Transcript of The Dirt of Geology. Soil is very important to us on this planet. We would not be able to survive...
- Slide 1
- The Dirt of Geology
- Slide 2
- Soil is very important to us on this planet. We would not be
able to survive without it. It is widely distributed, but it only
forms a very thin veneer on the Earths surface, compared to the
thick rock layers within the Earth
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- Soil is important in a multirole nature which means it has a
variety of definitions. Engineerswould define it as the material
upon which structures are built Farmers would define it as material
that supports plant growth Geology however define it as material
that can support vegetation
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- Soil is a mixture of mineral grains, organic material, water,
and air.
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- Mineral Grains These include clay, sand, silt, and rock
fragments created by the weathering (both mechanical and chemical)
of underlying parent rock. Organic Materials Is in the form of
humus, which is unrecognizable decaying organic material, i.e. when
a leaf ceases to look like a leaf because of decomposition
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- Living organisms are also part of the organic component of
soils There are as many as 3 billion organisms in one gram of soil
which include bacteria, fungi, insects worms, etc. Water This
enters the soil from infiltration of surface water or
precipitation
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- Air It enters the soil from diffusion from the atmosphere and
the work of organisms. The gases present in soil include carbon
dioxide, oxygen and hydrogen
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- This is an extremely slow process as on average, 2.5cm of soil
can form in 100 years It all begins with the weathering of rocks
where a thin layer of sediment (regolith) can form on the surface
of the rock. Organic material, water and air are added to the
regolith, producing soil.
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- Soil Formation
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- A soil can be classified as either: Residual - soils that
develop in place on the bedrock from which it was formed.
Transported soils that have been moved (by glaciers, streams, wind,
and/or gravity) and lie on bedrock other than the one from which
they formed
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- Residual soils develop distinct layers or horizons. transported
soils may not form horizons because of the transportation that was
involved. Soil horizons differ from one another in texture,
structure, composition and colour. Water filtration is what causes
the horizons to develop.
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- The soil horizons together comprise what is called the soil
profile. Soil profiles vary with the type of environment and soil-
forming conditions present. Most soil profile would contain four
distinct horizons, the O-horizon, the A-horizon, the B-horizon, and
C- horizon
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- This is the upper most zone and is not present in all soils. It
is dominated by organic matter and is the most biologically active.
It contains little in the way of minerals being that it is the
furthest from the bedrock. It is around a few centimetres
thick.
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- It is commonly called topsoil. This horizon is the zone of
leaching. Water (which is slightly acidic) dissolves ions like
calcium, iron, and aluminum and carries them away. There is an
amount of organic matter in the soil giving it a grey to black
colour.
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- Also called the zone of accumulation, as this is where the ions
taken from the A-horizon end up. There are few organisms and less
organic matter in this horizon
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- This horizon is of partially disintegrated and decomposed
parent rock material.
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- Characteristics of soils can differ dramatically from one
location to another. These characteristics include colour,
fertility, and thickness. The environmental factors affecting a
soils characteristics are; climate, organic activity, relief,
parent material, and time. Giving the acronym CLORPT.
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- This influence is the most influential factor, as rainfall and
temperature very important. The precipitation affects the degree of
leaching of soluble ions, which in turn affects fertility
Temperature and water dictate the weathering and amount of organic
material present.
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- The amount of organic activity affects the fertility of the
soil. Generally the more organic activity present, the more fertile
the soil, with one exception.
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- The slope of the land on which soil develops is called relief.
Generally, the greater the relief (the steeper the slope) the
thinner the soil profile. Valleys floors are usually given thick
soils, while hillsides are eroded.
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- The rock from which the soil originated will determine the
mineral matter and texture of the soil. Examples: Granite-Contains
feldspars that are converted to clays during weathering Quartzite-
consists of quartz, and upon weathering remains as sand, therefore
sandy soil.
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- The effect of time given that all other factors are equal would
be that more time would result in more weathering, and organic
activity which would give the thicker and more fertile soil.