Tectonics

• Convection currents


  The movement of the Earth's crustal plates is believed to be due to convection currents which occur in the semi-molten mantle
• Formation of convection currents


  1. Semi-molten rock in the mantle is heated

  2. It becomes less dense than its surroundings and rises

  3. As it reaches the crust above, it spreads out carrying the plates above with it

  4. As the semi-molten rock then cools, it gradually sinks back down to be re-heated
• Much of the heat that drives convection currents is generated by radioactive decay in the core
• Differences between oceanic and continental crusts


  • Continental plates are lighter (less dense) than oceanic plates
  • Oceanic crust is much younger in geologic age than continental crust
  • Continental crust is on average thicker than oceanic crust
• Divergent plate boundary


  What process occurs