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Chapter 4:
Section 1: Inside the Earth
• The Earth is made of different
layers which are described by
their Composition and Physical
properties
Composition
The Earth is divided into
3 main layers:
1. Crust
2. Mantle
3. Core
The Crust
• The crust is the outermost
layer of the Earth with a
thickness of 5 to 100 km
2 Types of Crust
Continental crust: - land bodies, usually 30
km thick! (Mostly granite)
Oceanic crust: - bottom of water bodies, 5-8
km thick. (Mostly basalt)
Two types of crust
The Mantle
•thickness of 2,900 km.
•It is so deep that… no one has
ever seen what it looks like.
•Contains most of the Earth’s mass
The Core
Is the center of the Earth and is
made of Iron with smaller amounts
of Sulfur, Aluminum and Magnesium,
and silicon and oxygen
Physical Properties
of Earths Layers
• Based upon structure, there
are 5 physical layers:
1.) Lithosphere
2.) Asthenosphere
3.) Mesosphere
4.) Outer core
5.) Inner core
1.) The Lithosphere
• Outermost layer
• made up of the crust and the rigid upper
part of the mantle.
• Divided into pieces called tectonic plates.
2.) The Asthenosphere
•This is the soft
layer of the mantle
on which pieces of
the lithosphere
move.
3.) Mesosphere
• Lower part of the mantle
4.) The Outer Core
• Outer liquid
layer of the
core
5. Inner Core
•Solid inner
layer of
the core
Tectonic Plates
• Pieces of the lithosphere that move
around on the asthenosphere.
• Made of continental crust, oceanic
crust or both
Depths of the Earth
• Scientists cannot
visit the depths
of the Earth like
the mantle and
the core but use
seismic waves
recorded during
earthquake
activity.
Seismic Waves
The device that
measures
seismic waves
is a
seismograph.
Section 1 Recap Questions
What are the 3 main layers of the Earth?
Crust, Mantle, Core
What are the 2 components of the crust?
Continental and Oceanic
What is the largest layer of Earth?
The Mantle
According to their characteristics, what are
the 5 layers Earth can be broken into?
Lithosphere, Asthenosphere, Mesosphere,
Outer core, Inner core
Alfred Wegener
1911
Developed a Theory called the Theory
of Plate Tectonics which states that
the Earth’s lithosphere is divided into
tectonic plates that move around on top
of the asthenosphere. The continents
once formed a single landmass, broke
up, and drifted to their present
locations
Wegener’s Theory explains
some observations:
1. The continents seem to fit together
2. Fossils of the same plant and animal
species are found on continents that
are on different sides of the Atlantic
Ocean.
3. Similar types of rock were found on
several continents.
4. Evidence of the same ancient climatic
conditions were found on several
continents.
Wegener proposed that all of the
separate continents that we see
today were once connected in a
giant landmass called Pangaea which
broke up about 180 M years ago and
formed 2 big pieces called Laurasia
and Gondwanaland. Then, about 65
MYA, these broke up and formed
the continents that we know today.
Sea Floor Spreading
• As the tectonic plates move away from each other,
the sea floor spreads apart and magma fills in the
gap.
Sea floor spreading is proven
by the ages of the rocks
• As this new crust forms,
the older crust gets
pushed away from the
mid-ocean ridge.
• The older crust is
farther away from the
mid-ocean ridge than the
younger crust is.
Magnetic
Reversal
• Throughout
Earth’s history,
the north and
south magnetic
poles have
changed places
many times.
How does
Magnetic
Reversal
Prove Sea
Floor
Spreading?
Plate Tectonics
Theory of Plate Tectonics states that
the Earth’s lithosphere is divided into
tectonic plates that move around on top
of the asthenosphere. The continents
once formed a single landmass, broke
up, and drifted to their present
locations
Boundary
• Boundary - is a place where tectonic
plates touch.
• 3 types of boundaries (depending on how
the plates are moving relative to one
another):
1.) Convergent
2.) Divergent
3.) Transform
Convergent Boundary
• Type of Crust  O-O, C-C, or O-C
• Type of Movement - 2 plates move together
often, 1 oceanic plate moves under another
oceanic or continental plate in a process
called subduction
• Arrows -

Divergent Boundaries
• Type of Crust  O-O or C-C
• Type of Movement - 2 plates move apart
• Arrows -
Stress
• Stress is: the amount of
force that is applied on a
given material.
• Deformation - when rock
changes shape due to stress
There are two main types of
stress that can act on a
rock.
1.Compression
2.Tension
Compression
Motion that Occurs
–Rock is squeezed & will fold
What type of boundary?
–Convergent
Tension
Motion that Occurs
–Rock is stretched and can
break
What type of boundary?
–Divergent
Folding
• Folding occurs when rock
layers bend due to stress in
the Earth’s crust.
3 Types of folding:
1. Anticline
2. Syncline
3. Monocline
Anticline
Description: rock folds downward
(like a hill)
Picture:
Syncline
Description: rock folds upwards
(like a “u”)
Picture:
Monocline
Description: layers of rock are
stacked but remain horizontal.
Picture:
Fault
• A crack in the Earth’s crust
along which rocks move.
Fault Blocks
• The blocks of crust on either
side of the fault
• If a fault is cut diagonally, it
usually has two specific sides.
• a)Hanging wall: the upper side of
the cut, the upper portion sticks
out.
• b)Footwall: the lower side of the
cut, the bottom portion sticks
out
Hanging wall & Footwall
Hanging
Wall
Footwall
3 Types of Faults
1.Normal
2.Reverse
3.Strike-slip
Normal Faults
• Description: Stress at a
divergent boundary pulls Hanging
wall down relative to the footwall
• Picture:
Reverse Fault
• Description: Compression pushes
Hanging wall moves up relative to
the footwall at a convergent
boundary
• Picture:
Strike-Slip Fault
• Description: Rock breaks &
moves horizontally (transform
boundary)
• Picture:
Mountains
• Mountains are formed when
tectonic plates undergo
compression or tension.
3 Types of Mountains
1. Folded
2. Fault-block
3. volcanic
Folded mountains
• Description: Rock layers are
squeezed together & pushed
upwards
Fault-Block Mountains
• Description: when there is enough
tension, a large number of normal
faults can result. Mountains are
tilted upwards by faulting & will
have sharp, jagged peaks.
Volcanic Mountains
• Description-When molten rock
erupts into the Earths surface,
magma pushes the surface of the
Earth upwards