WJEC Geology GL5 Lithosphere — Papers & Mark Schemes

Seismology questions require understanding of how P-waves and S-waves reveal the Earth’s internal structure. Draw clear travel-time curves and explain the velocity changes at each boundary: acceleration at the Moho (crust–mantle boundary), deceleration and refraction at the outer core (due to the liquid state), and the S-wave shadow zone caused by the inability of shear waves to propagate through liquid. Practise sketching wave paths through the Earth, marking the shadow zones between approximately 104° and 140°. Mantle convection models range from whole-mantle convection to layered convection separated at the 660 km discontinuity. Know the evidence supporting each model, including seismic tomography, the depth of subducting slabs, and the behaviour of hotspot plumes. Examiners value balanced evaluation of competing models. Palaeomagnetism questions test your understanding of how magnetic reversals recorded in ocean-floor basalts provide evidence for sea-floor spreading. Know how a magnetometer survey across a mid-ocean ridge produces symmetrical magnetic anomaly stripes, and how the reversal chronology is used to calculate spreading rates.