Topic 1: 1.7 Earth’s layered structure, and physical properties is key to plate tectonics — Edexcel GCSE Geography B
Verified courseTeaching note checked against the official specification.
Topic 1: 1.7 Earth’s layered structure, and physical properties is key to plate tectonics explained
Topic 1: 1.7 Earth’s layered structure, and physical properties is key to plate tectonics covers 2 specification points, including A.
Read the full explanation
Earth’s layered structure (including the… and B. How the core’s internal heat source…. Open a point below for its explanation and revision guidance.
a. Earth’s layered structure (including the asthenosphere), with different composition and physical properties (temperature, density, composition, physical state).
This statement requires you to describe Earth's layered structure, including the asthenosphere, and explain how each layer differs in temperature, density, composition and physical state. The inner core is solid iron-nickel under extreme pressure, while the outer core is liquid and generates Earth's magnetic field. The mantle is silicate rock, denser than the crust, and hotter with depth. Within the upper mantle, the asthenosphere is hot enough to be weak and partly plastic, so it flows slowly and allows plates to move. The crust is least dense: continental crust is around 2.7 g/cm³ and oceanic crust around 3.0 g/cm³.
b. How the core’s internal heat source (through radioactive decay) generates convection, the key foundation for plate motion.
This statement links three things: the Earth's internal heat source, the convection it generates, and plate motion. Heat from the core, together with heat released by radioactive decay (unstable isotopes such as uranium breaking down and releasing energy), warms the mantle above it. Warmer, less dense rock rises while cooler, denser rock sinks, creating convection currents in the mantle. These slow currents are the key foundation for plate motion because mantle flow is thought to drag the overlying lithospheric plates. Use a clear chain in answers: heat source, then convection, then plate movement, and explain each link rather than listing them.
Your focus
- Label the crust, mantle, asthenosphere, outer core and inner core on a diagram.
- Compare the composition and physical state of the outer core and inner core.
- Explain how the weak, partly plastic asthenosphere allows tectonic plates to move.
Show all 6 objectives
- State radioactive decay and core heat as sources of energy within the Earth.
- Explain how density differences caused by heating produce convection currents.
- Link mantle convection to plate motion using a sequenced explanation.
Topic 1: 1.7 Earth’s layered structure, and physical properties is key to plate tectonics exam tips
Marking Points
- Identifies the crust, mantle, outer core and inner core, and places the asthenosphere within the upper mantle.
- Describes the composition of each layer, such as silicate rock in the crust and mantle and iron-nickel in the core.
- Explains that temperature and density increase with depth, using the core as the clearest example.
- Explains physical state, such as a solid inner core, a liquid outer core and a partly plastic asthenosphere.
- Links the asthenosphere's weak, ductile properties to the movement of tectonic plates.
- Identifies the core and radioactive decay as internal heat sources that warm the mantle.
- Explains that heating makes rock less dense, so it rises, while cooler denser rock sinks, producing convection currents.
- Links mantle convection currents to the movement of the overlying lithospheric plates.
- Sequences the explanation as heat source, then convection, then plate motion, with each step explained.
- Recognises that convection is the key foundation for plate motion rather than a separate process.
Examiner Tips
- 💡Sketch a labelled cross-section and add temperature, density, composition and physical state to each layer before writing.
- 💡Explain the link to plate tectonics in each property you describe, not as a separate final paragraph.
- 💡Use the correct state for each layer: the outer core is liquid while the inner core is solid despite being hotter.
- 💡Name both heat sources before explaining convection so the first link is complete.
- 💡Use the word density when explaining why heated rock rises and cooled rock sinks.
- 💡Write one sentence per link in the chain so no step is skipped.
Common Mistakes
- Places the asthenosphere in the crust or treats it as the rigid outer layer; correct this by placing it in the upper mantle beneath the lithosphere.
- Describes the asthenosphere as fully molten; correct this to partly molten or plastic, solid but able to flow slowly.
- Assumes density decreases with depth; correct this by stating that density increases towards the centre.
- Treats the crust and the lithosphere as the same thing; correct this by recognising that the lithosphere includes the crust and the uppermost mantle.
- Treats the core as the only heat source and omits radioactive decay; name both sources.
- Describes convection without stating that heating changes density; state why hot rock rises.
- Assumes convection currents move the crust directly; explain that mantle flow drags the plates.