Soil is typically used to refer fertile dirt or earth. It is often composed of decaying plant and/or animal matter, particles of various minerals or rocks, and some amount of water in the form of moisture.
Soil is separated into 4 layers called “Horizons”.
The top layer is known as the “Organic layer”. It consists of decomposing or decomposed organic material. Mostly decomposed plant material such as dead leaves.
The second layer is known as the “Top Soil”. This is a largely mineral soil developed from the parent materials. Its dark color comes from leaching off of the organic layer.
The third layer is known as the “Sub soil”. This layer is mostly mineral soil with litter organic components. This soil is much more dense compared to the top soil making it more difficult for plant roots to extend downward.
The fourth layer is the unconsolidated material that was once the parent material. Due to it being so far removed from most biological activity and weathering, this layer retains most of the characteristics of the parent material.
Parental material, is the material from which the soil originated. This can range from bedrock, sand, till, or any combination of these materials depending on the region. Over time, erosion and weathering causes larger rocks to brake down into smaller particles and eventually soil.
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- Snippet from Wikipedia: Soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.
Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three-state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem.
Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm3, though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean.
Collectively the Earth's body of soil is called the pedosphere. The pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere. Soil has four important functions:
- as a medium for plant growth
- as a means of water storage, supply, and purification
- as a modifier of Earth's atmosphere
- as a habitat for organisms
All of these functions, in their turn, modify the soil and its properties.
Soil science has two basic branches of study: edaphology and pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation, description (morphology), and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the Moon and other celestial objects.