ATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 1.1 Introduction: The world beneath our feet
The surface of planet Earth is constantly changing. These changes may be due to surface (exogenic) forces such as weathering and erosion or internal (endogenic) forces such as moving magma. Internal and external forces combine constantly to produce the world we live in.
They are responsible for the amazing landscapeswe see and the terrifying forces that can kill. These forces have created oceans, landmasses and the atmosphere and they have determined where humans, plants and animals live and survive.
Fig. 1 Lava, a product of the earth’s internal heat
Fig. 2 Mount Eyjafjallajokull eruption, Iceland 1.2 The internal structure of the earth Sea Crust
5–100 km thick. Contains minerals such as quartz and feldspar found in igneous rock such as granite, sedimentary and metamorphic rocks.
Upper mantle The lowest layer of the lithosphere. Solid.
Asthenosphere The part of the upper mantle which can flow like treacle.
Outer core
2,200 km thick. Iron and nickel. Liquid and metallic.
Core
Fig. 3 View of the earth’s layered structure. The distance from the surface to the centre of the earth is 6,378 km.
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Mantle
Lower mantle Silica-rich minerals. Solid and rocky.
Outer core Inner core
1,250 km thick. Iron and nickel. Solid and metallic.
Lithosphere Mohorovicic discontinuity (Moho)
A thin band near the top of the upper mantle. It marks the change from crust to mantle.