Earth and Space Science: Earth Systems, Plates, and Cosmos
Earth and Space Science on this exam connects processes at different scales: Earth's interior and plates, seismic waves, the atmosphere and climate, and the structure and evolution of the solar system and stars. Expect diagram-free descriptions of processes and numerical items involving rates, distances, or ages.
Core rules
- Earth's interior is layered by composition and physical state: crust, mantle, outer core, and inner core. The outer core is liquid; the inner core is solid.
- Plate boundaries are divergent, convergent, or transform. Earthquakes and volcanoes cluster at boundaries, especially subduction zones.
- P waves are compressional and faster; S waves are shear waves and cannot travel through liquids. The S-wave shadow zone helps reveal the liquid outer core.
- Rock types reflect formation: igneous from cooling magma, sedimentary from deposition and lithification, metamorphic from heat and pressure.
- The atmosphere is mostly nitrogen and oxygen. Greenhouse gases absorb and re-emit infrared radiation, warming the surface.
- Kepler's third law relates orbital period and distance: $T^2\propto a^3$ for objects orbiting the same body.
Worked example
A seismic station records a P wave at 10:00:00 and an S wave at 10:00:08. If P waves travel at 8 km/s and S waves at 4 km/s, how far away is the earthquake?
Let distance be $d$. The travel-time difference is $d/4-d/8=8$ s. Then $d/8=8$, so $d=64$ km. The station is 64 km from the epicenter. Three stations are needed to locate the epicenter by triangulation.
Traps that cost marks
- Reversing P-wave and S-wave speeds or claiming S waves pass through the outer core.
- Confusing focus (underground origin) with epicenter (surface point above it).
- Treating apparent magnitude as intrinsic brightness; it depends on distance.
- Assuming all plate boundaries produce the same hazards.
- Ignoring units when comparing geologic or astronomical timescales.