Plate Tectonics

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Plate Tectonics

• The Earths Crust in Motion

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Earths Interior

• Scientists have not been able to directly study
  much of the earths interior due to high
  temperatures and pressures. They do get much of
  the information they possess from the study of
  seismic waves (shock waves produced by
  earthquakes). These are measured by an instrument
  known as a seismograph.
• There are 3 types of seismic waves
• Primary waves (P waves). These are the fastest
  seismic wave. They travel through any material
  but are slowed by less dense materials such as
  liquids gases. They are push/pull waves.
• Secondary waves (S waves). These are slower waves
  that will not travel through liquids. They are
  upward waves that cause the land they travel
  through to move at right angles.
• Surface waves (L waves). These bend and twist
  Earths surface cause the most damage at the
  surface.

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Structure of the Earths Interior
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The Core

• The center of the earth.
• The core is split into 2 layers the solid inner
  core and the liquid outer core. Both layers are
  made of iron and nickel.
• The composition of the core and rotation of the
  Earth causes a magnetic field called the
  magnetosphere.
• The inner core is very dense due to pressure
  has a temperature of around 50000C.
• The diameter of the inner core is approximately
  2600 km (1616 miles). It is found 5150 km (2781
  miles) below the surface.
• The outer core (liquid) is 2900 km (1802 miles)
  below the surface and 2250 km (1398 miles) thick.

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The Mantle

• The middle layer of the Earth.
• The largest layer of the Earth. (80 of volume
  68 of mass).
• The mantle is made mostly of silicon, oxygen,
  magnesium and iron.
• There is more iron as you get closer to the core.
  
• The temperatures range from 8700C near the crust
  to 22000C near the core.
• The mantle is a solid but it can flow like a
  liquid so it has a property known as
  plasticity(This is similar to mercury or Jell-O
  or silly putty).
• Sample of the mantle have been taken beneath the
  ocean.

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The Crust

• The thin outermost layer of the Earth.
• The crust is made mostly of silicon, oxygen and 6
  trace elements.
• There are 2 types of crust.
• Continental crust crust beneath the continents.
  Average thickness is 32 km (19.84 miles). It is
  thicker beneath mountains. Mostly made of igneous
  rocks granite and basalt.
• Oceanic crust crust beneath the ocean. Averages
  8 km (5 miles) thick. Mostly made of basalt.
• Lithosphere- The topmost solid part of the earth
  where life exists. The lithosphere is made of 7
  major plates that are split into minor plates.

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Continental Drift

• The theory made by German meteorologist Alfred
  Wegner in 1912. It said that the continents used
  to all be together in a supercontinent called
  Pangea which drifted apart and are still moving.
• 3 pieces of evidence to support this theory
• 1.continent boundaries fit together like a
  puzzle
• 2.fossils of same organisms found on different
  continents
• a. Mesosuras- reptile
• b. Glosopteris- fern plant
• 3.Glaciar evidence in different climates
• Wegner was not believed for a long time because
  he could not give a way for the continents to
  move. The discovery of lithospheric plates and
  sea floor spreading helped to give his theory
  more credibility.

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Supercontinent
Pangea means all lands
?Tens of Millions of years!
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Plate Tectonics and Sea Floor Spreading

• Plate tectonics theory that earths crust is
  made of plates that move driven by convection
  currents in the asthenosphere and sea floor
  spreading.
• (Based on continental drift ideas but stronger).
• Sea floor spreading a hypothesis that there is
  a crack between plates under the sea that allows
  magma to reach the surface and form new seafloor

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How does it work?
Plates pieces of the lithosphere Plates fit
closely together along cracks called Plate
Boundaries Convection Currents in asthenosphere
cause movement
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Earths Puzzle

• What plate do we live on?
• What plates do we border?
• USGS Earths Plates
• How far do we move every year?

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Types of Boundaries

• Divergent
• Convergent
• Transform

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• plates are moving apart
• new crust is created
• Magma is coming to the surface

• plates are coming together
• crust is returning to the mantle
• Subduction (pushing down) is occurring

• plates are slipping past each other
• crust is not created or destroyed

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2 oceanic plates or oceanic continental ?subduct
ion or underwater mountains
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The Big Picture
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The Big Picture 2