The Earths Interior, Continental Drift and Theory of Plate Tectonics

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The Earths Interior,Continental Drift and
Theory of Plate Tectonics
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• Formation of oceanic crust at rift zones
  located in the mid-oceanic floors. Upwelling of
  magma later solidifies beneath the oceans to
  produce the crust

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Earths Internal structure

• 5. The Crust the rigid outer cover of the earth
  stretching about 5 miles under Oceans and about
  40 miles under some mountains
• 6. Lithosphere comprises all materials that
  form the crust and the upper mantle (rocks, soil,
  etc)

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Earths Internal Structure

• The Earth is composed of rocks of different
  densities.
• 1.  Inner Core made up of solid iron
• 2. The Outer Core liquid iron
• 3.  The Mantle - a dense solid material that
  makes up about 80 of earth's material
• 4. Astenosphere upper part of the mantle

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Theory of Continental Drift

• The idea that the continents have originated from
  a single SUPER CONTINENT was first proposed as a
  scientific hypothesis in 1920-s by Alfred Wegener
  
• He hypothesized that a single super continent
  (Pangaea - "whole land") existed on Earth about
  250 million years ago.
• The super continent later broke down into two
  pieces
• a) a northern half called Eurasia and
• b) a southern portion called Gondwanaland.
• The Continental Drift Theory did not gain
  worldwide support because it could not account
  for the forces that break up and move the
  continents

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Continental Drift Theory
1915 Alfred Wegener proposed that landmasses
were once united called Pangaea
Pangaea later split into Laurasia Gondwanaland
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During this time, land masses have formed and
moved (continental drift)
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Theory of Plate Tectonics

• In the 1960s, the Continental drift theory was
  replaced by the theory of plate tectonics. The
  discovery of alternating patterns of rock
  magnetism in surface rocks and sea-floor
  spreading aided in the creation of the plate
  tectonics theory.
• Modern plate tectonic theory states that the
  surface crust of the Earth is composed of many
  independent segments called plates. These plates
  have the ability to move horizontally by gliding
  over the plastic asthenosphere .

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Continental Plates

• Plate tectonics theory explains that the
  Lithosphere consists of as many as 7 huge plates
  about 5 smaller plates that move as distinct
  units.
• The plates form the continents, islands, and the
  floor of the oceans.

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Convection Currents

• Modern tectonic theory explains that crustal
  movements are caused by a very slow thermal
  convection currents within the earth.
• Hot magma is rising from deep inside the earth
  until it reaches the crust, and crustal blocks
  are submerging into mantle.

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Lithosphere moves over the asthenosphere
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Types of Plate Movements -- 1

• Divergence - Plates move away from each other
  (e.g. mid-Atlantic ridge, East African rift
  valley)
• Lateral Movement as in Transform Plate boundaries
  where plates slide past one another along
  strike-slip faults such as the San Andreas Fault
  in California.

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Types of Plate Movements --2

• Lateral movements as in Subduction Zones where
  Oceanic plates slides beneath Continental
  plates (e.g. the coasts of Peru and Chile,
  Eastern Philippines and Japan). These are zones
  of deep ocean trenches.
• Lateral plate movements can cause Faulting and
  the FOLDING of the crust into mountains (e.g.
  Appalachian Rockies in US, the Alps of
  Europe, the Andes mountains of South America and
  the Himalayas mountains of Asia.

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Sea Floor Spreading Plate Boundaries
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Tectonic features of the world
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Divergent plate movement

• At some plate boundaries, plates are moving away
  from each other because of sea-floor spreading.
• An example is the mid-Atlantic Ridge between
  Africa and North America

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Collision of an Oceanic plate with a Continental
plate

• Subduction is fairly slow (2-3 cm per year)
• produces large earthquakes, volcanism, mountain
  ranges
• Nazca plate subducted under South America plate

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Formation of Himalayas Mountains

• Formation of the Himalaya Mountains.
  Compressional forces due to the collision of the
  Eurasian and Indian continental plates caused
  ocean sediments and continental rocks to be
  pushed upward in elevation. (Source U.S.
  Geological Survey).

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Collision of two Continental Plates

• When two continental plates collide, one of
  the crustal plates is subducted under the other
  producing a mountain range at the plate
  boundaries e.g. Himalayas.
• Sometimes earthquakes also occur at the plate
  boundaries.

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Collision of two Oceanic Plates

• In this type of a collision, (collision of North
  America and Pacific Plates (Aleutian Islands) one
  of the plates is subducted under the other
  creating a deep oceanic trench
• The Marianas trench in the Pacific ocean is
  created by the collision of the fast-moving
  Pacific Plate against the slower moving
  Philippine Plate.
• Convergence of two oceanic plates also creates a
  chain of volcanic islands called Island arcs.

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Features along continental margins

• Marginal features found at the interface of
  the continents and the ocean basins