SCI [4th Q -Incomplete]

• Plate Tectonic Theory


  The earth's lithosphere is composed of fragments or plates that move around and interact with each other
• Tectonicus

  To build
• Lithosphere


  Outermost layer of the earth, consisting of the upper mantle and the crust
• Types of crust


  • Continental crust - less dense but thicker
  • Oceanic crust - dense but thinner
• Abraham Ortelius


  • Observed in the 1500's that the continents across the Atlantic Ocean fit together like a puzzle, and that North and South America had been separated from Europe and Africa by earthquakes and floods
• Raisin Theory


  The earth is likened to a grape due to the Big Bang Theory
• Isostasy


  Rising/settling of a portion of the Earth's lithosphere that occurs when weight is removed in order to maintain equilibrium between buoyancy forces that push the lithosphere upward, and gravity forces that pull the lithosphere downward
• Edward Suess


  • Austrian geologist in the late 1800's who proposed that the southern continents had once been joined together in a single landmass named Gondwanaland
• Alfred Wegener


  • Proposed the continental drift theory in 1912, stating that the continents had once been joined as a single landmass called Pangaea which began to break apart 250 million years ago
• Evidence for continental drift

  • Rocks - similar rocks found in the Appalachian Mountains and Scottish Highlands, and in Brazil and Africa
  • Fossils - of animals like Lystrosaurus, Mesosaurus, and Cynognathus, and plants like Glossopteris, which could not have evolved the same way in different locations
  • Climate - coal deposits found in Antarctica, and glacier deposits found in Africa, India, Australia, and South America
• Arthur Holmes


  • Proposed that convection in the mantle could push and pull plates apart or together, but there was no evidence for this
• Plate boundaries

  • Divergent
  • Convergent
  • Transform
• Divergent boundary


  1. Plates moving apart

  2. Seafloor spreading (oceanic-oceanic) - new oceanic crust is created as magma cools

  3. Mid-ocean ridges (oceanic-oceanic) - mountain under the ocean where plates continue to separate

  4. Rift valley (continental-continental) - forms volcanoes and new land as continental plates pull apart
• Convergent boundary


  1. Plates coming together

  2. Mountains (subduction: continental-continental) - plates push up to form mountains

  3. Volcanic arc (subduction: oceanic-continental) - more dense oceanic crust goes under less dense continental crust

  4. Deep-sea trench (oceanic-continental) - depression in the ocean floor at the subduction zone
• Fault types

  • Normal faults - rock moves down
  • Reverse faults - rock moves upward
  • Strike-slip faults - rocks slide past one another in opposite directions
• Volcanoes


  An opening in the earth that erupts gases, ash and lava, caused by plate movement along boundaries. Magma is melted rock under the surface, and lava is melted rock above the surface.
• Hot spots


  A part of the mantle that is really hot, forcing magma up to the surface to create islands
• Earthquakes


  Caused by movement along a fault, occurring mainly at plate boundaries. The focus is the point under the earth's surface where an earthquake starts, and the epicenter is the place on the earth's surface directly above the focus.
• Earthquake waves

  • P-wave (primary wave) - fastest, moves back and forth
  • S-wave (secondary wave) - slower, moves up and down
  • L-wave (surface wave) - most dangerous, moves both back and forth and up and down
• Tsunamis


  Large ocean waves caused by an earthquake under the ocean, where the ocean floor moves along a fault to create a wave. Can also be caused by a landslide under or above the water.