Earth Systems and Cycles
Domain 2 covers the solid Earth, its surface and interior processes, the atmosphere and oceans, biogeochemical cycles, and geologic time. Items connect processes across systems: a plate boundary shapes a volcano, which adds rock and carbon to cycles that in turn affect climate.
Plate tectonics and Earth's interior
- Divergent boundaries create ocean ridges and rift valleys; convergent boundaries produce subduction, trenches, and volcanic arcs; transform boundaries produce strike-slip faults.
- Seafloor magnetic stripes record reversals and support seafloor spreading.
- Earthquake P waves compress and travel through solids and liquids; S waves shear and cannot pass the liquid outer core, creating the S-wave shadow zone.
- Hot spots produce chains like Hawaii as a plate moves over a mantle plume.
Rocks, weathering, and soil
- Igneous textures record cooling rate; Bowen's reaction series predicts mineral crystallization order.
- Clastic sedimentary rocks are classified by grain size; chemical rocks by composition.
- Soil horizons commonly run O, A, E, B, C, R. Porosity is pore space; permeability is connected flow.
- Chemical weathering is favored by warm, wet conditions; physical weathering increases surface area.
Cycles and time
- The hydrologic cycle moves water by evaporation, transpiration, condensation, precipitation, runoff, and infiltration.
- Carbon cycles through photosynthesis, respiration, combustion, dissolution, and carbonate burial.
- Relative dating uses superposition, original horizontality, cross-cutting relationships, and inclusions; unconformities mark gaps.
- Radiometric dating uses parent fraction = (1/2)^n, where n is the number of half-lives.
Worked example
A K–Ar sample has 25% of its original parent isotope remaining. Parent fraction = 0.25 = (1/2)^2, so two half-lives have passed. With a K–Ar half-life of about 1.25 billion years, age ≈ 2 × 1.25 = 2.5 billion years. A 75% daughter fraction confirms the parent is 25%; it is not three half-lives.
Traps that cost marks
- Reading daughter/parent ratios as parent fraction.
- Using carbon-14 for million-year-old rocks; its half-life is about 5,730 years.
- Confusing anticlines with synclines, or normal with reverse faults.
- Treating porosity and permeability as the same property.
- Forgetting that El Niño and thermohaline circulation redistribute heat, not create it.