Plate Tectonics

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Plate Tectonics

• Chapter 5

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Earths Interior

• Geologists have used two types of evidence
• 1. Rock Samples direct evidence, drilling,
  blast forces
• 2. Seismic Waves indirect evidence, produced
  from earthquakes, measure speed and paths the
  seismic waves take
• Journey to the Center of the Earth
• Temperature decreases to 20 meters then warms,
  1oC for every 40 meters
• Pressure increases as you go deeper

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Structure of the Earth

1. 1. Crust 5 40 km in most places, up to 70 km
   under mountains, thick outermost layer
2. Earths crust always changing and moving, basalt
   under ocean
3. 2. Mantle nearly 3000 km thick, very hot and
   solid
4. Lithosphere uppermost part of the mantle/crust
   (stone)
5. Asthenosphere - softer, still solid (weak)
6. Lower Mantle Solid
7. 3. Outer Core liquid, also iron and nickel
8. 4. Inner Core Solid dense, iron and nickel
9. Magnetic Field movements in liquid outer core

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Earths Structure

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   if

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Convection and the Mantle

• Three types of Heat Transfers
• 1. Radiation through space, sunlight
• 2. Conduction within a material or between
  materials that are touching
• 3. Convection movement of fluids, liquids and
  gases, caused by differences in density

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Radiation
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Causes of Plate Tectonics

• Convection Current a circular current in a
  fluid caused when the fluid is unevenly heated so
  that part rises and then cools and sinks causing
  circular movement
• Differences in density cause hot plastic like
  rock in the asthenosphere to be forced upward
  toward the surface when it reaches the
  lithosphere it moves horizontally and carries
  plates of the lithosphere with it

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Continental Drift

• Continental Drift continents have moved
  horizontally to their current locations
• Pangaea means all land
• Alfred Wegner (1912) proposed the theory of
  Pangaea that 200 million years ago the contents
  broke apart by a force

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ssils/pangaea.gif
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Evidence for Continental Drift

• Fossils found on multiple continents
• Mesosaurus swimming reptile found in South
  America and Africa
• Glassopteris fern found on Africa, Australia,
  India, South America and Antarctica
• Warm weather plants found on the island of
  Spitzbergen in the Arctic
• ocean
• Glacial deposits and
• groves
• found in South America,
• Africa, India and Australia

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Sea Floor Spreading

• 1960s Harry Hess proposed that hot rock material
  is forced upward toward Earths surface at
  mid-ocean ridges. The material turns and flows
  laterally, carrying ocean floor away from the
  ridge in both directions

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Sea Floor Spreading

• Two pieces of evidence
• 1. Age Evidence gathered from the Glomar
  Challenger drilled the rocks and found youngest
  rocks by the mid-ocean ridges
• 2. Magnetic Evidence gathered from basalt rock
  shows that the magnetic field reversed itself
  several times, iron in rocks align with magnetic
  pull
• 3. Eruption of Molten Material along mid-ocean
  ridge

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Theory of Plate Tectonics

• States that Earths crust and upper mantle are
  broken into sections called plates, these plates
  move around on the mantle
• Lithosphere crust and the upper crust, 100km
  thick and is less dense then the layer under it
• Asthenosphere plasticlike layer underneath th
  lithosphere, more dense

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Movement of Plates

• 1.Divergent Boundaries boundary between 2
  plates moving apart from one another
• Mid Atlantic Ridge In Atlantic Ocean North
  American plate moving away from the Eurasia and
  Africa plates
• Great Rift Valley eastern Africa
• 2.Convergent Boundaries 2 plates collide and
  one section is more dense and sinks
• Subduction zone place where the oceanic plate
  descends into the upper mantle, this is where
  Volcanos occur

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3 types of Convergent Boundaries

• A. ocean plate collides with less dense
  continental plate the denser ocean plate sinks
  under the continental plate Andes Mountains
• B. One ocean plate bends and slides under the
  other, occurs by plates colliding or seafloor
  that has become denser due to cooling begins to
  sink example is the Islands of Japan
• C. 2 continental plates collide but no
  subduction occurs because both plates are less
  dense these form mountain ranges Himalaya
  mountains when Indian plate collided with
  Eurasian plate form folding mountains

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• 3. Transform Fault Boundaries 2 plates slide
  right past each other earthquakes occur
  Californias San Andreas Fault with the Pacific
  Plate sliding past the North American Plate

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