Plate Tectonics

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Plate Tectonics

• By Sierra Boyle

Intended for eighth grade
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Historical Background

• Super-Continent Pangea
• Theory proposed by Alfred Wegner in 1912
• Evidence
• fitting of continents
• distribution of fossils
• similar rock sequences
• ancient climates
• Splitting of Pangea

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UnderstandingMake-up of Earth

• The Earth is divided into three chemical layers
  the core, the mantle and the crust.
• The outermost layers of the Earth can be divided
  by their physical properties into lithosphere and
  asthenosphere.
• Lithosphere-rigid outermost layer made of crust
  and uppermost mantle. The lithosphere is the
  "plate" of the plate tectonic theory.
• Asthenosphere-mantle that flows, a characteristic
  called plastic behavior. Part of mantle
  convection, which plays an important role in
  moving lithospheric plates.

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How Continents Drift ApartSea Floor Spreading

• New sea floor is produced at the rifts of
  mid-oceans ridges. The ocean floor, and the rock
  beneath it, are produced by magma that rises from
  deeper levels filling the gap to form new oceanic
  crust. This creates continental drift.
• Old sea floor is carried away from the ridge. The
  lithosphere arrives at the edge of a continent,
  where it is subducted or sinks into the
  asthenosphere.
• The dip accounts for earthquakes, and magma
  generated along the top of the sinking slab rises
  to the surface to form stratovolcanoes.
• Further Understanding of Concepts

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Distribution of Plates
Can you find the connection between these two
pictures?

• The term plate was coined for the broken pieces
  of the Earth's lithosphere .
• Earth's surface consists of 12 rigid plates that
  move relative to each other.
• Where plates interact, along their margins,
  important geological processes take place, such
  as the formation of mountain belts, seafloor
  spreading, earthquakes, and volcanoes.

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Plate Movement
Plates move in different ways dependant upon
location and relative motion
Explanation of Plate Movement
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Plates Relation to Volcanic Activity
Mount St. Helens

• Most of the world's active above-sea volcanoes
  are located near convergent plate boundaries
  where subduction is occurring.
• Convergent boundary volcanoes are called
  stratovolcanoes. They typically erupt with
  explosive force, because the magma is too stiff
  to allow easy escape of volcanic gases.

Before Eruption
After Eruption
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Plates Relation to Earthquake Activity

• An earthquake is the shaking of the ground caused
  by an abrupt shift of rock along a fracture in
  the Earth, called a fault.
• A fault is generally located along a transform
  plate
• An earthquake releases stress that has slowly
  accumulated within the rock.

Effects of Earthquakes
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• THE END