6 - LITHOSPHERE

LITHOSPHERE

• Solid outer part of the earth

• Earth’s internal structure is made out of core, mantle, asthenosphere, crust and lithosphere
• lithos = rocks, sphaeros = sphere

ROCKS

• Solid naturally occurring substances on the Earth’s lithosphere
• Composed of minerals, they are classified into igneous, sedimentary and metamorphic types
• It forms the earth’s crust and undergoes geological processes.

TYPES OF ROCKS

Igneous

• Forms from magma or lava solidification
• Hard, no layers
• Intrusive - Slow magma cooling (Granite)
• Extrusive - Rapid lava cooling (Obsidian)

Sedimentary

• Forms of sediment compaction
• Crumbly layer
• Clastic - Compacted broken rocks (Sandstone)
• Chemical - Compacted dissolved minerals (Limestone)
• Organic - Compacted biogenic matter (Coal)

Metamorphic

• Transformation of other rocks
• Relatively hard, may or may not have layers
• Foliated - has layers (Slate)
• Non-Foliated - no layers (Marble)

SOIL

• A mixture of minerals, organic matter, water and air
• Found in the uppermost layer of the earth known as the lithosphere or sometimes called “pedosphere”.
• Derived from the Latin word SOLUM; meaning earthy material in which plants grow
• Soil is the loose surface material that cover most land
• Soil is a biologically active porous medium present in the uppermost layer on the uppermost layer of the Earth’s crust
• PEDOLOGY – study of soil
  • Helpful in agriculture, horticulture, forestry, irrigation, use of fertilizers
  • Useful in science like: geology, petrology, mineralogy, paleobotany, paleozoology

FORMATION OF SOIL

• Soil forms through the weathering of rock.
• A change or difference in any of the weathering processes results to different kinds of soils.
• Likewise, the development of the same parent material under different climatic regimes and vegetation covers can result in different soils.

1. Weathering

• The disintegration of parents rocks by either physical, chemical or biological agents.
• Physical – temperature, water, ice, gravity, wind
• Chemical – solution, hydrolysis, oxidation, carbonation, hydration
• Biological – plant roots, lichen, algae, decaying plants

2. Pedogenesis

• Also known as soil development
• 5 principle factors:
  • Parent material - Local or transported rock/plant debris
  • Climate - Includes temperature and moisture
  • Topography - Shape and position
  • Living matter - Mainly microscopic and macroscopic plants, may also include animals that depend on the vegetation or the residue
  • Time - The period during which the interactions takes place

SOIL TERMS TO REMEMBER

1. Soil Moisture

• The volumetric water content of soil held within the spaces the soil particles or soil aggregates
• Two types:
  • Surface Soil Moisture - the water present on the upper layer of the soil
  • Root Zone Moisture - water available available to plants generally present within the soil
• Considered an indicator of the quality of soil and the fertility of the soil

2. Soil Gas

• Soil gases are different types of gases that are present within the pores between soil particles or soil aggregates
• Include carbon dioxide, oxygen, and nitrogen. Other atmospheric gases include methane and radon.
• Pores in the soil are filled by gases after the water present in such pores are evaporated or after they are absorbed by the root.
• In the case of environmental contaminants, soil gas might include gases diffused from landfill wastes, mining activities, and petroleum products.

3. Soil Matrix

• All the solid particles found in soil that include the soil particles, organic matter, and other inorganic materials.
  • Soil particles may either be sand, silk or clay
• Humus - Organic matter of soil
  • Humus - final stage degradation of dead plants and animals
  • It might even form organic colloid with water and other inorganic substances
• Determines various physical and chemical properties of soil like water retention capacity, nutrient content, and pH.

SOIL COMPOSITION

• 45% - Mineral Matter
• 5% - Organic Matter
• 25% - Air
• 25% - Water
• Mineral organic matter make up the solid part of the soil called the soil solids
• Air and water make up the pore space.
• Mineral Matter - obtained by the disintegration and decomposition of rocks.
  • Composed of sand, silt, clay, and gravel
• Organic Matter - obtained by the decay of plant residues and animal remains
  • Composed of organisms like bacteria, fungi, nematodes, 10% algae and 10% roots.
  • Contribute to stable soil aggregates by binding soil particles together and prevent soil erosion.
• Water - obtained from the atmosphere and the reactions in soil.
• Air or gases - from atmosphere reactions of roots, microbes and chemicals of the soil.

GENERALIZED SOIL PROFILE

• The horizons or layers may vary in number, composition, thickness depending on the type of soil
• Understanding the horizons can help assess soil fertility, drainage and the overall suitability for various purposes including agriculture and construction.

PROPERTIES OF SOIL

• Determined by the composition of the soil depending on different amounts of biotic and abiotic components
• The combinations of this components determine the physical and chemical property of soil

Physical

• Texture - Size of the soil particles
  • Gritty - Sand
  • Smooth - Silt
  • Stick and Moldable - Clay
• Structure - The textural components of soil including sand, silk and clay might result in aggregates as a result of their clumping
• Density - Average soil particle density ranges form 2.60 - 2.75 g per cm^3
• Porosity - The number of pores present within the soil
• Consistency - The ability of the soil to stick to itself or other objects and to resist deformation and rupture.
• Color - Determined primarily by the organic composition of the soil.
• Cation Exchange Capacity (CEC) - maximum amount of total cations that a soil sample is capable of holding at a given pH.
• Soil pH - reactivity of soil expressed in terms of soil pH which determines the acidity and alkalinity of the soil.
• Salinity - Salts in the soil are transported in salt tables in water resources that then accumulate due to evaporation.
  • The most common salts present in soil are: Magnesium Sulfate (MgSO4), Potassium Sulfate (K2SO4), and Carbon Trioxide (CO3).

MAJOR TYPES OF SOIL

1. Clay

• Comparatively heavy as it has higher water retention capacity and a higher concentration of nutrients
• Made up of over 25% clay particles that are smaller in size and thus hold a large amount of water
• Drains water slowly and thus takes longer to warm up in the summer without drying out
• However, it is a heavy and dense type of soil, it doesn’t provide space for plant roots to flourish

2. Loam

• A mixture of sand, silt, and clay soil that combines the properties of all three types of soil to make it more fertile
• Has enough pores as well as water retention capacity to promote crop production
• Has appropriate level of calcium and pH

3. Sand

• Contains a higher proportion of sand and less clay
• Light, dry, and warm
• Tends to be more acidic
• Larger particle size they have low water retention capacity and fewer nutrients
• Lack of moisture and nutrients makes the soil less suitable for crop production
• However, sandy soil can be made suitable by adding organic matter to increase water and nutrient content

Silt

• A light soil with a higher fertility rate with soil particles that are large than clay but smaller than sand
• Smooth and of fine quality that holds water better than the sandy soil
• Can also be easily transported by moving currents, and it is found near water bodies
• Considered the best type of soil for agricultural practices as it has sufficient nutrients and enough moisture for plant growth

FUNCTIONS OF SOIL

• Medium for plant growth, it provides an anchor for plant roots and acts as an water holding tank for necessary moisture
• The degradation of plant and animal matter
• Creates a pool of available water
• Acts as a regulator for water supplies
• Allows the cycling of different organic and inorganic compounds from the atmosphere to the soil and back
• A habitat for soil organisms
• Base for building homes, roads, and buildings, acting as a landscape or engineering medium
• Provides the raw material for different purposes like clay for ceramic production

LAND USE

• Term used to describe the human use of land
• Land Use denotes the sum of human activities and arrangements aimed at harnessing terrestrial ecosystem services.
• Classification:
  • Residential - Where people live
  • Commercial - use for buying and selling goods and service
  • Industrials - Land for used for industries (factories, power plants)
  • Institutional - Land occupied by schools, hospitals, government offices
  • Parks - lands for recreational use
  • Open Space - Land that is vacant, left in its natural state
  • Roads and Utilities - Use for moving people and goods from one place to another

SUMMARY

• Soil acts as a substratum for life on Earth that serves as a reservoir of water and nutrients, a medium for the breakdown of organic materials, and as a participant of various biogeochemical cycles.
• Soil in any particular area evolves through a series of weathering processes that are influenced by biological, topographical, climatic, and geological factors.
• Soil is one of the most important elements of an ecosystem as it contains both biotic and abiotic components.