Download Soil Composition

Soil Composition
In this presentation you will:
 explore the process of soil formation
 explore the composition of soil
 explore how human activity can damage the soil
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Soil Composition
The loose, top layer of the
Earth’s surface is made of soil.
This is called the pedosphere.
Atmosphere
The pedosphere interacts
with the four major
systems of the Earth:
Geosphere
 Geosphere – the solid
part of the Earth
Hydrosphere
 Atmosphere – the layer of
gases surrounding the Earth
Biosphere
 Hydrosphere – all water
on Earth
 Biosphere – all living organisms
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Question 1
What is the name given to the top layer of the Earth's surface that is
composed of soil?
A) Pedosphere
B) Atmosphere
C) Geosphere
D) Hydrosphere
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Question 1
What is the name given to the top layer of the Earth's surface that is
composed of soil?
A) Pedosphere
B) Atmosphere
C) Geosphere
D) Hydrosphere
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Soil Composition
Soil contains four
types of materials:
 Minerals – contained in
rock, sand, clay, and silt
 Organic material
(substances containing
carbon atoms derived
from living organisms)
Soil surface
Pores
Pores
 Water – soil contains holes
(pores) that fill with water
 Air – pores in soil
may also fill with air
Pores
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Soil Formation
Soil formation is a slow
process. It can take hundreds
or even thousands of years to
make just one handful.
Soil is mostly formed from
rocks which have been
weathered, or broken down to
form sediment. The rock from
which soil is formed is
referred to as parent material.
The weathering of parent
material can take place in
one of two main ways:
 Physical weathering
 Chemical weathering
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Physical Weathering
Physical weathering is the
process by which rocks are
broken down into soil. It is
usually the effect of water,
wind, ice, pressure, or heat.
For example, a drop in
temperature can cause
water that has seeped into
rock cracks to freeze. As the
water freezes, it expands,
pushing the rocks apart.
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Chemical Weathering
Chemical weathering is the
process by which the chemical
makeup of rock is changed,
causing it to deteriorate.
For example, water can
contain dissolved chemicals
that cause rock to break down.
Chemical weathering occurs
naturally, but can also be caused
or accelerated by pollution.
Harmful chemicals that are
released into the atmosphere as a
result of human action dissolve in
rain water to create acid rain.
When acid rain falls, it causes
rocks to crumble and disintegrate.
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Question 2
"Parent rocks can be physically weathered by water."
Is this statement true or false?
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Question 2
"Parent rocks can be physically weathered by water."
Is this statement true or false?
True
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Erosion and Deposition
Soil is often formed from parent
material that is not found in the
area where the soil is located.
This is due to the processes of
erosion and deposition.
Erosion occurs when solid
particles, known as sediment,
are moved by wind, water, ice,
or gravity. Sediment may
contain organic material, rock
or soil.
Sediment transported by erosion
is eventually deposited in a new
location. The deposited
sediment then becomes part of
the soil in the new location.
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Minerals
Rocks contain minerals.
Minerals are naturally
occurring solid substances.
Minerals are inorganic,
which means they do not
contain carbon atoms.
Rocks may be composed of
a single mineral or many
different minerals. For
example, limestone rock is
made from one mineral
(calcite) but sand is made up
of several different minerals,
such as silica and mica.
Soil contains the minerals
of its parent rocks.
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Organic Material
Organic material found in the
soil consists of decomposed
dead organisms, such as fallen
leaves and dead animals, as
well as living organisms.
Many organisms live in soil.
Underneath every footprint
that you make in soil are
thousands of organisms.
Most organisms, such as
earthworms, fungi, and insect
larvae, are beneficial to the soil.
However, some can be harmful
and bring damage to crops, and
disease to animals and people.
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Beneficial Organic Material
Decomposing organic material
contained in soil is known as
detritus. One of the most common
forms of detritus is leaf litter.
Detritus is broken down by
decomposers, which are
organisms, such as
bacteria and fungi, that
live in the soil.
Dead organisms contain nutrients.
When decomposers break down
detritus, these nutrients are
released into the soil.
Other organisms, such as
earthworms, move detritus
around, helping to spread
nutrients throughout the soil.
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Beneficial Organic Material
As detritus decomposes,
it becomes a brown
substance called humus.
Humus contains important
nutrients and retains moisture.
Plants grow at their best in areas
of soil that are rich in humus.
If the soil is lacking in nutrients,
fertilizers (substances
containing extra nutrients, such
as nitrogen and phosphorus)
can be mixed in with the soil to
encourage plant growth.
Fertilizers are commonly used
in farming and gardening.
Nutrients added
Nitrogen
Phosphorus
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Question 3
Which of the following statements is true?
A) Detritus is the name given to inorganic material in the soil
B) Decomposers break down detritus
C) Humus is another name for detritus
D) All of the above
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Question 3
Which of the following statements is true?
A) Detritus is the name given to inorganic material in the soil
B) Decomposers break down detritus
C) Humus is another name for detritus
D) All of the above
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Harmful Organic Material
Most soil organisms are
beneficial to other organisms
that use soil, but there are a
few which are harmful.
The bacteria Clostridium tetani
is found in most soils. It enters
organisms through broken skin
wounds, and causes the
disease known as tetanus,
which can paralyze muscles.
People who regularly work
outdoors must ensure that
they are vaccinated
against soil-borne
diseases such as tetanus.
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Water and Air
Rainwater seeps
into soil pores.
Soil surface
Pores
Pores
Pores of various sizes
retain the water, making it
easy for plant roots and
soil organisms to access
the water they need.
Water is used in many
metabolic reactions in
living organisms.
Pores
Water
Pores also hold air so
that soil organisms that
require oxygen to live
can breathe and survive
under the ground.
Oxygen
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Question 4
Which of the following statements is true?
A) Water and air are held in pores in the soil
B) Soil pores are various sizes
C) Water is needed for many metabolic reactions
D) All of the above
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Question 4
Which of the following statements is true?
A) Water and air are held in pores in the soil
B) Soil pores are various sizes
C) Water is needed for many metabolic reactions
D) All of the above
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Life and Soil
Soil supports most of
the plant life on Earth.
This is why it is important
that we look after our soil.
In areas all around the world,
soils are being damaged
because of human activity.
Soils are being stripped of
their nutrients, and with it,
their ability to support life.
The greater the soil
quality, the more
organisms it can support.
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Damaging Activities
There are several ways in
which soil damage can occur:
Soil mining – Farming of the
same crop in the same area for
a long time can drain the soil of
its available nutrients, as can
over-grazing by animals.
Chemicals – Insecticides and
herbicides (used to kill harmful
insects and weeds) sprayed onto
crops change the acidity of the
soil. This can cause changes in
all areas of an environment.
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Damaging Activities
Landfill sites – Over half of our
trash is buried underground in
landfill sites. Toxic chemicals
from the trash can leak into
the soil, killing organisms that
live in or rely on the soil.
Construction – Soil and plant
life is wiped away for the
creation of houses and
buildings. Tarmac and
concrete do not let air and
water through, so the soil
below it cannot support life.
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Question 5
Which of the following problems is associated with soil mining or overgrazing by animals?
A) Changes in soil acidity
B) Leaking of toxic chemicals
C) Lack of air and water in the soil
D) Lack of nutrients in the soil
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Question 5
Which of the following problems is associated with soil mining or overgrazing by animals?
A) Changes in soil acidity
B) Leaking of toxic chemicals
C) Lack of air and water in the soil
D) Lack of nutrients in the soil
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Damaging Activities
Hedges and trees are often
removed to make way for
agricultural land. Plants protect
soil from erosion. When plants
are removed, soil is blown away
by wind and carried away by rain.
The Dust Bowl, which formed in
the central United States and
Canada in the 1930s, was
caused by soil erosion resulting
from over-production of crops
and the over-plowing of soils.
Similar problems are now
occurring in parts of Africa,
resulting in fertile land becoming
a desert, or desertification.
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Soil Conservation
In order to stop more soil from
being damaged, humans must
limit these damaging activities.
We can renew already damaged
soil by methods known as soil
conservation. However, these
methods can take a long time to
repair the damage.
Reforestation is a method of
repairing damaged areas of
land by planting new plants
and trees to replace those
that have been removed.
This helps to protect the soil from
further erosion and attracts many
forms of life back into the area.
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Summary
In this presentation you have seen:
 soil composition and the formation of soil
 human activities that can damage the soil
End