Earth's Internal Structure
Crust - Mantle - Outer Core - Inner Core
Before you can understand tectonic plates, earthquakes, or volcanoes, you need a clear picture of the Earth's internal structure. This page breaks the planet into its main layers and shows why each one matters in Geography.
The Four Main Layers
| Layer | State | Thickness | Composition |
|---|---|---|---|
| Crust | Solid | 5-70 km | Silicates (rock) |
| Mantle | Semi-solid | ~2,900 km | Mg, Fe |
| Outer Core | Liquid | ~2,250 km | Molten Fe + Ni |
| Inner Core | Solid | ~1,220 km | Solid Fe + Ni |
Key Characteristics
Crust
Mantle
Convection currents drive tectonics.
Outer Core
Liquid iron-nickel - generates magnetic field.
Inner Core
Solid iron-nickel, >5,000C - immense pressure keeps it solid.
Important Terms
Moho: crust-mantle boundary. Lithosphere: crust + upper mantle.
Practice Games
six quick assessments - all reset buttons work
Quiz 1 - thickest layer
Quiz 2 - true/false
"Inner core is liquid"
Match
Fill: magnetic field
Fill: discontinuity
Order Outside to Inside
Key Recap
A good exam answer should show how the crust, mantle, outer core, and inner core differ in state, thickness, and function. The mantle drives plate movement, and the outer core helps produce the Earth's magnetic field.
How to Revise Earth Structure
Practise drawing a simple labelled diagram of the Earth before you read your notes again. Your diagram should show the crust, mantle, outer core, and inner core, with one short fact about each layer. This is a quick way to test whether you understand the order of the layers rather than only recognising the names when you see them.
In exam questions, pay attention to the words solid, liquid, density, and temperature. The crust is thin and solid, the mantle behaves like very slow-moving material, the outer core is liquid, and the inner core is solid because of extreme pressure. These differences help explain plate movement and why the Earth has internal heat.
Link this page to the next geomorphology topics by asking one question: how does the inside of the Earth affect the surface? Plate tectonics, earthquakes, volcanoes, folding, and faulting all make more sense when you understand that the Earth is layered and that heat from inside the planet drives slow movement over long periods of time.
A useful self-test is to cover the labels on your diagram and describe each layer from the outside inward. Include thickness, state, and one important role. If you can explain the layers aloud, you are less likely to confuse the mantle with the core in written questions.
When comparing layers, use one clear difference at a time, such as composition, state, temperature, or position. This keeps your answer organised and avoids repeating the same fact in different words.
Remember that Geography questions often test links between ideas. The structure of the Earth is not isolated; it prepares you to explain plate movement, earthquakes, volcanoes, and landform development.
