Summary

• Earth consists of four main layers – the crust, mantle, outer core and inner core.

• Each layer has distinct physical and chemical properties.

• Temperature, pressure and density all increase with depth below Earth’s surface.

• The crust is Earth’s outermost layer.

• It consists of solid rock composed mostly of silicates – minerals high in silicon and oxygen.

• The crust includes continental crust, which comprises Earth’s landmasses, and oceanic crust, which is covered by Earth’s oceans.

• Continental crust is thicker but less dense than oceanic crust.

• Continental crust consists mostly of granitic rock, whereas oceanic crust consists mostly of basaltic rock.

• The mantle is a mostly rigid layer lying beneath the crust.

• It is composed of silicates with a higher iron and magnesium content than the crust.

• The mantle consists of three distinct zones:

• The upper mantle (lithospheric mantle) – a region of rigid rock, which, together with the crust, makes up a region known as the lithosphere.

• The asthenosphere (transition zone) – a region of plastic rock that flows very slowly over long periods of time.

• The mesosphere (lower mantle) – a region of rigid rock.

• The outer core is a liquid layer located below the mantle.

• It is composed mostly of molten iron and nickel.

• The inner core is Earth’s innermost layer.

• It has a similar chemical composition to the outer core, but is solid.

• The lithosphere is divided into several large fragments called tectonic plates.

• These plates are able to move very slowly due to convection currents in the underlying asthenosphere.

• The movement of tectonic plates results in continental drift, which is accompanied by geological events such as earthquakes and volcanoes.

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