soil formation

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SOIL FORMATION The Dirt of Geology

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The D irt of Geology. Soil Formation. 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 Earth’s surface, compared to the thick rock layers within the Earth. Soil. - PowerPoint PPT Presentation

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Page 1: Soil Formation

SOIL FORMATIONThe Dirt of Geology

Page 2: Soil Formation

SOIL 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 Earth’s surface, compared to the thick rock layers within the Earth

Page 3: Soil Formation

Soil is important in a multirole nature which means it has a variety of definitions. Engineers–would 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

Page 4: Soil Formation

COMPOSITION OF SOIL Soil is a mixture of mineral grains,

organic material, water, and air.

Page 5: Soil Formation

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

Page 6: Soil Formation

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

Page 7: Soil Formation

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

Page 8: Soil Formation

FORMATION OF SOIL 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.

Page 9: Soil Formation

Soil Formation

Page 10: Soil Formation

TYPES OF SOIL 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

Page 11: Soil Formation

RESIDUAL SOIL 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.

Page 12: Soil Formation

HORIZONS 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

Page 13: Soil Formation

O-HORIZON 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.

Page 14: Soil Formation

A-HORIZON 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.

Page 15: Soil Formation

B-HORIZON 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

Page 16: Soil Formation

C-HORIZON

This horizon is of partially disintegrated and decomposed parent rock material.

Page 17: Soil Formation

CLORPT Characteristics of soils can differ dramatically

from one location to another. These characteristics include colour, fertility,

and thickness. The environmental factors affecting a soil’s

characteristics are; climate, organic activity, relief, parent material, and time. Giving the acronym CLORPT.

Page 18: Soil Formation

CLIMATE 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.

Page 19: Soil Formation

ORGANIC ACTIVITY

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.

Page 20: Soil Formation

RELIEF 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.

Page 21: Soil Formation

PARENT MATERIAL 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.

Page 22: Soil Formation

TIME 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.