Matter, Energy, and Change in Earth Systems
Matter, Energy, and Change in Earth Systems
This domain tests how energy flows and matter cycles through Earth’s spheres, and how density, phase changes, and feedbacks drive layering and motion. Questions often ask you to apply conservation laws and interpret energy-transfer diagrams.
Core rules and concepts
- Density = mass/volume, in g/cm³. Less dense material floats over denser material: continental crust (~2.7 g/cm³) over oceanic crust (~3.0 g/cm³), and both over mantle (~3.3–5.6 g/cm³).
- Energy is conserved but transfers by radiation, conduction, and convection. Convection needs a fluid, uneven heating, and gravity; it drives the mantle, atmosphere, and oceans.
- During a phase change, temperature stays constant while latent heat is absorbed or released.
- Water’s high specific heat moderates coastal climates; about 4.18 J raises 1 g of water by 1°C.
- Earth is open to energy but mostly closed to matter; feedbacks can amplify or damp change.
Worked example
A rock sample has mass 240 g and volume 80 cm³. Density = 240 ÷ 80 = 3.0 g/cm³. Because 3.0 g/cm³ matches oceanic crust (basalt/gabbro), the sample is likely oceanic crust, not continental granite at about 2.7 g/cm³.
Traps that cost marks
- Mixing mass and weight: weight changes with gravity, mass does not.
- Adding heat during melting and expecting the temperature to rise.
- Saying “heat rises”: hot fluid rises because it is less dense, not because heat has buoyancy.
- Forgetting that density changes with temperature and phase.