4.1 - Plate Tectonics

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 the core, kept liquified by intense heat from the 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, the earth’s surface

Plate Boundaries

• Divergent Plate Boundary

  • Plates move away from each other

  • Rising magma plume from the mantle forces plates apart

    • Forms: mid-oceanic ridges, volcanoes, seafloor spreading, and rift valleys (on land)

• Convergent Plate Boundary

  • Plates move towards each other

  • Leads to subduction (one plate is forced underneath another)

    • Forms: mountains, island arcs, earthquakes, and volcanoes

• Transform Fault Plate Boundary

  • Plates slide past each other in opposite directions

    • Forms: earthquakes

Convection Cycles (Divergent)

• Magma heated by the earth’s core rises towards the lithosphere

• Rising magma cools and expands, forcing oceanic plates apart

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

• Magma cools and solidifies into new lithosphere

• Spreading magma forces oceanic plates into continent (subduction zone)

  • Sinking oceanic plate melts back into magma

  • Also forces magma up, creating narrow, coastal mountains (Andes) and volcanoes on land

Convergent Boundary = Subduction Zone

• Oceanic-Oceanic: one plate subducts underneath other

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

    • Island arcs

  • Off-shore trench

• Oceanic-Continental: dense oceanic plate subducts beneath a continental plate and melts back into magma

  • Forces magma up to the lithosphere surface

  • Coastal mountains (Andes), volcanoes on land, trenches, tsunamis

• Continental-Continental: one plate subducts underneath the other, forcing the surface crust upward (mountains)

  • Ex. Himalayas

Transform Fault Boundary

• Plates sliding past each other in opposite directions create a fault (fracture in rock surface)

  • Earthquakes are the most common activity

  • Occur when rough edges of plate 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 that shakes the lithosphere

Tectonic Map

• Can predict…

  • Ring of Fire: pattern of volcanoes all around the pacific plate

    • Offshore island arcs (Japan)

  • Transform Faults: likely location of earthquakes

  • Hotspots: areas of especially hot magma rising up to the lithosphere

    • Mid-ocean islands (Iceland, Hawaii)

4.2 - Soil Formation and Erosion

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

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

• Soil filters rainwater + runoff (water) 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

• Soil provides habitats for organisms like earthworms, fungi, bacteria, moles, and slugs

Weathering and 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 a 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 matter adds humus to soil

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

• Effects on Soil Formation

  • 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

  • Organisms: soil organisms like bacteria, fungi, and worms breakdown organic matter

Soil Horizons

• O-Horizon: layer of organic matter (plant roots, dead leaves, animal waste, etc) on top of soil

  • Provides nutrients and limits H2O lost 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 topsoil dries out the 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

4.3 - Soil Composition and Properties

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 % of sand, silt, and clay in a soil

  • Always adds up to 100%

• 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, and silt %

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 and permeability

• H2O Holding Capacity: how well water is retained or held by a soil

  • More porous/permeable = lower H2O

  • 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 capacity

Soil Fertility

• ability of soil to support plant growth

  • Nutrients:

    • N, P, K+, Mg2+, Ca+, Na+

    • Factors that increase soil nutrients:

      • Organic matter (releases nutrients)

      • Humus (holds and releases nutrients)

      • Decomposer 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 capacity:

      • Aerated soil (biological activity)

      • Compost/humus/organic matter

      • Clay content

      • Root structure, especially natives

    • Factors that decrease H2O holding capacity:

      • Compacted soil (machines, cows)

      • Topsoil erosion

      • Sand

      • Root loss

• Characteristics and Tests of Soil Quality

  • Texture:

    • How to test:

      • Let soil settle in a jar of water. Measure 3 layers that form (sand, silt, clay)

    • What it tells you:

      • % of sand, sild, and clay - how porous or permeable soil is

  • Permeability:

    • How to test:

      • Measure 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 = optimal

  • pH:

    • How to test:

      • pH strop - 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:

      • Darker = more humus = 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, depletion

4.4 - Atmosphere

Gasses of Earth’s Atmosphere

• Nitrogen ~ 78%

  • Mostly in the form of N2 (unuseable to plants without being fixed)

• Argon ~ 0.93%

  • Inert, noble gas

• CO2 ~ 0.04%

  • Most important greenhouse gas; leads to global warming

  • Removed from atmosphere by photosynthesis

• Oxygen ~ 21%

  • Produced by photosynthesis in plants and needed for human/animal respiration

• Water Vapor ~ 0-4%

  • Varies by region and conditions; acts as a temporary greenhouse gas, but less concerning than CO2

  • Quickly cycles through atmosphere

Characteristics of Layers

• Exosphere: Outermost layer where the atmosphere merges with space

• Thermosphere: Therm= hottest temp

  • absorbs harmful X-rays and UV radiation

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

• Mesosphere: Meso = middle; 60-80 km, even less dense

• Stratosphere: “S” for second - 16-60 km; less dense due to less pressure from layers above

  • Thickest O3 layer is found here; absorbs UV-B and UV-C rays which can mutate DNA of animals (cancer)

• Troposphere: Tropo = change (weather occurs here) - 0-16 km, 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) and damages plant stomata, and forms smog

Temperature Gradient

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

  • Thermosphere: temperature increases due to the absorption of highly energetic solar radiation

    • Hottest place on earth (3,100 degrees Fahrenheit)

  • Mesosphere: temperature decreases because density decreases, leaving fewer molecules to absorb sun

    • Coldest place on earth (-150 degrees Fahrenheit)

  • Stratosphere: temperature increases because top layer of stratosphere is warmed by UV rays (like pool surface)

  • Troposphere: temperature decreases as air gets further from warmth of earth’s surface

4.5 - Global Wind Patterns

Air Properties

• Warm air rises

• Warm air holds more moisture than cold

• Rising air expands and cools

• Cool air can’t hold as much H2O vapor(condenses and becomes rain)

• After cooling and expanding, air sinks

Coriolis Effect

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

• Air at 30 degrees moves back to L pressure of equator

• Wind between 0-30 degrees moves from East to West

  • Because earth is spinning West to East

• Wind between 30-60 degrees moves West to East

  • Because earth spins faster at 30 degrees than 60 degrees

Global Wind Patterns

• Air moves out from 30 degrees to 0 degrees and 60 degrees due to high pressure at 30 degrees and low pressure at 0 and 60.

  • Air rising at equator = low pressure, air sinking down at 30 degrees = high pressure

• 0-30 degrees winds blow East to West (Eastern trade)

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

• 30-60 degrees winds blow West to East (Westerlies)

  • Drives weather patterns of North America

4.7 - Solar Radiation and Earth’s Seasons

Insolation: the amount of solar radiation (energy from sun’s rays) reaching an area

• Measured in Watts/m²

Solar Intensity and Latitude

• Solar intensity of insolation (W/m²) 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

Solar Intensity and Season

• The orbit of the earth around the sun and its tilt on the axis changes the angle of the sun’s rays

  • Causes varying insolation, varying length of day, and seasons

• Tilt of earth’s axis stays fixed during orbit

  • June and December Solstices: north or south hemisphere is maximally tilted toward sun (summer/winter)

  • March and September Equinoxes: north and south hemispheres equally facing sun

• Tilt of earth’s axis causes variation in:

  • angle of insolation (which changes intensity)

  • length of day

  • season

Albedo

• Albedo: the proportion of light that is reflected by a surface

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

  • Absorb less heat

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

  • Absorb more heat

Albedo and Surface Temperature

• Surface temperature is affected by albedo

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

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

• Urban Heat Island: urban areas are hotter than surrounding rural area due to low albedo of blacktop

• Polar regions are colder due to higher albedo

4.8 - Earth’s Geography and Climate

Climate and Geography

• Climate is largely determined by insolation (latitude → angle of insolation & atmosphere)

  • Higher latitudes receive less insolation: cooler, less precipitation (especially 30 degrees)

  • Equator receives most intense insolation: higher temp, 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 mtn, rises, cools (condensing H2O vapor & causing rain) → lush, green vegetation

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

  • Leads to arid (dry) desert conditions

• Ex. eastern trade winds blow moist air from Atlantic across SA

• 

  • Windward (E) side of Andes receives heavy rainfall

  • Leeward (W) side of Andes receives arid (dry) air

  • -30 degrees latitude also contributes to lack of rain

    • high pressure, dry, descending air from Hadley cell

4.9 - El Nino and La Nina

Global Ocean Surface Currents

• Gyers: large ocean circ. patterns due to global wind

  • (clockwise in N hemisphere, counterclockwise in S hemisphere)

• E→ W trade winds between 0-30o push eq. current E → W

• Westerlies between 30-60o push mid lat. 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

Thermohaline 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 at poles, is more dense, making it sink

• Spreads along ocean floor

• Rises back up into shallow warm ocean current at 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, rannier) to La Nina (cooler, drier) conditions along coast of South America

• Normal year:

  

  • Trade winds blow eq. water W ← E

  • Cool H2O upwelled off coast of SA (cool temp + good fi$herie$)

  • Warm eq. current brings heat & precip. to Australia & SE Asia

  • High pressure in east pacific (SA)

  • Low pressure in west pacific (Australia & SE Asia)

• El Nino:

  

  • Trade winds weaken, then reverse (W → E)

  • Warm eq. current brings heat & precip. to Americas (N & S)

  • Suppressed upwelling off SA coast (damaging fi$herie$)

  • Cooler, drier conditions in Australia & SE Asia

  • High pressure in West Pacific (Australia & SE Asia)

  • Low pressure in East Pacific (SA)

• La Nina:

  

  • Stronger than normal trade winds (W ← ← ← E)

  • Increased upwelling off SA coast brings cooler than normal conditions, extra good fi$herie$

  • Warmer & rainier than normal in Australia & SE Asia

Effects of El Nino and La Nina

• Effects of El Nino

  • Suppressed upwelling & less productive fisheries in South America

  • Warmer winter in much of North America

  • Increased precip & flooding in Americas (West coast especially)

  • Drought in South East Asia & Australia

  • Decreased hurricane activity in Atlantic ocean

  • Weakened monsoon activity in India & South East Asia

• Effects of La Nina

  • Stronger upwelling & better fisheries in SA than normal

  • Worse tornado activity in US & Hurricane activity in Atlantic

  • Cooler, drier weather in Americas

  • Rainier, warmer, increased monsoons in SE Asia