Earth Systems and Resources Study Notes

Overview of Earth Systems and Resources

Earth Systems and Resources encompasses key foundational concepts spanning the geosphere, soil science, atmospheric composition, climate mechanics, and oceanographic circulation patterns.

Earth's Four Major Spheres

Earth's global ecosystem is divided into four primary interconnected spheres:

• Lithosphere: The solid portion of Earth consisting of rocks, minerals, and crustal structures.

• Atmosphere: The surrounding layer of gases (the air) retained by Earth's gravity.

• Hydrosphere: All water present on Earth in liquid, solid (ice), and gaseous form.

• Biosphere: All living organisms across Earth's terrestrial, aquatic, and atmospheric zones.

The Geosphere

The geosphere includes all rocks and minerals located on and beneath Earth's surface.

Physical and Compositional Layers of the Geosphere

The geosphere is categorized by both its physical characteristics and compositional layers:

• Crust: The thin, cool, rocky outer skin of the Earth.

• Mantle: Located directly beneath the crust; it is very hot and mostly solid.

• Core: Divided into the molten metal outer core and the solid metal inner core.

When analyzed by mechanical and compositional behavior, the crust and upper mantle are structured as follows:

• Lithosphere: Comprises the crust and the rigid uppermost mantle. It is fractured into distinct pieces called tectonic plates.

• Asthenosphere: The soft, ductile middle section of the mantle located below the lithosphere. It is continuously heated by the outer core, generating thermal convection currents.

• Lower Mantle: Consists of solid rock extending down to the outer core boundary.

• Tectonic Plate Movement: Convection currents in the asthenosphere drive the movement of tectonic plates across Earth's surface. Collisions and separations of these plates build and modify major geological landforms.

Global Distribution of Plate Boundaries

Global patterns of plate boundaries are utilized by geologists to determine and predict the geographic locations of volcanoes, island arcs, earthquakes, hot spots, and geological faults.

Continental Drift and Plate Layout

• Pangaea: Approximately $225$\,Million Years Ago, Earth's landmasses were joined into a single supercontinent known as Pangaea, surrounded by the global ocean Panthalassa and the Tethys Sea.

• The $14$ Major Tectonic Plates: Earth's crust is divided into $14$ major plates:

  1. North American Plate

  2. Juan de Fuca Plate

  3. Cocos Plate

  4. Pacific Plate

  5. Caribbean Plate

  6. Nazca Plate

  7. South American Plate

  8. African Plate

  9. Eurasian Plate

  10. Antarctic Plate

  11. Indo-Australian Plate (including the Indian Ocean section)

  12. Philippine Plate

  13. Caroline Plate

  14. Fiji Plate

Key tectonic boundaries across these plates include collision zones, subduction zones, and spreading ridges offset by transform faults.

Types of Plate Boundaries and Landforms

Convergent Plate Boundaries

Convergent boundaries occur where tectonic plates collide or slide toward one another.

• Subduction: A physical process where one plate slides beneath another into the mantle.

• Associated Geological Events and Features: Earthquakes, volcanic eruptions, ocean trenches, island arcs, and continental mountain chains.

• Ring of Fire & Island Arcs: The Pacific Ring of Fire consists of long chains of active volcanoes and island arcs (e.g., Japan) created by ocean-under-continental or ocean-under-ocean plate subduction.

• Ocean-under-Ocean Subduction (Mariana Trench): Creates deep oceanic trenches. The Mariana Trench contains Challenger Deep, reaching a maximum depth of $11{,}035$\,meters below sea level. For comparison, Mt. Everest stands at $8848$\,meters above sea level.

• Continental-under-Continental Collision (Mountains): When two continental plates collide, neither subducts completely. The continental crust buckles, forming high plateaus and major mountain chains (e.g., in Asia). In North America, continental collision structures shape major features including the Continental Divide of North America, extending across regions from Canada, the United States, and Mexico down through Central and South America.

Divergent Plate Boundaries

Divergent boundaries occur where two tectonic plates move away from each other.

• Seafloor Spreading (Oceanic/Oceanic): As ocean plates separate, magma rises to form new oceanic crust along mid-ocean ridges.

• Continental Rifting (Continental/Continental): As continental landmasses pull apart, rift valleys form.

• Examples of Mid-Ocean Ridges and Rifts:

  • Mid-Ocean Ridge Features: Middle Valley, Juan de Fuca Ridge, Escanaba Trough, Guaymas Basin, Endeavour, Axial Seamount, Mid-Atlantic Ridge, Menez Gwen, Gakkel Ridge, Jan Mayan, Loki's Castle, Lucky Strike, Lost City, Rainbow, Broken Spur, $21^\circ\,\text{N}$, Piccard, Von Damm, TAG, Snake Pit, Logatchev, Red Sea, Ashadze, $9^\circ\,50'\,\text{N}$, East Pacific Rise, Galapagos Rift, Comfortless Cove, Turtle Pits, $17\text{--}21^\circ\,\text{S}$, $4\text{--}9^\circ\,\text{S}$, Chile Rise, East Scotia Ridge, Pacific-Antarctic Ridge, Central Indian Ridge, Dodo, Solitaire, Kairei, Edmond, Mariana Arc, Old City, Southwest Indian Ridge, Southeast Indian Ridge, Izu-Bonin Arc.

  • Rift Valleys: Great African Rift Valley, bounded by the Nubian Plate, Somalian Plate, Arabian Plate, Red Sea, Gulf of Aden, Nile River, Afar / Dezhi Depression, and Yusuf Kashim.

Transform Plate Boundaries

Transform boundaries occur where two plates slide horizontally past each other along strike-slip faults.

• Key Characteristics: Associated with frequent earthquakes; NO volcanic activity occurs along pure transform boundaries.

• Examples and Features: San Andreas Fault in California, displaying relative motion between the North American Plate and the Pacific Plate. Associated regional fault zones include Explorer Ridge, Blanco Fracture Zone, Mendocino Fracture Zone, Murray Fracture Zone, and Molokai Fracture Zone.

Hot Spots

Hot spots are volcanic regions fed by underlying mantle plumes that are not associated with plate boundary interactions. Volcanoes form in the interior of tectonic plates rather than at plate edges (e.g., Samoa, Yellowstone National Park).

Summary of Boundary Motion

• Overlap: Convergent plate boundary

• Sliding: Transform plate boundary

• Gap: Divergent plate boundary

Soil Science

Soil is a complex matrix formed at the intersection of Earth's four spheres.

Composition of Typical Soil

Typical soil is composed of four distinct components:

• Mineral particles: $45\%$ of typical soil volume.

• Organic matter: Approximately $5\%$ of typical soil volume.

• Water: Approximately $25\%$ of typical soil volume.

• Air: Approximately $25\%$ of typical soil volume.

• Soil Organisms: Includes organisms such as earthworms, moles, snails, slugs, soil fungi, bacteria, and protozoa.

Soil Formation Processes

Soil formation requires hundreds to thousands of years to produce just a few centimeters of topsoil. It forms when bedrock and parent material undergo weathering, erosion, and deposition (W.E.D.).

• Weathering: The breaking down of rock into smaller particles.

  • Physical Weathering: Caused by wind, rain, thermal expansion/contraction, and water freezing in cracks.

  • Chemical Weathering: Caused by chemical reactions with water and dissolved gases.

  • Biological Weathering: Driven by living organisms, such as tree roots expanding or lichens secreting organic acids.

  • Weathering Agents: Water, ice, wind, gravity, growing plants.

• Erosion: The physical transport of sediment and broken rock particles away from their original site. Agents of erosion include water, ice, wind, and animals.

• Deposition: The dropping or settling of sediment in a new location, forming features like sand dunes or new island structures.

• Vegetation: Native vegetation prevents excessive soil erosion by anchoring soil with root systems.

Watersheds and Erosion Mechanics

• Watershed Definition: An area of land that drains all surface runoff and groundwater into a common body of water (such as a river, lake, or ocean).

• Watershed Structural Features: Watershed divide, precipitation, surface runoff, streams/tributaries, main river channels, floodplains, lakes/oceans, ground seepage, and groundwater aquifers.

• Key Watershed Characteristics: Area, length, and slope.

• Erosion Dynamics: Steeper terrain slopes produce faster water velocities, causing significantly higher rates of soil erosion. Soil in lower floodplain areas is typically highly fertile due to accumulated deposition of nutrient-rich sediment.

Factors Influencing Soil Formation

1. Parent Material: The original bedrock/minerals from which the soil is derived.

2. Climate: Temperature and moisture govern weathering rates; soil forms much more slowly in cold climates due to reduced organic decomposition.

3. Topography: Surface slope angle and landscape arrangement.

4. Organisms: Recyclers (bacteria, fungi, earthworms) that break down organic matter.

5. Time: Older soils with long histories of lush vegetation cover are the most fertile.

Soil Horizons and Biome Classifications

Soil develops distinct layers called horizons over extended periods of time.

Master Soil Horizons

• O Horizon (Surface Litter): Consists of fallen leaves, organic detritus, and humus (partially decomposed organic matter).

• A Horizon (Topsoil): The primary zone of biological activity where plants grow. Rich in humus and organic matter; holds moisture and plant nutrients.

• E Horizon (Zone of Leaching): Zone where dissolved minerals and nutrients quickly leach downward. Not present in all soils.

• B Horizon (Subsoil): Composed of larger rock particles mixed with inorganic minerals; site of accumulation for leached minerals. Contains almost no organic matter.

• C Horizon: Consists of partially weathered parent rock fragments.

• R Horizon (Bedrock): Unweathered solid bedrock layer (e.g., sandstone, granite, limestone).

Developmental Stages of Soil

• Stage 1: Bare parent rock / bedrock.

• Stage 2: Disintegrating parent rock; organic material begins to build up from pioneer organisms like moss and lichen.

• Stage 3 (Immature / Young Soil): Weathered parent rock forms C horizon; thin layer of A horizon forms supporting grasses and small shrubs.

• Stage 4 (Mature Soil): Well-defined O, A, B, and C horizons overlying R bedrock; supports complex root systems (e.g., oak trees), burrowing animals (moles, earthworms), and diverse microbial populations (fungi, bacteria).

Soil Profiles Across Major Biomes

• Desert Soil (Hot, Dry Climate): Characterized by a surface mosaic of closely packed pebbles and boulders; weak humus-mineral mixture; dry, brown to reddish-brown color with variable accumulations of clay, calcium carbonate, and soluble salts.

• Grassland Soil (Semiarid Climate): Highly alkaline, dark, and rich in organic humus; heavy accumulations of clay and calcium compounds.

• Tropical Rain Forest Soil (Humid, Tropical Climate): Light-colored, highly acidic humus layer; acidic soils dominated by iron and aluminum compounds mixed with clay; nutrient-poor due to intense rainfall leaching.

• Deciduous Forest Soil (Humid, Mild Climate): Surface layer of forest litter leaf mold; rich humus-mineral mixture topsoil; light, grayish-brown silt loam; dark brown firm clay subsoil.

• Coniferous Forest Soil (Humid, Cold Climate): Thick acidic litter and humus layer; light-colored and strongly acidic soil; subsoil enriched with humus, iron, and aluminum compounds.

Physical, Chemical, and Biological Properties of Soil

Physical Properties

• Color: Serves as an indicator of soil composition and fertility (e.g., dark soils indicate high organic content).

• Soil Texture: Determined by relative proportions of particle sizes:

  • Clay: Smallest particle size (< 0.002\,\text{mm}).

  • Silt: Intermediate particle size ($0.002\text{--}0.05\,\text{mm}$).

  • Sand: Largest particle size ($0.05\text{--}2.0\,\text{mm}$).

  • Loam: Soil containing an even, balanced mixture of clay, silt, and sand.

• Porosity: Measures the total storage volume of open spaces between soil particles.

• Permeability: Measures the ease with which water flows through soil spaces. Particle size dictates flow rate (e.g., sand has high permeability; clay has low permeability).

Chemical Properties

• Soil pH: Measures the concentration of hydrogen ions ($\text{H}^+$) in soil solution. Dictates plant nutrient availability and prevents mineral leaching.

• Cation Exchange: Process by which plant roots absorb essential mineral nutrients:

  • Negatively charged soil particles (clay and humus) hold positively charged cations (such as calcium $\text{Ca}^{2+}$, magnesium $\text{Mg}^{2+}$, and potassium $\text{K}^+$).

  • Plant root hairs secrete hydrogen ions ($\text{H}^+$) to exchange with and release these nutrient cations from soil particles into solution.

• Cation Exchange Capacity (CEC): The measure of a soil's ability to hold cations and prevent nutrient leaching, directly enhancing plant nutrient availability.

Soil Property Comparison Table

Key: 0 = Low, + = Medium, ++ = High

Biological Properties

• $80\%$ of all living organisms in soil are composed of microscopic Bacteria, Fungi, and Protists.

• Earthworms, burrowing rodents, and soil fauna break down large organic matter fragments into humus.

• Humus: Fully decomposed, dark organic component of soil residing at the bottom of the O horizon.

Atmospheric Layering and Composition

The atmosphere is a thin, dynamic gas envelope surrounding Earth.

Atmospheric Gas Composition

• Primary Permanent Gases:

  • Nitrogen ($\text{N}_2$): $78\%$

  • Oxygen ($\text{O}_2$): $21\%$

  • Argon ($\text{Ar}$): $1\%$

  • Trace Permanent Gases: Neon ($\text{Ne}$), Helium ($\text{He}$), Hydrogen ($\text{H}_2$), Xenon ($\text{Xe}$).

• Variable Atmospheric Gases: Water vapor ($\text{H}_2\text{O}$), Carbon dioxide ($\text{CO}_2$), Methane ($\text{CH}_4$), Nitrous oxide ($\text{N}_2\text{O}$), Ozone ($\text{O}_3$), and Chlorofluorocarbons (CFCs).

Layers of the Atmosphere

1. Troposphere:

   • Bottommost layer extending from Earth's surface.

   • Site of virtually all planetary weather.

   • Thinnest layer vertically, but contains the vast majority of atmospheric mass and density.

   • Temperature decreases with increasing altitude.

   • Site of the Greenhouse Effect.

   • Tropopause: Boundary layer separating the troposphere from the stratosphere.

2. Stratosphere:

   • Drier and significantly less dense than the troposphere.

   • Temperature increases with altitude due to UV absorption.

   • Contains the Ozone Layer ($\text{O}_3$), which absorbs harmful ultraviolet solar radiation.

3. Mesosphere:

   • Characterized by extremely low air pressure.

   • Temperature decreases with increasing altitude.

4. Thermosphere:

   • Temperature increases with altitude due to high-energy solar radiation absorption.

   • Site of charged ion interactions creating the Northern Lights (Aurora Borealis).

5. Exosphere:

   • Outermost atmospheric layer gradually transitioning into vacuum space.

The Greenhouse Effect and Atmospheric Warming

Greenhouse Effect Mechanics

The greenhouse effect is the process by which atmospheric greenhouse gases (GHGs) absorb outgoing infrared radiation emitted by Earth's surface and re-radiate that thermal energy back toward the planet.

• Greenhouse Warming Potential (GWP): A measure of how much a single molecule of a compound contributes to global warming over a $100$-year timeframe relative to carbon dioxide, which has a baseline $\text{GWP} = 1$.

• GWP Relative Ranking: CFCs have the highest GWP, followed by nitrous oxide, methane, and carbon dioxide.

Major Greenhouse Gases Comparison Table

Key Characteristics of Primary GHGs

• Water Vapor ($\text{H}_2\text{O}$): Absorbs more total infrared radiation from Earth than any other greenhouse gas. It is the least directly impacted by human activity and has a short atmospheric residence time ($9$\,days).

• Carbon Dioxide ($\text{CO}_2$): Represents the overall greatest human contributor to global climate forcing due to emission volumes.

• Natural GHG Sources: Volcanic eruptions ($\text{CO}_2$), organic decomposition/digestion ($\text{CH}_4$), denitrification ($\text{N}_2\text{O}$), and evaporation/transpiration ($\text{H}_2\text{O}$).

Solar Radiation, Seasons, Albedo, and Rain Shadows

Global Climate Determinants

Global climate patterns are governed by four primary physical factors:

1. Uneven solar heating of Earth's surface due to its spherical shape.

2. Seasonal variations in temperature and precipitation.

3. Geology and geographical landscape barriers.

4. Atmospheric and ocean circulation currents.

Insolation and Solar Intensity

• Insolation: A quantitative measure of incoming solar radiation striking a surface over time.

• Angle of Incidence: Earth's curved geometry causes solar rays to strike the equator at a perpendicular angle ($90^\circ$), yielding maximum solar energy per unit surface area. Incoming solar intensity continuously decreases moving toward the polar latitudes.

Earth's Axis and Seasons

• Earth's axial tilt and rotation dictate seasonal changes and daylight duration:

  • Axial Tilt: Causes changes in solar radiation angle, driving seasonal transitions.

  • Rotation: Dictates daily photoperiod length.

  • Equinox: Occurs twice yearly when the Sun's direct rays cross the equator, producing equal daylight and night hours globally.

  • Solstice: The specific annual days exhibiting the maximum daylight hours (summer solstice) or minimum daylight hours (winter solstice).

Surface Albedo

Albedo measures the percentage of incoming solar light reflected off a surface back into space. Earth's overall average albedo is approximately $30\%$

• High Albedo Surfaces: Fresh snow ($80\text{--}95\%$), Sea ice ($50\text{--}90\%$), and Clouds ($10\text{--}90\%$).

• Low Albedo Surfaces: Cropland/Grassland ($10\text{--}25\%$), Forests ($10\text{--}20\%$), Water ($10\text{--}60\%$\ depending on solar angle), and Asphalt ($5\text{--}10\%$).

The Rain Shadow Effect

An environmental phenomenon where humid oceanic winds strike the windward side of a mountain range, forcing air upward where it cools, condenses, and releases precipitation. As the dried air descends along the leeward side, it warms and absorbs moisture, creating arid desert conditions in the mountain's shadow.

Atmospheric Circulation and Prevailing Wind Systems

Tropospheric Convection Dynamics

• Air pressure and air density are directly proportional to each other.

• Air density and air temperature are inversely proportional to each other.

• Warm surface air expands, becomes less dense, and rises into the upper atmosphere. Cold air is denser and sinks.

Global Convection Cells

Atmospheric circulation is driven by three pairs of major convection cells that regulate planetary heat:

1. Hadley Cells: Located between the equator and $30^\circ\,\text{N}$ and $\text{S}$ latitudes. Intense equator solar heating warms surface air, causing it to rise, expand, and drop heavy precipitation. This moisture sustains tropical rainforests.

   • Intertropical Convergence Zone (ITCZ): The latitude receiving the most intense sunlight where ascending branches of northern and southern Hadley cells converge.

2. Ferrel Cells: Located between $30^\circ$ and $60^\circ\,\text{N}$ and $\text{S}$ latitudes. Dry, cool air descending at $30^\circ$ creates high pressure and arid conditions, giving rise to major global deserts.

3. Polar Cells: Located between $60^\circ$ and $90^\circ\,\text{N}$ and $\text{S}$ latitudes. Air cools and subsides over the poles, creating extremely dry polar conditions.

Global Prevailing Wind Belts

Driven by atmospheric cell boundaries, high/low pressure gradients, and the Coriolis Effect (Earth's rotation):

• Doldrums: Calm surface wind zone near the equator ($0^\circ\text{--}5^\circ\,\text{N}$ and $\text{S}$).

• Trade Winds: Dominant winds between the equator and $30^\circ\,\text{N}$ and $\text{S}$ blowing from East to West (Northeast Trade Winds in Northern Hemisphere; Southeast Trade Winds in Southern Hemisphere).

• Westerlies: Dominant winds between $30^\circ$ and $60^\circ\,\text{N}$ and $\text{S}$ blowing from West to East.

• Polar Easterlies: Dominant wind zones blowing from East to West between $60^\circ\,\text{N}$ and $\text{S}$ and the poles.

Ocean Water Dynamics and Ocean Currents

Chemical and Physical Properties of Ocean Water

• Temperature & Density: Cold seawater is denser than warm seawater.

• Salinity & Density: Salinity and density are directly proportional; higher salt concentration increases water density.

• Spatial Salinity Patterns: Salinity is highest in subtropic surface waters due to high evaporation rates, and lowest near the equator due to heavy rain. Temperature plays a larger role in determining seawater density than salinity.

Ocean Circulation Patterns

• Surface Ocean Currents: Wind-driven currents that redistribute warm and cold surface waters globally.

• Deep Ocean Currents: Temperature- and density-driven currents that circulate nutrients from the sea floor to surface layers.

• Gyres: Large-scale circular surface water patterns driven by wind cells. Gyres rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

• Upwelling: The upward movement of deep, cold, nutrient-rich ocean water toward the surface caused by diverging wind currents along coastlines and open ocean regions.

• Thermohaline Circulation: A global ocean circulation pattern ("ocean conveyor belt") driven by differences in water temperature (thermo) and salinity (haline) that mixes surface and deep ocean waters across the Atlantic, Pacific, Indian, Antarctic, and Arctic oceans.

• Major Named Currents: Gulf Stream, North Atlantic Current, Labrador Current.

El Niño-Southern Oscillation (ENSO)

El Niño-Southern Oscillation (ENSO) is a periodic disruption ($3\text{--}7$-year cycle) of wind and ocean circulation patterns across the tropical Pacific Ocean.

• Thermocline: The thin transition layer in ocean water separating warm surface waters from cold, deep ocean waters.

Normal Walker Circulation Conditions

• Strong East-to-West Trade Winds push warm surface water westward toward Indonesia and Australia.

• Accumulated warm water produces high rainfall in Australasia and Western Pacific regions.

• Cold, nutrient-rich water upwells along the western coast of South America, supporting productive fisheries under a shallow eastern thermocline.

El Niño Conditions

• Equatorial trade winds weaken or reverse direction.

• Warm surface water drifts eastward toward the South American coast.

• Impacts: Heavy precipitation and flooding along coastal South America; severe drought in Australia and Indonesia; suppression of coastal upwelling, leading to marine ecosystem collapse; deep thermocline shift off South America.

La Niña Conditions

• Normal trade wind patterns intensify significantly.

• Warm surface waters are pushed farther westward, causing extreme rain in Northern Australia and Indonesia.

• Impacts: Exceptionally intense cold upwelling off South America with an extremely shallow thermocline; drier conditions across the Southwestern United States.