1. The Dirt of Geology

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

3.  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

4.  Soil is a mixture of mineral grains, organic material, water, and air.

5.  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

6.  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

7.  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

8.  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.

9. Soil Formation

10.  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

11.  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.

12.  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

13.  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.

14.  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.

15.  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

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

17.  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.

18.  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.

19.  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.

20.  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.

21.  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.

22.  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.