Lithosphere

To understand what is lithosphere, one must divide the word into

two portions, namely Litho and sphere. Litho is derived from a
Greek word, meaning stone, while sphere signifies a globe or
ball.
The lithosphere is the rigid, outermost shell on Earth.
This includes the crust and the uppermost mantle, which
constitute the hard and rigid outer layer of the Earth. The
uppermost part of the lithosphere that chemically reacts to the
atmosphere, hydrosphere, and biosphere through the soil-
forming process is called the pedosphere.
Lithosphere Composition
The earth’s crust is not a homogeneous substance; it has different
layers of rocks including sedimentary rocks on top, granitic and
metamorphic rocks in the middle, and basaltic rocks on the
bottom.
The earth’s crust also consists of several large dynamic tectonic
plates. These tectonic plates move slowly but continuously at an
average rate of around 10 cm. Considering this, there was no
Atlantic Ocean, and North America and Europe together were
one continent 180 million years ago. The Atlantic Ocean came
into being because of the drifting apart from the Eurasian and
North American plates.
Lithospheric Plates
A lithospheric plate, or more commonly known as a tectonic
plate, is a giant and irregular slab of solid rock that usually
comprises both the oceanic well as the continental lithosphere.
The size of these tectonic plates varies quite a lot.
How do these plates move?
The radioactive processes that take place within the Earth’s
interior surface generate a great amount of heat which causes the
tectonic plates to move away from or towards each other. This
movement of the tectonic plates is referred to as tectonic shift. It
is also sometimes called the plate motion.
Types of Lithosphere
There are two types of lithosphere:
 Oceanic: Which is associated with oceanic crust and exists
in the ocean basins.
 Continental: This is associated with continental crust.

Importance of Lithosphere
• The lithosphere is important for life to exist. Earth’s
biosphere relies greatly on the presence of this rocky terrain.
Tectonic plates forming lithosphere causes change, which, in
turn, gave rise to life as we know it today.
• The shifting of tectonic plates causes the formation of
mountains, volcanoes and even the continents.
• Volcanoes and earthquakes are destructive in the short
term, but give rise to fertile soil and lands in the long term.
These lands help in the growth of new vegetation and life.
• Biotic remains buried in this lithosphere undergo
gradual change over millions of years. These organic
compounds turn into coal, natural gas and oil, powering modern
equipment.
• The lithosphere is the source for useful minerals and
elements, such as iron, aluminium, copper, calcium, magnesium
and more. Human beings have used these materials to
construct and build machinery and tools.
• Lastly, the lithosphere, along with the hydrosphere and
atmosphere, is responsible for providing nutrients to animal life
on Earth. The layer offers nutrients to plants, which convert the
same into glucose. This glucose is derived by higher animals to
survive.

Below the Lithosphere

Part of knowing what the lithosphere is involved understanding
what is above and below this layer. While the lithosphere is
surrounded by an atmosphere above it, below this layer is the
asthenosphere layer.

Soil
 It forms the upper surface of the earth where life thrives and
is the base of all agriculture.
 Due to the physical and chemical weathering of rocks, it
comprises of minerals and gravel, microbes, insects,
decaying organic matter (humus), nutrients, water, and air.
 There are different types of soil differing based on the
geological composition, climate, rainfall the area receives
and is regularly removed and formed by the activities
(natural or human)
Humus
Humus is the organic component present in the soil formed by
the decomposition of plant materials by microorganisms present
in the soil. Humus is the rotting dead matter in the soil.
Weathering
Weathering is the breaking down or dissolving of rocks and
minerals on Earths surface. Water, ice, acids, salt, plants,
animals, and changes in temperature are all agents of weathering.
Soil profile
The soil profile is a composition of different layers of soil in a
vertical section.
Each layer is different from others because of its texture, colour,
depth and chemical composition.

The soil is arranged in layers or horizons during its formation.

These layers or horizons are known as the soil profile. It is the
vertical section of the soil that is exposed by a soil pit. The layers
of soil can easily be identified by the soil colour and size of soil
particles. The different layers of soil are:
Topsoil


 Subsoil

 Parent rock

Each layer of soil has distinct characteristics.

Soil profile helps in determining the role of the soil as well. It
helps one to differentiate the given sample of soil from other soil
samples based on factors like its colour, texture, structure, and
thickness, as well as its chemical composition.
.
Layers of Soil
The soil profile is composed of a series of horizons or layers of
soil stacked one on top of the other. These layers or horizons are
represented by letters O, A, E, C, B and R.
The O-Horizon
The O horizon is the upper layer of the topsoil which is mainly
composed of organic materials such as dried leaves, grasses,
dead leaves, small rocks, twigs, surface organisms, fallen trees,
and other decomposed organic matter. This horizon of soil is
often black brown or dark brown in colour and this is mainly
because of the presence of organic content.
The A-Horizon or Topsoil
This layer is rich in organic material and is known as the humus
layer. This layer consists of both organic matter and other
decomposed materials. The topsoil is soft and porous to hold
enough air and water.
In this layer, the seed germination takes place and new roots are
produced which grows into a new plant. This layer consists of
microorganisms such as earthworms, fungi, bacteria, etc.
Soil organic matter (SOM) is the organic matter component of soil,
consisting of plant and animal detritus at various stages of decomposition,
cells and tissues of soil microbes

The E-Horizon
This layer is composed of nutrients filtered from the O and A
horizons. This layer is more common in forested areas and has
lower clay content.
The B-Horizon or Subsoil
It is the subsurface horizon, present just below the topsoil and
above the bedrock. It is comparatively harder. It contains less
humus, soluble minerals, and organic matter.
This layer holds more water than the topsoil and is lighter brown
due to the presence of clay soil. The soil of horizon-A and
horizon-B is often mixed while ploughing the fields.
The C-Horizon or Saprolite
This layer is devoid of any organic matter and is made up of
broken bedrock. This layer is also known as saprolite. The
geological material present in this zone is cemented.
The R-Horizon
It is a compacted and cemented layer. Different types of rocks
such as granite, basalt and limestone are found here.
Types of Soil
Sandy Soil
The soil is classified on the basis of the proportion of particles of
various sizes. Sand tends to have large particles and the particles
are solid and have no pockets where water and nutrients can hold
to it. Because of this, water and nutrients tend to run out, and
because sandy soil lacks both water and nutrients, many plants
have a difficult time surviving in this kind of soil. It contains
80% sand &10% silt.
Clay Soil
The clayey soil consists of a larger proportion of finer
particles. Clay soils contain more than 30 percent fine clay
particles. Clays swell and shrink as they wet and dry, effectively
cultivating themselves. It contains 60% clay & 40% silt.

Loamy Soil
 When the proportion of larger and finer particles are equal,
then that type of soil is called as loamy soil.
 Loamy soil is a mixture of silt, clay and sand which is the
best topsoil for growing plants.
.

It contains 40% sand, 40% silt &20% clay.

Percolation Rate
Percolation
Percolation is the process of filtering liquid while passing
through a filter. Rainfall seeps underground through percolation,
where water travels downwards through the tiny spaces between
rocks and soil particles. The water eventually saturates the
underlying rock much like water fills the tiny holes of a sponge.
This helps to replenish aquifers under the ground.
Percolation rate of soil
 Percolation rate of soil is used to determine the absorption
rate of the soil.
 The rate of percolation is the ratio of the amount of water in

millimetres to the percolation time in minutes.

Percolation rate (mL/ min) = amount of water (mL)/percolation
time (min).

Crops and its relation to types of soil

Depending on the climatic factors and components of the soil
different types of crops are grown in different regions.
 Clayey soil and loamy soil – Good for growing cereals like
wheat and gram.
 Clayey soil, soils rich in organic matter and soils with good
capacity to retain water – Good for growing paddy, wheat.
 Loamy soil, soils with high draining capacity and can
hold plenty of water – Good for growing Lentils (masoor)
and other pulses, cotton.
Soil Moisture
 Water in the soil is referred to as soil moisture. Water
absorption in the soil is determined by various factors

Types Of Soil Moisture

The different types of water present in the soil include:
  Gravitational Water
The water that reaches the water table of the soil due to the
gravitational force is referred to as gravitational water. This is
not available to the plants.
 Hygroscopic Water
This water is also not available to the plants. It is a thin film of
water tightly held by the soil particles.
 Chemically Combined Water
The chemical compounds present in the soil particles contain
water. This is known as chemically combined water. This is also
not available to the plants.
 Capillary Water
This water is available to the plants for absorption. This water
exists between soil particles in small capillaries.
 Atmospheric Humidity
The hanging roots of the epiphytes absorb the moisture in the air
due to the presence of hygroscopic hairs and spongy velamen
tissues.

Soil Pollution
Soil pollution refers to the contamination of soil with abnormal
concentrations of toxic substances.
It is a serious environmental concern since it harbours many
health hazards.
The root cause of soil pollution is often one of the following:
 Agriculture (excessive/improper use of pesticides)
 Excessive industrial activity
  Poor management or inefficient disposal of waste
 Pollutants that Contaminate Soil
 Some of the most hazardous soil pollutants are xenobiotics –
substances that are not naturally found in nature and are
produced by human beings.


Several xenobiotics are known to be carcinogens. An illustration

detailing major soil pollutants is provided below.

The different types of pollutants that are found in contaminated

soil are listed in this subsection.
Heavy Metals
The presence of heavy metals (such as lead and mercury, in
abnormally high concentrations) in soils can cause it to become
highly toxic to human beings. Some metals that can be classified
as soil pollutants are tabulated below.
Toxic Metals that Cause Soil
Pollution

Arsenic Mercury Lead

Antimony Zinc Nickel

Cadmium Selenium Beryllium

Thallium Chromium Copper

These metals can originate from several sources such as mining

activities, agricultural activities, and electronic waste (e-waste),
and medical waste.
Polycyclic Aromatic Hydrocarbons
Polycyclic aromatic hydrocarbons (often abbreviated to PAHs)
are organic compounds that
1. Contain only carbon and hydrogen atoms.
2. Contain more than one aromatic ring in their chemical
structures.
Common examples of PAHs include naphthalene, anthracene,
and phenalene. Exposure to polycyclic aromatic hydrocarbons
has been linked to several forms of cancer. These organic
compounds can also cause cardiovascular diseases in humans.

Industrial Waste
The discharge of industrial waste into soils can result in soil
pollution. Some common soil pollutants that can be sourced from
industrial waste are listed below.
  Chlorinated industrial solvents
 Dioxins are produced from the manufacture of pesticides

and the incineration of waste.

The petroleum industry creates many petroleum hydrocarbon
waste products. Some of these wastes, such as benzene and
methylbenzene, are known to be carcinogenic in nature.
Pesticides
Pesticides are substances (or mixtures of substances) that are
used to kill or inhibit the growth of pests. Common types of
pesticides used in agriculture include
 Herbicides – used to kill/control weeds and other unwanted
plants.
 Insecticides – used to kill insects.

 Fungicides – used to kill parasitic fungi or inhibit their

growth.
However, the unintentional diffusion of pesticides into the
environment (commonly known as ‘pesticide drift’) poses a
variety of environmental concerns such as water pollution and
soil pollution. Some important soil contaminants found in
pesticides are listed below.
Herbicides
 Triazines
 Carbamates
 Amides
 Phenoxyalkyl acids
 Aliphatic acids
Insecticides
 Organophosphates
  Chlorinated hydrocarbons
 Arsenic-containing compounds
 Pyrethrum
Fungicides
 Mercury-containing compounds
 Thiocarbamates

 Copper sulfate

These chemicals pose several health risks to humans. Examples

of health hazards related to pesticides include diseases of the
central nervous system, immune system diseases, cancer, and
birth defects.
Effects on Human Beings
Soil contaminants can exist in all three phases (solid, liquid, and
gaseous). Therefore, these contaminants can find their way into
the human body via several channels such as direct contact with
the skin or through the inhalation of contaminated soil dust.
The short term effects of human exposure to polluted soil
include
 Headaches, nausea, and vomiting.
 Coughing, pain in the chest, and wheezing.

 Irritation of the skin and the eyes.

 Fatigue and weakness.

A variety of long-term ailments have been linked to soil

pollution. Some such diseases are listed below.
 Exposure to high levels of lead can result in permanent
damage to the nervous system. Children are particularly
vulnerable to lead.
 Depression of the CNS (Central Nervous System).
  Damage to vital organs such as the kidney and the liver.
 Higher risk of developing cancer.

Soil erosion
The process of removal of land by water, wind or ice is known as
erosion.
Soil Erosion Definition
“Soil erosion is the natural process in which the topsoil of a
field is carried away by physical sources such as wind and
water.”

Cause of Soil Erosion

Following are the important causes of soil erosion:
1.Rainfall and Flooding
soil erosion.
2.Agriculture
The farming practices are the major cause of soil erosion. The
agricultural activities disturb the ground. The trees are cleared
and the land is ploughed to sow new seeds. Since most of the
crops are grown during the spring season, the land lies fallow
during winters. Most of the soil is eroded during winters.
Also, the tyres of tractors make grooves on the land, making a
natural pathway for water. Fine soil particles are eroded by wind.
 3. Grazing
The grazing animals feed on the grasses and remove the
vegetation from the land. Their hooves churn up the soil. They
also pull out plants by their roots. This loosens the soil and
makes it more prone to erosion.
4. Logging and Mining
A large number of trees are cut down to carry out the
logging(cutting) process. Trees hold the soil firmly. The trees
protects the soil from heavy rainfall..
Mining activities also disturb the land and leave the soil more
prone to erosion.
5. Construction
The construction of roads and buildings exposes the soil to
erosion. The forests and grasslands are cleared for construction
purposes, which exposes the soil making it vulnerable to erosion.
6. Rivers and Streams
The flowing rivers and streams carry away the soil particles
leading to a V-shaped erosion activity.
7. Heavy Winds
During dry weather or in the semi-arid regions, the minute soil
particles are carried away by the wind to faraway lands. This
degrades the soil and results in desertification.
Effects of Soil Erosion
The major effects of soil erosion include:
1. Loss of Arable Land
Soil erosion removes the top fertile layer of the soil. This layer is
rich in the essential nutrients required by the plants and the soil.
The degraded soil does not support crop production and leads to
low crop productivity.
2. Clogging of Waterways
The agricultural soil contains pesticides, insecticides, fertilizers,
and several other chemicals. This pollutes the water bodies
where the soil flows.
3. Air Pollution
The dust particles merge in the air, resulting in air pollution.
Some of the toxic substances such as pesticides and petroleum
can be extremely hazardous when inhaled. The dust plumes from
the barren regions cause widespread pollution when the winds
move.
4. Desertification
Soil erosion is a major factor for desertification. It transforms the
habitable regions into deserts. Deforestation and destructive use
of land worsens the situation. This also leads to loss of
biodiversity, degradation of the soil, and alteration in the
ecosystem.
5. Destruction of Infrastructure
The accumulation of soil sediments (material from a liquid that
settles to the bottom) in dams and along the banks can reduce
their efficiency. Thus, it affects infrastructural projects such as
dams, embankments, and drainage.
Soil Erosion Prevention
Soil erosion is a serious environmental issue. Steps should be
taken to curb this problem. Following are some of the methods
of soil erosion prevention:
1. Plant trees on barren lands to limit erosion of soil.
2. Add mulch and rocks to prevent the plants and grass
underneath to prevent soil erosion.
3. Mulch matting can be used to reduce erosion on slopes.
4. A wall at the base of the slope can help in preventing the
soil from eroding.
5. Every household should have a proper drainage system so
that water flows down into proper water collecting systems.

Soil Conservation
The goal of soil conservation is to stop the degradation of the
soil’s topmost layer due to erosion or to stop the soil from
becoming less fertile due to overuse, acidification, salinisation,
or from other chemical soil pollution.
Various Soil Conservation Methods
1. Contour Ploughing
 This Photo by Unknown Author is licensed under CC BY-SA

With contour ploughing, furrows are oriented to follow the

contour lines of the farmland. Runoff is decreased because
furrows shift to the left and right to keep a steady altitude. For
slopes from two to ten per cent, the ancient Phoenicians used
contour ploughing. Crop yields can rise by 10% to 50% with
contour ploughing, in part due to better soil retention.
2. Terrace Farming

Creating almost level spaces on a hillside is a procedure known

as terracing. The terraces are like a succession of steps, each one
taller than the one before it. Other soil barriers shield terraces
from erosion. Small farms tend to use terraced farming more
frequently.
3. Keyline Design

This Photo by Unknown Author is licensed under CC BY-NC-ND

The improvement of contour farming known as keyline design
involves creating contour lines while taking into account all of
the characteristics of the watershed.
4. Windbreaks
On the windward side of a field of agriculture vulnerable to wind
erosion, windbreaks are adequately thick rows of trees.
5. Cover Crops/Crop Rotation

In order to cover the ground year round and serve as green

manure to replace nitrogen as well as other essential nutrients
cover crops including legume plants, white turnips, radishes, and
many other species are cycled alongside cash crops. In addition,
cover crops aid in weed control.
No-till farming (growing crops without disturbing the soil
through tillage)55, “green manures,” and other soil-improving
techniques are used in soil conservation
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Horizon
Each layer in a soil profile is defined as a horizon.
1. A- horizon or topsoil is the soft, porous layer which can
absorb and hold more water.
2. B-horizon or middle layer is the more compact and harder
layer.
3. C-horizon is the third layer made up of small rocks.
4. Bedrock is the fourth and hardest layer.