The Crust

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The Crust

Earth's Surface Seperated into Tectonic Plates

  • Lithosphere is divided into sections called tectonic plates.
  • Plated aare moving due to convection currents in the asthenosphere.
  • Places where plates meey are called boundaries or plate margins

Tectonic Plates Move Due to Convection Currents in the Mantle

  • Radioactive decay of some elements in the mantle and core e.g. urainium generates a lot of heat.
  • Lower parts of asthenosphere heat up become less dense and slowly rise.
  • As move towards top of asthenosphere they cool down, become more dense, then slowly sink.
  • The circular movement of semi-molten rock called convection currents.
  • Convection currents in asthenosphere create drag on base of teconic plates causing them to move.

Crust Created When Plates Move Apart

  • Rising convection currents diverge at the base of the lithosphere.
  • Drag of convection currents cause plates above to diverge too.
  • Magma rises up to fill gap created, cools to form new crust.
  • Over time new crust dragged apart and even more new crust forms between it.
  • When this happens at a plate margin under sea the sea floor gets wider.
  • Process is called sea floor spreading.
  • Creates structures called mid-ocean ridges - ridges of higher terrain on either side of margin.
  • Similar process of spreading occurs at land margins where plates are


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