Earth Science - Geology, Meteorology, and Astronomy
Earth science questions connect processes across scales: plate motions build mountains and earthquakes, atmospheric circulation drives weather, and orbital geometry explains seasons and phases. Expect rock types, tectonics, seismic waves, fronts and pressure systems, and basic astronomy.
Core rules
- Plate boundaries: divergent (new crust), convergent (subduction or collision), transform (lateral slip). Earthquakes occur mostly at boundaries.
- P waves are longitudinal and fastest; S waves are transverse and cannot travel through liquids. The S–P arrival time increases with distance.
- Rock cycle: igneous from magma, sedimentary from compaction and cementation, metamorphic from heat and pressure.
- Weather: low pressure favors rising air and precipitation; high pressure favors sinking air and clear skies. Cold fronts are steep and bring short, intense storms.
- Seasons are caused by axial tilt, not Earth–Sun distance. Moon phases depend on the Moon–Sun–Earth angle; eclipses require near alignment.
Worked example
A seismic station records P waves at 8 km/s and S waves at 4 km/s, with an S–P arrival difference of 5 s. Let distance be d. Then d/4 − d/8 = 5. Multiplying by 8: 2d − d = 40, so d = 40 km. The station is 40 km from the epicenter. With three stations, circles of this radius intersect at the epicenter. The calculation assumes constant speeds, which is an approximation.
Traps
- Confusing the focus (underground origin) with the epicenter (surface point above it).
- Explaining summer by closer distance to the Sun.
- Reversing Coriolis deflection: right in the Northern Hemisphere, left in the Southern.
- Treating all precipitation as associated with high pressure.
- Assuming the Moon is visible only at night or that phases are caused by Earth’s shadow.