AP Environmental Science Earth Systems and Resources Guide
Return to the AP Environmental Science exam guide.
Earth Systems and Resources in the AP Environmental Science blueprint
College Board assigns Unit 4, Earth Systems and Resources, 10–15% of AP Environmental Science multiple-choice questions. This range describes the multiple-choice section, not a percentage of the total exam score.
Earth Systems and Resources
- May 2027
- Bluebook
- Clean-room teaching
- Read the evidence surface.
- Trace the environmental mechanism.
- Check units, scale, and claim scope.
What Earth Systems and Resources covers
Earth Systems and Resources focus: Use these routes to connect official topics to evidence, calculations, and environmental decisions.
Unit 4: Earth Systems and Resources
4.1 Plate Tectonics
Earth Systems and Resources focus: Plate movement at divergent, convergent, and transform boundaries produces characteristic crustal formation, subduction, volcanism, and earthquakes.
4.2 Soil Formation and Erosion
Earth Systems and Resources focus: Soil forms from weathered parent material modified by climate, organisms, topography, and time; erosion transports exposed soil.
4.3 Soil Composition and Properties
Earth Systems and Resources focus: Soil texture depends on sand, silt, and clay percentages, which influence porosity, permeability, water retention, and nutrient holding.
4.4 Earth's Atmosphere
Earth Systems and Resources focus: The atmosphere is layered by temperature patterns; the troposphere contains most weather and the stratosphere contains protective ozone.
4.5 Global Wind Patterns
Earth Systems and Resources focus: Unequal solar heating, convection, Earth's rotation, and the Coriolis effect help produce global circulation cells and prevailing winds.
4.6 Watersheds
Earth Systems and Resources focus: A watershed is the land area that drains precipitation and groundwater toward a common outlet.
4.7 Solar Radiation and Earth's Seasons
Earth Systems and Resources focus: Seasons result from Earth's axial tilt changing solar angle and day length, not from large annual changes in Earth-Sun distance.
4.8 Earth's Geography and Climate
Earth Systems and Resources focus: Latitude, elevation, proximity to water, topography, and circulation shape regional climate.
4.9 El Niño and La Niña
Earth Systems and Resources focus: El Niño weakens or reverses normal equatorial Pacific upwelling patterns, while La Niña strengthens the normal pattern.
Vocabulary anchors
Plate Tectonics; Soil Formation and Erosion; Soil Composition and Properties; Earth's Atmosphere; Global Wind Patterns; Watersheds; Solar Radiation and Earth's Seasons; Earth's Geography and Climate; El Niño and La Niña are the official topic anchors used throughout this unit.
Evidence lab: Rainfall simulation on three soils
Rainfall simulation on three soils Equal 30-minute storms were applied to equal-area plots at the same slope. Plot | Sand (%) | Clay (%) | Vegetation cover (%) | Runoff (L) | Sediment (g) A | 72 | 8 | 15 | 38 | 510 B | 38 | 32 | 15 | 54 | 690 C | 40 | 30 | 82 | 17 | 105
Which comparison best estimates the effect of vegetation cover?
B and C — Their soil textures are similar while cover differs strongly.
Their cover is equal but texture differs. Both texture and cover differ. A controlled comparison is more diagnostic.
Identifies a near-matched pair in a multivariable table.
Why does greater clay content tend to reduce infiltration?
Small clay particles create narrow pores with low permeability. — Clay can hold water yet transmit it slowly because pore spaces are small.
Clay particles are much smaller. Gravity still acts on water. Permeability can be low without being zero.
Distinguishes porosity/water retention from permeability.
By what percent is sediment lower in C than B?
About 84.8% — The reduction is (690-105)/690 times 100, which is about 84.8%.
This is the remaining fraction, not the reduction. This divides the reduction by the smaller final value. This reports the gram difference as a percent.
Percent-change setup with a nontrivial denominator.
Which limitation prevents attributing the A-B runoff difference solely to clay?
The soils differ in both sand and clay fractions, and other texture fractions are not shown. — The comparison changes multiple composition variables and omits silt.
Equal duration is a control, not a limitation. Liters are appropriate for volume. Equal cover helps isolate texture.
Requires identifying compositional dependence and an omitted fraction.
A farm wants to reduce sediment without waterlogging clay-rich soil. Which test is best?
Compare cover crops, contour planting, and an untreated control while measuring infiltration, runoff, crop yield, and sediment across several storms. — The design evaluates erosion control and the stated drainage tradeoff with replication over variable storms.
A liner prevents infiltration and farming. No treatment comparison would be possible. Leaf color is not a sufficient erosion or drainage outcome.
Integrates erosion, infiltration, agricultural function, control, and repeated events.
Evidence lab: Idealized circulation observations
Earth Systems and Resources focus: Idealized circulation observations At 0° latitude, warm moist air rises. Earth Systems and Resources focus: Near 30° north, dry air descends. Earth Systems and Resources focus: Surface air moves from 30° north toward the equator and is deflected westward relative to Earth's surface.
Earth Systems and Resources focus: Which circulation cell is described between 0° and 30° north?
Hadley cellEarth Systems and Resources focus: — Hadley circulation includes equatorial ascent, poleward flow aloft, subtropical descent, and equatorward surface flow.
Polar circulation occupies high latitudes. Earth Systems and Resources focus: Thermohaline circulation describes ocean-water movement. Earth Systems and Resources focus: Walker circulation is primarily east-west rather than this north-south cross section.
Earth Systems and Resources focus: Identifies a named circulation cell from four defining features.
Earth Systems and Resources focus: Why are many deserts located near 30° latitude?
Earth Systems and Resources focus: Descending air warms and its relative humidity falls, suppressing cloud formation and precipitation.Earth Systems and Resources focus: — Subsidence creates dry conditions through adiabatic warming.
Earth Systems and Resources focus: The model specifies descending air at 30°. Earth Systems and Resources focus: Subtropical regions receive substantial solar energy. Earth Systems and Resources focus: Tides do not create the global desert belt.
Earth Systems and Resources focus: Connects vertical motion to adiabatic temperature and humidity change.
Earth Systems and Resources focus: What primarily causes the westward deflection of the surface return flow in the Northern Hemisphere?
Earth Systems and Resources focus: Earth's rotation and the Coriolis effectEarth Systems and Resources focus: — Moving air is deflected relative to the rotating surface.
Continue in the A+ teaching layer for the remaining evidence labs, figure, and final audit.
How the AP Environmental Science assesses Earth Systems and Resources
Earth Systems and Resources focus: Use this contract to connect unit study to the current APES exam.
| Item | Weight / count | What it means |
|---|---|---|
| Official topic denominator | 9 | Earth Systems and Resources focus: Every listed CED topic is taught on this page and remains owned by one frozen taxonomy leaf. |
| Multiple choice | 80 questions in 90 minutes | Earth Systems and Resources focus: The section includes discrete and shared-stimulus sets using models, data, maps, calculations, and text sources. |
| Free response | 3 questions in 70 minutes | Earth Systems and Resources focus: The task families are investigation design, quantitative-data analysis, and an environmental problem with calculations. |
| Calculation credit | Earth Systems and Resources focus: Setup and answer can be separate rubric lines | Earth Systems and Resources focus: Write the model, substitute with units, and preserve a reasonable final magnitude. |
| Administration | May 2027 | Earth Systems and Resources focus: This page is scoped to the current fully digital Bluebook administration and dated public facts. |
Runoff from a watershed storm
- Step 1Convert area: 2.5 km² = 2,500,000 m²; convert depth: 18 mm = 0.018 m.
- Step 2Rain volume is 2,500,000 m² × 0.018 m = 45,000 m³.
- Step 3Runoff volume is 45,000 m³ × 0.40 = 18,000 m³.
Key terms for Earth Systems and Resources
- Plate Tectonics
- Soil Formation and Erosion
- Soil Composition and Properties
- Earth's Atmosphere
- Global Wind Patterns
- Watersheds
- Solar Radiation and Earth's Seasons
- Earth's Geography and Climate
- The evidence must preserve spatial and temporal scale.
- El Niño and La Niña
Earth Systems and Resources FAQ
Why do plate boundaries matter in environmental science?
Boundary type helps predict earthquakes, volcanism, mountain building, and crust production or loss. Those hazards then interact with settlement patterns, soils, water systems, and risk management.
How should I read a soil-texture triangle?
Confirm that sand, silt, and clay percentages total one hundred, then follow each axis in its printed direction. Texture informs drainage and nutrient retention but does not determine fertility alone.
What is the difference between weather and climate evidence?
Weather describes short-term atmospheric conditions, whereas climate summarizes long-term distributions and patterns. One storm cannot establish a climate trend without a suitable temporal record and comparison.
How does the Coriolis effect enter a causal explanation?
Earth’s rotation deflects moving air relative to the surface, helping organize global circulation. It changes direction rather than initiating wind, which begins with unequal heating and pressure gradients.
Why do watershed boundaries matter when tracing pollution?
Water and transported materials move downslope toward common outlets, so the drainage divide defines likely source areas. Groundwater exchange and engineered transfers can complicate that surface boundary.
Continue through the APES system
How to study Earth Systems and Resources
Use layered maps for Unit 4 review: tectonic setting, rock or soil properties, atmospheric circulation, and watershed flow. Ask which layer supplies the driver and which layer controls exposure at the scale named by the prompt.
On soil questions, keep texture, structure, porosity, permeability, nutrient holding, and erosion distinct. Create matched examples where one property changes while others remain fixed, then predict infiltration, runoff, and plant-water availability.
For climate diagrams, start with unequal solar input and pressure gradients before adding rotation. Trace Hadley circulation, prevailing winds, rain shadows, seasons, or ENSO with arrows; do not let a memorized map substitute for the displayed legend.
