Download Chapter 7 Weathering and Soil

Chapter 7
Weathering and Soil
7.2 The nature of soil notes sheet.
Soil
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Soil is a mixture of weathered rock, decayed organic material, mineral
fragments, water, and air.
Soil can take thousands of years to form.
There are five characteristics that affect soil formation.
1. Climate
2. Slope of land
3. Types of rock
4. Types of vegetation
5. Amount of time
Different soils can develop in different climates; tropical soil is different
than polar soil
Soils that develop on steep slopes are different than soils that develop
on flat land.
Slope will effect soil
Erosion will effect soil…
The composition of soil
► The
rock and mineral fragments found in
soils come from rocks that have been
weathered.
► Organic matter in soil comes from plant
leaves, stems, and roots.
► Decayed organic matter turns to humus, a
source of nutrients for plants.
► Soil has many small between particles that
holds water and air.
Soil Profiles
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Different layers of soil are called horizons.
All the horizons of a soil form a soil profile.
There are three main horizons for most soils.
-A horizon: the top layer of soil.
-It is usually covered by litter, made up of leaves,
twigs, and organic matter, which helps prevent erosion and
evaporation of water from the soil.
-Also known as top soil.
-It is dark and fertile.
-B horizon: the middle layer of soil
-Because there is less organic matter in this horizon, it is
lighter in color than the A horizon.
-Contain materials from A horizon that were moved
down by leaching: the removal of minerals that have been
dissolved in water. Water reacts with humus and carbon
dioxide to form acid. The acid dissolves the minerals in the
A horizon and carries them to B horizon.
► C horizon: the bottom of the soil profile.
-Consists of partially weathered rock.
-The thickest soil horizon.
-Does not contain much organic matter and is not affected
by leaching.
-The soil layer that is the most like the parent material.
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At many places of Earth, land is covered by a thick layer of
sediment that is deposited by glaciers.
-This material is an unsorted mixture of clay, silt, sand, and boulders
that were left after the glacial ice melted. It is extremely fertile.
Soil Types
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different types of soil exist, based on climate
and slope.
► Desert soils are dry and have little organic matter.
► Prairie soils have thick dark A horizons because of
the grasses contributing lots of organic matter.
► Slope also affects soils.
-Steep slopes have poor soils because material moves
downhill before it can be weathered.
-Bottomland soils are thick, dark, and full of organic
matter because sediment and water are plentiful.
Prairie and Desert Soil
Temperate and Forest Soil