Rox, Weathering & Soils Slide Notes

Introduction to Earth's Resources

  • All of Earth’s resources are categorized as

    • METASTABLE: refers to materials that change with temperature and pressure.

    • Forms:

      • Ice

      • Water (H₂O)

      • Water Vapor

The Rock Cycle

  • Key processes involved in the rock cycle include:

    • Transportation

    • T & P (Temperature and Pressure)

    • Deposition

    • Sediments

    • Lithification

    • Sedimentary Rocks

    • Metamorphism

    • Metamorphic Rocks

    • Weathering

    • Uplift and Exposure

    • Igneous Rocks

    • Extrusive

    • Intrusive

    • Crystallization

    • Melting

    • Magma

    • Solidification

Basic Rock Concepts

  1. All rocks are composed of minerals.

  2. Rocks are categorized into three groups based on their mode of formation and temperature (T) & pressure (P) conditions:

    • Igneous: Crystallized from Magma

    • Sedimentary: Compacted and cemented sediments

    • Metamorphic: Recrystallized under high temperatures and pressures

  3. The type/name of rock is determined by the specific mineral composition that constitutes the rock.

Types of Rocks

Igneous Rocks

  • Examples include:

    • Granite

    • Gabbro

Sedimentary Rocks

  • Examples include:

    • Limestone

    • Sandstone

    • Shale

Metamorphic Rocks

  • Examples include:

    • Gneiss

    • Schist

The Rock Cycle Mechanism

  • T & P conditions in the rock cycle:

    • At 25°C and 1 atm: Weathering occurs

    • Greater than 1500°C and >900 atm: Igneous rock formation happens through cooling

    • Processes include:

    • Cooling of magma

    • Formation of sediment through lithification

    • Metamorphism of existing rocks

Understanding Meta-Stability

  • Meta-Stability:

    • The temperature (T) and pressure (P) conditions at which each rock type forms are the only stable conditions for that rock.

    • At all other T & P regimes, the rock is considered metastable.

    • Most rocks form under conditions of higher T & P than are typically found at the earth's surface (25°C and 1 atm).

    • As such, these rocks are metastable and will eventually disintegrate (either chemically or physically), a process known as Weathering.

Magmatic Differentiation and Bowen's Reaction Series

  • A sequence that explains how different minerals crystallize from magma at varying temperatures:

    • Discontinuous Series:

    • Olivine

    • Pyroxene

    • Amphibole

    • Biotite

    • Feldspars

    • Continuous Series:

    • Associated minerals where calcium-rich varieties lead to sodium-rich minerals.

    • Show a trend from least stable (Olivine) to most stable (Quartz).

Weathering Processes

Physical Weathering

  • Examples impacting rocks include:

    1. Thermal Expansion

    2. Freeze-Thaw Wedging

    3. Breakage during Transport

    • Processes include chipping, fracturing, etc.

  • Freeze-Thaw Process: Water enters rock cracks, freezes, expands, and fractures the rock.

  • Thermal Expansion: Rocks expand when heated and contract when cooled, leading to fracturing.

Chemical Weathering

  • Hydrolysis: Minerals dissolve in water leading to the formation of ions.

  • Oxidation: Minerals react with oxygen leading to rusting effects on certain minerals.

  • Dissolution by Acid Solutions: Organic acids and atmospheric acids (such as carbonic acid and sulfuric acid) contribute to decomposition.

Soil Formation and Development

Soil Profile

  • Different horizons within soil include:

    • O Horizon: Organic layer with rotting plants

    • A Horizon: Organic matter accumulation, composed of decomposed material

    • B Horizon: Clay accumulation from weathering processes

    • C Horizon: Parts of the parent material, subject to some weathering

    • R Horizon: Bedrock which is often not weathered

Humus and Organic Matter

  • Humus:

    • A component of soil organic matter derived from decomposed plant and animal material, supports soil structure and fertility.

    • Types of Humus:

    • Humic substances: High molecular weight components

    • Fulvic acids: Low molecular weight components

Global Soil Types

Major Soil Orders

  1. Entisols

  2. Inceptisols

  3. Aridisols

  4. Mollisols

  5. Vertisols

  6. Alfisols

  7. Andisols

  8. Spodosols

  9. Histosols

  10. Ultisols

Soil Texture Classification

  • Soil types based on particle size:

    • Clay: <0.002 mm

    • Silt: 0.002 - 0.05 mm

    • Sand: 0.05 - 2 mm

  • Soil textural triangle used to categorize by these proportions.

Hydrological Impacts on Soil

  • Impacts of water interaction such as evaporation, precipitation, and leaching on soil profiles and health.

    • Includes the erosion and deposition effects leading to soil fertility factors.

Climate Zones Relation to Soil Profile

  • Different climate zones impact soil thickness and type:

    • Polar areas have thin soil profiles.

    • Tropical regions have thicker soils due to high organic deposition and weathering rates.

Conclusion

  • Understanding rock types, the rock cycle, and the processes of weathering is vital for comprehending Earth's geological and environmental systems.

  • The complex interplay of temperature, pressure, and mineral composition dictates the stability and eventual transformation of Earth’s resources.