WJEC A-Level Geology F4 Earth Structure and Global Tectonics: a deep dive on the layered Earth, seismic evidence, plate tectonic theory and plate boundaries
A deep-dive WJEC and Eduqas A-Level Geology guide to F4, Earth Structure and Global Tectonics. Covers the compositional and mechanical layering of the Earth and the seismic evidence for it, the development and evidence of plate tectonic theory, and the three plate boundary types with their processes and driving forces, with exam-style worked questions.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What F4 actually demands
F4 sets out the unifying theory of the whole subject. Examiners want a clear grasp of the Earth's layered structure (told two ways, by composition and by mechanical behaviour), the seismic evidence that reveals it, the history and evidence of plate tectonic theory, and the processes at each boundary type. Diagrams and the ability to identify a boundary from its features are routinely tested.
This guide ties the three topics of the unit together. Each has a matching dot-point page with practice questions; this overview connects them.
The layered Earth and the evidence for it
By composition the Earth is crust (oceanic basaltic, continental granitic), mantle (dense silicate) and core (iron and nickel, liquid outer and solid inner). By mechanical behaviour it is the rigid lithosphere (the plates) over the weak asthenosphere. The structure is read from seismic waves: P waves pass through solids and liquids, S waves only through solids, and the S-wave shadow zone shows a liquid outer core.
Plate tectonic theory and its evidence
Plate tectonics grew from Wegener's continental drift. His evidence (continental fit, matching geology, matching fossils, palaeoclimate) was strong but lacked a mechanism. Sea-floor spreading and the symmetry of palaeomagnetic stripes about mid-ocean ridges supplied the decisive confirmation.
Plate boundaries and driving forces
Constructive margins make new crust at ridges; destructive margins destroy crust by subduction or collide into fold mountains; conservative margins slide past with earthquakes only. Plate motion is driven by mantle convection, ridge push and, most importantly, slab pull.
Check your knowledge
Attempt these under timed conditions, then check against the solutions.
- Distinguish the compositional layers from the mechanical layers of the Earth. (2 marks)
- Explain how the S-wave shadow zone shows the outer core is liquid. (2 marks)
- State two lines of evidence Wegener used for continental drift. (2 marks)
- Explain how magnetic stripes confirm sea-floor spreading. (2 marks)
- Name the features produced at an oceanic-continental destructive boundary. (3 marks)
- State the three forces that drive plate motion. (2 marks)
Sources & how we know this
- WJEC Eduqas A-level Geology specification — WJEC Eduqas (2017)