Chapter 22
Earth’s Interior
Objectives:
1. Describe
the
science of geology
2. Describe the main
layers of Earth’s
interior
Definition: geology
is the study
of planet Earth, including its
composition and structure
Definition: uniformitarianism is
the idea that the geologic
processes that operate today
also operated in the past
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Earth can be divided into 3 main layers:
the crust, the mantle and the core
Definition: the crust is the rocky outer
layer of Earth
We walk on the continental crust which
contains silicates
Definition: silicates are rocks made up of
silicon & oxygen and often contain
aluminum, iron or calcium
Aluminum is the most abundant element in
Earth’s crust
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Two types of crust exist: continental
crust and oceanic crust
Definition: continental crust is the rocks
that make up the continents
The rocks are less dense like granite
Continental crust ranges in thickness
from 8 to 75 kilometers
Definition: oceanic crust is the rocks
that make up the ocean bottom
Oceanic crust ranges about 7
kilometers thick & is thin compared to
continental crust
Definition: the
mantle is the layer of
Earth beneath the crust
The mantle is thick & made of hot, solid
rock
It is about 2850 kilometers thick
The mantle has 3 layers: the
lithosphere, asthenosphere, and
mesosphere
The lithosphere is about 100 km thick
& consists of cool rigid rock including
the uppermost part of the mantle and
the crust
The
asthenosphere is located beneath
the lithosphere
Is is weaker, softer rock thought to
have the consistency of bubble gum
It is believed to flow slowly
The mesosphere is located underneath
the asthenosphere
The mesosphere consists of stiffer rock
The mesosphere extends all the way
down to the upper surface of Earth’s
core
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The third and final main layer of Earth is
called the core
There are 2 parts to the core: the outer
core and the inner core
Scientists think that the core consists of
metals, mostly nickel and some lighter
elements
There is enormous pressure at Earth’s
core and the temperature is thought to be
about 5500°C (nearly equal to sun’s
surface)
In the outer core, high temperatures keep
the metal liquid
Because
of Earth’s rotation, the
flowing iron in the outer core is
believed to create Earth’s
magnetic field
The temperature at the inner
core is also very high but the
pressure is greater than the
pressure on the outer core
Therefore, the inner core is
believed to be solid
Objectives:
1. Distinguish
between
rocks and minerals
2. Explain several
properties used to identify
minerals
 Definition: a
rock is a solid combination
of minerals or mineral materials
 Definition: a mineral is a naturally
occurring inorganic solid with a crystal
structure and a characteristic chemical
composition
 Definition: inorganic solids are products
of nonliving things
 Minerals are the building blocks of
rocks
Some
properties of minerals include:
crystal structure, color, streak, luster,
density, hardness and fracture
Crystal structure means that the atoms
have a specific geometric shape
Some minerals have a characteristic
color
Streak is the color of the mineral’s
powder
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Luster is a measure of how shiny the mineral
is & it is the way its surface reflects the light
Density depends on the unique chemical
composition of the mineral & it is a unique
physical property of all substances
Density is mass divided by volume
Hardness is the resistance of the mineral to
scratching
Hardness of minerals is measured by Mohs
Hardness Scale which runs from 1 (softest) to
10 (hardest)
Talc or chalk is 1 and diamonds are 10
Fracture
is how the mineral
breaks
Some minerals split along a
geometric line or plane
Some minerals have other
properties such as solubility
(ability to dissolve) in certain
substances, florescence, electrical
charge when heated, cooled or
subjected to pressure or ability to
refract light
Objectives:
1. Classify
rocks as igneous,
sedimentary or metamorphic
2. Explain how different types of
rocks form
3. Describe the processes by which
rocks continually change from one
type to another in the rock cycle
 Rocks
are classified into 3 major groups:
igneous, sedimentary and metamorphic
 The classification is based on how they
form
 Definition: magma is a mixture of molten
rock and gases which forms underground
 Definition: lava is magma that flows out of
volcanoes
 Igneous rock forms from magma
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There are 2 types of igneous rock: intrusive
and extrusive
Intrusive igneous rock forms underground
slowly from hardened magma
Extrusive igneous rock forms faster at
Earth’s surface
Examples of intrusive igneous rock include
gabbro and granite
An extrusive rock is basalt
Some other kinds of igneous rocks include:
Obsidian (extrusive volcanic glass), Pumice,
& Rhyolite
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Definition: sediment consists of small pieces of
material that comes from rocks or living
organisms
The basic mechanism of formation has to do
with pressure and the presence of water,
weathering and erosion
as more and more sediments build up over
time, the deeper layers become compressed &
squeezed with dissolved minerals (usually in
water) seeping into the spaces creating the
cement that holds the layers of sediment
together
Geologists classify sedimentary rocks into 3
groups according to how they form: clastic
rocks, chemical rocks and organic rocks
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Definition: clastic rocks are sedimentary rocks
formed from broken fragments of other rocks
Clastic rocks are held together by cement
An example is conglomerate
Definition: chemical rock is sedimentary rock that
form when minerals precipitate out of solution
An example is calcium carbonate limestone or
shale
Definition: organic rocks form from once living
organisms such as dead coral, clams, and
mussels
An example is the White Cliffs of Dover
(England) composed of chalk from dead sea
organisms
Sandstone is also a sedimentary rock
Definition: metamorphic
rock is rock
that has been changed by temperature,
pressure or reactions with hot water
Most metamorphic rocks form under
high temperatures and pressure deep
underground
Slate, schist and gneiss are metamorphic
rocks that can be formed from the
sedimentary rock shale after
temperature & pressure
 Marble and Quartzite are also
metamorphic rocks
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Definition: the rock cycle is a series of
processes in which rocks continuously
change from one type to another
In the rock cycle, forces within Earth and at
the surface cause rocks to change form
Igneous rock forces include: magma, melting
and cooling
Sedimentary rock forces include:
weathering, erosion, compacting and
cementation
Metamorphic rock forces include: heat and
pressure
Objectives:
1. Explain
the hypothesis of
continental drift
2. Relate how the theory of plate
tectonics explains sea-floor
spreading, subduction and the
formation of mountains
3. Explain the mechanisms of plate
movement
 Definition: plate
tectonics is the theory that
pieces of Earth’s lithosphere, called plates,
move about slowly on top of the
asthenosphere
 The theory of plate tectonics explains the
formation and movement of Earth’s plates
 In 1912, a German scientist named Alfred
Wegner proposed the theory of continental
drift
 Wegner hypothesized that the continents were
once joined in a single supercontinent (called
Pangaea) which then broke into pieces and
moved apart
 Wegner’s
hypothesis and new evidence led
geologists to propose the theory of plate
tectonics
 In the mid 1900s scientists mapped a chain
of ocean mountain called the mid-ocean
ridge
 While mapping the ridge they also found a
deep valley running the length of the crest
 A geologist named Harry Hess proposed
the theory of sea-floor spreading to explain
this
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Definition: sea-floor spreading is the
process by which new oceanic crust is
created at the mid-ocean ridges as older
crust moves away
The ridge is a huge crack where magma is
pulled upward
Definition: subduction is the process by
which oceanic plates sink into the magma
of the mantle creating a trench
As sea-floor spreading occurs, old oceanic
plates sink into subduction zones
Definition: a trench is a depression in the
ocean floor caused by the plate sinking into
the subduction zone
 Sea-floor
spreading creates new oceanic
crust at mid-ocean ridges
 Subduction destroys old oceanic crust at
subduction zones
 Patterns of parallel magnetic stripes in the
rocks were identical and found on both
sides of the ridge
 The stripes exist because Earth has
reversed its magnetic field several times in
the past
 The stripes indicate that new ocean floor
was added to both sides of the ridge about
roughly the same time
 Sea-floor
spreading provided evidence
that pieces of Earth’s crust move
 The plate tectonics theory says that
Earth’s plates are constantly moving
independent of each other
 Each plate moves at a different rate and
direction
 Plate motions are the visible part of the
process of mantle convection
Definition: convection
is the transfer of
heat energy when particles of a fluid
move from one place to another
Convection currents usually exist in
circular patterns
The heat that drive plate tectonic
convection in the mantle comes from
the decay of radioactive isotopes in the
mantle & crust, and also from the
gradual cooling of the interior of Earth
Earth was hot when it was formed
There
are about a dozen major
tectonic plates
Most plate contain both continental
& oceanic crust
There are 3 types of plate
boundaries: divergent boundaries,
convergent boundaries & transform
boundaries
The plates move slowly, from 0.1 cm
– 10 cm per year
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Divergent plates move away from each other
The mid-ocean ridge is a major divergent
boundary
When plates move apart, magma from the
mantle rises, fills the gap, then forms new rock
Convergent plates move toward each other
Most convergent boundaries occur at
subduction zones where more dense oceanic
crust dives underneath continental crust,
slipping into the magma, melting and
destroying rock
At transform boundaries, the plates slide past
each other in opposite directions
Rock is neither created nor destroyed
The San Andreas fault of which we are a part, is
a transform boundary
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Mountains form along plate boundaries
At convergent boundaries where crust has the
same density, neither plate is subducted
during the collision
The crust buckles, folds, thickens and pushes
up tall mountains
Occasionally this happens between oceanic &
continental crust, but usually between
continental crust
At divergent boundaries, the mid-ocean ridge
forms a long chain of mountains on the sea
floor
No mountains are formed at transform
boundaries
Definition: an
earthquake is movement
of Earth’s lithosphere that occurs when
rock in the lithosphere suddenly shift,
releasing stored energy
Definition: seismic waves are energy
released during the earthquake and
carried by vibrations
Definition: a tsunami is a large sea wave
generated by an underwater
earthquake, volcano or landslide
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Definition: stress is a force that squeezes
rocks together, stretches or pulls them
apart, or pushes them in different directions
As tectonic plates move, they cause stress in
the crust which produces faults and folds
Definition: a fault is break in the mass of
rock along which movement occurs
Many faults along plate boundaries
Definition: a fold is a bend in the layers of
rock
Folds form where rocks are squeezed
together but do not break
They can be seen in rock layers that make
up some mountain ranges
Objectives:
1. Describe
the causes and effects
of stress in Earth’s crust
2. Explain why earthquakes occur
and how their energy is
3. Explain how earthquakes are
measured and how earthquake
data is used to learn about Earth’s
interior
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Earthquakes occur because stress forces
have exceeded the strength of the rock
As the rocks break and move, potential
energy is transformed into kinetic energy in
the form of seismic waves
Earthquakes produce 3 types of waves: P
waves, S waves and surface waves
P waves are primary waves
They are longitudinal waves similar to sound
waves
P waves compress and expand the ground
like an accordion
S
waves are secondary waves
They are transverse waves like
light or electromagnetic radiation
Surface waves develop when
seismic waves reach Earth’s
surface
Surface waves move more slowly
than P and S waves, but produce
larger ground movements and
greater damage
Geologists
record seismic waves
using seismographs to measure &
pinpoint the epicenter
Definition: a seismograph is a
device that detects and records
seismic waves
The Richter scale for
measurement is no longer used by
geologists
 The
moment magnitude scale gives a measure
of the amount of energy released
 It is the most useful of the scales currently
used
 The modified Mercalli Scale ranges from 1 to
12 and is based on observations of the
intensity of ground shaking and damage in the
areas affected by an earthquake
 An earthquake of 7 knocks over chimneys,
while 12 is total destruction of a city and
nearby towns
 Most earthquakes are concentrated along
plate boundaries, where many faults are found
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Objectives:
1. Describe the internal structure of a
volcano and how volcanoes form
2. Relate the type of volcanic eruption
to the characteristics of magma
3. Describe the different types of
volcanoes and where they are located
4. Describe several types of igneous
features and how they are formed
 Under
certain conditions, small amounts
of mantle rock can melt, forming liquid
magma
 The magma rises upward through the
crust, erupting at the surface as a volcano
 Before eruption, magma collects in a
pocket called a magma chamber
 The magma rises to the surface in a
vertical channel called a pipe
 The magma escapes on the surface at the
vent
 A large central vent in most volcanoes is
a bowl-shaped pit called a crater
 After
eruption, the magma chamber and
main vent may be empty of magma,
creating a hollow shell
 If the shell collapses inward, it creates a
depression called a caldera, located at the
top of the volcano
 Volcanoes erupt explosively or quietly
depending on the characteristics of the
magma
 Recall that viscosity is resistance to flow
 Magma with high viscosity erupts
explosively
Most
volcanoes occur along plate
boundaries
A few are located at hot spots in the
crust
The volcanoes at plate boundaries are
associated with subduction zones
Definition: a hot spot is a region where
hot rock extends from deep within the
mantle to the surface
Hawaii is built on active hot spot
There
are 3 major types of volcanoes
They are: shield volcanoes, cinder
cones, and composite volcanoes
A quiet eruption of low viscosity
produces a wide, flat shield volcano
An ash and cinder eruption produces a
steep-sided cinder cone volcano
Lava and ash explosive eruptions form
composite volcanoes
Mount Saint Helens is a composite
volcano
Magma
forms igneous features
such as batholiths, sills, dikes and
volcanic necks
Definition: a batholith is the largest
type of intrusive igneous rock mass
We live in the Sierra Nevada
Batholith & it is the core of our
mountain range which was born
out of volcanoes
 Definition: a
sill is magma that has
squeezed into a crack that is parallel to
the existing rock and hardened
 Definition: a dike is hardened magma
that has formed in a crack that cuts across
rock layers
 Definition: volcanic rock is magma that
has hardened in a volcano’s pipe
 The largest lava flows come from clusters
of long thin cracks in Earth’s crust (not
from volcanoes)
 Definition: a plateau is lava that has
spread and created a high level area