Chapter 4: Earth Systems and Resources

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4.1: Plate Tectonics

• Plate tectonic theory: It states that Earth’s lithosphere is divided into a small number of plates that float on and travel independently over the mantle, with much of Earth’s seismic activity occurring at the boundaries of these plates.

Continental Drift

• In 1915, Alfred Wegener proposed that all present-day continents originally formed one landmass he called Pangaea.
• Wegener believed that this supercontinent began to break up into smaller continents around 200 million years ago.
• He based his theory on the following six factors:
  • Fossils of extinct land animals were found on separated landmasses.
  • Fossilized tropical plants were discovered beneath Greenland’s ice caps.
  • Glaciated landscapes occurred in the tropics of Africa and South America.
  • Similarities existed in rocks between the east coasts of North and South America and the west coasts of Africa and Europe.
  • The continents fit together like pieces of a puzzle.
  • Tropical regions on some continents had polar climates in the past, based on paleo-climatic data.

Seafloor Spreading Theory

• During the 1960s, alternating patterns of magnetic properties were discovered in rocks found on the seafloor.

• Similar patterns were discovered on either side of mid-oceanic ridges found near the center of the oceanic basins.

• Dating of the rocks indicated that as one moved away from the ridge, the rocks became older, and suggested that new crust was being created at volcanic rift zones.

• The lithosphere is the solid, outer part of the Earth and is broken into huge sections called plates, which are slowly moving.

  • When one plate moves beneath another (subduction) or when two plates converge, it can result in earthquakes and volcanoes.

• Subduction zones: These are areas on Earth where two tectonic plates meet and move toward each other, with one sliding underneath the other and moving down into the mantle.

  

Types of Boundaries

• Convergent Boundaries: These occur where two plates %%slide toward each other%%.
  • Commonly forming either:
  • a subduction zone, where one plate moves underneath the other; or
  • an orogenic belt, if the two plates collide and compress.
  • When a denser oceanic plate subducts a less dense continental plate, an oceanic trench may form on the ocean side and a mountain range on the continental side.
  • Ex.: Cascade Mountain Range
• Divergent Boundaries: These occur when two plates %%slide apart from each other%%.
  • It can create massive fault zones in the oceanic ridge system and areas of frequent oceanic earthquakes.
  • Examples:
    • Oceanic Divergent Boundary — Mid-Atlantic Ridge and the East Pacific Rise;
    • Continental Divergent Boundary — East African Great Rift Valley
  • When two oceanic plates converge, they create an island arc — a curved chain of volcanic islands rising from the deep seafloor and near a continent.
  • They are created by subduction processes and occur on the continental side of the subduction zone.
  • Their curve is generally convex toward the open ocean.
  • A deep undersea trench is located in front of such arcs where the descending plate dips downward.
  • When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upward.
• Transform boundaries: These occur where plates %%slide past each other in opposite directions%%.
  • The friction and stress buildup from the sliding plates frequently causes earthquakes, a common feature along transform boundaries.
  • Example: The San Andreas fault.

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4.2: Soil Formation and Erosion

Soil

• Soils: These are a thin layer on top of most of Earth’s land surface.
  • This thin layer is a basic, natural resource, and its characteristics deeply affect every other part of the ecosystem.
• Soils are composed of three main ingredients:
  • Minerals of different sizes
  • Open spaces that can be filled with air or water
  • Organic materials from the remains of dead plants and animals
• Soil Profile
  • Surface Litter: Leaves and partially decomposed organic debris.
  • Topsoil: Organic matter, living organisms, and inorganic materials; it is very thick in grass lands.
  • Zone of leaching: Dissolved and suspended materials move downward.
  • Subsoil: Tends to be yellowish in color due to the accumulation of iron, aluminum, humic compounds, and clay leached from A and E horizons.
  • Weathered Parent Material: Partially broken-down inorganic materials.
• Soils develop in response to the following factors:
  • Climate: Measured by precipitation and temperature, which results in partial weathering of the parent material, which forms the substrate for soil.
  • Living organisms: Include the nitrogen-fixing bacteria Rhizobium, fungi, insects, worms, snails, etc., that help to decompose litter and recycle nutrients.
  • Parent material: Refers to the rock and minerals from which the soil derives. The nature of the parent rock, which can be either native to the area or transported to the area by wind, water, or glacier, has a direct effect on the ultimate soil profile.
  • Topography: Refers to the physical characteristics of the location.

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Soil Erosion

• Soil erosion: It is the movement of weathered rock and/or soil components from one place to another %%caused by flowing water, wind, and human activity%%.
  • It decreases the soil’s water-holding capacity, destroys the soil profile, and increases soil compaction.
• Poor agricultural techniques that lead to soil erosion include the following:
  • Improper plowing of the soil
  • Monoculture
  • Overgrazing
  • Removing crop wastes instead of plowing the organic material back into the soil

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Landslides and Mudslides

• Landslides: These occur when masses of rock, earth, or debris %%move down a slope%%.
  • These occur when %%water rapidly collects in the ground%%, causing a surge of water-soaked rock, earth, and debris. They can occur after heavy rains, droughts, earthquakes, or volcanic eruptions.
• Mudslides: It is also known as debris flows or mudflows, are a common type of fast-moving landslide that tends to %%flow in channels%%.
  • It usually %%begin on steep slopes and can be triggered by natural disasters%% in areas where wildfires or construction have destroyed vegetation.
• Some areas are more likely to experience landslides or mudslides, including the following:
  • Areas where landslides have occurred before
  • Areas where surface runoff is directed
  • Areas where wildfires or construction have destroyed vegetation
  • Channels along a stream or river
  • Slopes that have been altered for the construction of buildings and roads
  • Steep slopes and areas at the bottom of slopes or canyons

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Rock Types

• Igneous Rocks: These are formed by %%cooling and classified by their silica content%%.
  • Intrusive igneous rocks: Solidify deep underground, cool slowly, and have a large-grained texture.
  • Extrusive igneous rocks: Solidify on or near the surface, cool quickly, and have a fine-grained smooth texture.
  • Igneous rocks are broken down by weathering and water transport.
• Metamorphic Rocks: These are formed by %%intense heat and pressure, high quartz content%%.
  • Common examples: diamond, marble, asbestos, slate, and anthracite coal.
• Sedimentary: These are formed by the %%piling and cementing of various materials%% over time in low-lying areas.
  • Fossils form only in sedimentary rock.

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4.3: Soil Composition and Properties

Soil Components

• Gravel
  • Coarse particles.
  • Consists of rock fragments.
• Sand
  • Sedimentary material coarser than silt.
  • Water flows through too quickly for most crops.
  • Good for crops and plants requiring low amounts of water.
• Loam
  • About equal mixtures of clay, sand, silt, and humus. Rich in nutrients.
  • Holds water but does not become waterlogged. Particle size can vary.
• Silt
  • Sedimentary material consisting of very fine particles between the sizes of sand and clay.
  • Easily transported by water.
• Clay
  • Very fine particles.
  • Compacts easily.
  • Forms large, dense clumps when wet. Low permeability to water; therefore, upper layers become waterlogged.

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Humus

• Humus: It is the dark organic material that forms in soil when plant and animal matter decays.
  • The thick brown or black substance that remains after most of the organic litter has decomposed
• As this material decays, %%it breaks down into its most basic chemical elements and compounds%%, which are important nutrients for plants and animals that depend upon soil for life.
• Earthworms often help mix humus with minerals in the soil.
• Soil containing humus will crumble, allowing air and water to move easily through the loose soil, making root growth easier, reducing erosion, and stabilizing the pH.

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Components of Soil Quality

• Aeration: Refers to how well a soil is able to absorb oxygen, water, and nutrients.

  • Aeration, which reduces soil compaction, involves perforating the soil with small holes to allow air (especially oxygen), water, and nutrients to penetrate to the roots.
  • This helps the roots grow deeply and produce a stronger, more vigorous plant.
  • When there’s little or no light, plants require oxygen to break down the plant’s sugar(s) to release CO2, water, and energy.

• Degree of Soil Compaction: It is measured by dry unit weight and depends on the water content and compaction effort.

  • Heavily compacted soils contain few large pores and have a reduced rate of both water infiltration and drainage from the compacted layer.

• Nutrient-Holding Capacity: The ability of soil to absorb and retain nutrients so they will be available to the roots of plants.

  • The process of weathering greatly influences the availability of plant nutrients.
  • Initially, as soil particles begin to weather, primary minerals release nutrients into the soil.
  • As these particles decrease in size, the soil is able to retain greater amounts of nutrients.
  • The capacity to hold and retain nutrients is greatly reduced in highly weathered soils since most nutrients have been lost due to leaching.
  • Primary plant nutrients are nitrogen (N), phosphorus (P), and potassium (K).

• Permeability: The measure of the capacity of the soil to allow water and oxygen to pass through it.

  • Low permeability can lead to soil salinization.

• pH: It is the measure of how acidic or basic soil is.

  • Various plants have different soil pH requirements.
  • Acidic soils can be caused by pollutants, such as acid rain and mine spoiling, and are most often found in areas of high rainfall.
  • Alkaline (basic) soils have a high amount of potassium (K+), calcium (Ca²+), magnesium (Mg² +), and/or sodium (Na+) ions.

• Pore Size: Describes the space between soil particles.

  • It determines how much water, air, and nutrients are available for plant roots.

• Size of soil and particles: It determines the amount of moisture, nutrients, and oxygen that the soil can hold along with the capacity for water to infiltrate.

  • The particles which constitute the inorganic portion of soil and which are 2 mm or less in diameter.

• Water holding capacity: It is controlled primarily by the soil texture and the soil organic matter content.

  • Soil texture: A reflection of the particle size distribution of soil.
  • After the soil is saturated with water, all of the excess water and some of the nutrients and pesticides that are in the soil solution are leached downward in the soil profile.
  • Formula: Where Vw is the volume of the water required to saturate the soil and Vt is the total volume of the saturated soil (1 cm³ = 1 mL).

  

Soil Food Web

• Soil Food Web: It is the community of organisms living all or part of their lives in the soil, and it describes a complex living system in the soil and how it interacts with the environments, plants, and animals.

  

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4.4: Earth’s Atmosphere

Early History

• Atmospheric carbon dioxide (CO2) produced by volcanoes and methane (CH4) produced by early microbes, both greenhouse gases, likely %%produced a strong greenhouse effect and allowed the earliest life forms to develop%%.

• Great Oxidation Event (GOE) 2.5 billion years ago killed almost all life on Earth.

  • It was a time period when the Earth’s atmosphere and the shallow ocean experienced a rise in oxygen.

• As oxygen began to accumulate in the atmosphere, it is believed that there were two major consequences:

  1. Free oxygen oxidized atmospheric methane (GWP 25) to carbon dioxide (GWP 1), weakening Earth's greenhouse effect and causing planetary cooling and ice ages.
  2. Increased oxygen concentrations allowed biological diversification and major chemical changes between Earth's clay, rocks, and sand, atmosphere, and oceans.

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Atmosphere’s Current Composition

• Nitrogen (N2) — 78%
  • Fundamental nutrient for living organisms.
  • Found in all organisms, primarily in amino acids and nucleic acids.
  • Makes up about 3% of the human body by weight.
  • Deposits on Earth through nitrogen fixation and reactions involving lightning and subsequent precipitation.
  • Returns to the atmosphere through combustion of biomass and denitrification.
• Oxygen (O2) — 21%
  • By mass, the third most abundant element in the universe, after hydrogen and helium.
  • The most abundant element by mass in Earth’s crust, making up almost half of the crust’s mass as silicates.
  • Free elemental oxygen (O2) began to accumulate in the atmosphere about 2.5 billion years ago.
  • Highly reactive nonmetallic element that readily forms compounds.
  • Product in photosynthesis and reactant in cellular respiration.
• Water Vapor (H2O) — 0% to 4%
  • Largest amounts are found near the equator, over oceans, and in tropical regions.
  • Polar areas and deserts lack significant amounts of water vapor.
  • Besides evaporation, other sources of atmospheric water include combustion, respiration, volcanic eruptions, and the transpiration of plants.
• Carbon Dioxide (CO2) < 1%
  • Produced during cellular respiration, the combustion of fossil fuels, and the decay of organic matter.
  • Required for photosynthesis
  • Major greenhouse gas contributing to global warming
  • Average lifetime of a CO2 molecule in the atmosphere is ~100 years.

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Atmosphere’s Structure

• Troposphere: The lowest portion of Earth’s atmosphere, 0–6 miles (0–10 km) above Earth’s surface.

  • 75% of the atmosphere’s mass and almost all of the water vapor on the planet is contained within the troposphere, with weather also occurring in this layer.
  • The atmospheric pressure within the troposphere is highest at the surface and decreases with height, whereas the temperature of the troposphere decreases with height.

• Stratosphere: It is located 6–30 miles (10–50 km) above Earth’s surface.

  • In the stratosphere, ozone (O3) absorbs high-energy ultraviolet radiation from the sun and is broken down into atomic oxygen (O) and diatomic oxygen.
  • Temperature increases with altitude in the stratosphere.

  

Weather and Climate

• Weather: It is caused by the movement or transfer of heat energy, which results from the unequal heating of Earth’s surface by the sun.
  • It describes whatever is currently happening outdoors.
  • It influences the following physical properties:
  • Air pressure
  • Air temperature
  • Humidity
  • Precipitation
  • Sunlight reaching Earth affected by cloud cover
  • Wind direction and speed
• Climate: The average weather conditions prevailing in an area in general or over a long period.
  • The statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years.
• Convection: It is the primary way energy is transferred from hotter to colder regions in Earth’s atmosphere and is the primary determinant of weather patterns.
  • %%Warmer, more energetic air molecules move vertically and horizontally%%.
  • Air rises when it becomes warmer and less dense than the air above it, creating pressure differences that cause wind.
• Heat Index (HI): The measure of how warm it feels when factoring in relative humidity.

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Climate and Factors that Influence it

• Air Mass: A large body of air that has similar temperature and moisture content.

  • These can be categorized as equatorial, tropical, polar, Arctic, continental, or maritime.

• Albedo: An expression of the ability of surfaces to reflect sunlight.

  • Materials like ocean water have low albedo, whereas landmasses have moderate albedo.
  • Snow and ice have the highest albedo.

• Altitude: The distance above sea level.

• Carbon Cycle: The process in which carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere.

• Distance to Oceans: Oceans are thermally more stable than landmasses; the specific heat of water is five times greater than that of air.

  • Because of this, changes in temperature are more extreme in the middle of the continents than on the coasts.

• Fronts: When two different air masses meet, the boundary between them forms a “front.”

  • The air masses can vary in temperature, dew point and wind direction.
  • Cold Front: The %%leading edge of an advancing mass of cold air%% and is associated with thunderhead clouds, high surface winds, and thunderstorms.
  • Warm Front: The %%boundary between an advancing warm air mass and the cooler%% one it is replacing.
  • Stationary Front: A %%pair of air masses, neither of which is strong enough to replace the other%%, that tend to remain in essentially the same area for extended periods of time.

  

• Greenhouse Effect: %%Without this effect, Earth would be cold and inhospitable.%%

  • The most important greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
  • If taken too far, however, Earth could evolve into a hothouse.

• Heat: Climate is influenced by how heat energy is exchanged between air over the oceans and the air over land.

• Human Activity and Climate: Climate can also be influenced by human activity.

  • Increased pollution alone tends to increase the amount of rainfall in urban areas by as much as 10% when compared with undeveloped areas.
  • Climate is also influenced by urbanization and deforestation.

• Latitude and Location

  • Latitude: The measurement of the distance of a location on Earth from the equator.
  • The farther away from the equator, the less sunlight is available.
  • At the poles, the sun’s rays strike Earth at an %%acute angle%%, which spreads the heat over a larger area.
  • Climate is influenced by the %%location of high and low air pressure zones%% and where %%landmasses are distributed%%.

• Moisture Content of Air: It is a primary determinant of plant growth and distribution and is a major determinant of biome type.

• Pollution: Greenhouse gases are emitted from both natural sources and anthropogenic sources.

• Rotation: Daily temperature cycles are primarily influenced by Earth’s rotation on its axis.

  • At night, heat escapes from Earth’s surface, and daily minimum temperatures occur just before sunrise.

• Volcanoes

  • Sulfur-rich volcanic eruptions: It can eject material into the stratosphere, potentially causing tropospheric cooling and stratospheric warming.
  • Volcanic aerosols: These exist in the atmosphere for an average of one to three years.
  • Volcanic aerosols injected into the stratosphere can also provide surfaces for ozone-destroying reactions.

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4.5: Global Wind Patterns

Land and Sea Breezes

• Land Breeze: It occurs during relatively calm, %%clear nights when the land cools down faster than the sea%%, resulting in the air above the land becoming denser than the air over the sea.
• Sea Breeze: It occurs during relatively calm, %%sunny days, the land warms up faster than the sea%%, causing the air above it to become less dense.

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Atmospheric Circulation-Pressure

• Air closer to Earth's surface is warmer and rises due to Earth's rotation on its axis, revolution around the sun, and tilt.
  • Cooler, denser, higher-elevation air sinks, causing convection and winds.
  • Low-pressure weather systems have lower pressure at their centers than elsewhere.
  • Where winds meet low pressure, air rises.
  • Air rises, condensing water vapor into clouds and precipitation.
• High-pressure weather systems: They have higher pressure at their center than around them, so winds blow away from them.
  • They %%blow clockwise north of the equator and counterclockwise south of it%%, with air from higher in the atmosphere sinking down to fill the gaps left by outward-blowing air.
  • Cool, dense air descends toward Earth's surface and warms in high-pressure masses, which are usually associated with fair weather.
• Trade Winds: These are the prevailing pattern of easterly surface winds found in the tropics near Earth’s equator, within the troposphere or lower portion of Earth’s atmosphere.
  • It have been used by captains of sailing ships to cross the world’s oceans.
• Wind Speed: It is determined by pressure differences between air masses.
  • The greater the pressure difference is, the greater the wind speed.
• Wind Direction: It is based on the direction from which wind originated.
  • Easterly: Wind coming from the east.
  • Westerly: Wind coming from the west.
• Coriolis Effect: A phenomenon wherein earth’s rotation on its axis %%causes winds to not travel straight%%, which causes prevailing winds in the Northern Hemisphere to %%spiral clockwise out from high-pressure areas and spiral counterclockwise toward low-pressure areas%%.

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Hadley Air Circulation

• Air heated near the equator rises and spreads out north and south.
• After cooling in the upper atmosphere, the air sinks back to Earth’s surface within the subtropical climate zone.
• Surface air from subtropical regions returns toward the equator to replace the rising air.
• The equatorial regions of the Hadley cells are characterized by high humidity, high clouds, and heavy rains.
• Subtropical regions of the Hadley cell are characterized by low relative humidity, little cloud formation, high ocean evaporation due to the low humidity, and many of the world’s deserts.
• The climate is characterized by warm to hot summers and mild winters. The tropical wet and dry (or savanna) climate has a dry season more than two months long.

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Ferrel Air Circulation Cells

• Ferrel cells develop between 30° and 60° north and south latitudes.
• The descending winds of the Hadley cells diverge as moist tropical air moves toward the poles in winds known as the westerlies.
• Mid-latitude climates can have severe winters and cool summers due to mid-latitude cyclone patterns.
• Defined seasons are the rule, with strong annual cycles of temperature and precipitation.
• Climates of the middle latitudes have a distinct winter season.

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Polar Air Circulation Cells

• Polar cells originate as icy-cold, dry, dense air that descends from the troposphere to the ground.

• This air meets with the warm tropical air from the mid-latitudes and then returns to the poles, cooling and then sinking.

• Sinking air suppresses precipitation. As a result, the polar regions are deserts.

• Very little water exists in this area because it is tied up in the frozen state as ice.

• The amount of snowfall per year is relatively small.

  

Polar Vortex

• Polar Vortex: A low-pressure zone embedded in a large mass of very cold air that lies atop both poles.

• The bases of the two polar vortices are located in the middle and upper troposphere and extend into the stratosphere.

• Due to the equator-pole temperature difference, these cold, low-pressure areas strengthen in winter and weaken in summer.

• There is also a relationship between the chemistry of the Antarctic polar vortex and severe ozone depletion.

  

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Hurricanes

• Hurricanes, cyclones, and typhoons are all the same weather phenomenon.

  • Hurricanes: Term used in the Atlantic and Northeast Pacific.
  • Cyclones: Term used in South Pacific and Indian Ocean.
  • Typhoons: Term used in Northwest Pacific.

• Hurricanes begin over warm oceans in areas where the trade winds converge.

  • A subtropical high-pressure zone creates hot daytime temperatures with low humidity that allow for large amounts of evaporation, with the Coriolis effect initiating the cyclonic flow.

• Hurricane development requires %%tropical ocean thunderstorms and cyclonic circulation that starts to rotate them%%.

  • This cyclonic circulation allows them to pick up moisture and latent heat energy from the ocean.

• In the center of the hurricane is the eye, an area of descending air and low pressure.

• Storm Surge: A rise in sea level that occurs during tropical cyclones, typhoons, or hurricanes.

  • These storms %%produce strong winds that push the seawater toward the shore, which often leads to flooding%%.

  

Tornadoes

• Tornadoes: These are wirling masses of air with wind speeds close to 300 miles per hour (485 kph).
  • The center of the tornado is an area of low pressure.
• Formation of Tornadoes
  • Thunderstorm or hailstorm creates strong winds.
  • The strong winds begin to rotate (due to updrafts and downdrafts) and form a column of spinning air called a mesocyclone.
  • The mesocyclone meets warm air moving up and cold air moving down and creates a funnel.
  • The funnel, made up of dust, air, and debris, reaches the ground, and a tornado is formed.

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Tornadoes vs. Hurricanes

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Monsoons

• Monsoons: These are strong, often %%violent winds that change direction with the season%%.

• Monsoon winds: These blow from cold to warm regions because cold air takes up more space than warm air.

• Monsoons blow from the land toward the sea in winter and from the sea toward land in the summer.

  

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4.6: Watershed

• Watershed: A land area that drains rainfall and snowmelt into a lake, ocean, or aquifer.

• Mississippi River watershed: The largest watershed in the United States, which drains more than one million square miles or land.

• Watershed management: It reduces pesticides and fertilizers that wash off farm fields and into nearby waterbodies by using land, forest, and water resources in ways that don't harm plants and animals.

  

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4.7: Solar Radiation and Earth’s Seasons

Angle of Sunlight

• The amount of heat energy received at any location on Earth is a %%direct effect of the angle of the sunlight reaching the Earth’s surface%%.

• The angle at which sunlight strikes Earth v%%aries by location, time of day, and season due to Earth’s orbit around the sun and its rotation around its tilted axis%%.

• Seasonal changes in the angle of sunlight are caused by the tilt of Earth’s axis, which is the basic mechanism that %%results in warmer weather in summer than in winter%%.

• Sunlight shining on Earth at a lower angle %%spreads its energy over a larger area, making it weaker than if the sun were higher overhead%%.

  

  

Solar Intensity

• Factors that affect the amount of solar energy at the surface of Earth (which directly affects plant productivity) include the following:
  • The tilt of Earth’s axis (23.5°)
  • Atmospheric conditions
  • Earth’s rotation around the sun (once per year)
  • Earth’s rotation on its axis (once every 24 hours)

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4.8: Earth’s Geography and Climate

Bodies of Water Moderate Climate and Regulate Precipitation

• Over 70% of the Earth’s surface is covered in water.
• Oceans and lakes store solar radiation (heat), and as the water heats up it adds moisture to the air above it, beginning a process that drives the major air currents around the world.
• Large water bodies also tend to %%stabilize the climate of adjacent land masses by absorbing extra heat during warm periods and releasing it during cooler periods%%.
• Warm, moist ocean air is a driving force for precipitation patterns around the world as it is carried over cooler land masses.

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Higher Elevations Have Cooler Climates

• %%Climates become cooler and the cold season lasts longer as elevation increases%%.

• %%Higher elevations have lower air pressure%% due in part to there being fewer atoms and molecules per unit of air and, thus, cooler temperatures.

• Many high-altitude plains are technically deserts because they are on the downwind (leeward) side of a mountain range or continental mass.

• Latitude: A measure of distance either north or south from the equator.

• Tropic of Cancer: The northernmost latitude reached by the overhead sun.

• Tropic of Capricorn: The southernmost latitude reached by the overhead sun.

  

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Mountains Affect Air Flow

• Mountain ranges: These are barriers to the smooth movement of air currents across continents.

  • When an air mass hits mountains, it slows down and cools because the air is forced up into cooler parts of the atmosphere to move over the mountains.
  • The cooled air can't hold as much water anymore, so it rains on the side of the mountain range that faces the wind.

• The mountain range's leeward side is drier than the windward side because air on this side has less moisture.

  • Rain Shadow Effect: The drier situation which is directly responsible for the plants that grow there, which in turn affects the animals that live there.

  

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4.9: El Niño and La Niña

La Nada (Normal Conditions)

• During normal conditions, easterly trade winds move water and air toward the west.

  • The ocean is generally around 24 inches (60 cm) higher in the western Pacific, and the water there is about 14°F warmer.

• The trade winds, in piling up water in the western Pacific, make a deep warm layer in the west that pushes the thermocline down while it rises in the east.

  • Upwelling: It occurs when prevailing winds, produced through the Coriolis effect and moving clockwise in the Northern Hemisphere, push warmer, nutrient-poor surface waters away from the coastline
  • It is caused by winds pulling nutrient-rich water from below, increasing fishing stocks in this shallow eastern thermocline (90 feet or 30 m).

  

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El Niño (Warm Phase)

• Air pressure patterns reverse direction, causing trade winds to decrease in strength.
• This causes the normal flow of water away from western South America to decrease “pile up.”
• As a result, the thermocline off western South America becomes deeper and there is a decrease in the upwelling of nutrients, which causes extensive fish kills.
• A band of warmer-than-average ocean water temperatures develops off the Pacific coast of South America.
• Effects are strongest during the Northern Hemisphere winter because ocean temperatures worldwide are at their warmest.
• Increased ocean warmth enhances convection, which then alters the jet stream

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La Niña (Cool Phase)

• Trade winds that blow west across the tropical Pacific are stronger than normal.
• This then results in an increase in the upwelling off of South America.
• This then results in cooler-than-normal sea surface temperatures off of South America.
• This then results in wetter-than-normal conditions across the Pacific Northwest, and both drier- and warmer-than-normal conditions in the southern United States.
• This then results in an increase in the number of hurricanes.
• The southeastern US has warmer winters and the northwest cooler ones, while India and southeast Asia have heavier monsoons.

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Environmental Effects of ENSO Weather Patterns

• Warmer or cooler ocean temperatures

  • A decrease in upwelling, resulting in die-offs.
  • A negative impact on coral reefs.
  • Animal migration patterns may become disrupted.
  • Changes in weather patterns may increase insect-borne diseases.
  • Marine food webs and biodiversity may be disrupted by species that cannot tolerate warmer or cooler water temperatures.
  • Global warming decreases as warmer ocean water can hold less CO2.
  • Hurricanes and tornadoes may become stronger and more frequent.
  • Ocean currents and glacial melting may change with warmer ocean temperatures.

• Increase or decrease in the amount of normal rainfall

  • Reduced rainfall may increase food competition, agricultural output, migration patterns, starvation, species die-offs, forest fires, and water shortages.
  • An increase in rainfall may result in an increase in flooding, soil erosion, and leaching of nutrients from the soil.

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Chapter 5: Land and Water Use