Copy of 2023 APES Unit 4

Unit 4: Earth Systems and Resources

Geology

Structure of the Earth

• Crust: Thickness varies from ~3 to 5 miles (8 km) under oceans to up to 25 miles (32 km) under continents.

  • Composed mainly of granitic and mafic silicate rocks.

• Mantle:

  • Consists mostly of ultramafic silicates.

  • Divided into layers:

    • Lithosphere: Rigid layer including the crust and upper mantle (~60 miles or 100 km thick).

    • Asthenosphere: Partially molten layer beneath the lithosphere (~430 miles or 700 km thick).

    • Lower Mantle: More rigid than the asthenosphere, likely due to great pressure (~1800 miles or 2885 km thick).

• Core:

  • Consists primarily of iron, nickel, and sulfur. Divided into:

    • Outer Core: Liquid phase (~3200 miles or 5155 km).

    • Inner Core: Rigid phase (~3960 miles or 6371 km).

Plate Motion

• Driven by

  • Convection currents in the asthenosphere.

Plate Boundaries

Types of Plate Boundaries

• Divergent Boundaries: Plates move away from each other.

• Convergent Boundaries: Plates move towards each other.

• Transform Boundaries: Plates slide past each other.

Convergent Boundaries

• Oceanic crust subducts beneath continental crust, creating:

  • Subduction zones: deep ocean trenches.

  • Volcanoes on land from melting crust.

  • Example: Nazca Plate subducting under South American Plate creates Andes Mountains and Peru Trench.

Island Arcs

• Formed when two oceanic plates collide, creating volcanic islands.

• Examples include: Aleutian Islands, Japanese Archipelago.

Continental Collision

• Continental crust collisions create mountain ranges.

  • Example: Appalachian Mountains from North America and Africa; Himalayas from India and Eurasia.

Divergent Boundaries on Land

• Rift Valleys: When the continental crust stretches, it forms faults and long mountain ranges.

• Seafloor Spreading: Formation of new oceanic crust as plates diverge under the ocean.

Soil and Erosion

Soil Definition

• A mix of geological (rock) and organic (living) components including sand, silt, clay, humus, and nutrients (N, P, K, Mg).

Weathering and Soil Formation

• Weathering: Breakdown of rocks into smaller pieces through:

  • Physical processes (wind, rain, freeze/thaw).

  • Biological processes (roots breaking rocks).

  • Chemical processes (acid rain).

• Soil Horizons: Different layers of soil:

  • O-Horizon: Organic layer.

  • A-Horizon: Topsoil rich in humus.

  • B-Horizon: Subsoil with few nutrients.

  • C-Horizon: Least weathered soil near bedrock.

Soil Degradation

• Loss of soil fertility and ability to support plant life

  • Caused by erosion, compaction, and nutrient depletion.

Atmosphere

Composition of Earth’s Atmosphere

• Nitrogen (N2): ~78%, essential for plant growth.

• Oxygen (O2): ~21%, crucial for respiration.

• Argon: ~0.93%, noble gas with minimal reactivity.

• Carbon Dioxide (CO2): ~0.04%, a significant greenhouse gas.

• Water Vapor: Varies from 0-4%.

Temperature Gradient and Layers

• Thermosphere: Hottest layer, absorbs UV radiation.

• Mesosphere: Middle layer, coldest temperatures.

• Stratosphere: Contains ozone layer.

• Troposphere: Weather occurs here; most dense.

Seasonal Changes and Solar Radiation

• Insolation: Varies with latitude and the angle of sunlight.

• Solar Intensity: Affects temperature, precipitation, and seasonal patterns.

Global Wind Patterns

• Driven by solar heating, causing high and low-pressure systems.

• Coriolis Effect: Deflection of winds due to Earth's rotation.

Watersheds

Definition of Watersheds

• Areas of land that drain into specific bodies of water, playing a crucial role in hydrology.

Chesapeake Bay Watershed

• Mixed habitats providing filtration, habitat, and storm protection.

• Threats include nutrient pollution causing eutrophication and declining water quality.

Key Takeaways

• Plate boundaries lead to geological activity (earthquakes, volcanism).

• Soil composition affects fertility and plant growth.

• Watershed management is essential for maintaining water quality.