Structure of the Earth (AQA A Level Geography)

Revision Note

Rhiannon Molyneux

Written by: Rhiannon Molyneux

Reviewed by: Bridgette Barrett

Earth's Structure

  • The Earth has four main layers:

    • The crust 

    • The mantle 

    • The outer core

    • The inner core

Crust

  • There are two types of crust:

    • Continental - a thicker (up to 70km), less dense layer mainly composed of granite

    • Oceanic - a thinner (5-10km) , denser layer mainly composed of basalt 

Mantle

  • The mantle is between the crust and core and is the widest layer (2900km)

    • The upper mantle has two layers

      • The rigid layer above the asthenosphere which together with the crust makes up the lithosphere

      • The asthenosphere is a plastic-type layer which moves very slowly under high pressure and carries the lithosphere on top

    • The lower mantle is hotter and denser than the upper mantle 

    • The intense pressure, at depth, keeps the lower mantle solid

Core

  • The core is made up of two parts:

    • Inner Core - solid centre, mostly composed of iron 

    • Outer core - semi-molten, mostly liquid iron and nickel

structure-of-the-earth-1
Earth's structure
  • The lithosphere consists of seven major and several minor tectonic plates which float on top of the asthenosphere  

tectonic-plates-boundaries
Tectonic plates
  • The core is the hottest part of the Earth, and this heat is the main driver of tectonic activity

  • There are two key causes of this extreme heat:

    • Radioactive decay of elements such as uranium and potassium inside the earth’s core

    • Heat left over from the collisions of asteroids and other small bodies which resulted in the formation of Earth

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Rhiannon Molyneux

Author: Rhiannon Molyneux

Expertise: Geography Content Creator

Rhiannon graduated from Oxford University with a BA in Geography before training as a teacher. She is enthusiastic about her subject and enjoys supporting students to reach their full potential. She has now been teaching for over 15 years, more recently specialising at A level. Rhiannon has many years of experience working as an examiner for GCSE, IGCSE and A level Geography, so she knows how to help students achieve exam success.

Bridgette Barrett

Author: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.