General Geology and Earth Science
Domain focus
The General Geology and Earth Science section tests how well you integrate Earth's internal structure, plate tectonics, geologic time, the rock cycle, and basic map/structural readings. Expect questions that ask you to classify a boundary, order events, interpret a simple map scale or seismic record, and distinguish compositional layers from mechanical layers.
Core rules and concepts
- Earth's compositional layers: crust, mantle, core; mechanical layers: lithosphere, asthenosphere, mesosphere, outer core, inner core. The Moho is a compositional boundary, not a plate boundary.
- Divergent boundaries create new lithosphere; convergent boundaries destroy it; transform boundaries conserve it. Earthquakes mark brittle deformation; S-waves cannot pass through the outer core.
- Geologic time uses superposition, original horizontality, lateral continuity, cross-cutting relations, and faunal succession; absolute ages come from radiometric decay.
- The rock cycle links igneous, sedimentary, and metamorphic rocks through melting, weathering, burial, and uplift.
Worked example
A seismic station records P first and S 6.0 s later. Use Vp = 6.0 km/s and Vs = 3.5 km/s. Distance d satisfies d/Vs − d/Vp = 6.0 s, so d(0.2857 − 0.1667) = 6.0, giving d ≈ 50 km. The reasoning matters: the S−P time grows with distance, and the correct velocity units must match the time unit.
Traps
Do not equate crust with lithosphere; oceanic crust is mafic and thin, while continental crust is felsic and thick. Do not use S-wave arrivals beyond the outer core. On maps, check the scale bar and whether a dip is true or apparent. When ordering events, cross-cutting features are younger than the rocks they cut.