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Tectonic Hazards

Earth's internal structure and plate movement

  • 3 things to know
  • Component 3 Section A

Overview

Depth of the Gutenberg discontinuity and what it separates, two main sources of the Earth's internal heat and how mantle convection currents move tectonic plates.

What you need to know

Answer each one before you reveal it.

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Key term

Compare oceanic and continental crust on composition, density, thickness and age.

Key term

Name the four main layers of the Earth's interior, from the surface inwards.

Key term

What is the Moho, and where does it lie?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Name the four main layers of the Earth's interior, from the surface inwards.

    Model answer

    The crust, the mantle, the outer core and the inner core make up the interior. The crust and uppermost mantle together form the rigid lithosphere.

  2. 2

    What is the Moho, and where does it lie?

    Model answer

    The Mohorovičić discontinuity, or Moho, marks the boundary between the crust and the mantle. Depth ranges from around 5 km under oceans to 70 km under mountain belts.

  3. 3

    State the depth of the Gutenberg discontinuity and what it separates.

    Model answer

    The Gutenberg discontinuity lies at a depth of about 2,900 km. The boundary separates the solid lower mantle from the liquid outer core.

  4. 4

    Which discontinuity separates the outer core from the inner core?

    Model answer

    The Lehmann discontinuity separates the liquid outer core from the solid inner core, at about 5,150 km depth. Pressure there is high enough to keep the iron-nickel inner core solid.

  5. 5

    Contrast the density and composition of oceanic and continental crust.

    Model answer

    Oceanic crust is basaltic and dense, at roughly 3.0 g cm⁻³, and only 5–10 km thick. Continental crust is granitic and lighter, around 2.7 g cm⁻³, and 30–70 km thick.

  6. 6

    Why is oceanic crust much younger than continental crust?

    Model answer

    Oceanic crust is created at ridges and destroyed at subduction zones, so none is older than about 200 million years. Continental crust is too buoyant to subduct and survives for billions of years.

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