Plate Tectonics

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					Plate Tectonics

        Joy Nowak
     What is plate tectonics?
• A plate is a large, rigid slab of rock.
• The word tectonics comes from the
  Greek root “to build”.
• The Earths surface is built of plates.
• The theory of plate tectonics states
  that the Earths outermost layer is
  fragmented into twelve or more large and
  small plates that are moving relative to
  one another as they ride atop a hotter,
  more mobile material.
      Ocean and continental
• Continental plates are thicker but
  less dense.
• Ocean plates are thinner but more
               Earth’s top layers
• Top layer is called the lithoshere, which
  contains the crust and the uppermost
  part of the rigid mantle.
• Under the lithosphere is the
• Asthenosphere consists of of a solid but
  low viscosity which can make it flow like
• Below the asthenosphere is the deeper
  mantle which is more rigid.
                Continental drift
• The Earth’s plates are in constant
• The continents that we know today
  were once one super continent known
  as Pangaea.
• Over time the continent began to split
  slowly creating seven continents.
    What drives the plates?
• Harry Hess’ theory is that the
  plate-driving force is the slow
  movement of hot, softened mantle
  that lies below the rigid plates.
• Moving rock beneath the rigid
  plates is believed to be moving in
  a circular motion.
• The heated rock rises to the
  surface, spreads, cools, then sinks
  back to down. This cycle is called
  convection cell or convective flow
  which causes plate movement.
• The plates move very slowly on
  the surface, only about two inches
  a year on average.
             Plate boundaries
• There are three types of plate
  boundaries and are characterized
  by the way the plates move
  relative to each other.
• Each boundary causes different
        Transform boundaries
• Plates next to each other slide past
  each other.
• The plates grind past each other on
  transform faults causing earthquakes.
• The San Andreas fault in California is a
  transform boundary that has caused
  many earthquakes.
     Convergent boundaries
• Two plates slide towards each other
  causing either a subduction zone or a
  continental collision.
• A subduction zone is when one plate
  moves underneath the other which can
  cause Earthquakes, tsunamis, and
  volcanic activity.
• Continental collision causes the plates
  to hit each other and raise above the
  surface causing mountain ranges.
        Divergent boundaries
• Occur where to plates slide apart from
  each other.
• The separating plates move apart and
  new crust is created by magma pushing
  up from the mantle.
• The Mid-Atlantic ridge is a submerged
  mountain range from the Artic Ocean to
  beyond the southern most tip of Africa.
  This was caused by divergent
• This Dynamic Earth: The Story of Plate
  Tectonics by W. Jacquelyne Kious and
  Robert I. Tilling (online book through

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