Physical Science: The Earth: Atmosphere, Hydrosphere, Structure Features, Geologic Processes, and History
This domain covers Earth's interior, plate tectonics, rocks and geologic time, and the atmosphere and hydrosphere.
Structure and plate tectonics
Layers: crust (oceanic basalt, thin; continental granite, thick), mantle, liquid outer core, solid inner core. S-waves cannot pass liquids, which is how the liquid outer core was inferred. Plates diverge at mid-ocean ridges (seafloor spreading, magnetic striping), converge at subduction zones (trenches, volcanic arcs, mountains), and slide at transform faults (earthquakes). P-waves arrive first, then S-waves, then surface waves.
Rocks and the rock cycle
Igneous rocks crystallize from magma (intrusive = coarse-grained, extrusive = fine-grained). Sedimentary rocks form by compaction of clastics, chemical precipitation, or organic remains, preserving fossils and strata. Metamorphic rocks recrystallize under heat and pressure, often with foliation. Relative dating uses superposition, original horizontality, cross-cutting relationships, and index fossils; absolute dating uses radiometric decay.
Atmosphere and hydrosphere
The atmosphere is 78% N2 and 21% O2 with traces of argon and CO2. Layers: troposphere (weather; temperature falls with altitude), stratosphere (ozone absorbs UV), mesosphere, thermosphere. The greenhouse effect traps outgoing infrared. The hydrologic cycle moves water by evaporation, condensation, precipitation, runoff, and infiltration; aquifers store groundwater. Ocean currents redistribute heat, and the Coriolis effect deflects moving air and water.
Earth history
Geologic time runs Precambrian, Paleozoic, Mesozoic, Cenozoic. Mass extinctions - end-Permian and end-Cretaceous (asteroid impact, iridium layer) - punctuate the record.
Worked example
A basalt dike cuts horizontal sandstone but does not cut the shale above it. The dike is younger than the sandstone (cross-cutting) and older than the shale, because it does not penetrate that layer. Order: sandstone, dike, shale. Reasoning: cross-cutting features postdate what they cut, and undisturbed layered sequences are oldest at the bottom.
Traps
Calling P-waves transverse (they are longitudinal); confusing earthquake magnitude with intensity; attributing seasons or climate to distance from the Sun; thinking continental crust is thinner than oceanic; forgetting the inner core is solid despite high temperature because of pressure.