The Physical Environment: Earth Systems, Atmosphere, Hydrosphere, Lithosphere and Biogeochemical Cycles
Domain 1 covers the four Earth spheres, the cycles linking them, and Malta's own rock sequence, climate and hydrology. The examiner wants systems vocabulary - reservoir, flux, feedback, residence time - applied to unfamiliar data, plus local specifics on limestone stratigraphy and the mean sea level aquifer.
Systems principles
- A reservoir stores matter or energy; a flux is the rate of transfer between reservoirs; residence time = reservoir size ÷ flux (at steady state).
- Negative feedbacks damp change (more CO₂ → faster silicate weathering); positive feedbacks amplify it (warming peat → more CO₂).
- Steady state means inflows equal outflows, not that nothing moves.
Cycles you must be able to sketch
- Carbon: photosynthesis, respiration, decomposition, combustion, CaCO₃ formation and carbonation weathering.
- Nitrogen: fixation, ammonification, nitrification, denitrification, leaching, volatilisation.
- Phosphorus: no gaseous phase; released by weathering, often limiting, main cause of freshwater eutrophication.
- Water: evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater flow.
Malta's stratigraphy, bottom to top
Lower Coralline Limestone (hard, forms cliffs) → Globigerina Limestone (soft, traditional building stone) → Blue Clay (impermeable) → Greensand → Upper Coralline Limestone (caps plateaus). Because the clay is impermeable, water moving through the upper limestones emerges as perched springs, while the main aquifer lies in the lower limestones at mean sea level and floats on saline groundwater.
Worked example
How much CO₂ is locked into 1 tonne of limestone as CaCO₃? M(CaCO₃) = 100 g/mol, so 1,000 kg ÷ 100 = 10 kmol of carbonate. Each mole of carbonate holds one mole of CO₂, and M(CO₂) = 44 g/mol, so 10 kmol × 44 kg/kmol = 440 kg CO₂. Method to show: mass → moles → molar ratio → back to mass.
Traps that cost marks
- Over-abstraction of the mean sea level aquifer lowers the freshwater lens and draws seawater in - rising salinity is the signature, not just falling water level.
- Weathering is in-situ breakdown; erosion is transport. Never swap them.
- ~500 mm of annual rainfall looks adequate until you subtract high evapotranspiration and note that short, intense storms mostly run off.