Earth Systems
The Earth Systems domain tests how the geosphere, atmosphere, hydrosphere, cryosphere, and biosphere exchange energy and matter. Expect questions on insolation and climate, plate tectonics and the rock cycle, weathering and erosion, groundwater, streams, and coasts-often asking you to predict the effect of a change in one system.
Energy in the atmosphere and oceans
- Uneven insolation, albedo differences, and the greenhouse effect shape global temperature patterns.
- Convection transfers heat; the Coriolis effect deflects winds and currents (right in the Northern Hemisphere).
- Water's high specific heat moderates coastal climates and supplies hurricane energy.
- Weather is short-term atmospheric state; climate is the long-term statistical pattern.
Plate tectonics and the rock cycle
- Divergent boundaries create new crust; convergent boundaries produce subduction, trenches, and mountain belts; transform boundaries slide.
- Denser oceanic crust (~3.0 g/cm³) subducts beneath continental crust (~2.7 g/cm³).
- Igneous, sedimentary, and metamorphic rocks transform through melting, weathering, deposition, and heat/pressure.
- Earthquakes and volcanoes concentrate at plate boundaries and hotspots.
Water, soils, and landscapes
- Porosity is the fraction of void space; permeability is the ability to transmit water. Well-sorted coarse sediment is highly permeable.
- Stream gradient = elevation change ÷ distance; discharge = velocity × cross-sectional area.
- Steeper streams erode; flatter reaches deposit sediment. Coastal erosion and deposition respond to wave energy and sediment supply.
Worked example
A stream drops from 850 m at 2 km to 650 m at 7 km along its course. Change in elevation = 200 m; distance = 5 km; gradient = 200 ÷ 5 = 40 m/km. If the same 200 m drop occurred over 10 km, the gradient would be 20 m/km-halved-so the stream would flow more slowly and deposit more sediment.
Traps that cost marks
- Confusing porosity with permeability; clay is porous but nearly impermeable.
- Saying "heat rises" instead of explaining that heated fluid expands, becomes less dense, and is displaced upward.
- Mixing weather and climate.
- Blaming the ozone hole for global warming.