Soil Science and Pedosphere Concepts

The Pedosphere

• The pedosphere is the outermost layer of Earth, acting as an interface between the lithosphere, atmosphere, hydrosphere, and biosphere.
• It's crucial for life's sustenance.
• It's the "living skin" of the Earth.

What is Soil?

• Soil is a complex, dynamic system composed of:
  • Minerals: Inorganic materials from weathered rocks, supplying nutrients to plants.
  • Organic Matter: Decomposed plants and animals, enhancing soil fertility and structure.
  • Gases: Air spaces (pores) allowing oxygen to reach plant roots.
  • Liquids: Water held within soil pores, dissolving nutrients for plant use.
  • Organisms: Diverse communities (bacteria, fungi, earthworms), contributing to soil health by decomposing, cycling nutrients, and building soil structure.

Factors Affecting Soil Formation

• Parent Material: Underlying geological material (bedrock or sediment) influencing soil mineral composition.
• Climate: Temperature and precipitation affecting weathering rates and organic matter decomposition. Warm, moist climates speed up soil formation.
• Topography: Slope and elevation influencing water drainage and erosion rates. Steeper slopes lead to thinner soils.
• Biological Factors: Presence of plants, animals, and microorganisms contributing to soil formation through root penetration, organic matter decomposition, and nutrient cycling.
• Time: Soil formation is a slow process, leading to more developed soils over longer periods, with distinct layers (horizons) and higher nutrient content.

Soil Production

• Soil production is the conversion of solid rock into soil through weathering (physical and chemical) and biological activity.
• Weathering breaks down rocks into smaller particles.
• Biological activity (plant roots, microbes) adds organic matter.
• Soil thickness depends on the balance between soil production and transport downslope.

Soil Triangle

• A diagram used to classify soil types based on the relative percentages of sand, silt, and clay.
• Sand: Large particles, good drainage, low water retention.
• Silt: Medium-sized particles, moderate water retention and nutrient holding capacity.
• Clay: Smallest particles, high water retention and nutrient holding capacity.

Soil Horizons

• Soil is organized into horizontal layers called soil horizons, differing in composition, texture, and color.
• O Horizon (Organic Layer): Mostly organic matter (decomposed leaves, plants, animals).
• A Horizon (Topsoil): Minerals mixed with organic material (humus), major root activity zone.
• E Horizon (Eluviation Layer): Zone of leaching, minerals and nutrients washed out, lighter color.
• B Horizon (Subsoil): Minerals and metal salts leached from upper layers, often denser.
• C Horizon (Parent Rock): Partly weathered rock, the source material for the soil.
• R Horizon (Bedrock): Unweathered rock, the base of the soil profile.

Soil Conservation Practices

• Contour Farming: Plowing along contours of the land to minimize water runoff and soil erosion.
• Strip Cropping: Alternating different crops across slopes reduces erosion and retains soil moisture.
• Crop Rotation: Planting different crops sequentially to improve soil health, enhance nutrient balance, and reduce erosion.
• Cover Cropping: Growing cover crops (legumes, grasses) to protect soil from erosion, improve soil fertility, and increase moisture retention.
• Agroforestry: Integrating trees and shrubs into agricultural landscapes protects soil, improves biodiversity, and reduces erosion.
• Grassed Waterways: Creating grass-covered channels to guide surface runoff, preventing soil erosion and maintaining water quality.

Endogenic and Exogenic Movements

• Endogenic Movements (Internal Forces):
  • Diastrophic Movements (Slow): Gradual deformation of Earth's crust (e.g., mountain formation).
  • Catastrophism (Sudden): Rapid events causing immediate changes to Earth's crust (e.g., earthquakes, volcanic eruptions).
  • Epeirogenic (Continent Forming): Upward or downward movement of the Earth's surface, leading to changes in elevation over large areas.
  • Orogenic (Mountain Building): Formation of mountain ranges through tectonic forces.
• Exogenic Movements (External Forces):
  • Weathering: Breakdown of rocks by physical (e.g., frost wedging, exfoliation) and chemical (e.g., oxidation, hydration) processes, including biological processes.
  • Erosion: Movement of sediment from broken rock by forces like water, wind, ice, gravity.
  • Deposition: Dropping of sediment in a new location, shaping landscapes over time. 

Tectonic Plate Boundaries

• Divergent Boundaries: Plates move apart, creating new oceanic lithosphere (e.g., Mid-Atlantic Ridge).
• Convergent Boundaries: Plates move toward each other, with one plate often subducting beneath the other, creating deep ocean trenches and volcanic arcs (e.g., Andes mountains).
• Transform Boundaries: Plates slide past each other, causing no significant topographic changes (e.g., San Andreas Fault).

Mountain Formation

• Fold Mountains: Formed when two tectonic plates collide, causing layers of rocks and sediments to buckle and fold.
• Rift Valleys: Formed at divergent boundaries where tectonic plates move apart, causing magma from the mantle to rise, creating a rift, thinning the crust, and leading to a valley formation.

Subduction and the Formation of the Philippines

• Subduction is the process of one tectonic plate moving beneath another.
• The Philippines exists because of subduction between the Philippine and Eurasian plates, with the Philippine plate subducting beneath Eurasia.

The Rock Cycle

• Explains the processes by which rocks transform from one type (igneous, metamorphic, sedimentary) to another.
• These transformations are driven by internal (heat, pressure) and external (water, wind, gravity) forces.
  • Heat, pressure, weathering, and lithification drive the rock cycle.

Types of Rocks

• Igneous Rocks: Formed from the cooling and solidification of molten rock (magma or lava).
  • Extrusive: Cools quickly on Earth's surface, resulting in fine-grained or glassy textures.
  • Intrusive: Cools slowly beneath Earth's surface, allowing larger crystals to form.
• Sedimentary Rocks: Formed from the accumulation of eroded particles of minerals, rocks, and fossils.
  • Clastic: Formed from cemented pieces of other rocks.
  • Chemical: Formed from dissolved minerals precipitated from water.
  • Organic: Formed from compacted plant or animal remains.
• Metamorphic Rocks: Formed when existing rocks undergo changes due to extreme heat and pressure deep within the Earth, altering their mineral composition, texture, and structure.

Minerals vs. Rocks

• Minerals: Naturally occurring, inorganic solids with a definite chemical composition and ordered internal structure (crystalline).
• Rocks: Solid aggregates of one or more minerals or mineraloids, lacking a specific and definite chemical composition.

Mineral Physical Properties

• Identify minerals through key properties, including:
  • Hardness: Resistance to scratching (Mohs Hardness Scale).
  • Shape: External shape reflecting internal crystal structure.
  • Luster: How a mineral reflects light (metallic, dull).
  • Color: Outward appearance, often affected by impurities.

Top 6 Minerals in the Philippines

• Gold: Abundant mineral, important for the economy of the Philippines.
• Copper: Crucial for electronics and construction.
• Nickel: Essential for stainless steel and industrial products.
• Other minerals also listed (like chromite, iron, and aluminum) that are significant in the Philippines, often used by local communities for utensils and tools.

Mining

• Extraction of valuable resources (metals, minerals, etc.) from the Earth's crust.
  • Strip Mining: Extracting minerals from horizontal beds close to the surface..
  • Open-Pit Mining: Digging large holes to extract materials.
  • Underground Mining: Create tunnels to access materials deep beneath the surface.

Responsible Mining

• Considers environmental impact and local communities.

Fossil Fuels

• Still used due to established infrastructure, high energy density, and reliability in comparison to alternative energy sources.

Steno's Laws of Stratigraphy

• Explain the patterns in which rock layers are deposited.
  • Law of Superposition: Younger layers are above older layers in undisturbed sequences.
  • Law of Original Horizontality: Layers of sediment are generally deposited horizontally.
  • Law of Cross-Cutting Relationships: A feature cutting across another is younger than the feature it cuts across.
  • Law of Lateral Continuity: Layers of rock are originally continuous until encountering barriers.

Fossils

• Preserved remains or imprints of organisms from past life periods.
• Principle of Faunal Succession: Organisms evolve over time, creating a sequence in preserved remains (fossils) in rock layers, allowing age dating.
• Types:
  • Trace Fossils: Imprints of organism's activities.
  • Mold Fossils: Impressions of organisms.
  • Body Fossils: Actual remains (bones, shells).