Earth’s Internal Structure – Lesson Summary

This is a lesson summary. The full lesson can be viewed by purchasing an online course subscription.

Learning Objective

In this lesson we will learn about the four main layers that make up Earth – the crust, mantle, outer core and inner core.

Learning Outcomes

By the end of this lesson you will be able to:

  • Identify the main layers making up Earth.
  • Describe the structure and composition of Earth’s crust.
  • Compare continental crust and oceanic crust.
  • Describe the structure and composition of Earth’s mantle.
  • Differentiate between the upper mantle, asthenosphere and mesosphere.
  • Describe the structure and composition of Earth’s outer core.
  • Describe the structure and composition of Earth’s inner core.
  • Describe the lithosphere and explain what tectonic plates are.

 
earths internal structure online science lesson contents

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Lesson Topics

1 | Earth’s Layers

2 | The Crust

3 | The Mantle

4 | The Outer Core

5 | The Inner Core

6 | The Lithosphere and Tectonic Plates

7 | Summary

Lesson 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.

 
earths composition

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