Class 10 Science Solutions Nepal

MENDEL’S LAW OR MENDELISM

On the basis of the above crosses and results obtained from there, Mendel proposed
the following three laws and these laws are known as Mendelism.

(i) Law of dominance
(ii) Law of segregation or law of purity of gametes
(iii) Law of independent assortment

(i) Law of dominance (Mendel’s first law)

It states that, “when a cross is made between two pure (homozygous) organisms for a

pair of contrasting characters, only one of them can express itself in the F1-generation”.

Example- when a pure tall plant (TT) is crossed with a pure dwarf plant (tt) then

all F1-generation pea plants were tall phenotypically though they also contained
dwarfness in their genes. Thus, tallness is dominant character (as it expressed itself in

F1-generation) and dwarfness is the recessive. Pure dwarf

Pure tall

TT × tt

Gametes T T tt

F1 generation Tt Tt Tt Tt

A cross between pure tall and pure dwarf plant

Similarly, the black coat of guinea pig and the long wing of drosophilla are dominant
traits.

MEMORY TIPS
Mirabilis jalpa (four o’ clock plant) shows incomplete dominance as pink flowers are also
produced along with red and white in F1-generation.

ACTIVITY

Make a family of at least three generations of your family by taking any one character like colour
of skin, colour of eyes, height, etc. (by asking your parents and study the dominant and recessive
characters).

QUESTIONS
# Would Mendel have been succeed if he had used a frog instead of a pea for his experiment?

New Creative Science, Class 10 | 297

(ii) Law of segregation or law or purity of gametes

It states that, ‘At the time of gamete formation, the two members of the factor
controlling a pair of characters segregate so that each gamete receives only one factor
of each character. This shows that gametes are pure, and this law is also known as law
of purity of gametes.

For example, in Mendel’s monohybrid cross between pure tall and pure dwarf plants,

the genotypic ratio of the pure tall, hybrid tall and pure dwarf plants was found to be

1 : 2 : 1 in F2 generation. This is due to the separation of characters of the hybrid pea
plant during the gamete formation.

Hybrid tall Hybrid Tall

Tt × Tt

Gametes T t Tt

F2 generation TT tt tT Tt

A cross between Hybrid tall plant

Result

Phenotype ratio = 3 : 1
Genotype ratio = 1 : 2 : 1

Here in the above figure. 'Tt' allels of the hybrid tall pea-plant are separated or
segregated during the formation of gametes, therefore one type of the gametes have
got 'T' or tallness character and the other type of gametes have got 't' or dwarfness
character. This proves that characters are segregated during the formation of gametes
making them always pure. Gametes are never hybrid.

QUESTIONS
# What do you think are the reasons behind Mendel’s success?
# Do you think Mendel was lucky to choose a pea plant?

298 | Heredity

GENETIC CHARACTERS IN HUMAN BEINGS

The hereditary characters in human beings are as follows:

Dominant characters Recessive characters

1. Curled hair 1. Straight hair

2. Isolated ear lobule 2. Joint ear lobule

3. Presence of dimple mark 3. Absence of dimple marks

4. Straight thumb 4. Back turned thumb

5. Rolling of the tongue 5. No rolling of the tongue

6. Forebending of the tongue 6. No fore bending of the tongue

SEX-LINKED INHERITANCE IN HUMAN

Some of the characters in human beings are found in only one type of sex group; male
or female, these characters transfer from male to male only or female-to-female only.
Such a process is called sex-linked inheritance.
E.g. Haemophelia (unability of blood clotting at wounds) and Daltonism (colour
blindness) are found in male only. Females may only be the carrier of this diseases but
are not infected. These types of disease are called sex-linked diseases.

MEMORY TIPS
In colour blindness, a man cannot separate red and green colour.

ACTIVITY

Identify in your class how many of your friends have dominant characters and how many of them
have recessive characters in reference to the above six characters in human beings.

New Creative Science, Class 10 | 299

MUTATION

It is a sudden, large and discontinuous variation in an individual.

It is stable variation and is inheritable, e.g. hairless variety of dogs and cats, disability of
a baby by birth, six fingered man, fused fingers, cut at lips, etc. An individual suffering
from mutation is called mutant and the agents of mutation are called mutagens.
MODEL QUESTIONS ANSWER

1. Why did Mendel select a pea plant for his experiment?

Ü Mendel choose a pea plant (Pisum sativum) for his experiment because of the
following reasons.

(a) It has a short lifespan and can easily be grown.
(b) Self and cross pollination can be done in it.
(c) It has a number of distinguishable contracting characters like the height of

plant (tall or dwarf), colour of flower (red or white) etc.

2. Differentiate between genotype and phenotype.

S.N. Phenotype S.N. Genotype

1. It is the visible external characters 1. It is the genetic expression of an

of an organism. organism.

2. It is determined by the genotype. 2. The phenotype of an organism may
or may not be useful to determine the
genotype.

3. It can be changed by the influence 3. It cannot be changed by the

of environmental factors. influence of external factors.

4. It may or may not be inheritable. 4. It is inheritable.

3. State the law of dominance.

Ü It states that, in a cross between a pair of contrasting characters, only one of
them can express themselves in F1- generation.

4. Draw a chart to show the result in the first and second filial generations of the
offspring of a black father (BB) and a white mother (bb).

♀ \♂ B b

B BB Bb

b Bb bb

300 | Heredity

Black father (BB) White mother (bb)

Hybrid black Bb F1 generation

Bb Bb Bb bb F2 generation

Black White

Phenotypic ratio of black and white = 3 : 1

Genotypic ratio of pure black, hybrid black, pure white = 1 : 2 : 1

5. Mention Mendel’s law to the point.
Ü (i) Law of dominance

(ii) Law of segregation

(iii) Law of independent assortment

SUMMARY

 ‘Genetics’ is the branch of science, which deals with heredity and causes variation in
living organisms.

 The transfer of parental characters from one generation to the next is known as
inheritance.

 The phenomenon, by which each of the organisms is distinguished from the other is
called variation.

 Variation is responsible for evolution while heredity checks over uncontrolled variations.
 Sir Gregor Johann Mendel is known as ‘the father of genetics’.
 The genetic expression of an organism is known as genotype and the physical expression

of the organism is known as phenotype.
 The characters which can express themselves in F1- generation are called dominant

characters.
 The characters which cannot express themselves in F1 - generation are called recessive

characters.
 The cross considering between only one pair of alleles is called monohybrid cross.
 The cross considering between two pairs of alleles is called dihybrid cross.
 Mendel’s laws in genetics are–

(a) Law of dominance (b) Law of segregation (c) Law of independent
assortment
 The phenotypic ratio in monohybrid cross is 3 : 1 and the genotypic ratio is 1 : 2
: 1 in F2 - generation.
 The ratio of characters in dihybrid cross is 9 : 3 : 3 : 1 in F2 generation.
 Mutation is the sudden and discontinuous change.
 DNA and RNA are the two nucleic acids found in a cell of organism.

New Creative Science, Class 10 | 301

EXERCISE

1. Define heredity. Who is known as the father of genetics?

2. Why did Mendel select a pea plant for his experiment?

3. Define dominant and recessive characters and give their examples.

4. Differentiate between.

(a) Phenotype and genotype (b) Variation and mutation

(c) Monohybrid cross and dihybrid cross.

5. State the law of dominance and prove it with an example.

6. Why is the law of segregation known as the law of purity of gametes?

7. Show a chart showing the cross between a long winged drosophila with a short
winged drosophila. Also mention the phenotypic ratio and genotypic ratio up to
F2-generation.

8. When black and white guinea pigs are crossed, all the pigs of F1-generation are
found black. Explain this result in reference to Mendelism.

9. Do you think Mendel was lucky to choose a pea plant for his experiment? Why?

10. Define mutation. Draw a chart to show both phenotype and genotype of the result
obtained in the first and the second filial generation of the offspring of the mouse,
having black colour and white colour according to the Mendel’s experiment.

11. When the hybrid tall plants are self-pollinated then the result showed that the ratio
of a pure tall, hybrid tall and a pure dwarf plant is 1 : 2 : 1. Interpret this result.

12. What is the significance of variations?

13. Differentiate between clone and offspring.

14. Twins are the clone of each other but the offspring of their parents. Prove it.

15. Study the chart and answer the following questions.

(a) Results of which filial generation is shown in the figure?

(b) What is the genotypic ratio? ♀ \♂ T t

(c) What is the phenotypic ratio? T TT Tt
(d) Which law does this result prove? t Tt tt

(e) What is the cause of the reappearance of dwarfness in this generation
whereas it was not seen in the earlier generation?

A

B GLOSSARY
C

Beget : to make something happen
Traits : characters
Segregate : to separate
Drosophila : a kind of fruit fly
Macromolecule : a larger molecule

Assortment : a collection of different things or different types of something



302 | Heredity

UNIT

20 Environmental Pollution and
Management

About the Ozone hole INTRODUCTION

Ozone Depletion Human beings along with other living organisms interact
with each other and with the physical surroundings for their
Chlorofluorocarbons (CFCs) survival. Human beings, on the other hand, are modifying
are the chief air pollutants that the environment haphazardly to fulfill their increasing
are responsible for depletion of needs. This is disrupting the natural balance between the
ozone layer. Others are carbon- components of the environment resulting in continuous
tetrachloride, methyl chloroform, environmental degradation. Environmental pollution is one
methyl bromide etc. CFCs used of the major and long term consequences of environmental
in refrigerators, air conditioners, degradation. Have you ever noticed the air in an urbanized
spray cans after emitting into the and industrialized area of our country contains visible mass
atmosphere releases free chlorine of dust and smoke and is unpleasant to breathe. Fertile
(Cl) radical which involve in lands are used for construction buildings and dumping
chain reaction and destroys wastes. Effluents from industries, hospitals, market centres
protective stratospheric ozone. and households are discharged to water bodies. Such
As a result UV radiation passes activities of human results pollution of the air, water, land,
through the atmosphere and etc. Consumption of goods and services from the polluted
reaches the earth. UV radiation environment causes different diseases to human and even
causes skin cancer, damage to to other life forms. Besides, cumulative effects of such
eyes and immune system of pollutions results various global environmental problems
humans, causes mutation in like climate change, global warming, ozone layer depletion,
plants and animals and destroys etc. These problems can have adverse effects on the survival
living system. of living organisms in the earth. Therefore, this unit aims of
providing information regarding the major environmental
pollutions, their effects and measures to control, reduce and
prevent them along with the conservation and management
of forest and water resources.

ENVIRONMENTAL POLLUTION AND MANAGEMENT

Environmental pollution is defined as the introduction of
contaminants into a natural environment that cause undesirable
change in the physical, chemical and biological characteristics
of the environment. Environmental pollution makes the
environment unhealthy for living beings. Air, water and
soil are the major components of the natural environment
that are polluted directly or indirectly due to anthropogenic
activities. There are even natural activities like the
earthquake, volcano, storms, forest fires, etc. that pollute the

New Creative Science, Class 10 | 303

environment but they have less significance in comparison to anthropogenic activities.
Environment management is an attempt to control human impact and interaction with the
environment in order to conserve environmental resources. Environmental management
requires technical, administrative and legal interventions from the local to the global level.

AIR POLLUTION

Air is a mixture of different gases like nitrogen, oxygen, carbon dioxide, argon,
water vapour, etc. in definite proportion. Introduction of air borne contaminants into the
atmosphere that cause undesirable change in physical, chemical and biological characteristics
of the environment including adverse effects in human health and quality of life is called air
pollution. Carbon dioxide, methane, oxides of sulphur and nitrogen, lead, ozone,
volatile organic compounds, aerosols, asbestos, etc. are the major air pollutants.
Burning of fossil fuels like coal and petroleum is the major cause of air pollution. Air
pollutants are released in the form of vehicular and industrial emissions, radioactive
fallouts from nuclear wastes, biomass burning, forest fires, explosions, degradation of
organic substances, etc.

Based on the mode of formation, air pollutants are categorized as primary air pollutants
and secondary air pollutants. Air pollutants that are directly released in the atmosphere
from their source are primary air pollutants. Carbon dioxide, carbon monoxide,
lead, methane, oxides of sulphur and nitrogen, etc. are primary air pollutants. Air
pollutants that are formed in the atmosphere as a result of chemical reactions between
various primary pollutants are secondary air pollutants. Peroxy acetyl nitrate (PAN),
formaldehyde, photochemical smog, ground level ozone, nitric acid, sulphuric acid
etc. are secondary air pollutants.

Sources of air pollution

Sources of air pollution are divided into natural sources and anthropogenic sources.

a. Natural sources: These are the sources of air pollution that are resulted due to
the natural processes or activities. Prominent natural sources of air pollution are
eruption of volcanoes, forest fires, salt sprays from ocean, dust storms, decay of
organic matters, etc.

b. Anthropogenic sources: These are the sources of air pollution resulted from
human activities. Vehicular and industrial emission, emission through
incineration, household cooking and biomass burning, radioactive fallouts
from nuclear power plants, accidents, explosions and testing, emission from
agriculture practices, etc. are the major anthropogenic sources of air pollution.

Effects of air pollution

a. Adverse effects in human health: Gaseous air pollutants and particulate matters
affect the respiratory system of humans and other animals and cause a number
of short term and long-term health problems. Short term health effects include
irritation to the eyes, nose and throat, and upper respiratory infections such

304 | Environmental Pollution and Management

as bronchitis and pneumonia. Headaches, nausea, and allergic reactions are
very common. Short-term air pollution can aggravate the medical conditions of
individuals with asthma and emphysema. Long term health effects can include
chronic respiratory diseases, lung cancer, heart disease, and even damage to the
brain, nerves, liver and kidneys.

b. Ozone layer depletion: Chlorofluorocarbons (CFCs) are the chief air
pollutants that are responsible for the depletion of the ozone layer. Others are
carbon-tetrachloride, methyl chloroform, methyl bromide etc. CFCs used in
refrigerators, air conditioners, spray cans after emitting into the atmosphere
releases free chlorine (Cl) radical, which involves in chain reaction and destroys
the protective stratospheric ozone. As a result, UV radiation passes through the
atmosphere and reaches the earth. UV radiation causes skin cancer, damage to
eyes and the immune system of humans, causes mutation in plants and animals
and destroys the living system.

c. Greenhouse effect: Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O),
CFCs, water vapour, etc. are greenhouse gases. Among them CO2 is increasing
at an alarming rate. These gases allows short wave solar radiation to enter the
earth atmosphere but traps the heat radiated back from the earth. This is leading
to a global environmental problem of increase in earth’s temperature called
‘global warming’. Global warming is accelerating climate change.

d. Acid Rain: Harmful gases like nitrogen oxides and sulphur oxides are released
into the atmosphere during the burning of fossil fuels. In the atmosphere water
droplets combine with these air pollutants and forms acids like sulphuric acid
and nitric acid. The acidic water then falls on the ground in the form of acid
rain. Various monuments, buildings and statues are damaged due to corrosion
by the acid present in the rain. The soil also becomes acidic. The cumulative
effect is the gradual degradation of soil and a decline in forest and agricultural
productivity. It also affects plants and animals.

e. Eutrophication: Eutrophication is a condition in which high amount of nitrogen
present in some pollutants gets developed on the sea’s and turns itself into
algae. Air pollution is also responsible for eutrophication. It adversely affects
fish, plants and animal species. The green coloured algae that is present on lakes
and ponds is due to presence of this chemical only.

f. Effect on wildlife: Just like humans, animals also face some devastating effects
of air pollution. Toxic chemicals present in the air can force wildlife species to
move to new places and change their habitats. The toxic pollutants deposit over
the surface of the water and can also affect sea animals.

g. Ground-level ozone formation: Ground-level ozone is a colourless and highly
irritating gas that forms just above the earth's surface. It is formed by the reaction
of primary pollutants; nitrogen oxides (NOx) and volatile organic compounds
(VOCs) in the presence of sunlight. Breathing ozone can trigger a variety of

New Creative Science, Class 10 | 305

health problems including chest pain, coughing, throat irritation, congestion,
permanent scar in the lung tissue, etc.

h. Reduction in visibility: Polluted air concentrated with smoke containing
particulate matters reduces visibility. Smog which is a by-product of air pollution
is also responsible for reducing visibility. It can result a road accidents, air craft
accidents and disturbs transportation.

i. Reduction in solar radiation: Particulate matters remain in the air for a longer
time. Clouds of these particulate matters block solar radiation from reaching
the earth surface. As a result, temperature drops. It affects living organisms and
even retard the growth and development of plants.

Measures to control air pollution

Some of the major measures to control and reduce air pollution and its impact on
humans and the surroundings are mentioned below:
a. Relocate air polluting industries and factories far away from the settlement areas.
b. Use air pollution treatment and control technologies like bag house, electrostatic

precipitators, cyclone filters, etc. to filter gases and particulate matters before
emitting them in the atmosphere.
c. Increase the height of the chimneys of industries and factories so that the air
current dilutes the emission high in the sky and affects less to the surrounding
areas.
d. Use public mode of transportation especially mass transportation like buses,
trains, and practice carpooling wherever possible.
e. Conserve energy by switching off the devices when not in use as most of the
electricity in the world is generated from fossil fuels and nuclear plants.
f. Emphasize the use of clean energy sources like bio-gas, solar energy, wind energy,
etc. for daily energy consumption.
g. Use energy efficient devices like LED appliances, CFL, etc.
h. Promote clean energy vehicles like electric bikes, electric cars and buses more
often than fossil fuel-based vehicles.
i. Ban the use of old vehicles and impose high taxation on fossil fuel-based vehicles.
j. Reuse, recycle or reduce the consumption of the goods as most of industrial goods
pollute air during their production.

WATER POLLUTION

Water pollution is any change or modification in the physical, chemical and biological properties
of water that will have a detrimentals consequence on living things, especially on human
health and wellbeing. Water pollution occur when pollutants are discharged directly or
indirectly into water bodies without enough treatment to get rid of harmful substances.
There are both natural and anthropogenic causes of water pollution but pollutants
get into water mainly by anthropogenic causes or factors. Plants and animals require
water that is moderately pure, and they cannot survive if their water is loaded with
toxic chemicals or harmful microorganisms.

306 | Environmental Pollution and Management

Sources of water pollution

There are a number of natural and anthropogenic activities that cause water pollution.
However, pollutants from anthropogenic activities are the major sources of water
pollution. The prominent sources of water pollution are described below.

a. Domestic waste water and sewage: Domestic waste water includes water from
the kitchen and washing utilities. Such water is rich in cleansing chemicals
like soap, detergents. These chemicals deteriorate the chemical and physical
properties of water when it reaches water bodies. Household sewage contains
waste organic matter and lumps of micro-organisms in it. When sewage gets into
water bodies, micro-organisms spread in those water bodies and pollutes water.
Drinking water from such sources without treatment causes infectious diseases.

b. Industrial effluents: Industrial effluents are rich in numerous chemicals that are
byproducts of various industrial processes. Chemicals can be acids, bases, toxic
chemicals, heavy metals (mercury, lead, cadmium, etc.) etc. These chemicals
pollute water and cause different diseases to us when such water or aquatic
beings from such water are consumed. They also destroy physio-chemical
properties of water.

c. Agriculture chemicals: Fertilizers, insecticides, pesticides, herbicides, fungicides,
etc. are agriculture chemicals. Rainfall washes these chemicals from agriculture
fields and produce agricultural runoff which discharge water into nearby water
sources. These chemicals pollute water and may remain in water for longer
time causing long-term pollution. Pesticides like DDT (Di-chloro-di-phenyl-tri-
chloro-ethane), BHC (Benzene Hexachloride), Aldrin, Dieldrin, Carbosulfan,
Endosulfan, Malathion, etc. are toxic to human health, as well as terrestrial and
aquatic life forms.

d. Surface runoff: Surface runoff along with agricultural chemical carries
soluble and insoluble organic wastes, chemical substances, dust and dirt from
settlements and built up areas into water bodies. Turbidity is the major natural
water pollution resulted by solutes and suspended particles due to runoff. Urban
runoff sweeps different types of wastes into water sources. Concentration of
various pollutants from runoff in lakes and obstruction in flow of water also
causes water pollution.

e. Oil and petroleum: Oil and petroleum products pollute water bodies mainly
by means of accidental spills from ships, tanker trucks, pipelines, and leaky
underground storage tanks. Oil spills form a layer of oil in the upper surface
of water bodies obstructing the interaction of oxygen in water bodies. Oil
and petroleum products are poisonous if ingested by animals. Spilled oil also
damages feathers of birds and the fur of animals, often causing death.

f. Heat: Heat is the waste byproduct in many industrial processes. Water is used
as a coolant in such industrial processes, which increases the temperature of
water. Such heated water when discharged into water bodies affects the aquatic

New Creative Science, Class 10 | 307

life as most aquatic animal respond quickly in increased temperature. Warmer
water also holds less oxygen.

g. Radioactive substances: Uranium, radium, thorium, plutonium, etc. are
radioactive substances that produce radiations harmful to humans and other life
forms. Nuclear power plants and nuclear test programs are the major sources
of radioactive substances. These substances or traces of these substances even in
the form of nuclear waste pollutes water with nuclear radiations.

Measures to control water pollution

Water pollution can be controlled to a large extent on the principle, “the solution
to pollution is dilution.” The various methods for the control of water pollution are
discussed below:
a. Domestic waste water and sewage are subject to treatment into non-toxic/ less

toxic substances before discharging it into water bodies.
b. Target organism specific or less toxic or reduced pesticides uses or biological

control mechanism can be prioritized in agricultural activities.
c. Both domestic and industrial effluents can be stored in large shallow ponds for a few

days before releasing them into water bodies. Sunlight can break organic nutrients
and bacteria get adequate oxygen for decomposition of harmful organic matter.
d. Water from domestic uses can be recycled to get clean water for flushing, cleaning,
irrigating or can be reused directly for irrigating small household gardens.
e. Water cooling ponds can be used before discharging hot industrial water into
regular water bodies.
f. Oxidations ponds can be useful in removing low level of radioactive wastes before
discharging them into water bodies.
g. Awareness should be made regarding waste management especially disposal of
dead and decayed organic waste far from water sources.
h. Regular cleaning of nearby water bodies and maintaining proper sanitation
should be ensured.
i. Enactment of law and orders especially against mass water polluters should be
enforced.

SOIL POLLUTION

Soil is the uppermost layer of the earth’s crust composed of unconsolidated products
of rocks erosion and organic decay along with microorganisms. A typical soil is
composed of mineral matter (45%) and organic matter (5%) with pore space filled with
water (25%) and or air (25%) and soluble nutrients. Soil is an abiotic component of
the ecosystem, which supports plant growth on which all microscopic to macroscopic
life forms depends directly or indirectly. Soil pollution is the contamination of soil with
harmful substances that can adversely affect the quality of the soil and the health of those living
on it. Soil pollution results in the degradation of the physio-chemical and biological
properties of the soil. It finally hampers the growth and development of all life forms
including human beings.

308 | Environmental Pollution and Management

Source of soil pollution

Soil can be polluted by both xenobiotic (man-made) or natural sources. However,
the activities of human beings have disturbed a number of processes and cycles that
recycle nutrients in the soil causing pollution of soil. Some of the major sources of soil
pollution are given below.

a. Domestic waste: Waste foods, packages, paper waste, clothes, plastic, sewage,
etc. are domestic wastes. When such wastes are improperly disposed, it results in
soil pollution. Degradable domestic waste spreads harmful microorganisms that
affect both plants and animals in the soil including humans. The accumulation
of non-degradable waste on the land surface hampers plant growth and causes
degradation in soil productivity.

b. Commercial waste: Apart from the domestic waste, a large amount of waste is
produced from commercial centers like shopping malls, hotels and restaurants,
recreational parks, cinemas, etc. The waste consists of dried sludge and sewage
and urban refuse such as plastics, glasses, metallic cans, fibres, paper, rubbers,
street sweepings, fuel residues, leaves, containers, abandoned vehicles and other
discarded manufactured products. Leakey sewer systems can pollute soil on its
way to treatment centers. Urban refuse does not degrade easily and therefore
degrades the land where it is disposed of.

c. Agricultural practices: Modern agricultural practices use a large quantity of
synthetic fertilizers, insecticides, pesticides and fungicides to increase crop
harvest. However, the excessive and the long-term use of chemical fertilizers
changes the physical and chemical properties of soil and it even causes permanent
loss of productivity. Pesticides like DDT, parathion, malathion, BHC, Eldrin,
Carbosulfan, etc. persist on land for long periods. They not only kill the targeted
organism but also destroys the soil microorganisms. They do not degrade easily
and retard the growth of beneficial microorganisms and plants in the soil.

d. Industrial activity: Besides, management of domestic and commercial waste,
there is a big challenge to manage industrial waste. Rapid industrialization has
produced more chemical waste along with goods and services. These waste
ranges includes, dirt, toxic metals, plastics and other liquid toxic chemical.
All this waste on disposing on any land surface degrades the quality of land
beyond its use for any purpose. Mining of minerals for industrial activities has
also resulted in large surface of land unusable for other activities. This toxic
waste when reaches agricultural land by any means results in enormous loss in
production as wells as numerous disorder in crops.

e. Construction and demolition activities: Construction of new infrastructures on
the one hand degrades the soil usability by concrete pavements. While, on the
other hand, it results in concrete waste that clogs soil pores and destroys its
physical, chemical as well as biological properties. Apart from this demolition of
large buildings, nuclear facilities and industries have resulted in the degradation
of soil.

New Creative Science, Class 10 | 309

f. Accidental oil spills: Accidental oil spills especially the petroleum products
result in quick loss of soil characteristics including its productivity and usability
for other purposes. Accidental spills alter the chemical properties of soil, kill soil
organisms and plants and decrease soil productivity.

g. Hazardous waste: Dumping of toxic waste form pharmaceutical facilities,
battery industries, and hospitals also degrade soil quality and this may happen
for a long period. This hazardous waste first destroys the soil organisms and
plants or forces them away and gradually alters the physio-chemical properties.

h. Acid rain: Acid rain dissolves a number of soil nutrients from soil and causes
them to infiltrate deep down the soil strata or washes them away. It increases
acidity in the soil and hence decreases the productivity of soil.

i. Heat and radiation: Heat and radiation through nuclear tests, blasting, warfare
bombardments, etc. is also one of an major causes of soil pollution. Every year
thousands of hectares of lands from the world become a rubble or are barren
as a result of nuclear tests, bombardments or warfare consequences. Heat and
radiations result in immediate and long-term damage to soil properties.

Measures to control soil pollution

The activities of humans are the major sources of soil pollution and also humans are
the ultimate living beings to bear its consequences. The basic measures mentioned
below are need to be applied to control soil pollution and get less affected from its
consequences.
a. Recycle, reuse, reduce and repair are the most basic principle to get rid from

management of excess soil polluting domestic and commercial wastes.
b. Human sewage needs to be properly treated and nutrients can be recycled

before disposing them of in ponds or water bodies.
c. Sanitary landfilling, incineration, etc. should be used for conserving energy.
d. Sanitary landfill sites can be used as sports fields, recreational parks after their

life span.
e. Irrigating agricultural land through polluted water should be discouraged.
f. Organic manure, natural fertilizers and bio-pesticides need to be prioritized and

practiced and chemical fertilizers and pesticides should be gradually reduced.
g. Soil should be conserved by conserving forest, afforestation and providing

various engineering measures like embankments, walls and dams should be
checked wherever necessary.
h. Nuclear waste and other hazardous wastes should be safely managed beyond
the level of soil contamination.
i. Public should be regularly made aware through mass media regarding
management of their own waste and to treating them at the source level.
j. Worldwide banned toxic chemicals like DDT, cabosulfan, parathion, eldrin,
dieldrin, etc. should be extensively restricted for use by enacting law and order.

310 | Environmental Pollution and Management

CONSERVATION AND MANAGEMENT OF FOREST AND WATER SOURCES

Conservation and Management of Forest

Forest provides fresh oxygen to living organisms. Most of the human needs like food,
clothes, houses, water, etc. are derived or obtained directly from forest resources.
Forest is the habitat of numerous flora and fauna which are the resources for welfare
and development of human society. Forest also regulates the climate of a place. Soil
nutrients reach agricultural lands and river basins as decayed and decomposed organic
materials washed away by runoff from forest. Forest also checks the ground water
level from presenting it drop down below. Forest also checks soil erosion, landslide,
etc. Forest also acts as a sink for carbon dioxide, which is a major greenhouse gas.
Therefore, forest has numerous advantages to human and other life forms. Therefore,
forest needs to be conserved and managed well.

Some of the successful measures for the conservation and management of forest are
listed below:

For the conservation of forests, following steps can be taken:
i. Applying scientific forest management techniques of the cutting of trees
like clear cutting, selective cutting, shelter wood cutting, etc.
ii. Control over forest fires
iii. Reforestation in deforested areas and afforestation in unused or degraded
lands and their conservation
iv. Check over forest clearance for agricultural and other purposes
v. Proper utilization of forest product
vi. Redefining land use policies and provisions as per global and local
environment needs
vii. Enactment of law and order

Conservation of water resources

Water is another important natural resource for humans. It is also one of the most
essential abiotic components of the environment. About 71% of the earth surface is
covered by water but still water is not accessible to all people. Out of total water in
the earth surface, 97% water is salt water of the sea and ocean which are not usable
for human purposes. Remaining 3% is only fresh water resources, out of which 2%
of water stored in icebergs and the remaining 1% water resources supply water to
the world’s population. This 1% water which is distributed as water in ponds, lakes,
streams, and ground water is used for all human activities. Drinking, sanitation,
irrigation, hydropower production, industrial utilities, etc. all need water. Therefore,
water resources should be conserved properly. Some of the measures for conservation
of water resources are mentioned below:

i. Provide awareness to people for behavioural change in conserving water
through small efforts like reducing unnecessary water use, using water
efficiently, etc.

New Creative Science, Class 10 | 311

ii. Conserve watersheds by maintaining forest and check erosion, landslide
and deforestation in the watershed.

iii. Treat municipal and industrial effluents to at least a minimum acceptable
level before draining them into water bodies.

iv. Apply scientific irrigation techniques like drip irrigation, sprinkle
irrigation to avoid excess loss of water in agricultural fields.

v. Use waste water from the kitchen and other domestic processes in kitchen
garden.

vi. Trap rainwater to recharge ground water by constructing ground water
recharging pits, and harvesting rain water from roofs and floors into
household tanks for future use.

vii. Reduce or control the production of pollutants that are responsible for
water pollution and maintain sanitation around water sources.

SUMMARY

 There are other natural activities like the earthquake, volcano, storms, forest fires etc. that
pollute environment but they have less significance in comparison to anthropogenic activities.

 Carbon dioxide, methane, oxides of sulphur and nitrogen, lead, ozone, volatile organic
compounds, aerosols, asbestos, etc. are the major air pollutants.

 Natural sources like the volcano, forest fires, salt sprays from the ocean, etc. and anthropogenic
sources like vehicular and industrial emission; emission through incineration, household
cooking and biomass burning etc. pollute air.

 Major effects of air pollution are health of humans and animals, ozone layer depletion,
greenhouse effect, acid rain, reduction in visibility, etc.

 Use of clean energy, prioritizing public transportation, energy conservation, effective application
of air pollution control technologies in industries, etc. can control air pollution.

 Domestic waste water and sewage, industrial effluents, agriculture chemicals, surface runoff,
oil and petroleum, heat and radioactive substances are sources of water pollution.

 Treat of waste water and sewage and industrial effluents before discharging in water bodies;
reduction in use of chemical fertilizers and pesticides in agriculture; recycling domestic waste
water for flushing, cleaning, irrigating home garden, etc. can control water pollution.

 Various domestic waste, commercial waste, agriculture practices, industrial activities, construction
and demolition activities, oil spills, hazardous waste, etc. are the sources of soil pollution.

 Safe disposal of sewage and industrial effluents, sanitary disposal of wastes, reduction in the
use of chemical fertilizers and pesticides, proper land use planning, etc. can control soil pollution.

 Forest can be conserved and managed by applying scientific forest management techniques,
afforestation and reforestation, control forest fires, reducing forest clearances and enactment
of the law.

 About 97% of the earth’s water is salt water and only about 3% is fresh water usable for
humans. Out of 3% fresh water only 1% is distributed as ground water and surface water for
our uses while the remaining 2% is stored in icebergs and therefore is not accessible.

 Measures like efficient use of water, recycling of waste water after treatment, maintaining
watershed, applying scientific method of irrigating water, harvesting of rain water, etc. can
conserve water resources.

312 | Environmental Pollution and Management

EXERCISE

1. Define the following terms.

(a) Environmental pollution (b) Environment management

(c) Air pollution (d) Eutrophication

(e) Water pollution (f) Soil pollution

2. Differentiate between:

(a) primary and secondary pollutants

(b) air pollution and water pollution

(c) acid rain and greenhouse effect

3. Give reasons.
(a) Sulphuric acid is a secondary air pollutant.
(b) Acid rain decreases soil productivity.

4. Answer the following questions.
(a) Name any two natural sources and any four man made sources of air pollution.
(b) List any six effects of air pollution.
(c) Name any three ozone depleting air pollutants.
(d) What do you mean by greenhouse gases? Name them.
(e) List any six measures to control air pollution.
(f) Mention the sources of water pollution.
(g) How can water pollution be controlled? List some measures.
(h) How do agricultural activities does pollute soil.
(i) Write down the major sources of soil pollution.
(j) Write some measures to control soil pollution.
(k) What are the necessary steps for forest conservation and its management?
List them.
(l) How can water resources be conserved? Mention possible measures.

ACTIVITY

1. Prepare a detailed report of water pollution in your surroundings. In the report, list the local
sources of water pollution, its effects on the surrounding environment and measures taken
to control it through little efforts of local people and local bodies.

2. Climate change is the burning global environmental issue. Prepare a brief report listing its
causes and effects. Take help from news, newspapers, magazines and other available sources
of information.



New Creative Science, Class 10 | 313

UNIT

21 History of the Earth

About the Scientist INTRODUCTION

Charles Darwin The earth is the only planet in the solar system, which
(1809-1882) has the suitable condition for life such as suitable climatic
condition, temperature, pressure, air, water, etc. Thus, only
Charles Darwin set on a voyage, the earth, among all the heavenly bodies of the solar system
at the age of 22, on the ship has life in it. ‘Geology’ is the branch of science which deals
H.M.S. Beagle. Five-year with the study of the earth.
voyage from 1831 to 1836 took
him to South America and the There are many queries about the origin of the earth
Golapagos islands off its coast. but till now no one has given the satisfactory view about
During his survey expedition, it. However, many scientists have proposed their own
he made extensive observations hypothesis about the origin of the earth linking it with the
of animals and plants. He noted origin of the solar system as the earth being a member of the
a huge variety of life and also solar system. Some hypotheses about the origin of the earth
remarkable similarity among are described below.
organisms and their wonderful
adaptation to the environment. (1) Planetesimal hypothesis (George Wofan hypothesis)
After completing his voyage,
Darwin returned to England, According to this hypothesis, the earth along with other
stayed at home, and analysed the planets and satellites were formed when a large comet
observations of nature during his collided with the sun millions of years ago.
voyage. He also read population
theory given by Malthus. His Later in 1905, New planetesimal hypothesis was formulated.
observations during the voyage According to this hypothesis, the sun and the comet did not
and population theory of collide but they only came closer to one another. And as they
Malthus led him to formulate came together, due to the gravity of the comet, the materials
Darwin’s theory of natural raised from the sun and these materials broke away from
selection. He gave his theory in the sun and formed different heavenly bodies along with
his book entitled ‘The origin of the earth.
species’. He did not know the
mechanism whereby variations (2) Nebular hypothesis
arose in the species. He was also
not aware of Mendel’s work on According to this hypothesis, the origin of the earth and
inheritance. Besides theory of other heavenly bodies took place from Nebula.
evolution, Darwin also studied
the role of earthworms in soil Nebula is a very huge mass of dust, cloud and gases in the space.
fertility.
It states that, “the nebula in the sky began to collide with
one another due to gravity and it became larger due to the
accumulation of more masses, gases and clouds. As their
mass increased, their gravity also increased. Due to this,

314 | History of the Earth

they grew up and began to spin faster. When the surface was cooled, a ring of matter
was formed over the surface and the ring detached and became the heavenly bodies.
The core mass became the sun.

(3) Tidal Hypothesis

The tidal hypothesis was proposed by Jeans and Jeffreys in 1917 A.D. It states that, “as
the sun and a big star approached each other due to the gravity of the star, a tide of
materials of the sun was drawn from it. The tidal matter detached and the inner part
came back into the sun. The middle part formed planets and satellites.

(4) Dust-cloud hypothesis

According to this hypothesis, the dust and clouds of gases in the space formed larger
particles due to the light of the star. These large particles were attached to each other
by gravity and a large mass was formed. This mass is the sun. The nuclear reaction
started and it began to produce solar energy. The dust and cloud around the sun
formed the planets and other heavenly bodies.

Some facts about the Earth

Estimated age = about 4500 million years ago (4.5 billion years ago)

Diameter along equator = 12,756.3 km

Mass = 6 × 1024 kg

Satellite = 1 (Moon)

Average surface temperature = 20°C Source: The World Book Encyclopedia

GEOLOGICAL TIME SCALE

The total time of the earth’s history from its origin to the present days is called geological time
scale. It is divided into four types of time periods according to the origin of species i.e.
(I) Eon (II) Era (III) Period and (IV) Epoch

(I) Eon

It is the largest unit having more time period. It is divided into three parts as,
(A) Azoic Eon
(B) Cryptozoic Eon
(C) Phanerozoic Eon

(A) Azoic Eon

Its time period is 3500 my to 4500 my ago (my = million years). No life was originated
in this Eon.

(B) Cryptozoic Eon

It was extended in between 570 my ago to 3500 my. It is further divided into two eras. i.e.
(a) Archaeozoic era (2500 my ago – 3500 my ago)
(b) Proterozoic era (570 my ago – 2500 my ago)

New Creative Science, Class 10 | 315

These two eras are jointly known as pre-cambrian era. In Archaeozoic era, marine
invertebrates were formed among which few were containing shells. In Proterozoic
era, earliest plants like marine algae were formed. In this era, Gneiss and Granite rocks
were found.

(C) Phanerozoic Eon

This Eon started 570 my ago and it is present till now. A variety of plants and animals
originated and disappeared in this Eon. It is again divided into three Eras.

(a) Palaezoic Era: This Era began about 570 million years ago and ended about 225

million years ago. It is again divided into seven periods. They are

(i) Cambrian (ii) Ordovician (iii) Silurian

(v) Mississippian (vi) Pennsylvanian (vii) Permian

(iv) Devonian

The origin of fishes, amphibians and reptiles took place in the various periods of

this era.

MEMORY TIPS
Palaeozoic era is also called time of fish as they were dominant in this era.

(b) Mesozoic Era: It began about 225
million years ago and ended about
65 million years ago. This era is
again divided into three periods as,
(i) Triassic period
(ii) Jurassic period
(iii) Cretaceous period

This era was the time of reptiles because

in this era, reptiles were abundant.

Dinosaurs were originated in the Triassic Different types of dinosours

period; they were at their peak in Jurassic period and they become extinct in the

cretaceous period of this era.

First birds and mammals were formed during this time and conifers were also formed.

(c) Cenozoic Era: This era began about 65 million years ago and is still continuing.

It is divided into two periods:

(i) Tertiary period and

(ii) Quaternary period

(i) The Tertiary period lasted until 2 my ago. It is divided into 5 epochs. They are

1. Paleocene 2. Eocene 3. Oligocene

4. Miocene 5. Pliocene

316 | History of the Earth

(ii) The Quaternary period is again divided into two Epochs. They are

1. Pleistocene 2. Holocene

Birds and mammals along with human civilization developed in this era (Cenozoic).
The evolution of life in various time periods is given in the chart below.

Geological Era and Evolution of Life

Era Duration (years) Manifestation of life
Evolution of the Earth
Azoic or Evolution of the
Archaeozoic, Earth to 570 million
or Pre- (57 crore) years ago
Cambrian

Evolution of very simple unicellular micro-organism

Discovery of fossils of soft bodied invertebrates

Some marine animals

570 million years Different marine invertebrates
ago to 250 million
Evolution of green plants and fishes
Palaeozoic years ago

(57 crore years ago to Evolution of winged insects, development of fish
25 crore years ago) and evolution of plants

Evolution of reptiles and amphibians, evolution and
development of pteridophytes

Extinction of different vertebrates and invertebrates

250 million years Evolution of dinosaurs aves, turtles, reptiles,
ago to 65 million development of conifers

Mesozoic years ago Dominance of reptiles development of dinosaurs
Cenozoic
(25 crore years ago and aves

to 6 crore 50 lakh Evolution of angiosperms, and different arthropods
years ago) and extinction of dinosaurs and huge reptiles

Evolution of primary mammals and horses

Growth of different mammals, like owls, crocodiles,
bats, elephants, whales

65 million years ago Evolution of sharp teethed cats, rats, dogs and

to till today monkeys

(6 crore 50 lakh years Development of herbs and grasslands
ago to till today)
Evolution of ancient human beings

Primitive human beings, mammoths

Modern human beings other mammals, human
dominance

New Creative Science, Class 10 | 317

MEMORY TIPS

In Azoic era, there were no sedimentary rocks, indicating that no evolution of prominent life
had taken place in this era.

a) 'Epoch' are not the sub-division of 'periods'. They are the synonims of 'Era'.For eg.:

Azoic Era → Precanbrian Eopch (4500 m.y.ago to 570 m.y.ago)
Primary Epoch (570 m.y.ago to 240 m.y.ago)
Palaeozoic Era →

Mesozoic Era → Secondary Epoch ( 240 m.y.ago to 65 m.y.ago)
Cenozoic Era → Tertiary Epoch (65 m.y.ago to 1.8 m.y.ago)

Neozoic Era → Quaternary Epoch (1.8 m.y.ago to recent)

b) Azoic Era has 3 periods, i.e.

i) Proterozoic period (4500 m.y.ago to 3500 m.y.ago)

ii)Archeozoic period (3500 m.y.ago to 1000 m.y.ago)

iii) Eozoic period (1000 m.y.ago to 570 m.y.ago)

c) Palaeozoic Era has only 6 periods. They are Cambrian, Ordovician, Silurian, Devonian,
Carboniferous and Permian

But, Mississipian and Pensylvanian are only the sub-periods of Carboniferous period.

Therefore, the geological time-scale is : Eon → Era or Epoch → Period

d) Many fishes were/are much bigger and powerful than amphibians, therefore
palaeozoic Era is considered as the era of Fishes, not of Amphibians.

e) Because of historical and modern human's activities like standing on two legs, using
tools, fire and other things, the Quarternary Epoch (Pleistocene and Holocene
periods) is/can be kept in separate era called Neozoic Era.

ACTIVITY

Choose a nearby land or forest or a river near your locality. Find out the changes that took place
(asking your elders) in this place and write a report.

QUESTIONS
# Which period is known as ‘time of fishes’. Why?
# Why is the Mesozoic era known as the time of reptiles?
# When were human beings originated on the earth?

EVOLUTION OF LIFE

The earth is 4.5 billion years
old. And it is expected to last for
another 4.5 billion years. When
the earth first originated, it was
hot and molten. There was a large
ocean of molten rocks but no water,

318 | History of the Earth

oxygen, ozone or life on it. Over millions of years, the earth slowly started to cool
down. Millions of comets carrying ice crystals struck the earth forming oceans. In the
Pre-Cambrian Eon, the ocean along with hot chemical soup at its floor allowed the first
prokaryotic life- a bacterium to form about 3.8 billion years ago. These bacteria lived
in colonies and were called stromatolites. They started photosynthesis and produced
huge amount of oxygen. Slowly, life started evolving. Algae evolved and dominated
the oceans about 3.2 billion years ago.

Then, for the first time, marine invertebrates evolved in the Paleozoic era. Some of
them were called trilobites, brachiopods, etc. Gradually, the ocean was full of marine
invertebrates. These marine invertebrates slowly evolved into marine vertebrates and
terrestrial organisms. In the Paleozoic era, green plants and forests formed on the
land. The small-sized different fishes and several creatures were evolved. Most of the
animals were extinct towards the end of the Paleozoic era in the Permian period due
to volcanic eruption and low temperatures in Polar Regions.

After millions of years, again in the Mesozoic Era, large reptiles evolved and ruled the
world. Dinosaurs were dominant. There were flying dinosaurs, carnivore dinosaurs
and herbivore dinosaurs and so on. But, at the end of the Mesozoic Era, in the
Cretaceous period, a large meteorite struck the earth and killed all the dinosaurs. Only
few small organisms living on land, oceans and underground survived. After that,
flowering plants, arthropods and small mammals were evolved.

These few organisms evolved to form large mammals. For the first time, in the
Cenozoic era, in the Paleocene epoch, large mammals evolved. There were whales,
horses, rats, cats and then in the Pliocene epoch, ancient human beings evolved. These
ancient human beings looked like humans partially. Finally, in the Holocene epoch,
the modern man evolved. The scientists believe that humans first originated in Africa
and then moved to Asia, America and Europe. As there were several kinds of highly
developed large mammals in the Cenozoic era, it is also called the Era of mammals. It
is evident that the evolution of organisms is an ever going process.

FOSSILS

The remaining parts of dead
plants and animals or their
impressions which are buried
and preserved in the Earth’s
crust over a long period of
time are called fossils.

Most of the fossils are
found to be preserved in the
sedimentary rocks.

New Creative Science, Class 10 | 319

Fossils

Identification of fossils

Fossils can be identified by comparing them with different shapes and parts of the
organs. They can be identified as,
(i) They are usually found in the sedimentary rocks.
(ii) The fossils may be only the impression or the whole body part.
(iii) They may be in the form of mould.
(iv) We can see the hard covering of animal shells and inner wood of plants in the

sedimentary rock.
(iv) Fossils may be a part of the skeletal system or the whole body. From these

structures, we can identify them.

Process of fossil formation

Fossilization is the process of formation of fossils from the dead plants and animals.

Fossilization

320 | History of the Earth

When an organism dies, its soft part gets decayed due
to the bacterial action or consumed as food by other
scavengers and its hard part may be preserved inside the
soil, which later forms fossils.

Due to the natural disasters like the volcano, earthquake, flood, etc. plants and animals
may sink to the earth’s surface, where they are preserved from bacterial decomposition
and they form fossils.

When living beings die near the water source, the debris cover the organism layer by
layer preserving it. It also helps to form fossils.

New Creative Science, Class 10 | 321

QUESTIONS
# How do fossils form layer by layer?

Let us start 100 million years ago, some invertebrates on the sea-bed die and are buried
in the sand. More sand accumulates and sand stone forms under pressure.

Millions of years later, dinosaurs living in the area die and their bodies too are buried
in the mud. This mud is also compressed into rocks, above the rock containing the
earlier invertebrate fossils.

Again millions of years later, the bodies of horse-like creatures dying in the area are
fossilised in rock above these earlier rocks.

Much later, by erosion or water flow wears away some of the rocks and exposes the
horse like fossils. As we dig deeper, we will find older and older fossils.

Importance of fossils

The importance of fossils are listed below:
(i) The study of fossils helps us to know about the process of evolution in the

organisms.
(ii) They give us information about plants and animals, which were found on the

earth but are now extinct.
(iii) Some fossils are used to get energy, which are called fossil fuels.
(iv) The study of fossils helps us to investigate the deposits of coal and petroleum

inside the earth’s crust.
(v) They help to determine the comparative age of rocks, etc.

Fossil fuels

The fuels formed by the process of fossilization are called fossil fuels. Coal, petroleum,
natural gases are fossil fuels.

Coal

It is a black or brown carbonaceous deposit formed from plant fossils. It is found in the form

of a black hard solid taken out by mining. There are four types of coals according to

the amount of carbon content. They are:

(1) Lignite (2) Sub-bituminous (3) Bituminous (4) Anthracite

Out of them, anthracite is the best quality and lignite is the lowest quality of coal.

Formation of coal

Coal is formed from dead plants and animals. When plants and animals get buried
inside the earth’s crust due to the natural disasters like the earthquake, volcano, etc, these
remnants get pressed under high pressure and temperature for a long time and form
coal. The principal parts of the plants are cellulose and lignin. Lignin plays an important
role in the formation of coal as it contains protein, oil, organic acids mineral oils, etc.

322 | History of the Earth

MEMORY TIPS
A coal mine is found in the Dang district of Nepal.
Importance of coal
(i) It is used as fuel in railways, industries, brick factories etc.
(ii) It is used to generate electricity.
(iii) Coal tar obtained from coal is used in the manufacture of plastic.
(iv) It can also be used to make mineral fuels.
(v) It is used in steam engines to change water into steam.
(vi) Coal is also used to prepare various organic compounds.
Mineral fuel
Mineral fuel refers to the petroleum. It is a type of crude oil. It is a highly combustible
substance formed by hydrocarbons (90-95%) and other substances like N2, O2, S and
other minerals.
Formation of mineral oil
Mineral oils are formed due to the death, decay and decomposition of soft part of
plants and animals, which were buried under the earth crust millions of years ago. It
is a dark coloured liquid.
This liquid is taken out and purified to get various petroleum products.

Pipes to take out oil and gas

Hard rock
Gas

Oil
Water

Sand rock and gravel

Formation of mineral oil

Importance of mineral oil
(i) It is used as fuel for cooking food, generating electricity running vehicles,

industries, factories, etc.

New Creative Science, Class 10 | 323

(ii) It is used for making plastics, chemical fertilizers, pesticides, paints, explosives,
medicines, etc.

(iii) It is used for the construction of roads.
(iv) It is also used as a lubricant.

Some Petroleum Products and Their uses

SN Petroleum Products Uses

1. Petroleum gas It is used as a fuel for cooking, heating and lighting.

2. Petroleum ether It is used as a solvent to dissolve various substances and for
cleaning purposes.

3. Petrol It is used as a fuel in vehicles, generators, etc.

4. Diesel It is used as a fuel in the heavy vehicles, to generate electricity, etc.

5. Kerosene It is used as a domestic fuel for cooking, heating and lighting.

6. Lubrication oil, They are used to reduce friction in vehicles, engines, etc.
Grease, Vaseline

7. Paraffin wax It is used to make candles, matchsticks, laboratory trays, etc.

8. Petroleum coke It is used as a fuel

MEMORY TIPS
Petroleum products are a non-renewable source of energy. So, they should be used wisely.

ACTIVITY

Take a small paper box. Pour the solution of plaster of Paris (2CaSO4 . H2O). Put a part of the plant
like the root, stem or leaf. Again, put the solution of plaster of paris over it. When the solution sets
hard, take out the upper part and see; how can you explain this process?

MODEL QUESTIONS ANSWER

1. The earth originated about 4500 million years ago but human beings originated
about 2 million years ago only. Why?

Ü It is because, at the time of the origin of the earth, it did not have the atmosphere
and suitable conditions for life as it is in the present time. Thus, no organisms
were originated in along with the earth. But later, simpler organisms originated,
which gradually evolved to the higher form, and finally the highly developed
man originated about 2 my ago.

2. Mesozoic Era is called ‘the time of reptiles’. Why?

Ü It is because in this era, reptiles were abundant in the earth. The largest reptilia,
i.e. dinosaurs also originated in this era. The dinosaurs originated in the Triassic,
era reached in their peak in the Jurassic era and become extinct in the cretaceous
period of the same era.

324 | History of the Earth

3. Fossils are found in sedimentary rocks only. Why?
Ü Sedimentary rocks are formed due to the sedimentation of the sand and mud

from layer to layer. In course of its formation, it may trap and preserve the parts
of dead plants and animals, which remain as fossils. So fossils are found in
sedimentary rocks only.

4. Which eras are known as the ‘time of fish’ and ‘time of mammals’?
Ü Palaeozoic Era and cenozoic era are known as the ‘time of fish’ and the ‘time of

mammals’ respectively.

5. Fossils help to provide the evidence of evolution. How?
Ü By the study of fossils, we can say about the morphology, shape, age and size

of that organism. It is found that older fossils are found at the bottom layer and
new fossils are found at the top of the sedimentary rocks. From the comparative
study of their fossils, we can trace the evolution of an organism.

6. In which time period did the following events take place?

(a) Human beings originated.

(b) First amphibians originated.

(c) Dinosaurs were in their peak.

(d) First primates and horses originated.
Ü a) Pliocene period, tertiary epoch, cenozoic era, phanerozoic eon.

b) Devonian period, palaeozoic era, phanerozoic eon.

c) Jurassic period, mesozoic era, phanerozoic eon.

d) Paleocene period, tertiary epoch, cenozoic era, phanerozoic eon.

SUMMARY
 There are many hypotheses about the origin of the earth but non of them are really convincing.
 Planetesimal, nebular, tidal and dust-cloud hypotheses are some of the hypotheses given for

the origin of the earth.
 The branch of science which deals with the study of the earth is called geology.
 The geological time period is divided into eon, era, period and epoch.
 The eras in geological time scale are azoic, palaeozoic, mesozoic, and cenozoic (neozoic)
 Life was originated on the earth in the archeozoic period.
 The mesozoic era is called the time of reptiles.
 The cenozoic era is called the time of mammals.
 The palaeozoic era is called the time of fishes.
 Fossils are the remnants or impressions of dead plants and animals preserved inside the earth.
 Fossils support evolution and help to know about the plants and animals which have been extinct.
 Coal and mineral oil are called fossil fuels.
 Fossils are formed inside the earth’s crust under high temperature and pressure.
 They have various uses.

New Creative Science, Class 10 | 325

EXERCISE

1. State the planetesimal hypothesis and Kant’s hypothesis about the origin of the
earth.

2. How was the solar system originated according to the nebular hypothesis?
3. Define the geological time scale. How is it divided?
4. Write the major events that took place in the palaeozoic era.
5. Differentiate between

(a) Cenozoic era and Mesozoic era
(b) Palaeozoic era and Mesozoic era
6. Which era is known as the ‘time of reptiles’? Why?
7. Define fossils. How can you identify them.
8. Write the importance of fossils.
9. How are fossils formed? Describe.
10. How is coal formed?
11. Give three advantages of coal.
12. Define mineral fuel. Write its uses.
13. Why was life not possible in the azoic era?
14. Dinosaurs became extinct in the cretaceous period of the Mesozoic era. Why?
15. How do fossils give the evidence of evolution?
16. In which time periods did the following events take place?
(a) First fishes originated
(b) Conifers appeared on the earth.

(c) Development of human civilization

17. In which period are we living now?

A

B GLOSSARY
C

Planetesimal : the broken and shrunk solid particles from the sun from which planets are thought to be
Hypothesis formed

: an idea based on few facts but has not yet been proved to be true

Geological time : the time period of the earth

Mining : the process of getting coal and other minerals from under the ground

Encyclopedia : a book of set of books giving information about all areas of knowledge

Assortment : a collection of different things or different types of something



326 | History of the Earth

UNIT

22 Climate Change and Atmosphere

About the Scientist INTRODUCTION

Tycho Brahe The earth’s environment has three parts. They are
(1546-1601) atmosphere, hydrosphere and lithosphere. The atmosphere
extends over about 1600 km from the earth's surface.
Johannes Kepler
(1571-1630) Thus, the atmosphere is the thick layer (but thin in comparison
to the radius of earth like peel of an orange) of different gases
Danish astronomer Tycho Brahe surrounding the earth from all the sides. It consists of 78% of
made accurate observations N2 gas, 21% of oxygen gas, 0.3% of CO2 gas by its volume and
of the night sky. He also built the remaining percentage of other gases and water vapour.
the world’s first observatory The gravity of the earth holds the atmosphere towards it. It
and identified over 1000 stars. makes life possible on the earth, protects us from harmful UV
Tycho’s accurate measurements rays of the sun, maintains rain, etc.
later helped Johannes Kepler
to describe the orbits of planets The external part of the earth is divided into three major
around the sun regions. They are atmosphere, hydrosphere and lithosphere.
The lithosphere is the land part of the earth. Similarly, the
hydrosphere is the water part and the atmosphere represents
the air part. The atmosphere is a gaseous envelop of the
earth. In the atmosphere, there are many gases. These gases
make a homogeneous mixture. The changes in atmosphere,
lithosphere and hydrosphere are responsible for the climate
change and weather phenomena on the earth.

CLIMATE AND CLIMATE CHANGE

The average statistical weather patterns of a place estimated
over a 30 years period is known as climate. It is affected by
both natural and anthropogenic changes going on in the
earth. In the absence of human activities, the climate of a
place is more or less constant. But, for the last 1300 years
and especially after 1950 AD, the climate has changed at an
unexpected level due to increased anthropogenic causes.
The increased concentration of the carbon dioxide emission
along with other greenhouse gases has warmed the earth’s
atmosphere. The satellites, statistical calculations, computer
models and data from all over the world from Antarctica to

New Creative Science, Class 10 | 327

Amazon reveal that the climate is changing day to day. This gradual change in climate
due to anthropogenic causes is called climate change. The climate that is changing
now is the resultant effect of the emission that people generated several decades ago.
Likewise, the emission that we are generating today will have very adverse effects
after many years from now. So, there must be global efforts in reducing the change in
climate by global attempts. The climate in Nepal is also changing day by day. Some of
the evidences to suggest this fact are listed below:

a) The overall temperature of Nepal has increased by 0.060C. It seems
negligible but it is vast to cause adverse effects.

b) Draughts, drying up of water sources like springs, reduction in water flow
in rivers, etc. also suggest that the effect of climate change is becoming
serious.

c) The glaciers and Himalayan snow are also rapidly melting.
d) Increase in the incidences of outburst of glacial lakes.
e) Loss of biodiversity and habitat

These are only some of the geographical impacts. The impacts on the socioeconomic
areas are also huge. Nepal contributes only about 0.025% of global greenhouse gas
emissions but has to face a devastating effects because of global emission results.

In this chapter, we shall discuss about the composition of atmosphere, climate change,
effects of climate change, controlling measures of climate change, ozone layer,
industrial gases, etc.

NATIONAL AND INTERNATIONAL EFFORTS ON CLIMATE CHANGE
MITIGATION AND ADAPTATION

Climate Change has become a global problem. The effects of climate change are
recognized globally all over the world. These effects are also causing various problems
to underdeveloped countries, which are least responsible for climate change. Some
people are still debating on the consequences of climate change. The impact of climate
change may be minimal to challenge human survival but the adverse effects are already
being felt in the rest of the biodiversity. It affects directly on ecosystems, biodiversity,
weather patterns, oceanic and wind currents and human lifestyle. As suggested by
several researches, climate change has become a challenge to the survival of several
species of living organisms, many of which have become extinct.

Climate Change is the combined effect of both natural and human activities brought
by industrialization, urbanization and population growth. The industrial revolution
after the 19th century caused adverse effects to existing the climate pattern. Now
the challenges are very dangerous. Therefore, there should be global actions to
moderate climate change. A single country or society is unable to reduce it. Everyone
is more or less responsible for climate change. The United Nations has formulated

328 | Climate Change and Atmosphere

an international policy to check climate change. Various efforts have been made by
several governmental, non-governmental and private agencies to reduce the effects
of climate change. One of the greatest achievements in this step is the incorporation
of the chapter climate change in the textbooks of formal education in schools,
colleges and university levels. Its aim is to encourage, educate and warn the future
generations about the on-going climate change, its impacts and mitigation measures.
Small steps like use of public transportation, avoiding forest fires or even switching
off of a light bulb can contribute to the joint collaborative effort. Hence, mitigation of
climate change should not just be an international effort but also an individual one.
It should be noted that climate change cannot be stopped immediately but can be
slowed down. Measures that reduce the emission of greenhouse gases are already in
effect. The impact of changed climate is already affecting the countries worldwide.
Attention should be given to adaptation and elasticity measures from the effects of
climate change. Some of the national and international efforts in the mitigation and
resilience of climate change are given below.

Efforts in the national level:

The efforts to mitigate the climate change inside Nepal are called the national level
efforts. Some of the major efforts to bring resilience, awareness, adaptation and
mitigation regarding climate change are listed below:

a) National communication report
b) Climate Change Policy, 2067 B.S.
c) Strategic Program for Climate Change Resilience
d) National Adaptation program for Climate Change
e) Local Adaptation Programs for Climate Change
f) Other programs

a) National Communication Report

Nepal has submitted the national communication report to the United Nations
Framework Convention on Climate Change (UNFCCC), in the past. The report judges
the emission patterns of greenhouse gases (GHG) in Nepal from various sources.
This report also includes the effects of climate change in Nepal and its mitigating and
adaptation measures. This report also includes the susceptible sectors of Nepal which
are directly or indirectly affected by climate change. It also involves the capacity
building plans and policies to minimize the effects of climate change. This report
highlights the needs and necessities which are required in the areas that are mostly
affected by climate change. For example, transportation, industries, agriculture, forests,
health, waste management, etc. On the basis of these intensive studies, a separate
mechanism has to be set up for the scientific learning regarding climate change.

New Creative Science, Class 10 | 329

b) Climate Change Policy, 2057 B.S.

In the contest of Nepal, the impacts of climate change and global warming are adverse
in areas like agriculture, forests, public health, biodiversity, socioeconomic aspects,
etc. It is now essential to adopt the effective measures in checking, adapting and
mitigating the impacts on these areas with the raising of public understanding and
awareness. Likewise, there should be level wise capacity building plans in order to
tackle these needs. This policy also considers problems, challenges and needs to fight
against climate change. It also emphasizes on a clear vision, mission, target and the
goal oriented approach of the policy. This program has a clear way for the future
efforts in the climate adaptation and flexibility.

c) Strategic Program for Climate Change Resilience

Nepal is ranked as the 4th most climate change vulnerable nation in the world. It is
because Nepal has diversity in the climate and geography. Its altitude ranges from
59 m to 8848 m from the sea level. It has variety of ecosystems and biodiversity.
The Climate Investment Fund invited the Government of Nepal in 2009 A.D. to be a
part of its global pilot program for climate change resilience. This program provides
essential funding to underdeveloped countries in the field of climate resilience. The
SPCR planning project has engaged a large number of national and international
stakeholders in the field of climate change resilience support. The climate resilience
strategic program in Nepal is taken as a long term sustainable program and is divided
into five major categories as five investment programs:

i) Investment program 1: Building Climate Resilience of Watersheds in
Mountain Eco-Regions

ii) Investment program 2: Building Resilience to Climate-Related Hazards
iii) Investment program 3: Main streaming Climate Change Risk Management

in Development
iv) Investment program 4: Building Climate Resilient Communities through

Private Sector Participation
v) Investment program 5: Enhancing Climate Resilience of Endangered

species

d) National Adaptation Program for Climate Change

The National Adaptation program was formulated by the Government of Nepal in
2010 A.D. It mainly judges the impacts of climate change and related hazards. Its
major goals are improving the livelihoods of people by mitigating and adapting to
the adverse impacts of climate change. It also has a goal for low-carbon emissions
and socio-economic development. It supports the country's commitments to national
and international agreements related to climate change. It has 9 unified programs
including 250 sub-programs. The main objectives of the national programs are:

330 | Climate Change and Atmosphere

i) Integrated management of agriculture, water, forest and biodiversity to
promote community-based adaptation.

ii) Community-based disaster management for facilitating climate adaptation
iii) Adaptation in the public health caused due to climate change
iv) Disaster risk assessment and monitoring of Glacial Lake Outburst Flood (GLOF).
v) Capacity building and enhancement of vulnerable communities through

an improved system and access to service for agricultural development
vi) Forest and ecosystem management
vii) Ecosystem management for climate adaptation
viii) Empowering vulnerable communities through sustainable management

of water resources and clean energy supply
ix) Promoting climate friendly urban settlements

e) Local adaptation programs for climate change

The local adaptation programs for climate change are running for local and rural
communities of Nepal. Four guideline principles are adopted in Local Adaptation
program for climate change. The four guideline principles are bottom-up, inclusiveness,
responsiveness and flexibility. The local adaptation program for climate change
ensures the formation and coordinating of several programs related to the local
adaptation plans. Some of the issues that are supported by this program are:

i) To identify the most climate vulnerable Village Development Committee
(VDC), Municipality, wards and communities and their adaptation
challenges and opportunities

ii) To identify and prioritize the needs of the local people for adaptation
against climate change.

iii) To prepare local action plans to integrate them national plans.
iv) To identify and mobilize appropriate mechanisms and resources for the

proper implementation of the action plan.
v) To monitoring and evaluating the action plans.
vi) To search the cost effective adaptation plans.

f) Other programs

Some of the other programs are clean brick kiln programs, improved cooking stoves
and bio-gas plants program, encouragement programs for low-carbon emissions,
rain water harvesting programs, programs on early natural hazard warning systems,
conventions, meetings, seminars and conferences on climate change, etc.

Efforts in the international levels

The efforts to mitigate the impacts of climate change outside the national levels are
known as international level efforts. The efforts have been mostly conducted by the
organs, agencies and bodies of the United Nations, as a global attempt to address
this serious issue. Some of these international efforts to mitigate and adapt with the
impacts of climate change are:

New Creative Science, Class 10 | 331

a) United Nations Framework convention on climate change (The Rio Earth
Summit)

b) Conference of the Parties (COP) to the 1992 United Nations Framework
Convention on Climate Change(UNFCCC)

c) Agenda 21
d) Intergovernmental panel on climate change
e) Kyoto protocol
f) Emission control measures of greenhouse gases in Kyoto protocol
g) Reducing emission from deforestation and forest degradation

a) United Nations Framework convention on climate change
(The Rio Earth Summit)

From 3rd to 14th June, 1992 A.D., 154 countries of the world gathered in Brazil, Rio De
Janeiro to attend the Rio Earth Summit. The Convention was called United Nations
Framework Convention on Climate Change (UNFCCC). The main objective of the
summit was to control the greenhouse gases and their negative impacts. The summit
addressed the issues such as climate change, sustainable development and global
impacts created due to increasing anthropogenic causes. It also realized the fact that
we cannot stop climate change fully right away but we can develop ways to cope with
it, build resilience and implement mitigation measures. The UNFCCC came into effect
from 21st March, 1994 A.D. and now has 197 countries (as of December 2015) which are
known as the Parties to the UNFCCC. It also led to the Kyoto protocol that forced the
parties to reduce their carbon emission.

Nepal became a party of the conference on June 12th, 1992 A.D. After the declaration
of the related acts by the legislature, the directives of the Rio Summit were endorsed
by Nepal as regulations.

b) Conference of the Parties (COP) of UNFCCC

According to the UNFCCC, the signatory countries (called parties) should inform
about the progress and reformation works regarding climate change to other member
nations. For this, they set up a conference annually to exchange ideas. There have been
22 conferences of the Parties by the year 2016 A.D. Nepal also formulated the National
Climate Change Policy in 2011 A.D.

c) Agenda 21

Agenda 21 is the program related to the achievement of sustainable development and
climate change minimization and mitigation for environmental conservation. The 21
stands for the 21st century. The slogan for agenda 21 is ‘Think globally and act locally’.
This plan gives priority to the sustainable development, environment conservation
and balance in the society. Agenda 21 is a result of the Rio Earth Summit. It is just an
action plan of the UN and governments worldwide for the local and national level
implementation. The agenda document has 350 pages with 40 chapters and 4 sections.

332 | Climate Change and Atmosphere

The four sections of Agenda 21 are:
i) Section I: Social and Economic Dimensions: Its aim is to fight with
population growth, poverty and public health.
ii) SectionII:ConservationandManagementoftheResourcesforDevelopment:
Its aim is the protection of biodiversity, the conservation of environment
and pollution control.
iii) Section III: Strengthening the Role of Major Groups: It tries to bring the
underprivileged, disadvantaged, indigenous, women, youths, children,
farmers, businesses, NGOs, local authorities together to support their roles.
iv) Section IV: Means of Implementation: It includes sharing of science,
technology, education and financial mechanisms of the concerned goals.

d) Intergovernmental panel on climate change (IPCC)

The intergovernmental panel focuses on the study and investigation of climate change
and its impacts from an objective point of view. It is formed on the request of the
member nations of the UN jointly, by two UN organizations. They are the World
Meteorological Organization (WMO) and United Nations Environmental Programme
(UNEP) in 1988 A.D. The nations which are the members to WMO and UNEP can
be the members of the IPCC. The IPCC reports about the scientific, technical and
socio-economic information about the understanding of the scientific basis of risk of
human-induced climate change, its potential impacts and options for adaptation and
mitigation. The report also supports the United Nations Framework Convention on
Climate Change (UNFCCC), which is the main international treaty on climate change.
The scientific research carried out in IPCC is volunteered by thousands of scientists
from all over the world. Due to its exceptional role in the field of climate change
research, the IPCC received the Nobel peace prize in 2007 A.D.

e) Kyoto protocol

After the UNFCCC convention, the parties reached an agreement to form a protocol
that forms as a regulatory and enforcing body for the control of greenhouse gases
emission. The UNFCCC alone was not enough to do so because it was not an enforcing
body. Thus, 36 developed and 137 developing nation parties signed a treaty in Kyoto,
Japan, committing to reduce the greenhouse gases emission, in December 11th, 1997
A.D. The commitment period for the parties was from 2008 to 2012. This period was
called the first commitment period. During this period, the parties agreed to reduce
the carbon emission by 5.25% compared to the levels of 1990 A.D. There were some
amendments in the protocol during the Doha Meet on 8th December, 2008 A.D., known
as the Doha Amendment. According to this amendment, the developed nations have to
reduce their carbon emission during another commitment period i.e. from 1st January,
2013 A.D. till 31st December, 2020 A.D. by 18% below the levels of 1990 A.D. As of 29th
December, 2016 A.D., there are 75 parties ratifying the agreement.

New Creative Science, Class 10 | 333

f) Emission control measures of greenhouse gases in Kyoto protocol

Since the industrial revolution, the developed countries of the world have been turned
into industrial monsters. The carbon emission that these countries have produced is
mostly responsible for the climate change that the world is facing today. The Kyoto
Protocol makes the developed nations more responsible than the developing or
underdeveloped nations. Thus, the carbon emission reduction has to be more in the
developed nations. But, reducing greenhouse gases means affecting the development
process that is being conducted due to industrialization and urbanization. So, it is
very difficult to stop the emission immediately. The Kyoto Protocol encourages the
developed and developing nations to work on three mechanisms. They are international
emission trading, joint implementation and Clean Development mechanism.
According to these mechanisms, there is a certain limit up to which each nation can
emit carbon. If the limit exceeds, they will have to pay a fine for that and if it does not,
they may sell their carbon limit values to other countries in exchange of financial gain.
The developed nations have to help the developing and underdeveloped nations in
building the clean energy sources. In doing so, they also get credits to allow them to
do developmental activities.

Reducing emission from deforestation and forest degradation (REDD)

Among several greenhouse gases, carbon is the chief greenhouse gas. Carbon in the
environment can effectively be checked by the absorption and storage of carbon
dioxide thorough biological means (absorption and food making by the plants).
In this regard, the developed countries which emit more greenhouse gases should
stop deforestation. These developed nations have agreed theoretically on providing
compensation to the developing and underdeveloped nations in the area of forest
conservation and management in the future.

Layers of atmosphere

The earth's atmosphere has been divided into different
layers on the basis of the height, temperature and
composition of different gases. The atmosphere is
divided into five layers. They are;

(1) Troposphere
(2) Stratosphere
(3) Mesosphere
(4) Thermosphere
(5) Exosphere

1. Troposphere

It is the first, thinnest and lowest layer that extends

334 | Climate Change and Atmosphere

from the surface of the earth to an altitude of about 16km. Most of the moisture of the
atmosphere occurs in this layer. Therefore, many climatic events such as convection
current, cloud formation, lightening, thundering, etc. occur in this layer. The lower
part of troposphere is the reservoir of gases that are essential for the life i.e. N2, O2 and
CO2. It also contains dust particles, spores and pollen grains.
The temperature falls with the increase in height in this layer. About 6.5°C temperature
falls in this layer per km increase in altitude.

The uppermost part of this layer is called tropopause having temperature of about
–56°C.

2. Stratosphere

It extends between 16-50 km from the earth's surface. It has a protective ozone layer
that protects us from the harmful uv radiation of sunlight. So, it is also known as
ozonosphere. The temperature increases from – 56°C to –2°C in this layer. This layer
does not contain storms and clouds with negligible humidity. The upper boundary of
this layer is called stratopause. A uniform horizontal motion of air having 300 km/hr
is observed in this layer.

MEMORY TIPS
Jet planes fly in the stratosphere as this layer is clear and cloudless.

3. Mesophere

It is the third layer of the atmosphere which extends from 50 to 80 km above the earth’s
surface. The temperature first increases then decreases with height. This layer is the
coldest layer of the atmosphere having temperature variation from –2°C to –110°C. Its
upper boundary is called mesopause.

MEMORY TIPS
In mesosphere, strong wind blows from west to east during winter and from east to west
during the spring season. The streaks of hot gases released from meteors can also be
seen in this region.

4. Thermosphere

It is the fourth layer of the atmosphere that extends from 80 to 720 km above the
earth. The temperature increases with increase in altitude. The upper surface has
hydrogen and helium and the lower surface has nitrogen and oxygen. This layer is
near to the solar radiation. So, the radiation changes some of the atoms and molecules
into ions in the lower part of this layer. So, this layer is also known as ionosphere. The
radio waves are reflected back from ionized layers. So, this layer is very important for
communication.

New Creative Science, Class 10 | 335

MEMORY TIPS

The sun is regularly showering the ionized particles [not only for some time] which when
strike against the earth's magnetic line of force produce flashes of light called Aurora.
Since the concentration of magnetic lines of force is higher above the polar regions, aurora
is also more distinct above the polar regions.

5. Exosphere

It is the outermost layer extended beyond 720 km above the earth’s surface. So, it is
also known as the fringe region. The gravity is so weak that the atoms of this layer
escape to the space. The temperature varies from 1200°C to 6000°C in this region.

MEMORY TIPS

Venus and Mars do not have life in them as their atmosphere consists of 95.97% of CO2
gas and Venus has a thick cloud of sulphuric acid.

OZONE LAYERS

Ozone is a form of oxygen. A molecule of ozone contains three oxygen atoms (O3). It
is found in the stratosphere of the earth.

It is formed by the combination of molecular oxygen with atomic oxygen in the

presence of UV rays.

O2 uv rays O + O

O2 + O O3

In the stratosphere, ozone is being photo dissociated and generated by the absorption

of harmful short wavelength ultraviolet (uv) radiation coming from the sun.

O3 uv radiations O2 + [O]

These reactions are in equilibrium thereby maintaining the steady concentration of

ozone in the stratosphere. The ozone layer is commonly known as the ozone blanket.

For the dissociation as well as formation of ozone, it absorbs harmful uv rays thus,
acting as a shield to protect all types of life from harmful effects of uv radiations.

Effects of ozone layer

(i) The ozone layer protects us from severe burns due to uv rays.
(ii) It also protects us from skin diseases, cataracts, deficiency of immune power as

well as cancer due to the exposure to uv rays.
(iii) It plays a vital role in the balance of weather and temperature on the earth.
(iv) If the ozone comes near the earth’s surface, then it will be very harmful as it causes

the burning of throats and the destruction of lungs.

336 | Climate Change and Atmosphere

Ozone layer depletion

The thinning of the ozone layer or formation of hole in it is known as ozone layer
depletion.
Ozone is being depleted by air pollutants. CFCs methane, oxides of nitrogen, CO2, etc.
are air pollutants that are mainly responsible for the depletion of the ozone layer in
the stratosphere.

MEMORY TIPS
An English scientist J.C. Farmann found out for the first time the ozone layer depletion over
Antarctica in 1885 A.D.

Mechanism of ozone layer depletion

Chlorofluorocarbons (CFCs) is a synthetic, harmful chemical, which is widely used in
refrigerators and air conditioners as coolants: in fire extinguishers, aerosol sprayers as
propellants.

Once released in air, these harmful chemicals produce active chlorine (Cl and ClO

radicals) in the presence of uv rays. These radicals through chain reactions, then

destroy the ozone by converting it into oxygen as
uv rays
(1) CF2Cl2 uv rays CF2Cl + Cl
(2) Cl + O3 ClO + O2

Chlorine oxide

(3) ClO uv rays Cl + O
(4) O + O3 uv rays
O2 + O2

Hence, the ozone layer becomes thinner. A single ‘active chlorine’ converts one lakhs

molecules of ozone into oxygen.

MEMORY TIPS
The amount of atmospheric ozone is measured by Dobson spectrometer and is expressed
in Dobson units (DU).

Effects of ozone depletion

The thinning of the ozone layer allows more uv radiations to pass through it which
then strike the earth. This causes the following harmful effects on man and animals.

(i) UV radiations can cause skin cancer, cataract, damage to the immune system
etc. in human beings.

New Creative Science, Class 10 | 337

(ii) It decreases the crop yielding.
(iii) It adversely affects the fertility of animals.
(iv) It can cause global warming.

Conservation of ozone layer

The following methods should be applied for the conservation of the ozone layer:
(i) The use of CFCs should be reduced in refrigerators, air conditioners,
aerosols, etc. but alternative cooling should be developed.
(ii) The production of CFCs should be banned.
(iii) People should be aware of the ozone layer depletion, its possible effects and
the ways to protect it.

GREEN HOUSE EFFECT

The gases like carbon dioxide, methane,
CFCs, oxides of nitrogen, water vapour,
etc. are the green house gases. These gases
trap the infrared radiation reflected by the
earth. This heats up the atmosphere and
increases the temperature of the earth.

This phenomenon of increasing the
temperature of the earth as the effect of green
house gases is called green house effect.

Importance of greenhouse effect

Green house gases are important in keeping the earth warm. The average temperature
of the earth is around 20°C. In the absence of green house gases, it may drop to –20°C,
killing all forms of life on the earth. So, greenhouse effect is important for sustaining
lives on the earth.

Adverse effect of greenhouse effect

Greenhouse effect is necessary for the survival of life on the earth. But over greenhouse
effect may lead to the adverse effect to the living beings.
Men is adding a large amount of CO2 and CH4 to the atmosphere by burning fossil
fuels in houses, industries, automobiles as well as due to deforestation. Methane is
also added to the atmosphere by the decay of vegetation in the marshland, paddy
fields, etc. This leads to the problems like.

338 | Climate Change and Atmosphere

(i) The greenhouse gases trap the heat reflected by the earth. This heats up the
atmosphere and leads to the increase in earth’s temperature. This phenomenon is
called global warming.

(ii) The global warming means the increase of the temperature of the earth, which
causes melting of ice on the poles. This results rise in the sea level.

(iii) It changes the pattern of rainfall and weather condition.
(iv) It affects water cycles, soil moisture and soil composition. So, there is change in

harvesting and cultivating crops.
(v) It helps to increase the pathogenic insects which help to increase the number of

pathogenic diseases.
(vi) It has adverse effects on the ecosystem by imbalancing it.

Ways of controlling greenhouse effect

The over greenhouse effect can be controlled by controlling human activities:
(i) By decreasing deforestation and increasing afforestation.
(ii) By reducing the use of fossil fuel.
(iii) Banning CFCs.
(iv) Using the pollution free sources of energy like solar energy, wind energy, etc.

Artificial greenhouse

The houses made up of plastics or glass for the cultivation of plants and crops inside it are called
artificial greenhouses.

The glasses or plastics allow the sun’s radiation to enter them. But as the radiation
strikes the ground, it changes into the waves having less energy and longer wavelength.
These rays now can’t go outside and get reflected inside the house. As a result, due to
the accumulation of more infrared radiations, the temperature inside the greenhouse
is always more than that of outside.

Due to higher temperature inside the greenhouse, different types of plants like
vegetables, flowers, etc. can be grown in any season in any climatic region.

MEMORY TIPS
The earth is a natural greenhouse and the greenhouse gases on the earth are CH4, CO2,
NOx, H2O etc.

ACTIVITY

Visit a greenhouse and observe the plants there. Are they all from your locality? Are they all the
seasonal plants? Interpret your answer.

INDUSTRIAL GASES

During the manufacture of various substances in industries, different harmful

New Creative Science, Class 10 | 339

substances along with the harmful gases are released. These toxic gases like SO2,
CO2, CO, NOx, etc. produced from industries are called the industrial gases. They are
pollutants and cause air pollution, water pollution and soil pollution.

Effects of industrial gases

The industrial gases cause serious environmental problems which directly or indirectly
affect organisms.

(1) Acid rain: When the gases like SO2, NOx and CO2 mix with rainwater, they form
weak sulphuric, nitric and carbonic acids respectively. This causes acid rain.
Acid rain corrodes the historical monuments like statues, sculptures, temple,
etc. It increases the acidity of soil thereby reducing the crop yield. Moreover, it
causes different types of skin and respiratory diseases.

(2) Global warming: Many industrial gases are greenhouse gases, which lead to
global warming.

(3) Photochemical smog: These gases form photochemical smog, which causes eye
itching, and have negative effects on plant growth.

(4) Ozone layer depletion: Some industrial gases also cause ozone layer depletion.

(5) Human diseases
• Carbon monoxide reduces the efficiency of haemoglobin.
• Oxides of nitrogen cause lung diseases.
• Sulphur dioxide causes respiratory diseases, headache, etc.

MODEL QUESTIONS ANSWER

1. How does the atmosphere help for the living beings on the earth to survive?

Ü The earth’s atmosphere contains the necessary things for the life of an organism
like N2, O2, water vapour, CO2 etc. It also maintains suitable temperature on the
earth’s surface for the survival of living beings.

2. Stratosphere is also known as a protective layer. Why?

Ü Stratosphere consists of the ozone layer, which absorbs harmful uv rays from
the sun and protects the earth from its effects.

3. Why does temperature increase with the increase in altitude in stratosphere?

Ü It is due to ozone layer which absorbs solar radiation which makes it warmer.

4. Why is the greenhouse effect a must for the survival of living organisms on
the earth?

Ü If there is no greenhouse effect, then the temperature of earth’s surface falls
below – 20°C at which no creatures can survive.

5. Global warming is the consequence of the greenhouse effect. Why?
Ü The greenhouse gases like CO2, H2O, NOx and CH4 do not allow some of the

340 | Climate Change and Atmosphere

heat radiation to escape to the space after they enter the earth’s surface. So, due
to the accumulation of heat waves inside the atmosphere, the temperature of the
earth increases. It is called global warming.

6. How acid rain is harmful?
Ü Acid rain destroys monuments, temples, and statues. It also causes skin diseases

and decreases the fertility of soil causing acidity. So, acid rain is harmful.

7. Acid rain is more probable in the industrial areas. Why?
Ü When the industrial gases like SO2, NOx, CO2 etc. mix with the rainwater, it

changes into weak acid and falls in the form of rain, it is called acid rain. So, it is
more probable in industrial areas.

SUMMARY

 The thick layer of air which surrounds the earth’s surface is called atmosphere.
 Atmosphere can be divided into 5 layers i.e. troposphere, stratosphere, mesosphere,

thermosphere and exosphere.
 Troposphere is the lowermost layer which controls rainfall and other climatic activities.
 The ozone is a molecule made up of three oxygen atoms. It is formed in stratosphere by the

influence of uv rays on oxygen gas.
 Ozone layer absorbs uv rays and protects us from the harmful effects of uv rays.
 CFCs is the main chemical, which destroys the ozone layer.
 The effect of increasing temperature on the earth due to the greenhouse gases is called the

 greenhouse effect.

CO2, CH4, NOx and H2O are the main greenhouse gases.
The greenhouse effect maintains the temperature of the earth, which is suitable for the

survival of life.
 The greenhouse effect causes global warming, which is the burning problem of the present day.
 Industrial gases like CO2, CO, SO2 cause air pollution, global warming and acid rain.

EXERCISE

1. What is climate and climate change?

2. List out the efforts in national levels, which are made to reduce climate change.

3. What attempts have been done in international level to reduce climate change.

4. What is Kyoto protocol? Describe its actions.

5. What is climate change policy 2067 BS?

6. What are the different layers of atmosphere? Name them. In which layer does the
strong wind blow?

7. How are stratosphere and ionosphere beneficial to us?

8. Define stratopause and mesopause.

9. Write short notes on:

(a) Troposphere (b) Thermosphere

New Creative Science, Class 10 | 341

(c) Mesosphere (d) Stratosphere

10. Study the layer of atmosphere in the given diagram and answer the following
questions.

(a) Name the layers 2, 3 and 4.

(b) Which layer consists of ozone?

(c) From which layer are the radio waves reflected? 1
(d) In which layer do jet planes fly?
(e) In which layer is aurora is seen? 2
3
4

5

11. Why is stratosphere called the protective layer?

12. Write two advantages and two disadvantages of ozone.

13. How is ozone layer depleting?

14. Write two preventive measures for ozone layer depletion.

15. Define greenhouse effect. Can the earth be said as a natural greenhouse? Why?

16. What are the effects of global warming?

17. Give reasons:

(a) The use of CFCs must be banned.

(b) Summer vegetables can also be grown in winter inside a greenhouse.

(c) We should conserve the ozone layer.

18. It is warmer inside a greenhouse. Why?

19. Define acid rain.

20. Illustrate how the industrial gases are harmful.

A

B GLOSSARY
C

Fringe : an outer edge of area
Photo dissociation : dissociation by the help of light
Propellants : the gases that force out the content of aerosols
Aerosols : particles suspended in a gas like smog, ashes etc.
Global warming : increasing the worldwide temperature on the earth
Smog : the mixture of smoke and fog which decreases transparency in atmosphere

NOx : oxides of nitrogen NO2, N2O, NO, N2O5, N2O3



342 | Climate Change and Atmosphere

UNIT

23 The Earth in the Universe

About the Scientist INTRODUCTION

Stephen William The universe is the unimaginable vast space. Till now many
theories, hypothesis, facts are found yet there are many
Stephen William Hawking is unexplained areas of the universe.
a British theoretical physicist,
whose world-renowned scientific Everything that we have seen, unseen, felt, not-felt, heard,
career spans over 40 years. His not heard are the members of the universe. From the tiny
books and public appearances atoms to the biggest star, unicellular protozoans to higher
have made him an academic complex living organisms, all the waves, light, sound, sun,
celebrity and he is an Honorary stars, planets, satellites, all matters and all the energies, etc.
Fellow of the Royal Society of are the members of the universe. It is so vast that even the
Arts, a lifetime member of the fastest traveller (having velocity 3 × 108 m/s) takes millions
Pontifical Academy of Sciences, of years to travel from one star to another. So, we just cannot
and in 2009 was awarded the imagine the immense size of the universe.
Presidential Medal of Freedom,
the highest civilian award in the The universe is the aggregate of all the existing things
United States. including all celestial bodies and all the space.
Hawking has a neuro-muscular
dystrophy that is related to The solar system is only a very small particle of the universe.
amyotrophic lateral sclerosis
(ALS), a condition that has Astronomy is the branch of science in which we study about
progressed over the years and the universe.
has left him almost completely
paralysed. Some units to measure the distance in the universe

It is very difficult to measure the distance in the universe in
the units like metre, kilometre, etc. as the distance between
two heavenly bodies is very large. So, special units must be
used to measure the distance between the heavenly bodies.
Some of the units used to measure the distances in the
universe are:
(a) Astronomical unit (AU)
(b) Light Year
(c) Parsec

(a) Astronomical unit (AU)

It is defined as the mean distance between the sun and
the earth. Its value is 1.5 × 1011 m. It is used to measure
the distances between the members in the solar system i.e.
smaller distances in the universe.

New Creative Science, Class 10 | 343

MEMORY TIPS

Tittus Bode's concept about the distance of planets from the sun in AU is calculated by
applying the following rules:

a) Make a series of numbers starting from 0 and 3 and doubling afterward

i.e. 0 3 6 12 24 48 96 192 394

b) Add '4' on each number of the series

i.e. 0+4 3+4 6+4 12+4 24+4 48+4 96+4 192+4 394+4

c) Divide every 'sum' by 10

0 + 4 3 + 4 6 + 4 12 + 4 24 + 4 48 + 4 96 + 4 192 + 4 394 + 4
i.e. 10 10 10 10 10 10 10
10 10

d) The value of each fraction will be the approx distance in AU of the planets from sun i.e.

0+4 3+4 = 0.7 AU for Venus
10 = 0.4 AU for Mercury 10

6+4 = 1 AU for Earth 12 + 4
10 10 = 1.6 AU for Mars

24 + 4 48 + 4 = 5.2 AU for Jupiter
10 = 2.8 AU for Asteroids 10

96 + 4 = 10 AU for Saturn 192 + 4
10 10 = 19.6 AU for Uranus

394 + 4 = 98.8 AU for Neptune
10

[But, approx. distance of Neptune is 30 AU and that of Pluto is 39 AU from the sun]

(b) 1 light year
The distance travelled by light in one year is known as 1 light year. Its value is 9.46 ×
1012 km.

Method to calculate the value of one light year
We know that,
Velocity of light in vacuum (v) = 3 × 108 m/s
Time taken (t) = 1 year
We have, distance travelled = v × t = 3 × 108 m/s × 1 yr

= 3 × 108 × (1 × 365 × 24 × 60 ×60)s
= 9.46 × 1015 m
= 9.46 × 1012 km
∴ 1 light year = 9.46 × 1012 km

344 | The Earth in the Universe

(c) 1 Parsec
The distance which is equal to 3.26 light year is called 1 parsec.

∴ 1 Parsec = 3.26 light years

MEMORY TIPS

• Proxima Centauri, the second nearest star from our solar system lies 4.3 light years
away. Sirius is 8.6 light years and Vega is 26.5 light years away. (First nearest star is
the sun itself)

• Parsec = The parallax angle having the value of 1 second. 1° =1 minute, 1 min 1second.
60 60 =
Parallex angle means the angle which is obtained by bisecting the vertex of an isosceles

triangle by a perpendicular on its base.

If an angle of 1° is equally divided into 3600 fragments, then a single fragment of the
angle is called 1 second (1'')

Parsec is the vertical distance of the triangle (height of the perpendicular drawn from
the vertex to base) of the isosceles triangle whose base is taken the longest diameter
of earth's orbit. See the figure:

SOLAR SYSTEM

The sun and the celestial bodies which revolve around the sun form the solar system.
It consists of planets, satellites, comets, asteroids, meteors and very thin interplanetory
air, which revolve around the sun due to the gravitational attraction between the sun
and these bodies. The sun is the main member of the solar system. The eight planets
of the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and
Neptune. Our solar system lies in the Milky Way galaxy.

The international convention of astronomers held on 2006 in Prague of Czech Republic has
removed the Pluto from the list of the planets as it does not fit the new definition given
by IAU (International Astronomical Union). The new definition of planets given by
convention is as follows:

‘A planet should have its own round (elliptical) orbit around the sun which must not cross the
orbit of other planets.

As the orbit of Pluto crosses the orbit of Neptune, it was kept in the category of ‘dwarf
(or dropped) planet’ along with its satellite Charon. A new heavenly body named (2003
UB 13)/Jena was also discovered in our solar system.

New Creative Science, Class 10 | 345

Solar system

The sun

The sun is a medium sized yellow coloured star. It is the main and largest body in the
solar system. All the members of the solar system revolve around the sun. Some facts
about the sun are:

Diameter of the sun = 1,392,000 km

Distance of the sun from Core
Galactic centre of milky ways galaxy → 2.5 × 104 light years. Corona
Distance between sun and the earth → 1.5 × 108 km Chromosphere
Temperature of its surface → 6 × 103 °C
Photosphere

Temperature of its core → 1.5 × 107 °C

Mass of the sun = 2 × 1030 kg

The sun is composed of about 75% hydrogen and 25% helium. It takes 2.5 ×108 years
to complete one revolution around the galactic centre and this time period is known
as one cosmic year.

It consists of three-layers photosphere, chromosphere and corona. The sun producers an
enormous amount of energy due to the nuclear fusion reaction in which hydrogen is
continuously changing to helium.

Importance of the sun

The sun is the main member of the solar system as well as very important part of it.
The importance of the sun can be summarized as,
i. It helps to revolve other members of the solar system due to its strong gravitation.
ii. It gives heat and light energy to all the living beings on the earth.

346 | The Earth in the Universe