1.2A Tectonic theories

• Key discoveries:

  • Alfred Wegener's Continental Drift hypothesis in 1912 that postulated that now-separate continents had once been joined. 
  • The ideas of Arthur Holmes in the 1930s that Earth's internal radioactive heat was that driving force of mantle convection that could move tectonic plates.
  • The discovery in 1960 of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere, on which the latter moves.
• Subduction = the process of one plate sinking beneath another at a convergent plate boundary
• gravitational sliding =  Constructive margins have elevated altitudes because of the rising heat between them, which creates a 'slope' down which oceanic plates slide. This occurs at destructive margins. 
• slab pull = Cold, dense oceanic plate is subducted beneath less dense continental plate; the density of the the oceanic plate pulls itself into the mantle
• Mantle convention:

  • All tectonic hazards are caused by the Earth's internal heat engine.
  • Radioactive isotopes such as uranium-238 and thorium-232 in the Earth's core and mantle generate huge amounts of heat which flow towards the Earth's surface. 
  • This heat flow generates convection currents in the plastic mantle.