Unit 4: Earth Systems and Resources

4.1 Plate Tectonics

Plate Tectonics: Theory explaining the movement of the Earth’s rigid lithospheric plates is the result of convection processes in the underlying partially molten mantle

Earth’s Structure

• Core: Dense mass of solid nickel, iron, and radioactive elements that release heat

• Mantle: liquid layer of magma surrounding the core, kept liquefied by intense heat from core

• Asthenosphere: solid, flexible 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, and rift valleys (on land)

Convergent Plate Boundary:Plates move towards each other 

• Leads to subduction (one plate being forced beneath another)

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

Transform fault Plate Boundary: plates slide past each other in opposite directions

• Forms: earthquakes (occurs when the stress on lithospheric plates overcomes a locked fault, resulting in a release of energy)

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

• 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

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 cont. Plate & melts back into magma

• Forces magma up to lithosphere surface

• Coastal Mountains (Andes), Volcanoes on land, trenches, tsunamis

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

• Ex: Himalayas

Transform Fault Boundary

• Plates sliding past each other in opp. 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 that shakes the lithosphere

Ring of Fire: pattern of volcanoes all around pacific plate

• Offshore island arcs (Japan) 

Transform faults: likely location of earthquakes

Hotspots: areas of esp. hot magma rising up to lithosphere

• Mid-ocean Islands (iceland, Hawaii)   

4.2 Soil Formation & 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:

• 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

Soil Horizons 

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

• Provides nutrients and limits H2O loss to evap.

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 w/little to no org. matter

• Contains some nutrients

C-Horizon: least weathered soil that is closest to the parent material, sometimes called bedrock

Loss of Topsoil: tiling (turning soil for ag.) + 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

Minimizing erosion of topsoil into surface water:

• maintain/plant vegetated buffers between surface waters and crop fields (creates habitats to maintain biodiversity)

  • Create retention ponds to capture eroded soil (recharges groundwater by slowing flow of runoff and allowing infiltration, maintains biodiversity)

  • Maintain cover crops on fields after harvests (provides nutrients to next crop)

  • Use no-till agriculture (reduces fuel requirements, reduces releases of greenhouse gases associated w mechanized agriculture>decreases global climate change)

• Soil helps filter and clean water that moves through them

• Soil Erosion into bodies of water can create turbidity, reduce the penetration of sunlight (reducing photosynthesis), and clog the gills of aquatic organisms

4.3 Soil Composition & 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: is the % of sand, silt, and clay in a soil

  • Always adds up to 100% ex: 40-40-20

• B/c 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 is 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)

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

Nutrients

• N, P, K+, Mg2+, Ca+, Na+

• Factors that increase soil nutrients

  • Organic matter (releases nutrients)

  • Humus (holds and releases nutrients)

  • Decomposer activity (recycles nut.)

  • Clay (neg. charge binds pos. nutrients)

  • Bases (Calcium carbonate - limestone)

• Factors that decrease soil nutrients

  • Acids leach pos. charge nutrients 

  • Excessive rain/irr. leeches nutrients

  • Excessive farming depletes nut.

  • Topsoil erosion

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. (40% sand; 40% silt; 20% clay)

4.4 Atmosphere

• Nitrogen 78% Mostly in the form of N2 (unuseable to plants without being fixed)

Argon ~ 0.93%: Inert, noble gas

Oxygen ~ 21%: Produced by photosynthesis in plants & needed for human/animal respiration

Water Vapor ~ 0-4%: Varies by region & conditions; acts as a temporary GHG, but less concerning than CO2

CO2 ~ 0.04%: Most important GHG; leads to global warming

Removed from atm. by photosynthesis

Exosphere: Outermost layer where atm. merges with space

Thermosphere: Therm = hottest temp; 

• absorbs harmful X-rays & UV radiation 

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

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

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

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

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

Layers of earth’s atm. are based on where temp. gradients change with distance from earth’s surface

Thermosphere: temp. Increases due to absorption of highly energetic solar radiation

• Hottest place on earth (3,100oF)

Mesosphere: temp. decreases because density decreases, leaving fewer molecules to absorb sun

• Coldest place on earth (-150oF)

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

Troposphere: temp. decreases as air gets further from warmth of earth’s surface (temp drops with altitude)

4.5 Global Wind Patterns

4 Properties that determine how air moves

1. Density: less dense air rises and more dense air sinks

   1. Warm air is LESS (more likely to rise) dense than cool air

   2. As warm air rises from the equator, it condenses and spreads out due to rotation of the earth (A Hadley Cell) (Hadley happens where its hot)

      1. The precipitation from the condensation falls between 0 and 30 N/S latitude creating tropical rainforest

      2. At 30 N/S, the dryer air sinks back down to the surface= deserts

2. Water Vapor Capacity: how much water vapor can air hold?

   1. Warm air can hold more water vapor 

   2. Saturation point: max amount of water vapor air can hold

   3. Temp goes up, saturation point goes up; temp goes down, saturation point goes down

3. Pressure: as air rises, pressure decreases

   1. Increase in attitude, decrease in pressure, volume increases, temp drops = adiabatic cooling 

   2. Pressure and volume inversely proportional

   3. Altitude increases, pressure increases, volume decreases, temp increases = Adiabatic heating

4. Latent Heat Release: water vapor in the air condenses to form precipitation, to warm up air

Coriolis Effect:

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

  • Objects are deflected to the RIGHT in the northern hemisphere and to the LEFT in the southern

• The spinning of cyclonic storms (counterclockwise in the northern hemisphere and clockwise in the southern)=result of the coriolis effect

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

• West between 0-30 degrees moves from E>W

  • Because Earth spinning from W>E

• Wind between 30-60 movies W>E

  • Earth spins faster @ 30 degrees than 60 

• Throw ball from northern hemisphere(moving slower) > equator it moves to the right 

Global Wind Patterns

• Air moves out from 30 - 0 and 60 due to high pressure @ 30 and low pressure @ 0 and 60

  • Air rising @ equator = low pressure

  • Air sinking down at 30 = high pressure

• 0-30 winds blow E>W (EASTERN TRADE)

  • Drives ocean current clockwise in N hemisphere, counterclockwise in S hemisphere

• 30-60 winds blow W>E (WESTERLIES

  • Drives weather patterns of N America

4.7 Solar Radiation & Earth’s Seasons

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

Solar Intensity & Latitude:

• Depends on 

  • Angle: how directly rays strike Earth’s surface

  • The amount of atmosphere sun’s rays pass through

  • Equator = higher isolation 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 areas than at the equator

Solar Intensity & Season

• Orbit of earth around sun + tilt on axis changes angle of sun’s rays

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

  • Tilt of earth’s axis stays fixed during orbit

    • June/December solstices: N or S hemisphere is maximally tilted toward sun ( summer/winter(

    • March/Sept equinox: N and S hemispheres equally facing sun

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

• Positive feedback loop>>>

Albedo & Surface Temperature

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

  • Areas with lower albedo, absorb more sunlight light/hear

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

• Polar regions are colder due to high albedo

4.8 Earth’s Geography & Climate

Climate & Geography

• Climate is determined by insolation ( latitude>angle of insolation & atmosphere

• Higher latitudes receive less insolation ( cooler, less precipitation)

• Equator receives most intense insolation ( higher temp, air rises, high precip)

• Thermal inversion: cooler air at the surface becomes “trapped” by a later of warmer air above it

  • Increases intensity of surface air pollution

• mountains : disrupt wind, and produce rain shadow effect

• Oceans: moderate temp & add moisture to the air 

Rain Shadow

• A drier area of land next to a higher elevation, higher elevation (such as mtn.) blocks the precipitation from reaching the area

• Warm, moist air from ocean hits “windward” side of mts, rises, cools> lush, green vegetation

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

  • Leads to arid dry desert conditions

4.9 El Niño & La Nina

• El Nino (southern oscillation- ENSO) is a periodic, non-anthropogenic phenomenon that occurs in the southern pacficic ocean

  • Changes to patterns of rainfall, wind, ocean circulation occur that can cause climatic/environmental/economic disruptions 

  • Effects: Suppressed upwelling and less productive fisheries in SA; warmer winter in much of N America; decreased hurricane activity in atlantic ocean, increased precip/flooding in americas ( w coast esp)

• Effects of LA NINA: stronger upwelling and better fisheries in SA than normal; worse tornado activity in US & hurricane activity in atlantic; rainier/warmer/increased monsoons in SE Asia

Global Ocean Surface Currents

• Gyers: large ocean circ. Patterns due to global warming

  • Clockwise in N hemisphere, counterclockwise in S hemisphere

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

• Westerlies between 30-60 degrees and pushes mid lat. currents W>E

• Upwelling zones: areas of ocean where winds blow warm surface water away from a land mass, drawing colder/deeper water to replace it

  • Brings O2 + nutrients to surface = productive fishing

Thermohaline Circulation

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

  • War, water from Gulf of MX moves toward North Pole

  • Cools & Evaporates as it moves towards poles

  • saltier/colder @ poles , is more dense making it sink

  • Spreads along ocean floor

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