Unit 11: Geology and Earth’s Structure

1. Earth’s Layers

1. Lithosphere / Crust:

   • Outermost layer of Earth where we live.

   • Composed of tectonic (lithospheric) plates that “float” on the mantle.

2. Asthenosphere (Upper Mantle):

   • Softer region under the crust, with convection currents.

   • Causes plate movement.

3. Lower Mantle:

   • Hotter, denser, but largely plastic/flowing.

4. Core (Outer and Inner):

   • Outer core is molten iron and nickel.

   • Inner core is solid iron/nickel due to immense pressure.

2. Plate Tectonics

• Plates: 12 major plates that move relative to each other.

• Boundaries:

  1. Divergent boundaries: Plates move apart, creating new crust (e.g., mid-ocean ridges).

  2. Convergent boundaries: Plates collide; can form mountains, subduction zones (volcanoes, earthquakes).

  3. Transform boundaries: Plates slide past one another, causing earthquakes (e.g., San Andreas Fault).

Soil Formation and Erosion

1. Soil Formation

• Components: Minerals, organic matter, water, air.

• Processes: Weathering of rock (physical, chemical, biological) + decomposition of organic materials = formation of soil layers (horizons).

2. Soil Horizons

• O Horizon (Organic): Surface litter, decomposing leaves, etc.

• A Horizon (Topsoil): Mix of humus, minerals; crucial for plant growth.

• B Horizon (Subsoil): Accumulates leached minerals.

• C Horizon (Parent Material): Weathered rock fragments.

• Bedrock: Underlying solid rock.

3. Soil Erosion

• Causes: Wind, water (sheet, rill erosion), poor farming practices, deforestation, overgrazing.

• Consequences: Loss of fertility, sediment pollution in waterways, desertification.

• Prevention/Remediation:

  1. Contour plowing, terracing.

  2. Crop rotation, cover crops.

  3. Reduced tillage.

  4. Windbreaks, shelterbelts.

Mining and Its Environmental Impacts

1. Mining Methods

1. Surface Mining:

   • Strip Mining: Removing surface layers to reach shallow ore deposits; very disruptive to landscapes.

   • Open-Pit Mining: Digging a large pit; used when ore is near the surface but extends deep.

   • Mountaintop Removal: Blasting off top layers of a mountain to expose seams; common for coal in Appalachia.

   • Environmental Effects: Loss of topsoil, habitat destruction, heavy sediment runoff.

2. Underground (Subsurface) Mining:

   • Tunnels/Shafts to reach deeper ore.

   • Less surface impact than open-pit, but risks include mine collapse, subsidence, and worker hazards.

2. Ore Processing (Refining)

• Crushing and Grinding: Separates valuable minerals from waste rock (gangue).

• Chemical Methods:

  • Flotation, leaching, or smelting to extract metals (e.g., gold, copper).

  • Produces tailings (toxic leftovers).

• Environmental Concerns:

  • Tailings ponds can leak heavy metals or chemicals (e.g., cyanide for gold).

  • Air pollution from smelting (SO₂, particulates).

3. Impacts of Mining

1. Habitat Destruction: Surface mining drastically alters landscapes.

2. Water Pollution: Acid mine drainage (AMD), especially from abandoned mines.

3. Air Pollution: Smelting releases CO₂, SO₂, heavy metals.

4. Soil Erosion: Disturbed land easily erodes if not reclaimed.

5. Social/Economic: Provides raw materials but can displace communities, cause health issues.

4. Remediation / Reclamation

• Recontouring the land to original or stable topography.

• Replanting vegetation to prevent erosion and restore habitat.

• Treating or containing acid mine drainage (e.g., limestone channels, water treatment).

• Regulations: Some countries require bonds for reclamation costs.

Additional Notes on Ore and Resource Management

1. Overburden vs. Spoils:

   • Overburden: Soil and rock removed to reach ore.

   • Spoils: Waste rock or soil left over after mining.

2. Ore vs. Gangue:

   • Ore: Rock containing valuable minerals/metals.

   • Gangue: The non-valuable part that’s discarded as tailings.

3. Tailings:

   • Residue after ore processing, often in ponds or piles. Potentially toxic with heavy metals or chemicals.

4. Abandoned Mines:

   • Often left with open pits, waste piles, acid drainage.

   • Restoration is costly; if unaddressed, leads to long-term environmental harm.

Summary

• Geology & Plate Tectonics: Earth’s structure is layered; plate boundaries shape geological events (earthquakes, volcanoes, mountain building).

• Soil: Formed through weathering + organic matter decomposition. Prone to erosion if mismanaged.

• Mining: Provides crucial resources but can severely impact land, water, air, and ecosystems.

• Mitigation: Soil conservation practices, reclamation of mined lands, and pollution control help reduce harm and restore environments.

These digital notes capture the main ideas from your original paper notes on Earth’s structure, soil formation, mining, and associated environmental issues.