Earth's Systems and Processes
Thinking in systems
Earth science treats the planet as four interacting spheres: geosphere (rock, mantle, core), atmosphere, hydrosphere (including cryosphere) and biosphere. Energy from the Sun and from Earth's internal heat drives transfers of matter and energy between them. Candidates must be able to trace flows, identify reservoirs and explain feedbacks.
Core concepts
- Earth's internal structure and heat: differentiation produced a layered planet; radioactive decay and residual heat drive convection, plate motion, volcanism and seismicity.
- Plate tectonics: divergent, convergent and transform boundaries, with characteristic landforms, earthquake depths and magma chemistry.
- Rock and soil cycles: weathering, erosion, transport, deposition, lithification, metamorphism and melting.
- Uniformitarianism and deep time: present processes acting over vast time spans; relative and absolute dating.
- Feedbacks: positive feedbacks amplify change (ice-albedo loss), negative feedbacks stabilise (silicate weathering drawing down CO2).
Common traps
- Confusing weathering (in situ breakdown) with erosion (removal and transport).
- Assuming all boundaries produce the same hazards; transform boundaries give shallow, strike-slip quakes without volcanism.
- Mixing relative age (superposition, cross-cutting) with absolute age (radiometric).
- Treating feedbacks as always stabilising - check the sign.
- Forgetting that convection requires a heat source and a mobile medium.
Worked example: feedback reasoning
Question: sea ice melts, exposing dark ocean. Is this a positive or negative feedback? Rule of thumb - ask does the change amplify or oppose the original change? Darker ocean absorbs more solar radiation, warming the region and melting more ice: this amplifies the change, so it is positive (destabilising) feedback. A negative feedback would, for example, increase cloud cover and reflect more sunlight.