Chapter 7: Forces Shaping Earth

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Chapter 7Forces Shaping Earth

• Note-taking worksheets 1 2

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NTW 1 Earths Layers

• Geologists study earthquakes and surface rocks to
  indirectly observe Earths interior.

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When an earthquake occurs, energy is carried
through objects by seismic waves. These seismic
waves change speed and direction depending on the
density and material they travel through.
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With evidence from earthquake waves and exposed
rocks, scientists have developed a model of
Earths interior. This model shows Earth as
having four distinct layers.
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Quiz

• What do Geologists study so that they can
  indirectly observe Earths interior?
• How is energy carried through objects in an
  earthquake?
• What determines if a seismic wave will change
  speed and direction?
• How many layers does the Earths interior have?

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The Inner Core is the innermost layer of Earths
interior.

• This part of the Earths interior is very dense
  and composed mostly of solid iron.

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The Inner Core

• It is believed that the temperature is 5000
  degrees Celsius.

This layer experiences the greatest amount of
pressure.
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The Outer Core lies above the inner core.

• It is thought that this layer is composed mostly
  of molten metal, such as iron and nickel, making
  it a liquid.

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The Outer Core

• Seismic studies indicate that this layer is
  uneven in nature.

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Quiz

• What is the innermost layer of Earths interior
  called?
• What is the layer that lies above the inner core
  called?
• Which layer of Earths interior is very dense and
  composed mostly of solid iron?
• Which layer of the Earths interior experiences
  the greatest amount of pressure?
• Which layer of the Earths interior is composed
  mostly of molten metal making it a liquid?
• Which layer of the Earths interior has the
  greatest amount of pressure?

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The mantle is the largest layer of Earths
interior.

• Even though the mantle is a solid, the mantle
  flows slowly similar to putty. Most of the
  mantle is made of iron and magnesium.

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The Mantle

• The mantle is composed of two parts, the
  lithosphere which is closest to Earths crust and
  the asthenosphere.

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The crust is Earths outermost layer.

• Earths crust is thin when compared to the other
  layers, although the thickness varies. It is
  thinnest under the oceans and thickest through
  the continents. It is composed mostly of oxygen
  and silicon.

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Quiz

• What is the Earths outermost layer called?
• What is the largest layer of Earths interior
  called?
• List in order the four layers of the Earth
  starting from the center one.
• Which layer is a solid but flows slowly?
• Which layer of the Earth is the thinnest?
• What are the two parts of the mantle called?
• Where is the Earths crust the thinnest and where
  is it the thickest?

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Density, temperature and pressure are properties
of Earth that are lowest in the crust and
greatest in the inner core.
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Quiz

• Are density, temperature and pressure the same no
  matter where you are inside the Earth?
• Where are density, temperature and pressure the
  greatest?
• Where are density, temperature and pressure the
  lowest?
• Why do you think this happens?

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NTW 2 Earths Plates

• The rigid, upper part of Earths mantle is called
  the lithosphere.

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It is broken into about 30 sections or pieces
called plates that move around on the plastic
like asthenosphere which is also part of the
mantle.

• The major tectonic plates include Eurasian,
  African, Australian-Indian (Indo-Australian),
  Pacific, North American and South American.

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The movement of the plates is fairly slow, yet
over millions of years, plates and land masses
have moved great distances.
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The historical evidence that plates are moving
includes continents fit together like jig-saw
puzzle, same fossils found on different
continents and large amount of volcanic and
earthquake activity.
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Quiz

• The ________ is the rigid upper part of the
  Earths mantle and the ________ is the plastic
  like lower part.
• The lithosphere is broken into about 30 sections
  or pieces called ________.
• State one reason scientists believe plate
  techtonics occurred.
• How many major techtonic plates did we list?

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THREE WAYS PLATES MOVE

• 1) Plates Move Apart The pulling force called
  tension pulls two plates apart resulting in the
  formation of new lithosphere. This process of
  plate separation and lithosphere formation that
  takes place under the oceans is called mid-ocean
  ridges. High ridges often form.

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Quiz

• When plates move apart, the pulling force is
  called ______.
• When plates pull apart, they form new __________.

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THREE WAYS PLATES MOVE

• Plates That Collide
• A) When two plates of similar density collide
  the crusts pile up. This force is called
  compression. As rock layers are compressed, they
  fold and fault and pile up to form mountains.

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THREE WAYS PLATES MOVE

• Plates That Collide
• B) When two plates of different densities
  collide, the more dense plate plunges underneath
  the other, forming a deep trench. When one plate
  sinks underneath another plate, it is called
  subduction. Volcanoes many times form in these
  areas.

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Quiz

• When plates of similar density collide, what
  happens to the crusts?
• When plates of different densities collide, what
  happens to the crusts?
• When the plates collide, the force is called
  ___________.
• When one plate sinks underneath another plate, it
  is called _________.

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THREE WAYS PLATES MOVE

• 3) Sliding Plates - Plates can also slide past
  one another and the boundary where these plates
  meet is called a transform boundary. When a
  force pushes something in different directions it
  is called shearing. Where shearing occurs faults
  form and the area experiences many earthquakes.

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Quiz

• When plates slide past one another, the boundary
  where these plates meet is called a ____________
  boundary.
• What is shearing?
• What happens to the area where shearing occurs?
• What are the three ways a plate can move?

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Why Plates Move

• Scientists have come up with theories to explain
  the plate movements but do not know for sure why
  the large plates move. One theory is convection
  of the mantle when uneven heating causes cycling
  of material in the mantle to move.

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Why Plates Move

• Another theory is called Ridge-push where
  mid-ocean ridges cause plates to slide down a
  slope. Slab-pull happens as plates move away
  from mid-ocean ridges and become denser.

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Other Forces Shaping Earth

• Weathering is breaking down rock into sediment.
  Erosion moves the sediment. Deposition then
  leaves the sediment in a new place, creating new
  landforms.

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Two Types of Weathering

• a. Physical (Mechanical) weathering breaks down
  the rocks physically. Examples plant roots
  grow into rock, water freezes inside of cracks in
  the rock.

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Two Types of Weathering

• b. Chemical weathering occurs when a minerals in
  a rock are changed chemically. Examples oxygen
  reacts with iron in rocks to produce rust.

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Quiz

• What is the theory called where mid-ocean ridges
  cause plates to slide down a slope?
• What are the three other things shaping Earth?
• What are the two types of weathering?

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Write the following of the back sides of the
foldable for each of Earths layers.

• Inner Core
• Solid
• Made of iron
• Temperature of 5000 degrees Celsius
• Experiences the greatest pressure
• Outer Core
• Molten metal making it a liquid
• Mostly made of iron and nickel
• Uneven in structure
• Mantle
• Largest/thickest layer
• Solid yet flows slowly like putty
• Made mostly of iron and magnesium
• Two parts Asthenosphere and Lithosphere
• Lithosphere is on the top part of the mantle,
  right under the crust
• Crust
• Outermost layer
• Mostly made of oxygen and silicon
• Thinnest of all layers

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