WJEC A-Level Geography 601-8455-3
Coastal Landscapes
Glaciated Landscapes
Tectonic Hazards
Changing Places
Water and Carbon Cycles
Global Migration
Global Governance of the Oceans
EcosystemsContemporary theme
Economic Growth and Challenge: IndiaContemporary theme
Economic Growth and Challenge: ChinaContemporary theme
Development in an African ContextContemporary theme
Energy Challenges and DilemmasContemporary theme
Weather and ClimateContemporary theme
Fieldwork and Geographical Skills
Tectonic Hazards
The internal structure of the Earth
- 3 things to know
- AS Unit 1 and A2 Unit 4
Overview
Approximate radius of the Earth, mohorovičić discontinuity and how seismic waves show that the outer core is liquid.
What you need to know
Answer each one before you reveal it.
How does the thickness of continental crust compare with that of oceanic crust?
Why is oceanic crust denser than continental crust?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What are the four main layers of the Earth, working inwards from the surface?
Model answer
The crust, the mantle, the outer core and the inner core.
- 2
State the approximate radius of the Earth.
Model answer
It is about 6,371 km from the surface to the centre.
- 3
What is the Mohorovičić discontinuity?
Model answer
It is the boundary between the base of the crust and the top of the mantle, detected because seismic waves speed up sharply as they cross it.
- 4
How does the thickness of continental crust compare with that of oceanic crust?
Model answer
Continental crust is roughly 30 to 70 km thick, while oceanic crust is only about 6 to 10 km thick.
- 5
Why is oceanic crust denser than continental crust?
Model answer
Oceanic crust is basaltic and rich in iron and magnesium at about 3.0 g cm⁻³, whereas continental crust is granitic and richer in silica and aluminium at about 2.7 g cm⁻³.
- 6
Why is no oceanic crust older than about 200 million years when continental crust can be billions of years old?
Model answer
Oceanic crust is continually destroyed by subduction, while continental crust is too buoyant to be carried down and so survives.
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