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Standard Plate Tectonics






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    Standard Plate Tectonics Standard Plate Tectonics Presentation Transcript

    • Plate Tectonics
    • How old is the Earth?
      • 4.56 billion years old
    • Where is the crust the thickest? The thinnest?
      • The crust is thickest at
      • mountains and thinnest
      • under the oceans.
    • What is the lithosphere, what is the asthenosphere?
      • The lithosphere consists of the crust and uppermost part of the mantle and the asthenosphere is the layer below the lithosphere.
    • What is plate tectonics?
      • Plate tectonics is the theory that believes our Earth is covered by 7 major plates and several smaller ones that move within the lithosphere at a rate of 5 centimeters per year.
    • What is continental drift and who proposed it?
      • Alfred Wegener, in 1912, came up with the idea of continental drift. Continental drift is a theory that the continents move or drift from one location to the next over time.
    • http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml
    • What was the evidence to support continental drift?
      • The shapes of the
      • continents look like
      • puzzle pieces.
      • 2. The fossil remains of
      • Mesosaurus (a reptile)
      • were found in South
      • America and Africa
      • (it couldn’t swim that far,
      • so there had to be a
      • shallow sea between
      • these countries –
      • not a huge ocean!).
    • What was the evidence to support continental drift?
      • 3. Mountain ranges on one continent matched up with mountain ranges on another continent.
      • Before After
    • What was the evidence to support continental drift?
      • 4. There was
      • evidence of
      • similar climates
      • on different
      • continents that
      • are no longer
      • of similar
      • climates.
    • What was the problem with Wegner’s hypothesis?
      • He could not tell us HOW the continents moved! He believed the continents moved because of the tides, but other scientists proved that if the tides did this, then the tides would be strong enough to stop Earth’s rotation.
    • How did other scientists account for similar fossils on widely separate continents?
      • They believed there was a land bridge that allowed for the animals to move from one location to another.
    • What evidence finally proved the theory of plate tectonics?
      • Information from earthquakes and volcanic activity as well as the age of rocks on the ocean floor proved the theory of plate tectonics.
    • What is a mid-ocean ridge?
      • A mid-ocean ridge is a chain of volcanic mountains on the ocean floor.
    • What are the main types of plate boundaries?
      • The three main types of plate boundaries are divergent, convergent and transform.
    • What is a transform boundary?
      • A transform boundary is where two plates grind past each other without creating or destroying lithosphere. It looks like this:
      • Example: San Andreas Fault (in California)
      • http://www.tulane.edu/~sanelson/geol111/pltect.htm
    • What is a divergent boundary?
      • A divergent boundary is when two plates diverge, or separate (move apart) in the ocean. During this time, lava arises where they split apart and we create new crust. (This is called Seafloor spreading and only occurs at the mid-ocean ridges making it the youngest rocks in our oceans). They look like this:
      • Example: Mid-Atlantic Ridge
    • What is the Ring of Fire?
      • The ring of fire is the most active volcanic region in the world!
        • Approximately 90% of the world’s earthquakes occur here.
    • What is a convergent boundary?
      • A convergent boundary is when two plates move toward each other and collide, here we destroy the crust.
      • There are three types:
          • Oceanic - Oceanic
          • Oceanic - Continental
          • Continental - Continental
    • Oceanic – Oceanic Subduction
      • Example: Mariana Islands
    • Oceanic – Continental Subduction
      • Example: Western Coast of South America
    • Continental – Continental Collision
      • Example: Himalayas (tallest mountains in the world)
    • What is a subduction zone?
      • Subduction zones are when one plate is forced below another plate. They ONLY occur when oceanic crust is colliding. (Subducted means to be pulled under!).
    • What do subduction zones result in?
      • They result in deep-sea trenches, which are the deepest parts of the ocean floor.
    • What causes plates to move?
      • Plates move as a result of convection currents in the asthenosphere.
      • These three factors include:
      • Mantle Convection – because the mantle is extremely hot, it undergoes the process of convection. Thus, it is constantly flowing and causing the plates to move above it as it convects.
      • Ridge Push – happens when magma rises at the mid-ocean ridge and is higher than the ocean floor surrounding it. As it cools, it increases in density and begins to sink. This sinking puts pressure on the rock below it causing the ridge to separate more.
      • Slab Pull – occurs at a convergent boundary where one plate is being subducted (pulled down) below another plate. The heavier plate pulled down, because it is so heavy, will continue to pull the plate down into the mantle. Ex: keys and jacket on table!
    • How did the Appalachian Mountains form?
      • They formed when North America collided with Africa millions of years ago.
    • What did the Earth look like 250 million years ago?
      • During this time, all the continents were combined in one landmass called Pangea.
    • What happened to Pangea?
      • Over time, Pangea
      • began to break apart
      • to what we currently
      • see today.