The Earth's Structure

The Structure of the Earth

The Earth has four layers.

• Crust
• Mantle
• Outer Core
• Inner Core

The Crust

• The Crust: The thin, outer-shell of the earth.
• It is made up of solid rock called the lithosphere.
• There are two types:
  • The Continental Crust
  • The Oceanic Crust

The Continental Crust

• Lies beneath the continents
• Thickness - 30km to 70km
• Made of light rock e.g. Granite
• Made from silica and alumina

The Oceanic Crust

• Lies beneath the oceans
• Thinner than the continental crust- 3km to 10km
• Made of heavy rock e.g. Basalt
• Made from silica and magnesium

The Mantle

• The mantle lies between the earth's crust and core.
• The 'asthenosphere' lies close to the crust and sometimes become semi-molten. This is called magma and can flow in slow-moving currents, known as 'convection currents'.
  • Magma: Semi-molten underground rock.
  • Convection currents: Currents that circulate through fluids (liquids and gases), driven by temperature differences. Warmer, less dense fluids rise away from the heat source, while cooler, denser fluids sink towards the heat source. This creates a continuous circulation pattern.
• Lithosphere: The lithosphere includes the continents, ocean floors (the crust), and the upper mantle. The rocks in this region are solid.
• The lithosphere is made up of sections called 'tectonic plates'. There are seven major plates and many smaller ones.
• The Moho: a boundary in the lithosphere, dividing the upper mantle and the crust.

The Core

• Outer core: hot, liquid rock
• Inner core: largely made up of solid nickel and iron. It is the hottest part of the earth, where temperatures are greater than 4000°C. It remains solid due to intense pressure. The Earth's crust is made up of large plates that float on the semi-fluid mantle below. Heat escapes from the core, creating convection currents in the mantle. Convection currents cause plate movement.

How do the Plates Move?

Plate movement is caused by heat escaping from the core and the lower mantle.

• Heat escapes the extremely hot core, heating up the rocks in the lower mantle.
• These heated rocks slowly rise towards the earth's surface, creating currents of magma.
• When the magma reaches the asthenosphere, it has cooled.
• It moves sideways before sinking back down towards the core.
• The cycle repeats.
• This has created approximately 20 currents within the Earth.
• The friction between the plates and the convection currents leads to plate movement.