Lesson 3 Reading Guide - KC

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Lesson 3 Reading Guide - KC
The Theory of Plate Tectonics

• What is the theory of plate tectonics?
• What are the three types of plate boundaries?
• Why do tectonic plates move?

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Lesson 3 Reading Guide - Vocab
The Theory of Plate Tectonics

• plate tectonics
• lithosphere
• divergent plate boundary
• transform plate boundary
• convergent plate boundary

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Lesson 3 Reading Guide - Vocab
The Theory of Plate Tectonics

• subduction
• convection
• ridge push
• slab pull

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Lesson 3-1
The Plate Tectonics Theory

• The theory of plate tectonics, proposed in the
  late 1960s, states that Earths surface is made
  of rigid slabs of rock, or plates, that move with
  respect to each other.
• Plate tectonics suggests that Earths surface is
  divided into large plates of rigid rock and each
  plate moves over Earths hot and semiplastic
  mantle.

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Lesson 3-1
The Plate Tectonics Theory (cont.)
What is plate tectonics?
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Lesson 3-1
The Plate Tectonics Theory (cont.)

• Geologists use the word tectonic to describe the
  forces that shape Earths surface and the rock
  structures that form as a result.
• The cold and rigid outermost rock layer of the
  Earth is called the lithosphere.
• The lithosphere is made up of the crust and the
  solid, uppermost mantle.

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Lesson 3-1
Earths Tectonic Plates
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Lesson 3-1
The Plate Tectonics Theory (cont.)

• The lithosphere is thin below mid-ocean ridges
  and thick below continents.
• Earths tectonic plates are large pieces of the
  lithosphere that fit together like the pieces of
  a giant jigsaw puzzle.
• The layer of Earth below the lithosphere, called
  the asthenosphere, is so hot that it behaves like
  a plastic material and enables Earths plates to
  move.

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Lesson 3-2
The Plate Tectonics Theory (cont.)
plastic Science Use capable of being molded or
changing shape without breaking Common Use any of
numerous organic, synthetic, or processed
materials made into objects
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Lesson 3-2
Plate Boundaries

• A divergent plate boundary forms where two plates
  separate.
• When the seafloor spreads at a mid-ocean ridge,
  lava erupts, cools, and forms new oceanic crust.
• Divergent plate boundaries can also exist in the
  middle of a continent, where they pull continents
  apart and form rift valleys.

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Lesson 3-3
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Lesson 3-2
Plate Boundaries (cont.)

• A transform plate boundary forms where two plates
  slide past each other.
• As they move past one another, the plates can get
  stuck and stop moving.
• Stress builds up where the plates are stuck until
  they eventually break and suddenly move apart,
  resulting in a rapid release of energy as
  earthquakes.

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Lesson 3-3
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Lesson 3-2
Plate Boundaries (cont.)

• Convergent plate boundaries form where two plates
  collide.
• The denser plate sinks below the more buoyant
  plate in a process called subduction.
• The area where a denser plate descends into Earth
  along a convergent plate boundary is called a
  subduction zone.

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Lesson 3-2
Plate Boundaries (cont.)
subduction from Latin subductus, means to lead
under, removal
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Lesson 3-2
Plate Boundaries (cont.)

• When an oceanic plate and a continental plate
  collide, the denser oceanic plate subducts under
  the edge of the continent, creating a deep ocean
  trench and a line of volcanoes above the
  subducting plate on the edge of the continent.
• When two continental plates collide, neither
  plate is subducted, and mountains form from
  uplifted rock.

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Lesson 3-3
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Lesson 3-3
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Lesson 3-2
Plate Boundaries (cont.)
What are the three types of plate boundaries?
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Lesson 3-3
Evidence for Plate Tectonics

• Scientists can measure how fast continents move
  using a network of satellites called the Global
  Positioning System.
• Because plates are rigid, tectonic activity
  occurs where plates meet.

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Lesson 3-3
Evidence for Plate Tectonics (cont.)

• Volcanoes form where plates separate along a
  mid-ocean ridge or continental rift or collide
  along a subduction zone.
• Mountains can form where two continents collide.

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Lesson 3-3

• Notice the relationship between earthquake
  epicenters, volcanoes, and plate boundaries.

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Lesson 3-3
Evidence for Plate Tectonics (cont.)
How are earthquakes and volcanoes related to the
theory of plate tectonics?
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Lesson 3-4
Plate Motion

• Earths plates move because the asthenosphere
  moves underneath the lithosphere.
• Convection is the circulation of material caused
  by differences in density.
• Hot mantle material rises upward and comes in
  contact with Earths crust.

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Lesson 3-4
Plate Motion (cont.)

• As the mantle cools, it becomes denser and then
  sinks, forming a convection current.
• Convection currents in the asthenosphere act like
  a conveyor belt moving the lithosphere above it.
• There are three forces that interact to cause
  plate motion basal drag, ridge push, and slab
  pull.

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Lesson 3-4
Plate Motion (cont.)
What causes convection?
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Lesson 3-4
Plate Motion (cont.)

• Basal drag refers to how convection currents in
  the asthenosphere circulate and drag the
  lithosphere like a conveyor belt.
• Rising mantle material at mid-ocean ridges
  creates the potential for plates to move away
  from the ridge with a force called ridge push.

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Lesson 3-4

• As a slab, or dense plate, sinks, it pulls on the
  rest of the plate with a force called slab pull.

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Lesson 3-5
A Theory in Progress

• Plate tectonics has become the unifying theory of
  geology, but several unanswered questions remain.
• Why is Earth the only planet in the solar system
  that has plate tectonic activity?
• Why do some earthquakes and volcanoes occur far
  away from plate boundaries?

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Lesson 3-5

• What forces dominate plate motion?
• What will scientists study next? This is a 3-D
  image of seismic wave velocities from a new
  technique called anisotropy.

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Lesson 3 - VS

• Tectonic plates are made of cold and rigid
  slabs of rock.
• Mantle convectionthe circulation of mantle
  material due to density differencesdrives plate
  motion.

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Lesson 3 - VS

• The three types of plate boundaries are
  divergent, convergent, and transform boundaries.

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Lesson 3 LR1
What word do geologists use to describe the
forces that shape Earths surface?
A. semiplastic B. lithosphere C. tectonic D. mantl
e
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Lesson 3 LR2
Which of these is made up of the crust and the
solid, uppermost mantle?
A. seafloor B. lithosphere C. biosphere D. hydrosp
here
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Lesson 3 LR3
What type of boundary forms where two plates
separate?
A. convergent plate boundary B. transform plate
boundary C. new plate boundary D. divergent plate
boundary
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Lesson 3 - Now
Do you agree or disagree?
5. Continents drift across a molten
mantle. 6. Mountain ranges can form when
continents collide.