Plate tectonics

• A rift valley is a landform that forms when diverging plates are beneath the land, causing the crust to stretch and fracture, with areas of crust dropping down between faults to create a valley.
• An island arc is a curved chain of volcanic islands forming where submarine volcanic eruptions lead to crust building up and rising above sea level at oceanic-oceanic destructive boundaries.
• Hot spots are areas around the core of the Earth where radioactive decay is concentrated, creating extreme heat.
• Convection current theory explains tectonic plate movement as the result of heat from radioactive decay in the core moving upwards in the mantle, creating currents that carry the lithospheric plates above.
• Wegener used evidence such as:

  • The fit of continents.
  • Fossil distributions.
  • Rock type and structural similarities.
  • Past climatic evidence.
• Gravitational sliding (or ridge push) is the process where gravity pulls the lithosphere down the slope created as new oceanic crust cools and becomes denser. This pushes the crust forward.
• Palaeomagnetism is evidence that the sea floor has gradually moved apart at a mid-ocean ridge. It is shown by the alignment of minerals in cooled lava with the Earth's magnetic field.