AP Environmental Science Unit 4:
Earth Systems and Resources

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4.1 Plate Tectonics

• Lithosphere

• The layer of the earth below the crust

• Broken up into tectonic plates; their interactions can lead to geographic formations

Source: age-of-the-sage.org

• Divergent boundaries

• Occur when two tectonic plates move away from one another

• Can lead to seafloor spreading, rift valleys, volcanoes

• Convergent boundaries

• Occur when two tectonic plates move toward one another

• Can create mountains, island arcs, volcanoes, trenches

• Transform boundaries

• Occur when two tectonic plates shift against one another

• Can lead to earthquakes

• Focus

• The point of the earthquake within the crust where the earthquake is centered

• Epicenter

• The central point of the earthquake located vertically above the focus

• The epicenter is the “center” of the earthquake on the earth’s surface

4.2 Soil Formation and Erosion

• Weathering

• The process by which rocks break down into smaller pieces

• Physical weathering involves wind, rain, freezing, and melting
• Chemical weathering involves acid
• Biological weathering involves biological activity such as growing tree roots fragmenting a rock

• Erosion

• The process by which pieces of sediment are carried to new locations

• Deposition

• The stage where the sediment lands or “deposits” in its new place

• Humus

• The biological material in soil resulting from organic matter breakdown

• Limestone

• Increases the pH of soil
• Compost decreases the pH of soil

Source: sciencefacts.net

4.3 Soil Composition and Properties

Source: soils.landcareresearch.co.nz

• Loam

• A combination of different soil particles (the ones pictured above)

• Soil texture

• Determined by the distribution of clay, sand, and silt within a type of soil

• Porosity

• The amount of space that soil has within it (for holding water/air)

• Clay has the least porosity and the least permeability
• Since sand is larger, the “gaps” between sand particles are larger, so it has a greater porosity

• Permeability

• The ability of soil to allow water to quickly move through it

• Too much permeability leads to leaching, while too little permeability leads to waterlogging

• Water holding capacity

• The ability of soil to hold water

• Clay soil has the greatest water holding capacity because it has the least permeability

• Water cannot travel through the clay material as quickly

• Soil fertility

• The ability of soil to support plant growth

• Organic matter and clay increase the nutrients in soil as well as the soil’s water holding capacity
• Acids and topsoil erosion decrease the nutrients in soil as well as the soil’s water-holding capacity

4.4 Earth’s Atmosphere

Source: flightdeckfriend.com

• Thermosphere

• Absorbs dangerous X-rays and UV radiation
• Temperature increases as you get farther from Earth

• Mesosphere

• Temperature decreases as you get farther from Earth

• Stratosphere

• Temperature increases as you get farther from Earth

• Troposphere

• Holds most of the atmosphere’s gas molecules
• Most dense layer of the atmosphere due to pressure from the other layers
• Temperature decreases as you get farther from Earth

• Nitrogen

• Composes 78% of the Earth’s atmosphere
• Mostly exists as N₂; must be fixed before plants can use it

• Oxygen

• Composes 21% of the Earth’s atmosphere
• Necessary for respiration; created through plants’ photosynthesis

4.5 Global Wind Patterns

Source: fowlerearthscience.weebly.com

• Air circulation

• Hot air can hold more moisture, and it rises
• Once it rises, it cools, and then the air sinks back down

Source: britannica.com

• Coriolis effect

• Deflection of objects and air due to the Earth’s rotation

• Since the Earth is spinning while objects are moving, an object thrown in a “straight” direction will appear to travel in a curved path

Source: sciencefacts.net

• Global wind patterns

• Wind patterns create high pressure at 30 degrees latitudes
• They also create low pressure at 0 and 60 degree latitudes

• Jet streams

• Powerful winds that circle the globe

4.6 Watersheds

Source: rcrcd.org

• Watershed

• The area of land that drains into one body of water
• Higher slopes of land mean that the water will travel faster

• Infiltration

• When water goes into the ground and “recharges” the groundwater/aquifer
• Vegetation helps with this by absorbing water as it travels across land
• Higher soil permeability also helps more water go into the ground

• Runoff

• When water “runs” along the surface instead of going into the ground
• Runoff may pick up pollution and chemicals

• For example, if water runoff is occurring in a city with a lot of pavement, then the water may become contaminated as it travels along the impermeable pavement

• Estuaries and wetlands

• Tend to be more environmentally friendly and productive
• Often contain fresh water, salt water, and/or nutrients
• Also protect against storms and floods because the water is being absorbed into the ground instead of accumulating above ground

• Eutrophication

• When humans pollute water sources with too much nitrogen (N) and phosphorus (P), algae bloom can grow on the surface of the water and “steal” sunlight/nutrients from the plants below, killing off diversity
• Sewage waste, fertilizer, and animal waste from manmade farms can also pollute water sources

4.7 Solar Radiation and Earth’s Seasons

Source: quizlet.com

• Solar intensity

• Areas closer to the equator will experience a higher solar intensity because they are receiving more/stronger direct sunlight due to being closer to the sun

Source: weather.gov

• Seasons

• The tilt of the Earth’s axis causes different seasons based on the Earth’s position when revolving around the sun
• If the northern hemisphere is tilted closer to the sun, then at that time, the northern hemisphere will experience summer

• And the southern hemisphere will experience winter

• Since it is farther away from the sun’s heat/solar energy

• Areas experiencing summer will also experience longer days

• Solstice

• Occurs when one of the hemispheres is at its maximum tilt toward the sun

• Equinox

• Occurs when both hemispheres are equally facing the sun

Source: eli.lehigh.edu

• Albedo

• The proportion of light that is reflected by the Earth’s surface
• “Colder” surfaces, such as icy ones, have a higher albedo

• Because more heat is reflected away from the surface, less heat is absorbed into the surface

• This causes the “colder” surface temperature

• “Hotter” surfaces have a lower albedo

• More heat is absorbed into the surface

• Urban heat island

• Cities with blacktop pavement tend to have hotter surfaces

• Blacktop pavement has a very low albedo, meaning that a lot of heat is absorbed into those surfaces

4.8 Earth’s Geography and Climate

• Weather

• A “snapshot” of the atmosphere in an area at a specific time

• Climate

• The long-term/usual weather patterns in an area

• Areas closer to the equator tend to have higher temperatures and higher precipitation
• Oceans lead to more moderate temperature and increase the humidity in an area

Source: montananaturalist.org

• Rain shadow effect

• Winds going toward a mountain’s “windward” side from the ocean carry the warm, moist air from the ocean

• This creates lush vegetation on the mountain’s “windward side”

• Once the winds reach the top of the mountain and go over, they no longer carry warm, moist air

• This is because the air cooled and condensed while traveling up the mountain
• This dry air descends and creates arid conditions on the “leeward” side of the mountain (the side that doesn’t face the ocean)

Source: socratic.org

• Occluded front

• Occurs when a cold front overtakes a warm front
• The warm air is lifted off the ground

• Stationary front

• Occurs when a warm air mass and a cold air mass run into one another
• They either stop moving or move very slowly

Source: crops.extension.iastate.edu

• Temperature inversion (or thermal inversion)

• Created when a layer of warmer air sits above a layer of cold air in the troposphere (the layer closest to Earth)
• This traps pollutants in the lower cold layer of air

4.9 El Niño and La Niña

Source: globalsolochallenge.com

• Gyers

• Large ocean circulation patterns caused by global wind
• Gyers are clockwise in the northern hemisphere and counterclockwise in the southern hemisphere

• Upwelling zones

• When winds blow warm ocean water away from the coast, causing deeper/colder water to “well up” and rise to the surface

• This colder “upwelling” water brings O2 and nutrients to the surface from below, which is beneficial for fishing

Source: thecolumn.ahacentre.org

• El Niño Southern Oscillation

• A southerly flowing warm current that generally develops off the coast of Ecuador around December
• Occasionally it will move further south into Peruvian coastal waters and cause the widespread death of plankton, fish, and other organisms dependent upon fish for food

• Trade winds weaken, then reverse, traveling from West region to East region
• Less productive fisheries in South America
• Warmer weather in a significant portion of North America
• Increased precipitation/flooding along the west coast of the Americas
• Drought in southeast Asia and Australia
• Decreased hurricane activity in the Atlantic ocean

• La Niña

• Causes cooler-than-normal conditions along the western coast of South America
• Creates warmer-than-usual conditions along the eastern coast of Australia

• Trade winds become stronger than usual while still traveling in their normal direction (from East to West)
• Stronger upwelling and better fisheries in South America compared to normal conditions
• Worse tornado activity in the U.S. and worse hurricane activity in the Atlantic
• Cooler, drier weather in the Americas
• Rainier, warmer weather with increased monsoons in southeast Asia