Earth Science (Basic Earth Science)
What the exam tests
Basic Earth Science covers the solid Earth, plate tectonics, rocks and minerals, the atmosphere and weather, and astronomy. It tests spatial reasoning and the ability to read maps, cross-sections, and graphs.
Core rules
- Earth's interior: crust, mantle, liquid outer core, solid inner core; seismic waves reveal layers.
- Plate boundaries: divergent, convergent, and transform; earthquakes and volcanoes concentrate at boundaries.
- Rocks: igneous by cooling, sedimentary by deposition, metamorphic by heat and pressure.
- Weather: air moves from high to low pressure; the Coriolis effect deflects moving air; fronts bring changes.
- Astronomy: seasons come from axial tilt, not distance; Moon phases depend on Sun-Earth-Moon geometry.
Worked example
A station records a 10 s difference between P and S arrivals. If vP=8 km/s and vS=4 km/s, then d/4 - d/8 = 10, so d/8=10 and d=80 km. Reasoning: each wave travels the same distance; the slower S wave takes longer, and the time difference gives distance.
Traps
Using the wrong wave speed; confusing focus and epicenter; identifying minerals by color alone; assuming Moon phases are caused by Earth's shadow; and misordering geological events. In weather maps, check pressure gradients and front symbols before predicting.