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AP Environmental Science Unit 4 Visual Review

A 9-slide visual walkthrough of every Topic 4.1-4.9 concept — plate tectonics, soil, the atmosphere, global wind patterns, watersheds, seasons, climate, and El Niño/La Niña — built right into the page.

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TOPIC 4.1 Plate Tectonics CONVERGENT (collision) DIVERGENT (spreading) TRANSFORM (sliding) Three boundary types, three outcomes Convergent — plates collide, forming mountains (or subduction zones with volcanoes/earthquakes). Divergent — plates pull apart, magma rises to form new crust (mid-ocean ridges, rift valleys). Nearly every major mountain range, volcano belt, and earthquake zone sits on a plate boundary. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.2 Soil Formation and Erosion O — organic litter A — topsoil (humus) B — subsoil (mineral accumulation) C — weathered rock R — bedrock How soil forms Four factors, working over centuries: Parent rock weathers physically & chemically. Climate (temp/moisture) speeds weathering. Organisms add organic matter & mix layers. Time — soil takes centuries to build, years to lose. Erosion strips it away Wind and water carry away exposed topsoil — worsened by deforestation, overgrazing, and tilling that leaves soil bare. Contour plowing, terracing, and cover crops slow it down. The O and A horizons hold nearly all the nutrients — lose those, and the field's fertility is gone for generations. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.3 Soil Composition & Properties CLAY SAND SILT loam % sand / silt / clay determines the texture class Texture: particle size mix Sand (largest) drains fast, holds little water. Clay (smallest) holds water & nutrients, but drains poorly and compacts easily. Loam — the balanced mix — is ideal for farming. Porosity vs. permeability Porosity — the total space BETWEEN particles (how much water/air it can hold). Permeability — how easily water moves THROUGH those spaces. Clay can be porous but impermeable — tiny, disconnected pores. Loam's balance of sand, silt, and clay makes it the most agriculturally productive texture class. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.4 Earth's Atmosphere Troposphere Stratosphere (ozone layer) Mesosphere Thermosphere surface ↑ altitude Composition 78% nitrogen (N₂), 21% oxygen (O₂), <1% argon and trace gases — including CO₂ and other greenhouse gases that trap heat and regulate Earth's temperature. The layer that matters most Nearly all weather happens in the troposphere — the thin bottom layer. The stratosphere above it holds the ozone layer, which absorbs harmful UV radiation. Temperature actually rises with altitude in the stratosphere — the opposite of the troposphere below it. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.5 Global Wind Patterns equator Hadley Hadley Ferrel Ferrel warm air rises at equator, sinks near 30° N/S Why the cells exist The equator receives more direct sunlight than the poles. Warm equatorial air rises, cools, and sinks around 30° latitude — creating the Hadley, Ferrel, and Polar circulation cells. The Coriolis effect Earth's rotation deflects moving air — right in the Northern Hemisphere, left in the Southern. This bends straight north-south airflow into the trade winds and westerlies we actually observe. Deserts cluster near 30° N/S latitude because that's exactly where the sinking, dry Hadley-cell air lands. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.6 Watersheds watershed boundary (divide) outlet (lake/river) Definition A watershed is all the land area that drains into a single body of water. It's bounded by a divide — a ridge of higher elevation. Every point on Earth belongs to some watershed. Land use anywhere affects the outlet Fertilizer, pesticides, and sediment from ANY point in the watershed can wash downstream to the outlet — this is why a farm miles from a lake can still cause the eutrophication seen in Topic 1.6. Impervious surfaces (roads, parking lots) shrink infiltration and speed runoff straight to the outlet. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.7 Solar Radiation and Earth's Seasons sun N tilted toward sun (N summer) N tilted away (N winter) Why seasons happen Earth's axis is tilted about 23.5°. As Earth orbits the sun, that fixed tilt points different hemispheres toward the sun at different times of year — NOT distance from the sun, which barely changes. More direct sunlight AND longer days both follow from the same tilt — that's why summer days feel endless. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.8 Earth's Geography and Climate: Rain Shadow moist ocean air rain on windward side dry descending air desert (rain shadow) Four regional shapers Latitude — sets baseline temperature. Elevation — higher = cooler, thinner air. Ocean currents — warm/cool coastlines. Rain shadow — mountains force air up, it cools, drops moisture on the windward side, then descends dry on the leeward side. Classic example: the Sierra Nevada creates California's Death Valley rain shadow desert. Same storm, two outcomes: lush forest on the windward slope, desert just miles away on the leeward side. The Review Hub · AP Environmental Science Unit 4 TOPIC 4.9 El Niño and La Niña NORMAL CONDITIONS trade winds → warm water piles up (west) cold upwelling (east) EL NIÑO weakened winds warm water shifts east — no upwelling ENSO — a Pacific-wide seesaw El Niño: trade winds weaken, warm water spreads east, cutting off the cold upwelling that normally feeds Pacific fisheries. La Niña is the reverse: stronger trade winds, cooler eastern Pacific, intensified upwelling and normal patterns exaggerated. El Niño years often mean fewer fish off South America — the upwelling that feeds them briefly shuts off. The Review Hub · AP Environmental Science Unit 4
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This covers every one of Unit 4's 9 CED topics, from plate tectonics through the El Niño Southern Oscillation.