Unit 4: Earth Systems and Resources
AP Environmental Science: 52 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 4 covers the physical planet: plate tectonics, soil, the atmosphere, and the circulation patterns that drive climate and weather.
Plate tectonics
The lithosphere's plates move on the asthenosphere. Boundaries: divergent (plates apart — mid-ocean ridges, rifts), convergent (plates collide — mountains, trenches, volcanoes), transform (plates slide — faults, earthquakes). Plate motion drives earthquakes, volcanoes, and tsunamis.
Soil
Soil forms from weathered rock plus organic matter over centuries. Horizons: O (litter), A (topsoil), B (subsoil), C (weathered rock). Texture (sand/silt/clay) sets porosity and permeability; clay holds water, sand drains fast. Erosion by wind and water strips topsoil; practices like terracing, contour plowing, and no-till conserve it.
Atmosphere and circulation
The atmosphere's layers: troposphere (weather), stratosphere (ozone layer), mesosphere, thermosphere. Uneven solar heating drives convection: warm air rises at the equator, sinks at 30°, creating Hadley cells and global wind belts. The Coriolis effect deflects winds right in the Northern Hemisphere and left in the Southern, shaping trade winds and westerlies.
Ocean and climate
Ocean currents redistribute heat (gyres, thermohaline circulation). El Niño (weakened trade winds, warm water shifting east, suppressed upwelling off Peru) and La Niña (strengthened trades, strong upwelling) flip global weather every 2–7 years. Watersheds collect precipitation and deliver it downhill; everything drains to a common outlet.
Exam traps
Coriolis deflection direction depends on hemisphere. Ozone is in the STRATOSPHERE (protective), while ground-level ozone is a pollutant. Clay soils are porous but not permeable — water enters slowly. El Niño suppresses, not strengthens, Peruvian upwelling.