Earth Systems and Their Interactions
Systems thinking
Earth and Environmental Science treats Earth as four interacting spheres: the geosphere (solid rock, mantle, core), the hydrosphere (oceans, ice, groundwater), the atmosphere (gases and aerosols), and the biosphere (living organisms, including humans). Each sphere stores matter and energy, and fluxes (flows) move material between reservoirs (stores). A useful rule is that a change in one sphere produces a feedback in another: a feedback that amplifies the original change is positive; one that dampens it is negative and stabilising.
Concepts to master
Know the difference between open and closed systems: Earth as a whole is essentially closed to matter but open to energy from the Sun. Understand residence time (amount stored divided by rate of flow) and equilibrium versus perturbation. Be able to trace a pathway - for example, carbon moving from the atmosphere to the biosphere by photosynthesis, to the geosphere by burial and lithification, and back to the atmosphere by volcanic outgassing or combustion. Link the rock cycle, water cycle, carbon cycle, and nitrogen cycle to sphere interactions.
Common traps
Students often label a feedback by whether it is 'good' or 'bad' rather than by whether it amplifies or dampens. Another trap is confusing a reservoir with a flux, or assuming a large reservoir must have a long residence time (it depends on the flux). Questions may ask you to distinguish a cause from a response in a chain of interactions; read carefully to see which is being tested.
Worked example
Suppose the atmosphere stores 800 units of carbon and the flux into the biosphere is 120 units per year. Residence time = 800 ÷ 120 ≈ 6.7 years. If warming increases that flux, the residence time shortens - a change in flux, not in the store, alters the calculation.