Plate Tectonics

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Plate Tectonics

• Chapter 8
• BHS Earth Science

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Hollywoods Version
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Continental Drift

• Wegeners continental drift hypothesis stated
  that the continents had once been joined to form
  a single supercontinent.
• Wegener proposed that the supercontinent,
  Pangaea, began to break apart 200 million years
  ago and form the present landmasses.

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Continental Drift Evidence

• Jig-Saw Fit
• Continents fit together like Puzzle pieces
• Fossil Evidence
• fossils of same age and species were found in
  connecting bands on different continents
• Rock Types and Structure
• Similar bands of rocks types and mountain belts
  connect
• Ancient Climates
• PANGAEA!

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Connecting Mountain Ranges
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Top 100 Greatest Discovery
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Rejecting the Hypothesis

• Most scientists rejected Wegeners ground
  breaking hypothesis because he could not provide
  an explanating of how the plates moved
• A NEW THEORY EMERGES!

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Seafloor Spreading

• In Wegeners theory, continents plowed through
  the sea like bull-dozers.
• Not the case. Continents are actually connected
  to plates, which move
• Continents actually move with lithospheric plates
  that are pushed by Mid-Ocean ridges

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Harry Hess

• Discovered Mid-Ocean Ridges
• Spreading centers for tectonic plates
• Noticed magnetic stripes on the ocean floor which
  proved that new crust was being created at these
  ocean ridges
• Provided the mechanism for how the plates moved.

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Top 100 Greatest Discovery
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Topographic Map of the World
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Plate Tectonics

• The theory explaining how the movements of
  earths TECTONIC PLATES or moving plates
  create the geologic events like earthquakes,
  volcanoes and tsunamis.
• Lithospheric Plates- giant puzzle pieces
  connecting on the surface of earth.
• These sit on top of mantle so they can move around

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Plate Boundaries

• Three types
• Divergent Boundary
• Convergent Boundary
• Transform Boundary

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Divergent Boundary

• Plate moving apart
• Examples
• Mid Atlantic Ocean Ridge
• East Pacific Rise
• Plates are being pushed apart as they are pushed
  apart, magma rises from the mantle and fills the
  void.
• Mechanism for plate movement

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Ocean Ridges

• Oceanic ridges are continuous elevated zones on
  the floor of all major ocean basins. The rifts at
  the crest of ridges represent divergent plate
  boundaries.

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Rift Valleys

• Tears in the earth
• Also caused by Divergent Boundaries

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Convergent Boundaries

• Two plates crashing together
• Collliding
• Three types
• Continental to Continental
• Ocean to Ocean
• Ocean to Continental

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Continent to Continent collision

• When two continents collide, you will get
  mountain ranges
• Example Himalayans (India crashing into Asia)

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India and Asia
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Ocean to Ocean Convergance

• Two oceanic slab converge together. One is pulled
  under the other
• Often forms volcanoes on seafloor
• Volcanic Island Arcs
• Aleutian Islands
• Alaska

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Ocean to Ocean Convergent

• Aleutian Island, Alaska, US

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Ocean to Continental Convergance

• ALSO KNOWN AS SUBDUCTION ZONE
• Oceanic plate is forced down into the mantle
  beneath a second continental plate
• Creates volcanoes and deep ocean trenches
• Examples Andes and Marianna Trench
• Marianna Trench is deepest place in the WORLD!
  35,000 feet deep!!!!!

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Subduction Zone
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Subduction Zne
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Subduction Zone process

• Denser ocean slab pulled underneith continent
• As it is pulled under, the oceanic crust begins
  to melt.
• When crust begins to melt, magma rises
• Magma rises to surface and creates volcanoes

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Transform Boundaries

• Plates grind past each other without destroying
  or creating new lithosphere
• Like cars passing each other on a highway
• Creates tremendous earthquakes
• Example San Andreas Fault

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Transform Boundaries
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How do Plates Move?

• The crust lies on top of the mantle.
• It is believed that convection currents cause
  movement in the asthenosphere. Heat rises from
  interior.
• Areas where the asthenosphere is raising causes
  plates to move apart (diverge) and areas where
  the asthenosphere is sinking causes plates to
  move together (converge).

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Why do plates move?

• Clear answer is yet unknown
• There are theories for Ridge Push, Trench
  Suction, and just plain old Gravity

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