Unit 4

Plate Tectonics

Topic 4.1

Earth’s Structure

  • Core

    • Dense mass of solid nickel, iron and radioactive elements that release massive amounts of heat

  • Mantle

    • Liquid layer of magma surrounding core, kept liquified by intense heat from core

  • Asthenosphere

    • Solid, flexible outer layer of mantle, beneath the lithosphere

  • Lithosphere

    • Thin, brittle layer of rock floating on top of mantle

    • Broken up into tectonic plates

  • Crust

    • Very outer layer of the lithosphere

    • Earth’s surface

Plate Boundaries

  • Divergent Plate Boundary

    • Plates move away from each other

    • Rising magma plume from mantle forces plates apart

    • Forms

      • Mid-oceanic ridges

      • Volcanoes

      • Seafloor spreading

      • Rift valleys (on land)

  • Transform Fault Plate Boundary

    • Plates slide past each other in opposite directions

    • Forms

      • Earthquakes

  • Convergent Plate Boundary

    • Plates move towards each other

    • Leads to subduction

      • One plate being forced beneath another

    • Forms

      • Mountains

      • Island arcs

      • Earthquakes

      • Volcanoes

Convection Cycles (Divergent)

  • Magma heated by earth’s core rises towards lithosphere

  • Rising magma cools & expands, forcing oceanic plates apart

    • Creates mid ocean ridges, volcanoes, spreading zones or “seafloor spreading”

  • Magma cools and solidifies into new lithosphere

  • Spreading magma forces oceanic plates into cont. (subduction zone)

    • Sinking oceanic plate melts back into magma

    • Also forces magma up, creat narrow, coastal mountains (Andes)

Convergent Boundary = Subduction Zone

  • Oceanic-Oceanic

    • One plate subducts under other

    • Forces magma up to lithosphere surface, forming mid ocean volcanoes

      • Island arcs

    • Off-shore trench

  • Oceanic-Continental

    • Dense oceanic plate subducts beaneath continent

    • Plate melts & back into magma

    • Forces magma up to lithosphere surface

    • Coastal Mountains (Andes)

    • Volcanoes on land

    • Trenches

    • Tsunamis

  • Continental-Continental

    • One plate subducts other

    • Forcing surface crust upward (mountains)

    • Himalayas

Transform Fault Boundary

  • Plates sliding past each other in opposite directions creates a fault

    • Fracture in rock surface

  • Earthquakes

    • Most common activity

    • Occurs when rough edges of plates get stuck on each other

    • Pressure builds as plates keep sliding, but edges stay stuck

    • When stress overcomes the locked fault, plates suddenly release, slide past each other and release energy

Tectonic Map Can Predict…

  • Ring of Fire

    • Pattern of volcanoes all around pacific plate

    • Offshore island arcs

      • Japan

  • Transform faults

    • Likely location of earthquakes

  • Hotspots

    • Areas of especially hot magma rising up to lithosphere

    • Mid-ocean Islands

      • Iceland

      • Hawaii

Soil Formation & Erosion

Topic 4.2

What is soil?

  • Mix of geologic (rock) and organic (living) components

    • Sand, Silt, Clay

    • Humus

      • Main organic part of soil

      • Broken down biomass like leaves, dead animals, waste, etc

    • Nutrients

      • Ammonium

      • Phosphates

      • Nitrates

    • Water and Air

    • Living Organisms

  • Plants

    • Anchors roots of plants and provides water, shelter, nutrients (N, P, K, Mg) for growth

  • Water

    • Filters rainwater + runoff by trapping pollutants in pore spaces + plant roots

    • Clean water enters groundwater + aquifers

  • Nutrient Recycling

    • Home to decomposers that break down dead organic matter + return nutrients to the soil

  • Habitat

    • Provides habitat for organisms like earthworms, fungi, bacteria, moles, slugs

Weathering + Erosion

  • Weathering

    • Breakdown of rocks into smaller pieces

      • Physical

        • Wind

        • Rain

        • Freezing/Thawing of ice

      • Biological

        • Roots of trees crack rocks

      • Chemical

        • Acid rain

        • Acids from moss/lichen

    • Weathering of rocks = soil formation

      • Broken into smaller and smaller pieces

      • Carried away and deposited by erosion

  • Erosion

    • Transport of weathered rock fragments by wind and rain

    • Carried to new location and deposited

      • Deposition

Soil Formation

  • From below

    • Weathering of parent material produces smaller and smaller fragments that make up geological/inorganic part of soil

      • Sand, silt, clay

      • Minerals

  • From above

    • Breakdown of organic matters adds humus to soil

    • Erosion deposits soil particles from other areas, adding to soil

  • Effects on Soil Form

    • Parent material

      • Soil pH

      • Nutrient content

    • Topography

      • Steep slope = too much erosion

      • More level ground = deposition

    • Climate

      • Warmer - faster breakdown of organic matter

      • More precipitation = more weathering, erosion + deposition

Soil Horizons

  • O-Horizons

    • Layer of organic matter (plant roots, dead leaves, animal waste, etc) on top of soil

      • Provides nutrients and limits H2O loss to evaporation

    • A-Horizon

      • Aka topsoil

      • Layer of humus (decomposed organic matter) and minerals from parent material

        • A-Horizon has most biological activity (earthworms, soil microbes) breaking down organic matter to release nutrients

    • B-Horizon

      • Aka subsoil

      • Lighter layer below topsoil, mostly made of minerals with little to no organic matter

        • Contains some nutrients

    • C-Horizon

      • Least weathered soil that is closest to the parent material

      • Sometimes called bedrock

Soil Degradation

  • The loss of the ability of soil to support plant growth

  • Loss of Topsoil

    • Tiling (turning soil for agriculture) & loss of vegetation disturb soil and make it more easily eroded by wind and rain

      • Loss of top soil dries out soil, removes nutrients & soil organisms that recycle nutrients

  • Compaction

    • Compression of soil by machines (tractors, bulldozers, etc), grazing livestock, and humans reduces ability to hold moisture

      • Dry soil erodes more easily

      • Dry soil supports less plant growth, less root structure, leading to more erosion

  • Nutrient Depletion

    • Repeatedly growing crops on the same soil removes key nutrients (N, P, K, Na, Mg) over time

      • Reduces ability to grow future crops

Soil Composition & Properties

Topic 4.3

Soil Particle Size, Texture, and Porosity

  • Geologic (rock) portion of soil is made up of 3 particles

    • (Biggest to smallest) Sand > Silt > Clay

  • Soil Texture

    • The percent of sand, silt, and clay in a sooil

      • Always adds up to 100%

        • Example

          • 40-40-20

  • Because sand is bigger, it has bigger pores (empty spaces between particles)

    • This allows air & water to enter sandy soil easily

    • Clay has smallest pores, so it's harder for air & water to enter clay-heavy soils

  • Porosity

    • The amount of pore space a soil has

    • More sand in a soil = more porous/higher porosity

      • Easier for water & air to enter

    • More clay in a soil = less porous/less porosity

      • Harder for water & air to enter

Soil Texture Chart

  • Soil texture is determined by clay, sand, silt percentage

    • Example

      • 40-40-20, sand, silt, clay

        • 45% sand, 35% silt, 20% clay

  • Tips for using Soil Texture Chart

    • Always start on bottom with sand percentage

    • Move out to point where sand & silt meet

    • Then go straight over to clay

    • Make sure it adds up to 100%

Porosity, Permeability, and H2O Holding Capacity

  • Porosity

    • The pore space within a soil

      • More sand, more porous

  • Permeability

    • How easily water drains through a soil

  • More porous/higher porosity = more permeable/higher permeability

    • Positive relationship between porosity & permeability

  • H2O holding capacity

    • How well water is retained, or held by a soil

    • More porous/permeable = lower H2O holding capacity

    • Inverse relationship between porosity/permeability  and H2O holding capacity

  • Effect on Soil Fertility

    • Soil that is too sandy (too permeable) drains water too quickly for roots & dries out

    • Clay-heavy soil doesn’t let H2O drain to roots, or waterlogs (suffocating them)

    • Ideal soil for most plant growth is loam, which balances porosity or drainage with H2O holding cap

Soil Fertility

  • Ability of soil to support plant growth

  • Nutrients

    • N

    • P

    • K*

    • Mg^2*

    • Ca*

    • Na*

  • Factors that increase soil nutrients

    • Organic matter (releases nutrients)

    • Humus (holds and releases nutrients)

    • Decomposor activity (recycles nutrients)

    • Clay (negative charge binds positive nutrients)

    • Bases (Calcium carbonate - limestone)

  • Factors that decrease soil nutrients

    • Acids leach positive charge nutrients

    • Excessive rain/irrigation leeches nutrients

    • Excessive farming depletes nutrients

    • Topsoil erosion

  • Water

    • Needs to hold water, but not too much

    • Factors that increase H2O holding cap

      • Aerated soil (biological activity)

      • Compost/humus/organic matter

      • Clay content

      • Root structure, especially natives

    • Factors that decrease H2O holding cap

      • Compacted soil (machines, cows)

      • Topsoil erosion

      • Sand

      • Root loss

Characteristics and Tests of Soil Quality

  • Texture

    • How to Test

      • Let soil settle in jar of water

      • Measure 3 layers that form (sand, silt, clay)

    • What it tells you

      • Percentage of sand, silt, and clay

      • How porous or permeable the soil is

  • Permeability

    • How to test it

      • Time for H2O to drain through column of soil

    • What it tells you

      • How easily water drains through soil

      • Too high, soil dries out

      • Too low, roots don’t get water or drown

      • Medium = optional

  • pH

    • How to test

      • pH strip

      • H+ ion concentration

    • What it tells you

      • How acidic (low pH) or basic/alkaline (high pH) soil is

      • More acidic soil = less nutrient availability

  • Color

    • How to test

      • Compare with soil book color chart

    • What it tells you

      • The darker, the more humus

      • The more nutrients and moisture

  • Nutrient Level

    • How to test

      • Measure ammonium, nitrate or phosphate level

    • What it tells you

      • Higher nutrient levels = more plant growth

      • Low level could indicate acidic soil

Atmosphere

Topic 4.4

Gasses of Earth’s Atmosphere

  • Nitrogen

    • ~78%

    • Mostly in the form of N2

    • Unuseable to plants without being fixed

  • Oxygen

    • ~21%

    • Produced by photosynthesis in plants

    • Needed for human/animal respiration

  • Argon

    • ~0.93%

    • Inert, noble gas

  • Water Vapor

    • ~0-4%

    • Varies by region & conditions

    • Acts as a temporary Green House Gas

      • Less concerning than CO2

    • Quickly cycles through the atmosphere

  • CO2

    • ~0.04%

    • Most important Green House Gas

    • Leads to global warming

    • Removed from atmosphere by photosynthesis

Characteristics of Layers

  • Exosphere

    • Outermost layer where atmosphere merges with space

  • Thermosphere

    • Therm = Hottest temperature

    • Absorbs harmful X-rays & UV radiation

    • Charged gas molecules glow under intense solar radiation producing northern lights (aurora borealis)

  • Mesosphere

    • Meso = for middle

    • 6-80km

    • Even less dense

  • Stratosphere

    • “S” for second

    • 16-60km

    • Less dense due to less pressure from layers above

    • Thickest O3 layer is found here

    • Absorbs UV-B & UV-C rays which can mutate DNA of animals (cancer)

  • Troposphere

    • Tropo = change (weather occurs here)

    • 0-16km

    • Most dense due to pressure of other layers above it

    • Most of atmosphere’s gas molecules are found here

    • Ozone (O3) in the troposphere is harmful to humans (respiratory irritant), damages plant stomata & forms smog

Temperature Gradient

  • Layers of earth’s atmosphere are based on where temperature gradients change with distances from earth’s surface

  • Thermosphere

    • Temperature increases due to absorption of highly energetic solar radiation

    • Hottest place on Earth

      • 3,100°F

  • Mesosphere

    • Temperature decreases because density decreases, leaving fewer molecules to absorb sun

    • Coldest place on Earth

      • -150°F

  • Stratosphere

    • Temperature increases because top lay of stratosphere is warmed by UV rays

      • Like pool surface

  • Troposphere

    • Temperature decreases as air gets further from warmth of Earth’s surface

Global Wind Patterns

Topic 4.5

Air Properties

  • Warm air rises

  • Warm air holds more moisture than cold air

  • Rising air expands & cools

  • Cool air can’t hold as much H2O vapor (condenses->rain)

  • After cooling & expanding, air sinks

  • Steps

    • 1: More direct sunlight @ equator warms air

    • 2: Warm air rises, cools and expands. H2O vapor condenses into rain

    • 3: Air continues to rise, cool and expand

    • 4: Cooling, expanding air spreads out

    • 5: Cool, dry air sinks back down to Earth @ 30° North & South

      • Deserts form here due to lack of moisture in air

  • 30°

    • H Pressure

  • 0°

    • L Pressure

Coriolis Effect

  • Deflection of objects traveling through atmosphere due to spin of Earth

  • Air @ 30° moves back to L pressure of equator

  • Wind between 0-30° moves from East->West

    • Happens because Earth is spinning West->East

  • Wind between 30-60° moves West->East

    • Because Earth spins faster @ 30° than 60°

Global Wind Patterns

  • Air moves out from 30° to 0° and 60° due to H pressure @ 30° & L pressure @ 0 & 60

    • Air rising @ equator = low pressure, air sinking down @ 30° = high pressure

  • 0-30° winds blow East-> West (Eastern trade)

    • Drives ocean current clockwise in Northern hemisphere, counterclockwise in Southern hemisphere

  • 30-60° winds blow West->East (Westerlies)

    • Drives weather patterns of North America

Watersheds

Topic 4.6

Watersheds

  • All of the land that drains into a specific body of water

    • River

    • Lake

    • Bay

  • Determined by slope

    • Ridges of land divide watersheds

      • Different runoff directions

  • Vegetation, soil composition, slope play a large role in how watersheds drains

    • More vegetation

      • More infiltration & groundwater recharge

    • Greater slope

      • Faster velocity of runoff & more soil erosion

    • Soil permeability

      • Determines runoff vs infiltration rates

  • Human activities of a watershed impact H2O quality

    • Agriculture

    • Clearcutting

    • Urbanization

    • Dams

    • Mining

Chesapeake Bay Watershed

  • 6 state region that drains into a series of streams/rivers & eventually into Chesapeake Bay

    • Mix of fresh & salt water + nutrients in sediment make estuary habitats like the salt marshes in the bay highly productive

  • Estuaries & wetlands provide ecosystem services

    • Tourism revenue

      • Hotels, restaurants, permits

    • Water filtration

      • Grass roots trap pollutants

    • Habitats for food sources

      • Fish & crabs

    • Storm protection

      • Absorbing & buffering floods

Human Impacts on Chesapeake Bay

  • Nutrient pollution (N & P) leads to eutrophication in the Bay

    • Algae bloom due to increase N/P -> Decreased sunlight -> Plants below surface die -> Bacteria use up O2 for decomposition -> hypoxia (low O2) & dead zones

  • Major N/P sources

    • Discharge from sewage treatment plants (N/P levels from human waste)

    • Animal waste from CAFOS

      • CAFOS

        • Concentrated Animal Feeding Operations

    • Synthetic fertilizer from agricultural fields & lawns

  • Other major pollutants

    • Endocrine disruptors

      • From sewage treatments

    • Sediment pollution

      • Deforestation, urbanization, tilling agricultural fields

        • Increases turbidity (reduced photosynthesis) & covers over rocky streamed habitats

Effects of Clearcutting on Watersheds

  • Soil Erosion

    • Caused by loss of stabilizing root structure

    • Removes soil organic matter & nutrients from forest

    • Deposits sediments in local streams

      • Warms water & makes it more turbid (cloudy)

  • Increased soil & stream temperature

    • Loss of tree shade increases soil temperature

      • Soil has lower albedo than leaves of trees

    • Loss of tree shade along rivers & streams warms them

      • Erosion of sediments into rivers also warms them

Solutions to Watershed Pollutants

  • Cover crops

  • Riparian buffers

  • Animal manure management

  • Septic tank upgrades

  • Biological nutrient removal

  • Enhanced nutrient removal

Solar Radiation & Earth’s Seasons

Topic 4.7

  • Insolation

    • The amount of solar radiation (energy from the Sun’s rays) reaching an area measured in Watts/m^2

Solar Intensity & Latitude

  • Solar intensity of Insolation (W/m^2) depends on

    • Angle

      • How directly rays strike Earth’s surface

    • The amount of atmosphere sun’s rays pass through

  • Equator

    • Higher insolation than higher latitudes

  • At high latitudes…

    • Sunlight must pass through more atmosphere

    • Loses more of its energy

    • A given amount of solar energy is spread over a larger surface area than at the equator

Math Problems

  • Insolation=Solar Radiation/Area

  • A flat rooftop receives 3,000 kWh of solar radiation over an area of 60m^2. What is the solar insolation (in kWh/m^2) on the rooftop?

    • 3000/60=50 kWh/m^2

    • Solving for Insolation

  • A solar panel has an area of 25m^2 and an insolation of 120 kWh/m^2. What is the total solar radiation (in kWh) received by the panel?

    • 25*120=3000 kWh

    • Solving for Solar Radiation

  • A solar farm receives 18,000 kWh of solar radiation with an average insolation of 300 kWh/m^2. What is the total area (in m^2) of the solar farm?

    • 18000/300=60m^2

    • Solving for Area

Solar Intensity & Season

  • Orbit of Earth around sun & tilt on axis changes angle of Sun’s rays

  • This causes varying insolation, varying length of day and seasons

  • Tilt of Earth’s axis stays fixed during orbit

    • June & December Solstices

      • Northern or Southern hemisphere is maximally tilted toward sun

        • Summer/Winter

    • March & September Equinox

      • Northern or Southern Hemisphere equally facing sun

Tilt of Earth’s Axis Causes Variation in…

  • Varies…

    • Angle of Insolation

      • Which changes intensity

    • Length of day

    • Season

  • March Equinox

    • Equator receives most direct insolation

    • N & S hemisphere get 12 hours of sunlight

    • Spring in N/Fall in S hemispheres

  • June solstice

    • N titled max toward Sun

    • Longest day in North

      • Start of Summer

    • Shortest day in South

      • Start of Winter

  • September Equinox

    • Equator receives most direct insolation

    • N & S hemisphere get 12 hours of sunlight

    • Fall in N/Spring in S hemispheres

  • December Solstice

    • S hemisphere tilted max toward Sun

    • Longest day in South

      • Start of Summer

    • Shortest day in North

      • Start of Winter

Albedo

  • Definition

    • The proportion of light that is reflected by a surface

  • Surfaces with higher albedo reflect more light and absorbs less (ice/snow)

    • Absorb less heat

  • Surfaces with low albedo reflect less light and absorb more (water)

Albedo & Surface Temperature

  • Surface temperature is affected by albedo

  • When sunlight is absorbed by a surface, it gives off infrared radiation (heat)

    • Areas with lower albedo, absorb more sunlight light (heat)

  • Urban Heat Island

    • Urban areas are hotter than surrounding rural area due to lw albedo of blacktop

  • Polar regions are colder due to higher albedo

Earth’s Geography & Climate

Topic 4.8

Climate & Geography

  • Climate is largely determined by insolation

    • Latitude -> angle of insolation & atmosphere

    • Higher latitudes receive less insolation

      • Cooler, less precipitation (especially 30°)

    • Equator receives most intense insolation

      • Higher temperatures, air rises, high precipitation

  • Geography also plays a role

    • Mountains

      • Disrupt wind & produce rain shadow effect

    • Oceans

      • Moderate temperature & add moisture to the air

Rain Shadows

  • Warm, moist air from ocean hits the “windward” side of the mountain, rises, cools (condensing H2O vapor & causing rain) -> lush, green vegetation

  • Dry air descends down “leeward” side of mountain, warming as it sinks

    • Leads to arid (dry) desert conditions)

  • Eastern trade winds blow moist air from Atlantic across South America

    • Windward (East) side of Andes receives heavy rainfall

    • Leeward (West) side of Andres receives arid (dry) air

  • -30° latitude also contributes to lack of rain

    • High pressure, dry, descending air from Hadley cell

4.9

Global Ocean Surface Currents

  • Gyers

    • Large ocean circ, patterns due to global wind

      • Clockwise in Northern hemisphere, counterclockwise in Southern hemisphere

  • E->W trade winds between 0-30° push eq. Current E->W

  • Westerlies between 30-60° push mid latitude currents W->E

  • Upwelling Zones

    • Areas of ocean where winds blow warm surface water away from a land mass, drawing up colder, deeper water to replace it

      • Brings O2 & nutrients to surface->productive fishing

Thermhaline Circulation

  • Connects all of the world’s oceans, mixing salt, nutrients and temperature throughout

  • Warm water from Gulf of Mexico moves toward North Pole

  • Cools & evaporates as it moves toward poles

  • Saltier & colder water @ poles is more dense, making it sink

  • Spreads along the ocean floor

  • Rises back up into shallow warm ocean current @ upwelling zones

El Nino Southern Oscillation (ENSO)

  • ENSO

    • Pattern of shifting atmospheric pressure & ocean currents in the Pacific ocean between South America and Australia/Southeast Asia

      • Oscillates, or shifts regularly from El Nino (warmer, rainier) to La Nina (cooler, drier) conditions along coast of South America

Effects of El Nino & La Nina

  • El Nino

    • Suppressed upwelling & less productive fisheries in South America

    • Warmer winter in much of Norther America

    • Increased precipitation & flooding in Americas

      • West coast especially

    • Drought in South Eastern Asia & Australia

    • Decreased hurricane activity in Atlantic ocean

    • Weakened monsoon activity in India & Southeastern Asia

  • La Nina

    • Stronger upwelling & better fisheries in South American than normal

    • Worse tornado activity in the US & hurricane activity in Atlantic

    • Cooler, drier weather in Americas

    • Rannier, warmer, increased monsoons in Southeastern Asia