Plate Tectonic Theory

• What theory is an extension of Alfred Wegener's work?

  Plate tectonics
• When was the theory of plate tectonics developed?

  In the mid-1900s
• What is the outer shell of the Earth called?

  Lithosphere
• What are the pieces of the lithosphere called?

  Lithospheric plates
• What types of crust are found in the lithosphere?

  Oceanic and continental crust
• What is the density of continental crust made of granite?

  About 2.7 g/cm³
• What is the density of oceanic crust made of basalt?

  About 3.0 g/cm³
• What layer lies beneath the lithosphere?

  Asthenosphere
• What is the asthenosphere described as?

  A gooey, plastic layer
• What drives the movement of tectonic plates?

  Convection currents in the mantle
• What happens to hot material in convection?

  It becomes less dense and rises
• What are convection cells?

  Rising and sinking currents in the mantle
• What is a divergent boundary?

  Where plates are pulled apart
• What geological activity occurs at plate boundaries?

  Earthquakes, volcanoes, and mountains
• What is a transform boundary?

  Where plates slide past one another
• What is a characteristic feature of transform boundaries?

  Frequent earthquakes
• What is the San Andreas Fault?

  A transform boundary in California
• What happens at convergent boundaries?

  Plates collide with each other
• What is a subduction zone?

  Where oceanic crust sinks beneath continental crust
• What forms at subduction zones?

  Active volcanoes and deep ocean trenches
• What is an island arc?

  Volcanic islands formed by oceanic crust subduction
• What is a collision zone?

  Where continental crust collides with continental crust
• What mountain range is formed by the collision of India and Eurasia?

  The Himalayas
• What happens at divergent boundaries?

  Plates drift apart from each other
• What is a rift zone?

  Where land rips apart into two
• What is the Mid-Atlantic Ridge?

  A divergent boundary in the Atlantic Ocean
• What is a hotspot?

  An area of magma rising through a plate
• How do hotspots create volcanic islands?

  Magma rises and forms volcanoes as plates move
• What is a mantle plume?

  A hot spot of magma rising from the asthenosphere
• What happens to volcanoes formed over a hotspot as the plate moves?

  They become extinct and new ones form
• How do extinct volcanoes indicate plate movement direction?

  They show the path of the moving plate
• What are the three types of plate boundaries?

  • Transform boundaries: plates slide past each other
  • Convergent boundaries: plates collide
  • Divergent boundaries: plates drift apart
• What features are associated with each type of plate boundary?

  • Transform: earthquakes
  • Convergent: mountains, volcanoes, trenches, earthquakes
  • Divergent: volcanoes, mid-ocean ridges, minor earthquakes
• What geological activities are common at plate boundaries?

  • Earthquakes
  • Volcanoes
  • Mountain formation
• What is the significance of the Earth's magnetic record in rocks?

  • It shows the history of plate movement
  • It indicates the age of the rock
  • It proves divergence at mid-ocean ridges