The Crust

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…