oceanic crust
oseismic waves show that the crust is thickest under geologically young mountain
ranges
othe continental crust is also dense than the oceanic crust
othe boundary that separates the crust from the mantle is called the Mohorovicic
discontinuity
othe mantle lies closer to the earths surface beneath the ocean than it does
beneath continents
www.notesolution.com
the mantle
omade of solid rock
obecause P waves travel at about 8 km per second in the upper mantle, it appears
that the mantle is a different type of rock from either oceanic crust or continental
crust
othe best hypothesis that geologists can make about the composition of the upper
mantle is that it consists of ultramafic rocks such as peridotite
ultramafic rock is dense igneous rock made up of ferromagnesian minerals
such as olivine and pyroxene
some ultramafic rocks contain garnet, and all of them lack feldspar
othe crust and the upper mantle form the lithosphere
the outer shell of earth that is relatively strong and brittle
makes up the plates of plate tectonics theory
averages about 70km thick beneath oceans and may be 125-250 km thick
beneath continents
seismic waves increase in velocity with depth as increasing pressure alters
the properties of the rock
they travel more slowly than they do in shallow layers
so this zone is called the low velocity zone
oextends to a depth of about 200 km
oalso called the asthenosphere
othe rocks in this zone may be closer to their melting point than
the rocks above or below the zone
if the rocks of the asthenosphere are close to their melting point, this
zone may be important for two reasons:
oit may represent a zone where magma is likely to be generated
othe rocks here may have relatively little strength and therefore,
are likely to flow
if mantle rocks in the asthenosphere are weaker than they are in the
overlying lithosphere, then the asthenosphere can deform easily by
plastic flow
because pressure increases with depth into the earth, the boundaries
between mantle layers possibly represent depths at which pressure
collapses the internal structure of certain minerals into denser minerals
the core
oseismic wave data provide the primary evidence for the existence of the core of the
earth
othe region between 103 degrees and 143 degrees, which lacks P waves, is called
the P-wave shadow zone
can be explained by the refraction of P waves when they encounter the core
boundary deep within the Earths interior
oP waves can travel through solids and fluids, An S waves can travel only through
solids
oAn S-wave shadow zone is larger than P-wave shadow zone
Seems to indicate that S waves do not travel through the core at all
If this is true, it implies that the core of the Earth is liquid, or at least acts like
a liquid
www.notesolution.com

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Description
Chapter 4 The Earths Interior the earths crust is a thin skin of rock earth is divided into three major layers o the crust o the mantle o the core seismic reflection and refraction suggest that the continents are largely igneous and metamorphic rock, such as granite and gneiss, overlain by a veneer of sedimentary rocks geophysics the application of physical laws and principles to a study of the earth seismic reflection the return of some of the energy of seismic waves to the earths surface after the waves bounce off a rock boundary o these reflected waves are recorded on a seismogram, which shows the amount of time the waves took to travel down to the boundary, reflect off it, and return to the surface seismic refraction the bending of seismic waves as they pass from one material to another o as a seismic wave strikes a rock boundary, much of the energy of the wave passes across the boundary o as the wave crosses from one rock layer to another, it changes direction occurs only if the velocity of seismic waves is different in each layer What is Inside the Earth? it was the study of seismic refraction and seismic reflection that enabled scientists to plot the three main zones of the earth the crust o the outer layer of rock, which forms a thin skin on earths surface o it is thinner beneath the oceans than beneath the continents o seismic waves travel faster in oceanic crust than in continental crust o the two types of crust are made up of different kinds of rock o seismic P waves travel through oceanic crust at about 7 km per second, which is also the speed at which they travel through basalt and gabbro o the upper part of the oceanic crust is basalt, and the lower part is gabbro o seismic P waves travel more slowly through continental crust o continental crust is often called granitic o the continental crust is highly variable and complex, consisting of a crystalline basement composed of granite, other plutonic rocks, gneiss, and schists, all capped by a layer of sedimentary rocks o felsic (rocks high in feldspar and silicon) is used for continental crust o mafic (rocks high in magnesium and iron) is used for oceanic crust o seismic waves show that the crust is thickest under geologically young mountain ranges o the continental crust is also dense than the oceanic crust o the boundary that separates the crust from the mantle is called the Mohorovicic discontinuity o the mantle lies closer to the earths surface beneath the ocean than it does beneath continents www.notesolution.com
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