Rocks, Weathering and Earth Movements: notes

Earth and Rocks

• Layers: crust, mantle, outer core, inner core. The crust is split into moving plates.
• Igneous: formed from cooled magma. Granite (slow cooling, inside) and basalt (fast cooling, outside).
• Sedimentary: layers of sediment pressed together. Sandstone, limestone. May hold fossils.
• Metamorphic: rock changed by heat and pressure. Marble from limestone, slate from shale.

Weathering

• Physical: breaking without changing the minerals. Heat then cool makes rock flake (exfoliation).
• Chemical: rainwater with weak acid dissolves rock such as limestone.
• Biological: roots and burrowing animals split rock.

Earth Movements

• Folding: squeezed layers bend into fold mountains.
• Faulting: rock cracks and moves. A block that drops between two faults is a rift valley.
• Volcano: magma reaches the surface through a vent. Earthquake: sudden release of stress along a fault.
• Zimbabwe: the Great Dyke is a long band of igneous rock rich in chrome and platinum.