Theory of Plate Tectonics

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http//www.youtube.com/watch?vhSdlQ8x7cuk
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The Theory of Continental Drift
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Continental Drift Theory

• Proposed by Alfred Wegener in 1912
• 250 million years ago, all of the continents were
  combined into one super-continent called
  Pangaea
• The continents gradually drifted apart to where
  they are today

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Evidence to Support the Theory
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Puzzle Pieces

• Continents look like they could be part of a
  giant jigsaw puzzle

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Distribution of Fossils

• Plant and animal fossils found on the coastlines
  of different continents

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Sequence of Rocks

• Same rock patterns found in South America, India,
  Africa, Antarctica and Australia

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Ancient Climates

• Tropical plant remains (coal deposits) found in
  Antarctica
• Glaciation in Africa, South America, India, and
  Australia during the same time

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Problems With The Theory

• No mechanism for movement of continents
• Wind and currents could possibly move fossils
• Theory was not accepted by scientists

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Theory of Plate Tectonics

• Plate Tectonics
• Plate Boundaries
• Causes of Plate Tectonics

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What is Plate Tectonics

• The Earths crust and upper mantle are broken
  into sections called plates
• Plates move around on top of the mantle like rafts

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What is the Lithosphere?

• The crust and part of the upper mantle
  lithosphere
• 100 km thick
• Less dense than the material below it so it
  floats

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What is the Asthenoshere?

• The plastic layer below the lithosphere
  asthenosphere
• The plates of the lithosphere float on the
  asthenosphere

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2 Types of Plates

• Ocean plates - plates below the oceans
• Continental plates - plates below the continents

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Questions...

• What is the theory of plate tectonics?
• What is the lithosphere?
• What is the asthenosphere?
• What is the connection between the two?
• What are the two types of plates?

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Plate Boundaries
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Divergent Boundaries

• Boundary between two plates that are moving apart
  or rifting
• ? ?
• RIFTING causes SEAFLOOR SPREADING

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Features of Divergent Boundaries

• Mid-ocean ridges
• rift valleys
• fissure volcanoes

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Convergent Boundaries

• Boundaries between two plates that are colliding
• ? ?
• There are 3 types

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Type 1

• Ocean plate colliding with a less dense
  continental plate
• Subduction Zone where the less dense plate
  slides under the more dense plate
• VOLCANOES occur at subduction zones

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Andes Mountains, South America
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Type 2

• Ocean plate colliding with another ocean plate
• The less dense plate slides under the more dense
  plate creating a subduction zone called a TRENCH

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Aleutian Islands, Alaska
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Type 3

• A continental plate colliding with another
  continental plate
• Have Collision Zones
• a place where folded and thrust faulted mountains
  form.

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Transform Fault Boundaries

• Boundary between two plates that are sliding past
  each other
• EARTHQUAKES along faults

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San Andreas Fault, CA
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Questions...

• What are the three types of boundaries?
• What direction do plates go for each?
• Which boundary has a subduction zonewhat occurs
  at a subduction zone?

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Causes of Plate Tectonics
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Convection Currents

• Hot magma in the Earth moves toward the surface,
  cools, then sinks again.
• Creates convection currents beneath the plates
  that cause the plates to move.

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Questions...

• What causes plates to move?
• How is a convection current formed?