plate tectonic theory

• What is the plate tectonic theory?

  The theory that the Earth's crust is divided into plates that move around on the top of the mantle.

  
  

  The study of plates
• what are the 3 peices of evidence for plate tectonic theory

  -wegeners continental drift theory

  -the distribution of earthquakes and volcanoes

  -paleomagnetism

  -hot spots
• what is wegners contiental drift theory

  Alfred Wegener proposed that the continents were once united into a single supercontinent named Pangaea

  
  

  He suggested that Pangaea broke up long ago and that the continents then moved to their current positions

  
  

  he found evidence for this when he noticed that continental shelf shapes fitted together eg the east coast of south america and the west coast of africa

  - and matching fossils from different parts of the world togethersuch as the cynognathus reptile found in the east coast of south america and the west coast of africa that lined up with the shelf shapes matching
• how does the distribution of earthquakes and volcanoes provide evidence to plate tectonics

  they are found on plate boundaries, such as the ring of fire
• how is the movement of plates driven

  by:

  mantle convection

  slab pull

  subduction

  seafloor spreading
• what is mantle convection


  heat produced by the decay of radioactive elements in the earths core heats the lower mantle

  - creating convection currents

  
  

  the hot liquid magma currents are thought to move in circles in the asthenosphere and cause the plates to move
• what is slab pull

  Process of slow plate movement that occurs in the mantle below a convergent plate boundary when a denser plate sinks beneath another less dense plate.

  - and is pulled down
• what is subduction


  as new crust is created in one place it is destroyed in another

  
  

  one plate slides under the other and into the mantle where it melts
• what is sea floor spreading

  when hot magma is forced up thorugh the asthenosphere and hardens it forms a mid ocean ridge, forming new crust

  
  

  this new crust pushes plates away from each other
• what does paeleomagnetism confirm

  sea floor spreading
• what is paleomagnetism


  every 400k years or so the earths magnetic fields change direction - causing magnetic N and S to swap

  
  

  when lava cools and becomes rock, minerals in the rock line up with the earths polarity (magnetic direction) of the time

  
  

  when scientists studies mid ocean ridges, they found the same pattern of magnetic direction on either side of the ridge eg

  
  

  //\/\ RIDGE /\/\\

  
  

  this could only happen if rock was being formed on both sides at the same time