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1. Soil formation
Soil = mixture of mineral grains, organic
material and pores spaces filled with
variable amounts of air and water.
soil is largely derived from weathering of
rock ,the physical disintegration and/or
chemical decomposition of rock .

2. Soils are made of four components – mineral
matter, organic matter, air and water. Air and
water occupy pore spaces in the soil. The
example above is fairly typical.

3. SOIL: A PRODUCT OF WEATHERING
Weathering is normally
thought of as destructive.
However, if it were not for
weathering, we would not
have soils, which are an
important natural byproduct
of weathering.

4. MECHANICAL WEATHERING
•When the forces of weathering break rocks into
smaller pieces but do not change the chemical
makeup of the rocks, the process is
called mechanical weathering.
During mechanical weathering, rocks are broken
into different shapes and smaller pieces. At the
beginning the edges are jagged, as weathering
continues, they become round.

5. CAUSES OF MECHANICAL
WEATHERING
•There are several causes of mechanical
weathering.
•Temperature
•Frost action
•Organic activity
•Exfoliation or unloading
•abrasion

7. PHYSICAL WEATHERING BREAKS
ROCKS INTO SMALL MINERAL
PARTICLES.

9. CHEMICAL WEATHERING
• When the chemical makeup of the rocks is
changed it is called chemical weathering.
During chemical weathering, changes occur
in the mineral composition of rocks.
• Minerals can be added, removed or broken
down (decomposed).Many substances react
chemically with rocks to break them down.

10. TYPES OF CHEMICAL WEATHERING
•There are several causes of chemical
weathering.
•Water/ Hydrolysis
•Oxidation
•Carbonation
•Acid Rain
•Plant acids

11. CHEMICAL WEATHERING DISSOLVES
AND CHANGES MINERALS AT THE
EARTH’S SURFACE.

14. Hydrolysis

15. Oxidation

17. Carbonation

22. Plantacids

23. SOIL FORMATION
The five most important factors that
contribute to the way soils are formed are...
1. Parent material – the source of the soil
material. Where did the soil come from?
Did it come from granite, sandstone, glacial
till?

24. 2. Time – The longer a soil has been
forming, the thicker it becomes; the more
mechanical and chemical weathering it
has been exposed to.

25. PARENT MATERIAL AND TIME

26. 3.Climate – The affect of climate on weathering
is similar to the affect of climate on soils.
Hot, humid climates have the most intense
chemical weathering and as a result the soils
are generally unproductive (poor in nutrients).
Colder climates sometimes experience
mechanical weathering (frost wedging,
contraction/expansion etc.), but there is very
little chemical weathering, so the soils are
often more productive (nutrient rich).

27. 4. Organisms – Living organisms also
contribute to soil formation.
Bacteria and fungi can help to break down
the dead plants and animals and put nutrients
into the soil.
Earthworms and other burrowing animals
help to aerate and hydrate the soil with air
and water.

28. SOIL AND ORGANISMS

29. 5. Slope – The steepness of a slope can
also play a factor in soil formation.
Steeper slopes are affected more by
erosion and have less soil than flat
ground.

30. SOIL AND SLOPE