Unit 2: How Does the Earth Support Life?
Core concepts
Unit 2 focuses on Earth's spheres and the processes that make the planet habitable. You must understand the atmosphere (composition, layers, greenhouse effect), hydrosphere (water cycle, ocean currents, salinity), lithosphere (rock types, soil formation, plate tectonics) and biosphere, and how they interact. Study climate and weather distinctions, biomes and the factors determining their distribution (temperature, rainfall, latitude, altitude), and adaptations of organisms to their environments. Understand soil as a system: texture, profile horizons, pH, organic matter, and how land management affects it. Include the carbon, nitrogen and water cycles, human impacts on them, and the concept of sustainability and biodiversity at genetic, species and ecosystem levels.
Traps
Students frequently confuse weather (short-term) with climate (long-term averages). Another trap is assuming the greenhouse effect is entirely harmful; it is essential, and human enhancement of it is the issue. Questions may ask you to interpret a soil profile or climate graph and draw conclusions, so practise reading axes carefully. Be precise about which sphere a process belongs to and how changes cascade between spheres.
Worked example / rule of thumb
When interpreting a climate graph, check rainfall bars against temperature line: high rainfall with high temperature suggests a tropical rainforest biome, while low rainfall and high temperature suggests a desert. Rule of thumb: describe patterns using data (quote values and trends) before explaining causes.