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Chapter 17 Plate Tectonics. Powerpoint -a-long!. Earth’s Structure (layers of the Earth). The inner core - the solid layer located at the very center of the Earth The outer core - the liquid layer located between the Inner Core and Mantle

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chapter 17 plate tectonics

Chapter 17 Plate Tectonics


earth s structure layers of the earth
Earth’s Structure (layers of the Earth)
  • The inner core- the solid layer located at the very center of the Earth
  • The outer core- the liquid layer located between the Inner Core and Mantle
  • Mantle- The largest layer of the Earth located above the Outer Core
  • Crust- The outermost layer of the Earth, thickest on land, thinnest on oceans
  • Made up of “Tectonic plates”– huge rock slabs that float on the semi fluid mantle
  • Lithosphere– outer layer of the mantle and crust
continental drift theory
Continental Drift Theory
  • Theory developed Alfred Wegener(1912)
  • States that:
    • Earth’s continents were once all joing into a single landmass called “Pangea”
      • Existed about 200 million years ago (mya)
      • Name means “all the earth” in Greek
    • Continents have moved horizontally to their current locations over a long period of time.
  • Got the idea from “puzzle like” appearance
  • pieces look like they should fit together.
evidence of continental drift
Evidence of Continental Drift
  • 1.Fossil Clues
    • Mesosaurus: prehistoric freshwater reptile found in S. America and Africa
    • Glossopteris: prehistoric fern found in completely different climates (Africa, Antartica, S. America)
evidence of continental drift1
Evidence of Continental Drift
  • Rock Clues- Appalachian Mountains similar to mountains in Greenland, S. America mountains similar to ones in Africa
evidence of continental drift2
Evidence of Continental Drift
  • Sea-floor Spreading – Molten material in the mantle is forced upward
    • Material surfaces at mid-ocean ridges (undersea mountain ranges with steep valleys) in the form of magma. This pushes the continents further apart from each other
    • In some areas, pieces of the crust slip back below the surface and are re-melted.
evidence of continental drift3
Evidence of Continental Drift
  • 4. Age Evidence– no rocks found on sea floor older than 160 mya
    • Some rocks of continents over 4 Billion years old
evidence of continental drift4
Evidence of Continental Drift
  • 5. Magnetic Clues– Rocks take on current magnetic properties as they form
    • Iron molecules in the magma “line up” with Earth’s magnetic north and south pole as they cool and crystallize
    • Magnetic Orientation reverses periodically on Earth, and when it does, any rock being laid down show the opposite magnetic orientation
    • Rocks being formed now have “reversed” orientation
evidence of continental drift5
Evidence of Continental Drift
  • 6. Climatic Evidence –
    • Coal deposits form in swamps when dead plants are buried under mud
      • Antarctica has coal deposits and we’ve found fossils indicating it used to be a temperate swamp
    • Glacial deposits in India, Africa, and Australia indicate that these areas used to be much colder (probably nearer to the poles!)
the plate tectonic theory
The Plate Tectonic Theory
  • The theory of plate tectonics says that:
    • Earth’s crust and rigid upper mantle are broken into enormous slabs called “plates”
    • Tectonic plates move in different directions at different rates over Earth’s surface
    • The plates interact at places called plate boundaries
the plate tectonic theory1
The Plate Tectonic Theory
    • Divergent boundaries: two tectonic plates are moving apart
  • Mostly found on the ocean floor where they form Mid-ocean ridges
  • Lots of Volcanoes, hydrothermal vents, and earthquakes in these areas as magma surge up towards the surface
  • When continental plates separate, it forms a rift valley like that found in Africa
the tectonic plate theory
The Tectonic Plate Theory
  • Convergent boundaries: where two plates are moving towards each other
    • Can be continental-continental, continental-oceanic, or oceanic-oceanic
    • Two possible results:
      • Subduction: one plate slides under the other
        • Creates a deep-sea trench ( Mariana’s Trench – over 6.8 miles deep)
        • Recycles and melts down the crust as it enters the mantle
      • Mountain building: plates push each other upwards to form mountains!
        • Ex. - Himalayas
the plate tectonic theory2
The Plate Tectonic Theory
  • Transform Boundary: plates slide horizontally past each other
    • Crust is deformed or fractured (cracked) – lots of earthquakes!
    • Ex. San Andreas Fault
causes of plate motions
Causes of Plate Motions
  • Mantle convection:
    • Convection: transfer of heat energy through the movement of heated matter
      • Heated air or water rises because it is less dense, colder parts sink because they are more dense
    • Heat from the Earth’s core causes magma to rise up towards the crust
    • Cooler parts of the crust sin at convergent boundaries
  • We don’t know if these are permanent or not, how big they are, or how they form