Earth Science
Key concepts
Earth science on this exam emphasizes systems and cycles rather than isolated facts. Know Earth's layered interior (crust, mantle, outer core, inner core) and how density and seismic-wave behavior support that model. Plate tectonics explains earthquakes, volcanoes, mountain belts, and seafloor spreading; convection in the mantle is the usual driving mechanism. The rock cycle links igneous, sedimentary, and metamorphic rocks through melting, cooling, weathering, deposition, compaction and cementation, heat, and pressure. Distinguish weathering (breakdown in place) from erosion (transport) and deposition (placement). The water cycle-evaporation, transpiration, condensation, precipitation, runoff, infiltration-drives weather and shapes land. For astronomy, know that seasons come from axial tilt and revolution, not distance from the Sun; Moon phases come from the Moon's orbital position as seen from Earth, while eclipses require near-perfect alignment.
Traps: many items offer “distance from the Sun causes seasons,” “Earth's shadow causes phases,” or treat weathering and erosion as synonyms. Also watch relative-age wording: superposition places oldest rock layers at the bottom in undisturbed sequences, but cross-cutting faults or intrusions are younger than the rocks they cut.
Worked example: A sequence has limestone at the bottom, shale above it, then a sandstone layer cut by a vertical igneous dike. Rule: apply superposition first, then cross-cutting relationships. The limestone is oldest; shale is younger; sandstone younger still; the dike is younger than all three because it cuts across them. If a layer were overturned, superposition alone would mislead, so check for clues such as graded bedding.
Rule of thumb: in undisturbed sequences, bottom is oldest; anything that cuts across is younger.