Earths Interior and Plate Tectonics

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Earths Interior and Plate Tectonics
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Key Terms

• crust
• mantle
• core
• lithosphere
• plate tectonics

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Key Terms

• asthenosphere
• magma
• subduction
• fault

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Objectives

• Identify Earths geologic layers
• Describe plate tectonics
• Identify plate boundaries and structures that
  form
• Explain how magnetic bands on ocean floor support
  the theory

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What is Earths interior like?

• Crust (we live here)
• cool, hard, solid rock
• oceanic crust 4-7 km thick continental crust
  20-40 km thickdeepest beneath high mountains (up
  to 70 km thick)
• Mantle
• denser than crust
• never been there, but can guess from earthquakes
  and volcanoes

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What is Earths interior like?

• Mantle
• 2900 km thick 80 of Earths volume
• outer mantle more solid inner mantle hot and
  plastic
• Core
• mainly iron and nickel (we think)
• outer core liquid, inner core solid (pressure)

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Earths interior gets warmer with depth

• South African gold mines, 3 km deep, approach 50º
  C (120º F)
• quick whats that in Kelvins?
• (add 273)
• Mantle is hotter than crust (temps exceed 1250º
  C)
• Core is hotter still (6000º C )

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Radioactive elements and residual heat contribute

• core contains radioactive isotopes (ie uranium,
  thorium and potassium)
• huge quantity of energy
• I didnt see The Core but heard it panned...

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Did you get those terms?

• crust the othermost and thinnest layer of Earth
• mantle the layer of rock between the Earths
  crust and its core
• core the center of a planetary body

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Plate Tectonics

• Early 20th C Alfred Wegener (German scientist)
  noticed how the continents fit together
• Pangaea, one land mass maybe 200 million years
  ago
• Fossil evidence supports the concept

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More evidence

• In the 1960s, structures on the ocean floors
  gave evidence of continental drift

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Earth has plates that move over the tar-like
mantle

• Lithosphere (100 km thick), the crust and upper
  portion of mantle is made up of 7 large (and
  several smaller) pieces--tectonic plates
• They move.

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Theory is that they move because of convection
currents

• asthenosphere, the hot, plastic portion of the
  mantle, is slowly flowing, and might circulate
  like mushy oatmeal
• remember when we talked about convection currents
  in fluids?

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Did you get those terms?

• lithosphere the thin (100 km) outer shell of
  Earth, consisting of the crust and rigid upper
  mantle
• plate tectonics the theory that Earths surface
  is made up of large moving plates

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Did you get those terms?

• asthenosphere the zone of the mantle beneath the
  lithosphere that consists of slowly flowing solid
  rock

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Divergent plate boundaries

• diverge means to come apart
• two plates come apart and hot molton rock (magma)
  rises from the asthenosphere and cools, forming
  new lithospheric rockwhich then gets pulled away

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Mid-oceanic ridges

• underwater mountain ranges that form at divergent
  rift boundaries
• large central rift valley
• magma pushes up

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Convergent plate boundaries

• Con means with or together, so
• plates come together as well
• oceanic plates dive under continental plates as
  they collide

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Subduction

• the denser oceanic plate dives beneath the
  continental plate
• ocean trenches, mountains and volcanoes
• the oceanic crust melts when it subducts

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Colliding continental plates

• colliding continental plates create mountains
• Like the Himalayas
• Everests peak is 8850 m above sea level

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Transform fault boundaries

• Plate movement causes breaks in the lithosphere,
  and they pieces scrape
• faults
• Earthquakes

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Strong evidence for plate tectonics

• 1960s
• bands of rock on the ocean floor with alternating
  magnetic polarities
• molten minerals align themselves with the Earths
  magnetic field

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Magnetic field has reversed about every 200 000
years

• symmetrical bands on either side of the
  mid-Atlantic ridge support the theory
• The farther away, the older the rocks.

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Did you get those terms?

• magma molten rock within the Earth
• subduction the process in which a tectonic
  plate dives beneath another tectonic plate and
  into the asthenosphere

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Did you get those terms?

• fault a crack in the Earth created when rocks on
  either side of a break move