Science and Environment 10

Dominant and Recessive genes

A single gene can function in alternate forms. These are called alleles. One of the two
alleles of a gene is super ruling, i.e. dominant (expresses its characteristics) while the
other is submissive, i.e. recessive (it is hidden or suppresses itself in presence of dom-
inant gene). For example, brown eye colour in human beings is a dominant hereditary
trait while the blue eye colour is recessive. Similarly, most of us are right-handed. This
is because right handedness is a dominant hereditary trait in man while left handed-
ness is recessive. Some other common hereditary traits in man are given below.

Eearlobe trait Tongue-rolling trait

Chin dimple trait Thick and thin lips trait

Cheek dimple trait Curly and straight hair trait Hitcher's thumb trait

1. Dimpled cheeks (dominant) and non-dimpled cheeks (recessive)
2. Free ear lobe (dominant) and attatched ear lobe (recessive)
3. Kinky hair (dominant) and non–kinky hair (recessive)
4. No hitcher's thumb (dominant) and hitcher's thumb (recessive)
5. Rolling of tongue (dominant) and non-rolling of tongue (recessive)

Activity -1

Human beings contain a number of dominant and recessive characteristics. Study five types
of dominant and recessive characteristics present in your body. Compare the hereditary
characteristics of your own family members and prepare a list of those characteristics.

Certain characteristics found in human beings depend on the sex of an individual. Due to
this, certain diseases are found only in males and others are found only in females. Such
diseases are called sex-linked diseases. For example, baldness and color blindness are
found only in males whereas breast cancer and uterine cancer are found only in females.

19.5 Mendel's Experiment

Mendel had an idea that a plant inherits two genes of information for a single characteristic, one
from each parent in every generation. So he selected seven pairs of contrasting characteristics
in the garden pea. He concentrated his attention on only one pair of characteristics at a

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time, and traced them carefully through many successive generations. Mendel controlled
his experimental conditions carefully, ensuring that pea plants were pollinated only by the
pollen grains he transferred. He made careful observations and performed his experiments
repeatedly keeping meticulous records.

Mendel crossed homozygous (pure) tall pea plant (2 m tall) and a homozygous dwarf pea
plant (0.5 m tall). He carried out his experiment by transferring pollen grains of the tall plant
to the stigma of the dwarf plant. He prevented self–pollination by removing all stamens of
the dwarf plant. The seeds produced by the dwarf plant were collected and sown. The plants
obtained in this generation were called F1–generation. He found that all plants obtained in
F1–generation were tall.

These tall plants of F1–generation were allowed to self–pollinate. The seeds were collected and
sown. The plants obtained were called F2–generation. In this generation, some plants were tall
and a few were dwarfs in the ratio of 3 : 1.

The seeds of F2–generation were sown again and allowed to self-pollinate. This gave the
F3 - generation. In this generation, Mendel found that the dwarf plants of F2 - generation
produced dwarf plants. Out of tall plants of F2-generation, one third were pure tall, and the
remaining two thirds were hybrid tall. Pure tall plant of F2- generation produced pure tall plant in
F3 - generation.

Mendel's experiment can be demonstrated as follows:

Parents → Pure tall pea plant Pure dwarf pea plant
Genotype → TT tt

Gametes → T t

All hybrid tall→ Cross - pollination
Tt F1 - generation

If the F1 - are bred together
Tt Tt

Possible gametes → T tT t
Self-pollination → Tt Tt tt F2 - generation
TT

Gametes Tt Tt tt F3 - generation
TT TT Tt Tt tt

meticulous /məˈtɪkjələs/ - paying careful attention to every detail

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Where, TT – pure tall
Tt – hybrid tall
tt – pure dwarf

19.6 Law of Dominance: Mendel's First Law

According to Mendel's experiments, the law of dominance states, "In crossing between pure
(homozygous) organisms for contrasting characteristics of a pair, only one characteristic of the
pair appears in the first filial generation."

This law can be explained as follows:

Let us consider a pure tall pea plant (TT) and a pure dwarf pea plant (tt). When a pure tall
pea plant is cross - pollinated with a pure dwarf plant, all pea plants become tall (genetically
hybrid tall) in the first filial generation. Here, tallness appears by suppressing the dwarfness.
In this cross, tall is the dominant characteristic as it appears in F1–generation whereas dwarf is
the recessive characteristic as it remains hidden in F1–generation.

Parents → Pure tall Pure dwarf
Genotype → TT tt

Gametes T T t t

Cross-pollination

Offspring in Tt Tt Tt Tt

F1-generation Tall Tall Tall Tall

19.7 Law of Segregation: Mendel's Second Law

Mendel's second law of inheritance, i.e., law of segregation states, "The hybrids obtained in
F1–generation contain two contrasting characteristics of dominant and recessive nature. Those
characteristics remain together for a long period of time in hybrids but do not mix with each
other and separate or segregate at the time of gamete formation so that each gamete gets only
one characteristic, either dominant characteristic or recessive characteristic." This law is also
called law of purity of gametes.

Mendel's second law can be explained by the monohybrid cross between a pure red-flowered
pea plant (RR) and a pure white flowered pea plant (rr) upto the second filial generation.

segregate /ˈseɡrɪɡeɪt/ - to separate organisms according to characteristics

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Parents - Pure red Pure white flowered

flowered pea plant pea plant

RR rr

Genotypes

Gametes R Rr r

Cross-pollination Rr Rr Rr Rr F1 - generation

Gametes R r R r Self - pollination

RR Rr Rr rr F2 - generation
Pure red Hybrid red Pure white

Phenotypic ratio of Red : White is 3 : 1.
Genotypic ratio of Pure red : Hybrid red : Pure white is 1 : 2 : 1.

In F1–generation, all pea plants produce hybrid red (Rr) with dominant (R) and recessive
characteristic (r). Both characteristics remain together for a long period of time without mixing
and finally separate into two different pure gametes, either red (R) or white (r). Those hybrids,
after interbreeding, produce three different types of offspring, i.e., pure red, hybrid red and
pure white in the ratio of 1 : 2 : 1 in the second filial generation. It is possible due to the
segregation or purity of the gametes.

Mendel also experimented on other pairs of alternative characteristics, and he found that, in
every case, the characteristics followed the same scheme of inheritance. Thus in the garden
pea, he found that purple (red) flower was dominant over white flower, yellow seed over
green seed, tall plant over dwarf plant, and smooth seed over wrinkled seed.

19.8 Significance of Mendelism

Mendel's laws can be used for solving many problems of genetics. The significance of
Mendelism is stated below:
1. Disease resistant and high yielding varieties of plants and animals can be produced by

the application of Mendelism.

2. Hybrids with desired characteristics can be produced.

3. The genotypes and phenotypes likely to be produced in successive generations can be
predicted before the cross is made.

4. Dominant and recessive characteristics of the organisms can be known.

assortment /əˈsɔːtmənt/ - a collection of different things or of different types of the same thing

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19.9 Variation

Individual members of a species differ widely

from one another in their genetic make

up and therefore in their characteristics.

The structural differences that provide

individuality to each member of a species is

called variation. Variation gives rise to new

characteristics and heredity to living beings. Fgi. 19.9 Variation in human beings

Various factors like food, light, temperature,

humidity, etc. are responsible for bringing out variation. Variation also depends on parental

characteristics. It occurs either gradually or suddenly. The variation that occurs gradually is called

continuous variation. For example, the difference in height, color, etc. Similarly, the variation

that occurs suddenly is called discontinuous variation, or mutation. For example, a newly born

baby without leg, with an extra finger, etc. Variation is responsible for organic evolution.

The main factors that bring out genetic variation are as follows:

i. Mutation ii. Genetic recombination

i. Mutation

Normally, chromosomes and genes are passed Fgi. 19.4 Mutation in human beings
from one generation to another generation
without changing. The structure of the genes,
or chromosomes, gets altered on rare occasions.
Such a change in the gene, or chromosome,
is called mutation. It is a permanent change.
Mutation is inherited only if the mutation
occurs in the gametes, or reproductive cells.
Such mutation brings out variation.

ii. Genetic recombination
New combination of characteristics appears in the offspring after mating heterozygous

parents. Such a process is called genetic recombination. This process also brings out
variation.

Differences between Mutation and Variation

S.N. Mutation S.N. Variation

1. A sudden heritable change in the 1. The structural difference that provides

genetic material of an organism is individuality to each member of a species

called mutation. is called variation.

2. Various factors like ultra–violet 2. Structural and functional differences of a

rays, X-rays, gamma rays and gene and environmental factors like food,

different chemicals are responsible light, temperature, etc. are responsible

for mutation. for bringing out variation.

mutation/mjuːˈteɪʃn/ - a process in which the genetic material of an organism changes in structure when it is passed to
the offspring causing different physical characteristics to develop

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Significance of variation
1. Variation increases the chance of survival of an organism in a changing
environment.
2. Variation helps in organic evolution.
3. Variation provides individuality to an organism of a species from other members
of the species.

Activity -2

To study the variation among students
• Group the students of your class on the basis of height of body, color of skin, etc.
• Prepare a short report and discuss in the class.

SUMMARY

• Genetics is the branch of biological science which deals with the nature and behaviour
of genes. Gregor Mendel is considered as the father of genetics.

• Heredity is the phenomenon by which living organisms transmit parental
characteristics to their offspring. It is also called inheritance.

• Genes are tiny units of heredity located in the chromosomes.
• Hereditary characteristics are the characteristics of the parents which are transmitted

to their offspring.
• When both alleles of a particular gene are identical, it is called homozygous.
• When two alleles of a particular gene are not identical, it is called heterozygous.
• The characteristics which are prominent and appear in successive generations are

called dominant characteristics.
• The characteristics which remain unexpressed in successive generations are called

recessive characteristics.
• Phenotype is the external appearance of an organism for a contrasting characteristic.

For example, tall, dwarf, etc.
• Genotype is the genetic make up of an organism. For example, Tt, RR, etc.
• Hybrids are the organisms produced after cross fertilization between two genetically

different organisms. The process of obtaining hybrids is called hybridization.
• Monohybrid cross is the cross in which only one pair of contrasting characteristics is taken

into consideration.

heritable /ˈherɪtəbl/ - that can be passed from one generation to another

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• Dihybrid cross is the cross in which two pairs of contrasting characteristics are taken
into consideration.

• Law of dominance states, "In crossing between pure (homozygous) organisms for
contrasting characteristics of a pair, only one characteristic of the pair appears in the
first filial generation."

• Law of segregation states, "The hybrids obtained in F1–generation contain two
contrasting characteristics of a dominant and recessive nature. Those characteristics
remain together for a long period of time in hybrids but do not mix with each other
and separate at the time of gamete formation so that each gamete gets only a pure
characteristic."

• The structural differences that provide individuality to each member of a species is
called variation.

• A sudden heritable change in the genetic material of an organism is called mutation.

Exercise

Group-A
1. What is heredity?
2. What is meant by gene? Write down its function.
3. Where are genes located?
4. Who is considered as the father of genetics?
5. What is dominant characteristic?
6. What is recessive characteristic?
7. Define phenotype.
8. Define geneotype.
9. What is monohybrid cross? Give one example.
10. What is dihybrid cross? Give one example.
11. What is a hybrid?
12. Write any two recessive characteristics seen in human beings.
13. What is variation?
14. Name the types of variation.
15. What is environmental variation?

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16. What is genetic variation?

17. What is mutation?

18. What are the causative factors for mutation?

19. Define continuous variation.

Group-B

1. Write any two reasons for selecting pea plants by Mendel for his experiment.
2. Write any two differences between dominant and recessive characteristic.

3. The characteristic of having red flower is called dominant characteristic and that having
white flowers is called recessive characteristic, why?

4. Write any two differences between variation and mutation.

5. Every living being reproduces its own kind offspring, why?

6. Explain the reason that only one characteristic is found expressed in F1 generation of
Mendel's experiment.

7. Write any two differences between monohybrid and dihybrid cross.

8. Mating of black and brown dogs takes place and all the offspring produced in
F1-generation are black. Why isn't there brown offspring?

Group-C

1. How is hybrid obtained? Write in brief.

2. Do Mendel's laws apply in human beings too? What difficulties would Mendel have
faced if he had carried out his experiment on human beings instead of pea plants?

3. If the monohybrid cross between black male cat and brown female cat takes place, all
offspring of F1-generation were black. Why were not brown offspring of F1-generation?
Show this process with the help of chart upto F2 generation. Write down geneotype ratio
of this process.

4. Every living beings reproduces its own kind offspring, why? A hybrid tall pea (Tt) plant
is crossed with a dwarf pea (tt) plant to get F1-generation. Show it with geneotype and
phenotype.

5. What are the laws derived from Mendel's experiment? Show in chart the feature of
F1-generation of round and wrinkled seed of pea plant when they are cross-pollinated.

6. When the black and brown dogs were mate together all the offspring in F1-generation
were found to be black. Why weren't there any brown dog? Show it with the help of
necessary chart.

Group-D O B b
Bb
1. The result obtained by crossing a black rat with a white rat is shown O bb
+

in the given checker board. On this basis, answer the following B BB
questions.

b Bb

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i) Which filial generation does this result belong to?

ii) Write down the ratio of dominant and recessive characteristics.

iii) Which one is pure black rat?

2. Explain Mendel's law of purity of gametes with an example.

3. Draw a chart to show both phenotype and geneotype of the result obtained in the first
and second filial generation of offspring of mouse, having black colour and white colour
according to Mendel's experimental result. With the help of the same chart write the
ratio of phenotype and geneotype of second generation.

4. Show the genotype and phenotype of offspring produced by crossing drosophila with
long wings and short wings upto second filial generation.

5. The result obtained by first cross pollination and then self O
O
pollination between pure red flowering pea plant (RR) and pure R r
white flowering pea plant (rr) is shown in table. Answer the + Rr

questions below: R RR

i) Which filial generation does this result belong? r Rr rr

ii) What is hybrid? What is the percentage of hybrid pea plant in
this generation?

iii) Which pair of geneotype indicates the pure white flowering pea plant?

6. Why is Mendel called "Father of Genetics"? Draw a filial chart to show the result obtained
in the F1 and F2-generation by cross-pollination between red and white flowered pea plant.

7. A pure black guinea pig (BB) is crossed with a pure white guinea pig (bb) to get offspring
in the first and second filial generations and show it with geneotype and phenotype.
Also, write genotypic ratio of black and white guinea pigs in the second filial generation.

8. A tall (T) pea plant and a dwarf (t) pea plant were first O
O
cross-pollinated and then self-pollinated. The given table shows T t
Tt
the result of this experiment. Answer the following questions with + tt

the help of the table. T TT

i) Which filial generation does this result belong to? t Tt

ii) What is a hybrid? What is the percentage of pea plants
having hybrid character in this generation.

iii) Which pair of genes indicate the pure tall plant?

10. The result obtained by crossing pure red flowering pea plant O
O
(R) and pure white flowering pea plant (r) is shown in the given R r
RR Rr
checker board. +

i) Which filial generation does this result belong to? R

ii) What is the ratio of the plant having dominant and recessive r Rr rr
character?

iii) Which one is pure red flowering plant?

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UNIT 20 Estimated teaching periods

Theory 7

Practical 2

ENVIORNMENT

POLLUTION AND

MANAGEMENT

Objectives

After completing the study of this unit, students will be able to:
• explain causes, effects and preventive measures of air pollution, water pollution

and soil pollution and behave accordingly.
• explain the methods of conservation and management of forests and water

resources.

20.1 Introduction

A variety of environmental components natural, biological, social, cultural, etc. are found
in our surroundings. Land, air, water, soil, minerals, etc. are the natural components of the
environment. Human beings are exploiting the environment to meet their requirements.
Social norms and values, religion, customs, etc. are the social and cultural aspects of the
environment. This is called man-made environment. Various human activities and natural
disasters degrade the quality of the environment.

20.2 Effects of Human Activities on Environment

People use natural resources for their survival and development activities. They exploit
resources in excess to fulfill their needs. Overuse of natural resources results in many adverse
effects on environment. We have heard about river pollution, reduction in water table, air
pollution, noise pollution, etc. We suffer from various diseases in a polluted environment.
Environmental pollution increases the amount of carbon dioxide in the atmosphere. It affects
the entire environment and living organisms.

20.3 Environmental Pollution

Pollution is the introduction of contaminants into the natural environment that causes adverse
change. The contamination of the environment due to mixing of harmful and unwanted
substances, which make the environment impure is called environmental pollution.
Environmental pollution can be classified into the following types:

352 Oasis School Science - 10 BIOLOGY

1. Air pollution 2. Water pollution

3. Land pollution 4. Noise pollution

In this unit, we will study about air pollution, water pollution and land pollution

1. Air pollution

Air is a mixture of various gases.

It contains about 78.08% nitrogen,

20.94% oxygen, 0.93% argon and 0.03%

carbon dioxide gas. If there is mixing of

foreign elements, their ratio changes,

and the quality of air degrades. The

contamination of air with unwanted

and harmful substances is called air

pollution. Air pollution is caused due

to mixing of harmful gases like carbon Fig. 20.1 Air pollution
monoxide, sulphur dioxide, chlorofluro

carbons, oxides of nitrogen, etc. and

dust particles in air. Unwanted and harmful substances like smoke, dust particles and

harmful gases released from vehicles and industries are the major air pollutants.

The pollutants that cause air pollution are divided into two types. They are primary
air pollutants and secondary air pollutants. The pollutants that cause air pollution
immediately after entering into atmosphere are called primary air pollutants, e.g., smoke
released from automobiles and industries, dust particles, etc. Various substances like
compounds of nitrogen and oxygen, small and large molecules, halogens, radioactive
radiation, etc. are released into the air cause air pollution. Secondary air pollutants are
formed due to chemical reaction between the primary pollutants, e.g., formaldehyde,
peroxyl, acetyl nitrate, etc.

Causes of air pollution

i. Burning of fossil fuels in industries

releases smoke, dust particles and Fact File - 1

harmful gases into the atmosphere. These Human beings breathe about 22000 times
substances cause air pollution. in a day.

ii. Burning of plastics and rubber produces

excessive amount of harmful gases like

carbon dioxide, carbon monoxide. These gases cause air pollution.

iii. In rural areas, agricultural residues are directly burnt in field. Similarly, local people
use traditional sources like firewood, dung cake, etc. to cook their food. These activities
cause air pollution.

iv. Polluted land, polluted water resources and decaying organic matter emit a bad smell in
the surroundings, which causes air pollution.

v. In deforested land, the dust particles are easily blown away by wind and cause air
pollution.

vi. The dust particles released during construction works also cause air pollution.

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Sources of air pollution

The sources of air pollution are divided into the following two types.
1. Natural sources 2. Artificial sources
1. Natural sources
The sources of air pollution that are produced in nature are called natural sources of

air pollution. Volcanic eruption, forest fire or wildfire, soil erosion, vapor released from
plants, etc. are examples of natural sources of air pollution.

Fig. 20.2
2. Artifical sources
The sources of air pollution that are produced by human beings are called artificial

sources of air pollution. Industrial gases like CO, NO, CO2, NO2, Cl2, NH3, SO2, etc.
industrial solid wastes, wastes released from hospitals, atomic power plants, automobiles
and agricultural wastes are some examples of artificial sources of air pollution.

Fig. 20.3

Effects of air pollution

i. Air pollution affects the human health in various ways. It causes irritation to the eyes
and affects the nose, throat and upper respiratory tract. It may cause headache, nausea
and allergic reaction. Similarly, long-term health effects of air pollution include chronic
respiratory diseases, lung cancer, heart disease, tuberculosis, asthma, bronchitis, skin
diseases, etc.

ii. Air pollutants damage buildings and historical monuments when sulphur pollutants
fall on buildings made of limestone and sandstone. They react with minerals in the stone

354 Oasis School Science - 10 BIOLOGY

and gradually corrode them.

iii. Harmful gases like sulphur dioxide, nitrogen oxide, etc. damage the leaves of crop
plants. Polluted air inhibits biological growth of plants.

iv. Air pollution can cause acid rain which damages crop plants, trees, buildings, metal
structures, statues and historical monuments.

v. Air pollution causes greenhouse effect, which results in global warming and climate
change.

vi. Air pollution reduces visibility which may increase road accidents as well as accident of
aeroplanes.

vii. Air pollution depletes the ozone layer which has many negative impacts on living beings.

viii. Air pollution causes reduction in solar radiation on the earth.

Measures to control air pollution

The following measures should be adopted to control air pollution:
i. Industries should be established away from human settlements as they produce harmful

gases.

ii. The harmful gases released from industries should be converted into harmless gases
before releasing them into the atmosphere.

iii. Tall chimneys should be installed in industries to reduce air pollution.

iv. Afforestation should be encouraged, and deforestation should be discouraged.

v. Alternative sources of energy like solar energy, wind energy, hydroelectricity, etc. should
be used instead of fossil fuel energy.

vi. Establishment of atomic power plants should be banned

vii. Population growth should be controlled.

viii. Solid wastes should be managed properly.

ix. Public awareness should be generated to reduce air pollution.

2. Water Pollution Fig. 20.4 Water pollution

About 71% of the earth's surface is
covered by water. Despite that only
less than 1% water can be used for
drinking. Rivers, streams, springs,
waterfalls, lakes, etc. are the sources
of fresh water. Such sources are being
polluted due to human activities.
As a result, the limited fresh water
resources are also decreasing day by
day. Everyday many unwanted and
harmful substances are thrown into
rivers and lakes.



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The contamination of rivers and lakes with unwanted and harmful substances is called
water pollution. Water is said to be polluted when it becomes unfit for drinking and
bathing due to an adverse change in the physical, chemical or biological condition.
Polluted water is harmful to living beings. Water is polluted due to natural as well as
artificial causes.

Causes of water pollution
i. Mixing of drainage directly into the water bodies causes water pollution.
ii. Dumping of untreated sewage from the cities into rivers and lakes causes water pollution.
iii. Discharging of untreated wastes, like hospital wastes, industrial wastes, municipal

wastes, institutional wastes, etc. into the rivers or lakes causes water pollution.
iv. Defecation in open fields and near water sources causes water pollution.
v. Washing clothes and utensils and throwing waste materials at the sources of water cause

water pollution.
vi. Excessive use of chemical fertilizers, pesticides and insecticides (DDT, BHC, aldrin,

dialdrin, etc.) in agricultural land causes water pollution.
vii. Bursting or cracking of drinking water pipes and drainage pipes cause water pollution.
viii. Excessive use of synthetic detergents causes water pollution.
ix. Various industrial wastes, like pieces of metals, petroleum products, electricity, etc.

contain a lot of heat. When these wastes reach the sources of water, they cause water
pollution and affect the aquatic animals and plants adversely.
x. A blockade in the flow of water also causes water pollution.
xi. Water is also polluted due to mixing of radioactive substances in the sources of water.

Effects of water pollution

i. Water pollution causes water-borne diseases like hepatitis A and E, diarrhoea, cholera,
ascariasis, typhoid, dysentery, etc.

ii. Hard water causes cardiovascular diseases.
iii. Drinking water with excessive levels of nitrates lowers the oxygen carrying capacity of

the blood.
iv. Polluted water containing harmful chemicals, like insecticides, pesticides damages our health.
v. Water pollution lowers the dissolved oxygen level which affects aquatic plants and

animals.
vi. Polluted water spreads bad smell and causes air pollution.

Measures to control water pollution

i. The waste water produced from houses and industries should be treated properly before
allowing it to mix at the sources of water.

ii. Sewage should be managed properly.

356 Oasis School Science - 10 BIOLOGY

iii. We should keep the sources of water clean.

iv. Bathing, washing clothes and throwing wastes into the sources of water should be
avoided.

v. Overuse of insecticides and chemical fertilizers should be avoided.

vi. We should plant trees near the sources of water.

vii. Throwing dead animals at the sources of water should be avoided. Dead animals should
be buried properly away from the sources of water.

viii. Public awareness should be generated to reduce water pollution.

3. Land (Soil) Pollution Fig. 20.5 Land pollution

Land is the part of the earth that is not
covered by water. The surface layer of land
is called soil. Soil is a renewable resource.
But it is produced very slowly. Various
human activities are responsible for land
pollution. The contamination of land due
to accumulation of harmful substances and
waste materials that changes the composition
of soil is called land pollution. Various human
activities are responsible for land pollution,
or soil pollution.

Causes of land pollution or soil pollution

i. Excessive use of chemical fertilizers and insecticides in agricultural fields causes land
pollution.

ii. Dumping of household solid wastes from cities and municipalities on soil causes land
pollution.

iii. Disposal of industrial and agricultural wastes causes land pollution.

iv. Throwing non-degradable wastes causes land pollution.

v. Use of polluted water for irrigation also causes land pollution.

vi. Acid rain also caused land pollution.

Effects of land pollution

i. Land pollution decreases the fertility of soil and thus decreases crop production.
ii. It causes adverse effects on soil organisms.
iii. Polluted land spreads a bad smell and causes air pollution.
iv. Polluted land causes ground water pollution.
v. Land pollution causes contamination of crops.

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Measures to control land (soil) pollution

i. Overuse of insecticides should be avoided. Insects
should be controlled by biological method.

ii. The use of polluted water for irrigation should be
avoided.

iii. Radioactive wastes should be managed
scientifically.

iv. Compost manure should be used instead of Fig. 20.6
chemical fertilizers.

v. Household wastes should be managed properly.

vi. Non-biodegradable wastes should be managed properly.

vii. Human wastes and animal wastes should be managed properly.

viii. The loss of soil due to flood, landslide, etc. should be reduced.

ix. Public awareness should be generated to reduce soil (land) pollution.

20.4 Conservation of Forests

Forest is one of the important natural resources. Human beings obtain firewood, timber,
fodder, grass, etc. from the forest. Human beings clear forests for settlement, farming and
urbanization. About 2000 trees are cut down in the rain forests per minute and about half
of the world’s tropical forest has been cleared. Deforestation is the permanent destruction of
forests or clearing of trees in order to make the land available for other uses. Deforestation
is considered to be one of the contributing factors to climate change. Deforestation occurs
throughout the world, however, tropical rain forests are particularly targeted.

Effects of deforestation

Forests play a great role in maintaining environmental balance. Forests regulate the water
cycle, carbon cycle, oxygen cycle, etc. in nature. Deforestation leads to an imbalance in the
environment. Deforestation contributes to global climate change. The major effects of
deforestation are given below:

i. Wild animals lose their habitats which can lead to Fig. 20.7
extinction of wildlife.

ii. Deforestation leads to global climate change,
which affects plants and animals.

iii. Deforestation affects water cycle, which affects the
agricultural pattern.

iv. Deforestation increases the occurrence of natural
disasters, like floods, landslides, soil erosion, etc.

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v. Deforestation leads to loss of timber, firewood and medicinal plants.

vi. Deforestation increases the amount of carbon dioxide and decreases the amount of
oxygen in air.

vii. Deforestation affects the fertility of soil.
viii. Deforestation leads to drying of water resources and degrades water quality.

All of these factors have adverse effect on the environment. Therefore, we should conserve
forest resources by the wise and economic use of forest, controlling forest fires and reducing
overgrazing and encouraging afforestation.

The following measures should be adopted for the conservation and management of forests:

i. Plants should be cut and planted in a planned way. Fig. 20.8

ii. Afforestation should be encouraged, and
deforestation should be discouraged.

iii. Forest products should be used wisely and
economically.

iv. Plantation should be done on barren land and
slopes.

v. Conservation areas should be established in
different parts of the country to conserve forests.

vi. Forest fire or wild fire should be controlled.

20.5 Conservation of water resources

The sources of water available on the earth are called water resources. Rain water, surface
water and undergound water are three main sources of water on the earth. Water resources are
very useful for human beings and other organisms. Much of human uses requires fresh water.

Fig. 20.9 Sources of water

Surface water is the water in a river, lake or wetland. Surface water is naturally replenished by
precipitation (rain) and naturally lost through evaporation. Two-thirds of the earth is covered
by water. In our country, there are various sources of surface water, such as rivers, lakes,

BIOLOGY Oasis School Science - 10 359

wetlands, watersheds, fountains, streams, etc. Glaciers are the major sources of water in Nepal.
Hydroelectricity can be generated on a large scale from the rivers of hilly and Himalayan
regions of Nepal.

Importance of water resources

Water resources are the sources of water that are very useful. Uses of water include agricultural,
industrial, household, recreational, transport and environmental activities. The importance of
water resources is given below:

i. Water resources are used to generate hydroelectricity.
ii. The hydroelectricity generated with the help of water resources is used to run industries.
iii. Water resources are used for irrigating crops.
iv. Water resources are used for drinking, cleaning, cooking, swimming, bathing, washing

and gardening.
v. Water resources are used for boating, rafting, rowing, etc.
vi. Various means of transport like cable cars, trolly buses, trains, etc. can be operated by

hydroelectricity generated with the help of water resources.

vii. Water resources are essential to conserve forests, vegetation, wildlife, etc.

viii. Water is also used in many large-scale industrial processes, such as thermoelectric power
production, oil refining, fertilizer production, natural gas extraction, etc.

ix. Water resources are important for maintaining environmental balance.

Water resources are very useful for human beings and other organisms. Nowadays water
resources are widely used to meet the needs of the increasing population. The unmanaged
and overuse of water resources will bring a crisis in water resources in the future. We should
not pollute water resources. Water resources should be conserved to save the habitat of aquatic
animals. Water resources are utilized by human beings to meet their needs. Water resources
provide a habitat to aquatic animals. Similarly, water resources help maintain a balance in the
environment and natural cycle. Thefore, we should conserve water resources.

Following measures should be adopted to conserve water resources:

i. We should conserve watersheds and glaciers.
ii. The use of poison and electric current to kill fishes should be avoided.
iii. Plantation should be done in areas hit by soil erosion, floods, landslides, etc.
iv. Misuse and overuse of water should be avoided.
v. The storage and distribution of water should be done scientifically.
vi. The existing sources of water should be conserved.
vii. The waste water should be filtered and purified.

viii. Public awareness should be generated to conserve the source of water.

360 Oasis School Science - 10 BIOLOGY

SUMMARY

• Various human activities and natural disasters degrade the quality of the
environment.

• Environment pollution increases the amount of carbon dioxide in the
atmosphere. It affects the entire environment and living organisms.

• Pollution is the introduction of contaminants into the natural environment
that causes adverse change. The contamination of the environment due to
mixing of harmful and unwanted substances, which make the environment
impure is called environmental pollution.

• Air is the mixture of various gases. It contains about 78.08% nitrogen, 20.94%
oxygen, 0.93% argon and 0.03% carbon dioxide gas.

• Burning of fossil fuels in industries releases smokes, dust particles and harmful
gases into the atmosphere. These substances cause air pollution.

• The sources of air pollution that are produced in nature are called natural
sources of air pollution.

• Air pollution affects human health in various ways. It causes irritation to the
eyes and affects the nose, throat and upper respiratory tract. It may cause
headache, nausea and allergic reaction.

• Air pollution results in global warming and climate change.

• Alternative sources of energy like solar energy, wind energy, hydroelectricity,
etc. should be used instead of fossil fuel energy.

• About 71% of the earth's surface is covered by water. Despite that only less
than 1% water can be used for drinking.

• The contamination of rivers and lakes with unwanted and harmful substances
is called water pollution.

• The contamination of land due to accumulation of harmful substances and
waste materials that changes the composition of soil is called land pollution.

• We should conserve forest resources by wise and economic use of forest,
controlling forest fire and reducing overgrazing and encouraging afforestation.

• The unmanaged and overuse of water resources will bring a crisis in water
resources in the future. We should not pollute water resources.

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Exercise

Group-A
1. What is environmental pollution?
2. Mention any two adverse effects of environmental pollution.
3. What is air pollution?
4. What are two main sources of air pollution?
5. What are natural sources of air pollution?
6. What is water pollution?
7. What are main sources of water pollution?
8. What is land pollution?

Group-B
1. What is meant by environmental management?
2. Define artificial sources of air pollution with examples.
3. How does air pollution deplete ozone layer?
4. Air pollution causes acid rain, how?
5. What is meant by land pollution?
6. Industrial wastes cause land pollution, how?
7. How does acid rain cause land pollution?
8. What is meant by conservation and management of forests?
9. What is meant by conservation and management of water?

Group-C
1. Write any three effects of air pollution.
2. Write any three effects on human health due to air pollution.
3. Write any three control measures of air pollution.
4. Mention any three effects of water pollution.
5. Mention any three measures to control water pollution.
6. Write any three measures to control land pollution.
7. Write any three measures of conservation and management of forests.
8. Mention any three measures of conservation and management of water.

Group-D
1. How does air pollution increase greenhouse effect? Explain.
2. How does air pollution cause climate change? Describe in brief.

362 Oasis School Science - 10 BIOLOGY

3. Which effects have you seen in your locality due to air pollution? Write.
4. Write a short note on land pollution.
5. Write the main sources of land pollution and describe any two of them.
6. Excessive use of insecticides causes air pollution. Justify this statement.
7. Forest is very important for environmental balance? How?
8. Describe in brief the importance of water for human beings.
9. Environmental pollution affects ecosystem. Justify this statement.
10. Environmental pollution would not occur if there were no existence of human beings on

the earth. How?
11. Describe the role of human beings for environment conservation and management.

BIOLOGY Oasis School Science - 10 363

Part 4 : Geology and Astronomy

Scope and sequence of the subject matter

Area Unit Syllabus
Earth and Geological
Activities 21. History of the • History of the earth
Earth • Development of organisms
• Mineral fuels

22. Climate change • National and international efforts for
and Atmosphere reduction and adaptatiion of climate change

• Various layers of atmosphere (Including
ozone layer)

• Effect of chloroflurocarbon on ozone layer
• Greenhouse effect
• Artificial greenhouse and its uses
• Adverse effects of industrial gases

Universe 23. The Universe • Structure and shape of the solar system
• Comet and Meteor
• Galaxy
• Zodiacs and superstitions related to zodiacs
• Natural and artificial satellite

SEE Specification Grid-2074

S.N. Unit (K) (U) (A) (HA) Total Remarks
21. History of the Earth 1×4 7

22. Climate Change and Atmosphere 1×1 1×2 -

23. The Universe

364 Oasis School Science - 10 Geology and Astronomy

UNIT 21 Estimated teaching periods

Theory 4

Practical 1

HISTORY OF THE

EARTH Earth

Objectives

After completing the study of this unit, students will be able to:
• explain the history of the earth with the help of rocks and fossils.
• explain evolution of organisms with the help of fossils.
• identify fossils and describe the formation of fossils and fossil fuels.
• describe the importance of fossil fuels.

21.1 Introduction

The earth is one of the members of the solar system. It originated along with other planets, but
only on the earth’s surface is the climatic condition suitable for the survival of living organisms.
The branch of science in which we study about the earth is called geology. The question about
the origin of the earth remains unsolved. Many scientists have put forward their own opinions
regarding the origin of the earth. But no universal theory of the origin of the solar system has
been proposed yet. Some of the hypotheses regarding the origin of the earth and solar system
are discussed below:

1. Planetesimal hypothesis or George Wofan's hypothesis

A French scientist, George Wofan, put forward a hypothesis in 1749 AD. According to
this hypothesis, the earth along with other planets and satellites were formed when a
comet revolving around the universe struck the sun millions of years ago.

2. Nebular hypothesis or Kant Laplace nebular hypothesis

A German philosopher, Immanent Kant, in 1755 AD put forward another hypothesis
which is called nebular hypothesis. It was modified by a French mathematician Laplace
in 1796 AD. According to this hypothesis, the whole of our solar system, including other
heavenly bodies, was in the form of a nebula, i.e., an extremely large mass of gas and
dust. The nebula began to contract due to its own gravity. During this process, an outer
ring was detached from the central core, which started to revolve around the central core.
The masses began to collide with one another and broke into small masses due to the effect
of gravitation. These small masses began to revolve around the central mass. This central
mass became the sun, and other revolving bodies became planets and satellites, including
the earth.

3. Tidal hypothesis or Jeans and Jeffery’s hypothesis

According to the hypothesis given by Jeans and Jeffery in 1917 AD, a big star orbiting

Geology and Astronomy Oasis School Science - 10 365

round the sun finally approached it. A large mass of gas was ejected from the sun due
to the tidal effect. In the course of cooling, the tidal matter fragmented into small pieces
forming planets, satellites, etc. As a result, the solar system was formed.

By scientific study of rocks and fossils as well as their radioactivity, the age and structure
of the earth have been estimated. Different geologists and zoologists have different
views about the age of the earth. Some of the important statistical data about the earth
according to the citation in the World Book Encyclopedia is given below:

Estimated age – 4.5 billion years
Total surface area – 509,700,000 sq.km
Part of land – 148,400,000 sq. km
Body of water – 361,300,000 sq.km
Diameter – 12756.3 km
Mean density – 5.5 g/cm3
Mass – 6 × 1021 metric tons
Number of satellites – 1 (moon)

21.2 Geological Time Scale

On the basis of existence of living beings, the geological history is divided into four parts.
They are eon, era, period and epoch.

Eon is the longest duration of time, i.e., billions of years, in the geological history which is
divided into eras. The entire geological history has been divided into four eons. They are
Hadean eon (4.5 to 4 billion years ago), Archean eon (4 to 2.5 billion year ago), Proterozoic
eon (2500 to 541 million years ago) and Phanerozoic eon (541 million years ago to recent). The
largest unit of the geological time scale is the eon whereas the smallest one is the epoch. In this
unit, we will study about four geological eras. A geological era is a division of an eon in which
important changes took place. The entire geological history is divided into four geological
eras. They are as follows:

1. Precambrian era (4.5 billion years ago to 57 crore years ago)

2. Palaeozoic era (57 crore years ago to 25 crore years ago)

3. Mesozoic era (25 crore years ago to 6 crore 50 lakh years age)

4. Cenozoic era (6 crore 50 lakh years ago to recent)

1. Precambrian era

The duration of this era was 4.5 billion years to 570 million years ago. In this era, the
origin of the earth took place. There was no existence of living beings before 3.8 billion
years ago. Rocks like gneiss and granite were formed in this era. Bacteria evolved about
3.8 years ago and algae came into existence about 3.2. billion years ago. There is evidence
of the dominance of invertebrates at the end of this era.

eon / i ː ə n / - an extremely long period of time spanning tens of thousands of years

epoch / ˈ i ː p ɒ k / - a length of time which is a division of a period

366 Oasis School Science - 10 Geology and Astronomy

2. Palaeozoic era
The duration of this era was in between 570 million years ago to 250 million years ago.

This era has been divided into six periods. They are the Cambrian, Ordovician, Silurian,
Devonian, Carboniferous and Permian. The main events of this era are as follows:

i. Sedimentary rocks were formed in this era.
ii. Change in weather and atmosphere took place.

iii. Fossils of different types of animals and plants were formed.

iv. Aquatic and terrestrial invertebrates and vertebrates were formed. For example:
winged insects, fishes, amphibians and first reptiles.

v. Different types of green plants like bryophytes and pteridophytes were formed.

3. Mesozoic era

The duration of this era was in between 250 million years ago to 65 million years ago.
In the Mesozoic era, a large number of reptiles evolved on the land and sea. Therefore,
Mesozoic era is also called the golden era of reptiles. This era is divided into three
periods. They are the Triassic period, Jurassic period and Cretaceous period. The main
events of the Mesozoic era area as follows.
i. Different types of hills and mountains were formed in the Mesozoic era.
ii. Climatic condition was suitable to sustain aquatic, terrestrial and aerial animals
like dinosaurs, tortoises, toothed birds, etc.
iii. Evolution, development and extinction of dinosaurs and other huge reptiles
took place.
iv. Coniferous plants were developed in this era.
v. Mammals began to evolve at the end of this era.

Fig. 21.1 Dinosaurs

4. Cenozoic era
The duration of this era is in between 65 million years ago to the present. It is also known

as recent era or era of human beings. This era has been divided into seven periods. They
are the Paleocene period, Eocene period, Oligocene period, Miocene period, Pliocene
period, Pleistocene period and Holocene or recent period. The main events of this era are
given below:

i. Evolution of human beings took place in this era.

Geology and Astronomy Oasis School Science - 10 367

ii. Breaking and expansion of rocks, volcanic eruptions, etc. took place in this era.

iii. The climatic condition was changing with decreasing temperature. As a result,
mountain peaks were covered with ice.

iv. Neanderthal man, toothed animals, gymnosperms and angiosperms evolved.

Reasonable Fact-1

Origin of earth and human beings did not occur at the same time. Give any one scientific
reason.
Ans: The study of radioactivity of rocks and fossils of human beings present on the earth provides
evidence that the origin of the earth and human beings did not occur at the same time.

Reasonable Fact-2

Why is the Mesozoic era called the golden age of reptiles?
Ans: In the Mesozoic era, there was the dominance of various types of large reptiles like dinosaurs, turtles,
etc. on land and marine water. Therefore, the mesozoic era is also called the golden age of reptiles.

Reasonable Fact-3

Living beings evolved after millions of years of the formation of the earth, why?
Ans: The earth evolved about 4.5 billion years ago. At the time of evolution of the earth, it was very
hot and there was no suitable environment for the evolution and survial of living organisms. So there
were no life at the time of the evolution of the earth.

21.3 Evolution of Life

About 600 million years ago, there was no favorable environment for the evolution of
organisms on the earth. After continuous change in the climatic condition, it became favorable
to support/sustain life. During the course of evolution, various kinds of organisms evolved,
developed and became extinct. The organisms which became extinct from the earth left some
evidences called fossils on the sedimentary rocks. After the complete study and analysis of
these fossils, scientists discovered the process of evolution of life on earth.

In the Precambrian era, there were no sedimentary rocks, which indicates that evolution of
life did not take place then. In this era, evolution of unicellular organisms and development
of multicellular organisms took place. In the Palaeozoic era, rainfall occurred after various
change in water, land and weather, which created a favorable condition for the evolution and
development of organisms. In the Palaeozoic era, different types of aquatic as well as terrestrial
animals evolved. Fishes, amphibians and some primitive reptiles evolved and well developed
in this era. In the Mesozoic era, several types of reptiles like dinosaurs, toothed birds evolved,
developed and became extinct also. So, the Mesozoic era is also called the age of reptiles or the
age of dinosaurs. In the Cenozoic era, primitive humans evolved. Many mammals like the cat,
rat, dog, elephant, crocodile, bat, etc. evolved and developed.

A brief description of the geological history and evolution of life is summarized in the given
table. This description is based on the book "The ICC's Geologic Time Scale, 2012".

368 Oasis School Science - 10 Geology and Astronomy

Geological history and evolution of life

Era Duration Evolution of life
Precambrian
4.5 billion years ago to Origin of the earth
57 crore years ago
Evolution of unicellular organisms and development of
multicellular organisms

Palaeozoic 57 crore years ago to Development of a few marine organisms
25 crore years ago
Mesozoic Development of vertebrates in marine water
Cenozoic 25 crore years ago to 6
crore 50 lakh years ago Evolution of life on land, green vegetation and develop-
6 crore 50 lakh years ment of fishes
ago to the present
Evolution of winged insects, development of fishes and
plants

Evolution of amphibians and reptiles,
development of fern plants

Extinction of many invertebrates and vertebrates, devel-
opment of reptiles

Evolution of dinosaur, reptiles and coniferous plants

Dominance of reptiles, well developed dinosaurs, birds
and other organisms

Evolution of flowering plants and different insects, ex-
tinction of dinosaurs and other large reptiles

Evolution of first mammal and horse

Development of various mammals like elephant, whale,
etc. and development of owl

Evolution of sharp-toothed cats and monkeys

Development of grasses

Evolution of human beings

Development of Stone Age human beings and giant
hairy elephants, i.e., mammoths

Development of modern human beings and other mam-
mals, dominance of human beings

21.4 Fossils

The dead remains of animals and plants or their impressions which are buried in the earth
crust over a long period of time are called fossils. In general, fossils are present in sedimentary
rocks. There are several processes by which fossils are formed.

Fig. 21.2 Fossil of a Dinosaur Oasis School Science - 10 369
Geology and Astronomy

Process of fossil formation

The process by which fossils are formed is called fossilization. Some parts of organisms or the
whole body of organisms decay in the soil while some are preserved after they are buried in
the sand, mud, etc. In this process, a fossil is formed by the impression of preserved parts and
skeleton after they are pressed by rocks. The fossils are saved by sedimentary rocks.

Due to natural disasters like volcanoes, earthquakes, floods, etc. the plants and animals may
sink into the earth's ground. The delicate parts of organisms decay in the soil while hard parts
remain pressed down in the ground. The external morphology of those hard parts is formed
in the soil, sand, etc. in the form of all impression. In this way, fossils are formed.

Fig. 21.3 Formation of fossils

Identification of fossils
The methods for the identification of fossils are as follows:
i. The impression of a whole or a part of any organ of dead body remains in the hard

ground or stone. Fossils are identified by studying these impressions.

ii. The whole skeleton of animals and plants are pressed in rocks. Fossils can be
identified from the study of such structures.

iii. The fossils are also identified by the morphology of the hard parts of organisms
like the teeth, bones, skeletons, shoots, etc.

Importance of fossils
The study of fossils is very important for human beings because of the following reasons:
i. The study of fossils helps us to discover the evolutionary trend of plants and

animals on the earth.

ii. The study of fossils helps us to investigate the deposits of coal and oil inside the
earth's crust.

iii. The study of fossils helps us to determine the age of rocks, to know the geological
history and to know about the organic evolution on the earth.

sedimentary /sedɪˈmentri/ - formed from the sand, stones, mud, etc.

370 Oasis School Science - 10 Geology and Astronomy

21.5 Fossil Fuels

The fuels which are formed in nature by the decomposition and preservation of organic matter
under high temperature and pressure for a long period of time are called fossil fuels. Coal, oil
and natural gas are the most important fossil fuels.

a. Coal

Coal is a hard black mineral that is found below the ground and burnt to produce heat.
Coal is a fuel formed from fossils. So it is called a fossil fuel.

Formation of coal

In ancient times, plants and animals were buried under the earth crust due to different
geological phenomena like earthquakes, volcanoes, etc. Then the remnants were pressed
under high pressure and temperature for a long time. Elements like carbon, hydrogen
and oxygen are present in coal. When a whole or a part of a plant remains in swamp
land in the form of a fossil for a long time, it is converted into coal. The principal parts
of plants are cellulose and lignin. These are formed from protein, oil, organic acid and
mineral oil, etc. Thus, lignin plays an important role in the formation of coal.

Fig. 21.4 Formation of coal

Importance of coal
i. Coal is used as fuel in railway transportation, industries, brick factories, iron

factories, etc.
ii. Coal is used to generate electricity, for manufacturing petrol, natural gas, coke, etc.
iii. It is also used for making various organic compounds, like benzene, phenol, etc.

b. Mineral fuel (or mineral oil)
Mineral fuel is a mixture of hydrocarbons (about 90% to 95%) and other substances like

oxygen, nitrogen, sulphur, etc. Mineral fuel is formed after the compression of fossils
under sedimentary rocks for millions of years. For example, petroleum products.

Geology and Astronomy Oasis School Science - 10 371

Formation of mineral fuel (or mineral oil)
Mineral fuels are formed in nature by the decomposition of parts of plants and animals

that are buried under the earth's surface for a long period of time. When the hard parts
of plants and animals are pressed by sedimentary rocks under high temperature and
pressure, various chemical reactions occur. As a result, crude oil is formed from the
hydrocarbons. In this way, mineral oils are obtained by the purification of crude oil.
These fuels are obtained by drilling holes in the earth's surface.

Pipes to take out oil and gas

Hard rock
Oil
Gas
Water

Stand rock and gravel

Fig. 21.5 Process of extracting mineral oil

Importance of mineral fuel (or mineral oil)
i. It is used as fuel in vehicles, industries, factories, etc.
ii. It is used for generating electricity, cooking food, etc.
iii. It is used for making various types of chemicals like plastics, fertilizers, insecticides, etc.

The main uses of the given petroleum products are mentioned below:

Petroleum products Main uses
Natural gas As a fuel
Paraffin wax For making candles, matches, etc.
Petroleum coke As a smokeless fuel
Petroleum ether As a good solvent, for cleansing purpose
Lubricating oil, grease, vaseline For lubrication
Gas oil and diesel oil As fuel in vehicles
Kerosene As a fuel
Petrol As a fuel in vehicles

372 Oasis School Science - 10 Geology and Astronomy

Reasonable Fact-4

Why is natural gas considered a good fuel?
Ans: Natural gas is considered as a good fuel because of the given reasons:
(i) It burns completely without leaving any residue.
(ii) It burns with a smokeless flame and does not cause air pollution
(iii) It does not produce harmful chemicals on burning.
(iv) It has high calorific value, i.e., 55 kJ/g.

SUMMARY

• The entire history of the earth is divided into four different divisions. They are
the eon, era, period and epoch.

• A geological era is the duration of time in geological history in which important
changes took place.

• In the history of the earth, there are four eras. They are the Precambrian era,
Palaeozoic era, Mesozoic era and Cenozoic era.

• Igneous rocks were formed in the Precambrian era and sedimentary rocks were
formed in the Palaeozoic era.

• Hills and mountains were formed in the Mesozoic era.
• Dinosaurs evolved, developed and became extinct in the Mesozoic era. So, this

era is also called, era of reptiles, or the golden age of dinosaurs.
• Most mammals and human beings evolved and developed in the Cenozoic era.
• Fossils are the dead remains of plants and animals or their impression, which

were buried in the earth crust over a long period of time.
• The process by which fossils are formed is called fossilization.
• Coal, petrol, natural gas, etc. are the examples of fossil fuels which are used to

run industries, factories, automobiles, etc.

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Exercise

Group-A

1. Define eon and era.

2. What is geological period?

3. Which is the largest unit of the geological history?

4. Into how many eras is the evolution of organisms on the earth divided?

5. What is geological epoch?

6. What is the duration of Mesozoic era?

7. List any two events that occurred in Mesozoic era.

8. What is the duration of Cenozoic era?

9. List the major events that occurred in Cenozoic era.

10. What is the duration of Precambrian era?

11. What is a fossil?

12. Name the branch of science which deals with the study of fossils.

13. What is mineral oil?

14. Name the main elements found in the mineral oil.

15. In which period did following organisms evolve?

(a) Insects with wings (b) Fern

17. In which era did evolution of modern human being take place?

18. In which era did evolution of fish and dinosaur take place?

19. In which era did evolution of monkey and flowering plants take place?

20. In which era the evolution and development of mammals took place?

21. In which era did fish and dinosaur evolve?

22. Name the era in which whale evolved.

23. How old is the earth?

24. Write two features of Mesozoic era.

Group-B

1. State the hypothesis propounded by George Wofan about the origin of the earth.

2. Write down the hypothesis propounded by Jeans and Jeffery about the origin of the solar
system.

3. Describe in brief the Kant-Laplace nebular hypothesis about the origin of the earth.

4. Why is Mesozoic era called golden era of dinosaurs? Give reason.

374 Oasis School Science - 10 Geology and Astronomy

5. Cenozoic era can be called golden era for human beings, why?
6. Write any two differences between cenozoic era and mesozoic era.
7. Write any two differences between palaeozoic era and cenozoic era.
8. What is the view regarding the origin of the earth according to Kant?
9. Which era is called era of creeper why?
10. Why are fossils not found in igneous rock?
11. Natural gas is found mostly on the top of mineral oil in nature, why?
12. Why did dinosaur evolve earlier than man?
13. Write any two differences between palaeozoic era and mesozoic era.
14. Write any two methods for identification of fossils.
15. How is it known that there were dinosaur on the earth in ancient time? In which period

were they dominant?

Group-D

1. Write down the importance of fossils in brief.
2. Write short notes on fossil fuel and coal.
3. Describe in brief the method of coal formation.
4. Give a brief account of the earth according to "The World Book Encyclopedia".
5. Draw a labeled diagram showing the process of formation of coal and natural gas.
6. Explain the evolution process occurred on the Mesozoic and Cenozoic era. Also, mention

their differences.

Geology and Astronomy Oasis School Science - 10 375

UNIT 22 Estimated teaching periods

Theory 4

Practical 0

ATMOSPHERE AND

CLIMATE CHANGE Joseph Charles Farman
(1930-2013 AD)
Objectives

After completing the study of this unit, students will be able to:

• explain different layers of the atmosphere including the ozone layer.
• describe the effects of chlorofluorocarbons on the ozone layer.
• describe the adverse effects of industrial gases.
• explain in brief climate change and the national and international efforts for the reduction

of and adaptation to climate change.

22.1 Introduction

The earth is surrounded by a thick layer of air. This thick layer of air is called the atmosphere.
The thick layer of air that surrounds the earth's crust is called the atmosphere. The biosphere
of the earth consists of three different spheres, which are: hydrosphere, lithosphere and
atmosphere. The atmosphere consists of different types of gases like nitrogen, oxygen, carbon
dioxide, neon, argon, etc. It also consists of water vapour and dust particles. The atmosphere
covers the lithosphere and hydrosphere of the earth in the form of a canopy. Therefore,
atmosphere is the canopy of air around the earth. The air present in the atmosphere keeps on
moving due to the effect of the earth's gravity.

22.2 Structure of Atmosphere Exosphere Ozone layer
(Above 720 km)
As the altitude increases, the layer of atmosphere
becomes thinner, and the temperature also Thermosphere
varies at different heights. According to the (80–720 km)
altitude and temperature, the atmosphere is
divided into five different layers. They are as Mesosphere
follows: (50–80 km)

1. Troposphere Stratosphere
2. Stratosphere (16–50 km)
3. Mesosphere Troposphere
4. Thermosphere (0–16 km)

5. Exosphere Earth
Fig 22.1 Various layers of atmosphere

canopy /ˈkænəpi/ - a layer of something that spreads over an area like a roof

376 Oasis School Science - 10 Geology and Astronomy

1. Troposphere

The troposphere is the lowermost layer of the atmosphere which extends upto 16km
from the surface of the earth. It contains a large amount of heavy gases like nitrogen,
oxygen, carbon dioxide, inert gases, water vapour, dust particles, etc. Various
activities related to the weather like cloud formation, wind, light, rain, hail stone,
lightning, fog formation, etc. take place in this layer. Therefore, the troposphere is
very important for meteorologists. Scientists forecast the weather by studying this
layer. The temperature of the troposphere changes according to the height. So, this
layer is also called a variable layer. There is a fall of about 6.5 0C in temperature in
this layer per kilometer increase in altitude. The troposphere is thinner at the poles.
About 95% of the atmosphere lies in the troposphere. The uppermost part of this
layer is called the tropopause. It separates the troposphere and stratosphere. It has
about –560C temperature. The troposphere lies at about 8 to 10 km from the poles and
about 16 km from the equator.

Reasonable Fact-1

Why is the troposphere also called variable layer?
Ans: The temperature of the troposphere varies according to its height. It decreases as the height
increases. So the troposphere is also called a variable layer.

Reasonable Fact-2

The troposphere is very important for meteorologists, why?
Ans: The troposphere is very a important layer for meteorologists because various activities related
to the weather like cloud formation, lightning, rain, frost, hailstorm, fog, etc. occur in this layer. By
the study of the troposphere, meteorologists forecast the weather.

2. Stratosphere

The stratosphere is the second layer of the atmosphere located between the troposphere
and mesosphere. This layer extends from 16 km to 50 km vertically upward from the
earth’s surface. The stratosphere consists of the ozone layer at its upper surface. So, it is
also called the ozonosphere. The ozone layer is formed and destroyed at about 20-25km
upwards in the presence of solar radiation. The ozone layer absorbs most of the solar
radiations and stops it from entering the earth which creates favorable condition for
living beings of the earth. In the stratosphere, the temperature increases from –560C to
–2°C as the height increases. The temperature of the lower layer of the stratosphere is
about –530C. This layer contains thin cloud. There is negligible amount of humidity in
this layer. The uppermost boundary of this layer is called the stratospause. It separates
the stratosphere and mesosphere.

Reasonable Fact-3

The temperature of the stratosphere increases as the height increases, why?
Ans: The uppermost layer of the stratosphere contains the ozone layer. This thick layer of air
absorbs much of the solar radiation. Due to absorption of the solar radiation, the temperature of the
stratosphere increases as the height increases.

meteorologist /ˌmiːtɪəˈrɒlədʒɪ st/ - aansdciietnstcishtanwgheos studies meteorology, i.e. the scientific study of the earth's atmosphere

Geology and Astronomy Oasis School Science - 10 377

Reasonable Fact-4

Why is the stratosphere called a protective sphere?
Ans: The uppermost layer of the stratosphere contains the ozone layer. This thick layer of
air absorbs much of the solar radiations and shields the earth from the harmful ultraviolet
radiation. It prevents us from dangerous diseases. Therefore, the stratosphere is called a
protective sphere.

3. Mesosphere

The mesosphere is the third layer of the atmosphere located between the stratosphere and
thermosphere. It extends from our altitude of 50 km to 80 km above the earth's surface.
The temperature of the mesosphere decreases with increase in height. The temperature
of this layer varies from –2°C to –109°C with the increase in height. In the mesosphere,
strong wind blows from the west to the east during winter and from the east to the
west during spring season. The streaks of hot gases released from meteors can be seen
in this layer. This layer does not determine the climate and weather. The uppermost
boundary of the mesosphere is called the mesopause. It separates the mesosphere and
thermosphere. The temperature of the mesosphere is about –1090C during summer.

4. Thermosphere

The thermosphere is the layer of atmosphere located between the mesosphere and
exosphere. It extends from 80 km to 720 km vertically upward from the earth's surface.
This sphere occupies about 0.01% of the total region of the atmosphere. The lower region
of the thermosphere contains ions of nitrogen, oxygen, etc. The gaseous molecules
like nitrogen, oxygen, etc. undergo ionization and give ions due to the effect of UV-
radiation of sun. Therefore, thermosphere is also called the ionosphere. In this layer,
there is very high temperature due to the effect of solar radiation. The upper region of
the thermosphere mainly contains hydrogen and helium.

5. Exosphere

The exosphere is the outermost layer of the atmosphere, which extends beyond the
thermosphere. The temperature of this layer is very high, i.e., about 1200°C to 6000°C.
In exosphere, the density of air is very low, but the wind blows at high speed. This
layer is very far from the earth's surface, so there is no effect of gravity. The exosphere
mainly contains hydrogen and helium. The exosphere forms the outermost edge of the
atmosphere. So, it is also called the fringe region.

Reasonable Fact-5

The atmosphere is called a protective umbrella, why?
Ans: The ozone layer present in the atmosphere absorbs most of the solar radiation and shields
the earth from harmful UV-radiation. It protects the living organisms from various diseases and
disorders. Therefore, the atmosphere is called a protective umbrella.

22.3 Ozone Layer

The layer of pale-blue gas, i.e., O3 present in the stratosphere is called the ozone layer. This
layer absorbs about 99% harmful solar radiation like UV-rays, X-rays, gamma rays, etc. This
layer protects living organisms from harmful ultraviolet radiation as well as helps to maintain
the temperature of the earth. Therefore, the ozone layer is also called a protective layer.

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Ozone formation is a natural process, which is formed by the combination of three oxygen
atoms due to the influence of ultraviolet radiation. When an oxygen molecule absorbs high
energy solar radiation, it dissociates into nascent oxygen. The nascent oxygen is highly reactive
and thus combines with oxygen molecule, and forms one molecule of ozone.

O2 UV-rays [O] + [O] (Nascent oxygen)
O2 + O O3 (ozone)

16-50 km
0-16 km

Ozone layer Fig. 22.2 Ozone hole

Importance of ozone layer

The ozone layer protects the earth from harmful ultraviolet radiation. The ozone layer
not only absorbs ultraviolet radiation but also radiations of wave length less than
3 × 10–7m. It prevents us from dangerous diseases like cataracts (blindness), skin burning, skin
cancer and immune deficiency due to over exposure to ultraviolet radiation. It also helps to
balance the weather and temperature of the earth and to reduce the greenhouse effect.

Depletion of ozone layer

Decreasing the thickness of the ozone layer or formation of a hole in it, is called ozone layer
depletion. An English scientist J.C. Farmann had reported ozone depletion for the first time

above Antarctica. According to environmental scientists, the CFCs (chlorofluorocarbons) and

oxides of nitrogen, when released from the lower atmosphere reach the stratosphere and

destroy the ozone layer. A CFC is a stable non-toxic, non-inflammable and cheaply produced

chemical. It is released by aerosol spray cans, refrigerators, air conditioners, industries,

research laboratories, etc. When this CFC reaches the stratosphere, it undergoes photolytic

dissociation due to the influence of ultraviolet radiation. As a result, it gives nascent chlorine

and converts ozone into oxygen. This process takes place as follows:

CFCl3 UV-rays CFCl2 + Cl

Cl + O3 O2 + ClO

2ClO UV-rays 2Cl + O2

Chlorofluorocarbon (CFC) is a major industrial chemical that depletes the ozone layer. It was
discovered by Thomas Mitts in 1930 AD. It is of two types: CFC - 11 and CFC-12. It is cheaper

aerosol /ˈeːrəsɒl/ - a metal container in which a liquid is kept under pressure and released as a spray

Geology and Astronomy Oasis School Science - 10 379

than ammonia. So, it is used as a coolant in refrigerators. Along with CFCs, methyl chloroform,
methyl bromide, carbon tetrachloride, etc. are also responsible for ozone layer depletion.

Similarly, oxides of nitrogen, like nitric oxide (NO), nitrogen dioxide (NO2), etc., which are
liberated by aeroplanes, rockets and chemical fertilizers, react with ozone and convert it into

oxygen. Hence, oxides of nitrogen also deplete the ozone layer.

NO + O3 NO2 + O2

2NO + O3 N2O3 + 2O2

The extremely cold temperature, i.e., – 850C to – 900C, in Antarctica plays a significant role in
ozone layer depletion. Ozone and chlorine containing molecules are absorbed on the surface
of ice crystals at high altitudes in Antarctica. In the presence of solar radiation, chlorine ions
are liberated, which react with ozone and form oxygen gas.

Effects of ozone layer depletion

The depletion of ozone layer affects the physical as well as biological aspects of the earth. The
major effects of ozone layer depletion are as follows:

1. In human beings, UV-rays cause various diseases like cataract (blindness), sun burn, eye
burn, skin cancer, breast cancer, leukaemia, etc. The immune system of human beings is
also weakened.

2. Over exposure to UV-rays may lead to mutation in different generations.

3. Over exposure to UV-rays hampers the growth and development of plants and animals.

4. Due to ozone layer depletion, more solar radiation enters the earth’s surface, which
increases the temperature of the earth and causes the greenhouse effect.

5. UV-rays reduce the rate of photosynthesis and crop production.

6. Due to more heat, various species of plants and animals may go extinct.
7. Ozone layer depletion brings out significant changes in climatic condition.

Protection of ozone layer

Ozone layer depletion can be protected by reducing the production of CFCs and oxides of
nitrogen. Some ways to reduce the amount of CFC and oxides of nitrogen in the environment
and hence to protect ozone layer are given below:

1. Alternative chemicals should be used in refrigerators, air conditioners and other
machines instead of CFCs.

2. The production and use of chlorofluorocarbons and oxides of nitrogen should be banned.

3. Public awareness should be generated about ozone layer depletion and its protection.

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Reasonable Fact-6

'The main cause of depletion of ozone layer is human being.' Clarify this statement.

Ans: The ozone layer is depleted by air pollution caused due to the production of industrial
gases. Various industrial gases that deplete the ozone layer are produced only due to human
activities on earth. So we can say that the main cause of ozone layer depletion is human
activities on earth.

22.4 Industrial Gases

In many industries, during the process of production, different types of toxic gases, lead,
metal, complex compounds, etc. are released. Various toxic gases like carbon dioxide, sulphur
dioxide, carbon monoxide, nitrous oxide, etc. which are produced from industries are called
industrial gases. When these gases reach the atmosphere they react with each other as well
as with the water of the atmosphere. For example, sulphur dioxide combines with oxygen to
form sulphur trioxide. Similarly, nitric oxide combines with ozone to give nitrogen dioxide
and finally nitrogen pentoxide.

2SO2 + O2 2SO3

(Sulphur dioxide) (Sulphur trioxide)

NO + O3 NO2 + O2

(Nitric oxide) (Ozone) (Nitrogen dioxide)

4NO2 + O2 2N2O5

(Nitrogen dioxide) (Nitrogen pentoxide)

The mixture of industrial gases, dust, smoke, lead, etc. released from factories cause air
pollution. It hinders human muscular functioning, mental functioning, etc. Human beings
suffer from various diseases like pneumonia, bronchitis, respiratory distress, eye-diseases, etc.
Different types of air pollutants like industrial gases, acids, solid particles remain in the form
of layer above the industrial cities. This is called industrial smog. As a result, there is a mist in
the city and the area becomes clouded. It also affects the weather.

22.5 Climate Change

Climate is the atmospheric phenomenon over a long period of time. Climate change refers to
the variation in the earth's global climate or in the regional climate over time. Human beings are
responsible for change in the climate of a region. The main factor for climate change is increase
in the level of carbon dioxide in the atmosphere. Overuse of fossil fuels, deforestation, burning
of firewood, forest fire, etc. increase concentration of carbon dioxide in the atmosphere.

Climate change is a change in the statistical distribution of weather patterns when that change
lasts for an extended period of time, i.e., decades to millions of year. It may refer to a change
in average weather conditions or in the time variation of the weather around longer-term av-
erage condition. Nepal has different climatic conditions due to variation in the geographical
structures. Nepal extends from 60 m to 8848m. Nepal has been divided into the Terai, Hilly

pathogenic /pæθəˈdʒenɪk/ - related to agents that cause diseases

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and Himalayan region. The climate of Nepal ranges from extreme hot to extreme cold. So,
Nepal is a sensitive country in terms of climate change, and change in the climate is a burning
issue for Nepal.

Causes of climate change

Climate change is caused by various factors such as biotic processes, variations in the solar
radiation received by the earth, tectonic movements, volcanic eruptions, etc. Certain human
activities like deforestation, industrialization, excessive use of chemical fertilizers, etc. play a
significant role in climate change. The major causes of climate change are given below:

1. Increase in temperature

Different parts of the earth receive different amounts of solar radiation due to geograph-
ical variation. The parts of the earth that receive more solar radiation become hotter than
the parts that receive less solar radiation. The increase in temperature is one if the causes
of change.

2. Release of greenhouse gases

Different types of greenhouse gases like carbon dioxide, chlorofluorocarbons, methane,
nitrous oxide, ozone, etc. are released in the atmosphere due to various human activities.
These greenhouse gases are responsible for climate change.

3. Deforestation

Forests help to maintain a balance between carbon dioxide and oxygen in the atmos-
phere as green plants use carbons dioxide gas for photosynthesis. The amount of carbon
dioxide gas in the atmosphere increases due to deforestation, which results in increase
in the temperature and climate change.

4. Excessive use of chemical fertilizers
Greenhouse gases are released due to excessive use of chemical fertilizers. Similarly,

overuse of chemical fertilizers makes the land dry. As a result, the temperature of the
earth increases, and change in climate takes place.

5. Industrialization

Various types of gases like carbon dioxide, sulphur-dioxide, etc. are released in the
atmosphere while running industries. There gases contribute to greenhouse effect, which
results in change in climate.

6. Volcanic eruption

Dust particles and compounds of sulphur are released during volcanic eruption. These
substances accumulate in the stratosphere and block solar radiation, which results in
climate change.

Effects of climate change

(i) It causes loss of biodiversity.
(ii) It decreases agricultural production and changes the crop pattern.
(iii) It melts snow in the polar region and the Himalayan region.
(iv) It increases the sea level, due to the melting of ice in the polar region.

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(v) It decreases the amount of fresh water.
(vi) It affects the global water cycle.
(vii) It changes wind circulation and affects the pattern of rainfall of a particular place.
(viii) It causes improper distribution of rainfall.

Measures of climate change management

1. Deforestation should be discouraged and afforestation should be encouraged.
2. Plantation should be done on bare parts of land.
3. Water resources should be conserved and managed.
4. Overuse of fossil fuels should be reduced.
5. Alternative sources of energy should be developed and used.
6. Environment pollution should be minimized.
7. Release of greenhouse gases should be stopped.
8. Use of chlorofluorocarbons should be banned.
9. Proper management of waste materials should be done.
10. Natural environment should be conserved.
11. Agriculture system should be improved.
12. Unmanaged development works should be controlled.
13. Proper use and management of automobiles should be ensured.
14. Overuse of chemical fertilizers should be discouraged.

15. Public awareness should be generated.

Climate change can be minimized by conserving the environment. It is the duty of every
person to do something for environment conservation to minimize climate change.

22.6 National and International Efforts to Reduce and Adapt to
Climate Change

At present, climate change has become a global issue due to its adverse impacts on the
physical and biological environment. Its adverse effects are seen all over the world. It has
many negative impacts on all living beings including human beings. Various studies and
researcher have shown that the escalation of rapid climate change may create crisis in
the existence of living beings. Therefore, it is the need of the time to adopt various ways
to minimize climate change. To solve the problem of climate change, the United Nations
Organization has taken a good initiation. It is possible to minimize the burning issue of
climate change through institutional and organized efforts. Among the various efforts
in this regard, the effort of including this subject matter in curriculum of school, college,
university, etc. has vital role in generating awareness to reduce climate change. There
are many efforts that have been made in national and international levels to minimize
climate change and its adverse effects.

mist /mɪst/ - a cloud of very small drops of water in the air

monument /ˈmɒnjʊm(ə)nt/ - a building, column, statue, etc. built to remind people of a famous person or event

Geology and Astronomy Oasis School Science - 10 383

National efforts for reduction and adaptation to climate change

The efforts that have been made inside Nepal to reduce and adapt to climate change are called
national efforts.

Some of the major efforts

1. National Communication Report

2. Climate Change Policy, 2067

3. Climate Change Adaptation strategic Program

4. National Adaptational Program

5. Local Adaptational Program Related to Climate Change

6. Other programs

1. National Communication Report
Regarding the issue of climate change, Nepal has submitted its first National

Communication Report to the COP of the United Nations Organization Protocol. In this
report, adverse impacts of climate change in Nepal and ways for its adaptation, plans
for capacity building to go against climate change and implementation of policies and
laws to combat climate change, have been mentioned. This report also includes the need
of study and research in sectors like transportation, industry, agriculture, forest, health,
management of garbage and wastes that are affected by climate change. It is emphasized
that it is necessary to establish an independent mechanism for scientific learning to
reduce climate change and its adverse impacts on the natural environment.

2. Climate Change Policy, 2067

Climate change causes increase in atmospheric temperature. The increase in temperature
has negative impacts on agriculture, forest, human health, biodiversity, socio-economic
aspects, etc. in Nepal. Thus, it is essential to generate awareness regarding ways to
adapt to and reduce climate change and its negative effects on different sectors. Also,
it is necessary to build the capacity of the people at various levels regarding of climate
change. In this regard, Climate Change Policy, 2067 has been developed with specific
objectives and policies.

3. Climate Change Adaptation Strategic Program

In May 2008, Climate Investment Fund invited the Nepal Government to take part in
the global model program regarding adaptation to climate change. The World Climate
Model Program provides financial support to poor countries to adopt various ways to
adapt to climate change. The Climate Change Adaptation Program of Nepal has been
taken as a long-term program by dividing it into five sectors.

(i) Climatic adaptation of watersheds that lie in the ecosystems of the hilly regions.

(ii) Adaptation to risks induced by climate

(iii) Mainstream flow of 'Climate Change Risk Management' in development projects

(iv) Building a 'Capable Community' for climate change adaptation with the active
participation of the private sector

(v) Promotion of climate change adaptation for vulnerable species

384 Oasis School Science - 10 Geology and Astronomy

4. National Adaptation Program

This program was prepared by the Nepal Government in September 2010 AD. The main
objective of this program is to evaluate the risks of climate change. It has conducted 250
programs in the form of nine integrated programs.

5. Local Adaptation Program Related to Climate Change

This program has been conducted at the community level in the rural areas. It selects the
process of climate adaptation and equi-adaptation on the basis of four theories. They are
progressive, inclusive, capability and flexibility. This program prepares and co-ordinates
local and national level programs related to climate change. Various programs related
to minimizing the adverse impacts of climate change at the local level are conducted to
provide suitable services to highly endangered communities, region and family.

6. Other Programs

Under these programmes, various programs related to improved brick factories,
improved stove and biogas, encouragement program on carbon storage, rainwater
harvesting program, pre-information system related to natural disasters, seminars and
conferences are conducted.

International efforts for reduction and adaptation to climate change

The efforts made outside Nepal for the reduction and adaptation to climate change are called
international efforts. These efforts are described below:

1. The United Nations Framework Convention on Climate Change (UNFCCC)

This is an international treaty negotiated at the 'Earth Summit' in Rio de Jenerio from
3 to 14 June 1992, which entered into force on 21 March 1994. The UNFCCC objective
is to stabilize greenhouse gas concentrations in the atmosphere at a level that would
prevent dangerous anthropogenic interference with the climate system. This framework
convention addressed various issues like increasing environmental pollution, sustainable
development program, condition induced due to climate change. Climate change cannot
be stopped completely. Therefore, our lifestyle should adapt to the changing climate.
Nepal signed in the UNFCCC treaty on 12 June 1992. The parliament of Nepal adopted
the treaty in 1994 AD, and the articles of the treaty are being implemented in Nepal.

2. UN Climate Change Conference

On the basis of the treaty of UNFCCC negotiated at the 'Earth Summit' in June 1992,
countries that signed the treaty must inform the works and programs conducted in their
countries related to climate change to their member countries. The UN Conference on
Climate Change has been conducted 19 times till 2013 AD, and the 20th conference was
held in Peru in 2014. In 2011, Nepal prepared the Climate Change Policy on the basis of
the UNFCCC and is implimenting accordingly.

3. Agenda 21

Agenda 21 is a comprehensive plan of action to be taken globally, nationally and locally
by organizations of the United Nation's System, Government and Major groups in every
area which human impacts on the environment.

Geology and Astronomy Oasis School Science - 10 385

Agenda 21, the Rio Declaration on Environment and Development and the statement
of principles for the sustainable management of forest were adopted by more than
178 governments at the United Nations Conference on Environment Development
(UNCED) held in Rio de Janerio, Brazil, 3 to 14 June 1992. The commission on sustainable
Development (CSD) was created in December 1992 to ensure effective follow-up of
UNCED, to monitor and report on implementation of the agreements at the local national,
regional and international levels. It was agreed that a five year review of 'Earth Summit'
progress would be made in 1997 by the United Nations General Assembly meeting in
special session.

The full implementation of Agenda 21, programme for further implementation of
Agenda 21 and the commitments to the Rio principles, were strongly reaffirmed at the
World Summit on Sustainable Development (WSSD) held in Johannesburg, South Africa
from 26 August to 3 September 2002.

4. Intergovernmental Forum

It is a scientific and intergovernmental body, under the auspices of the United Nations,
set up at the request of member governments, dedicated to the task of providing the
world with an objective, scientific view of climate change and its political and economic
impacts. It was first established in 1988 by two United Nations organizations, the World
Meteorological Organization and the United Nations Environment Programme. It
produces reports that supports the UNFCCC. Its reports cover the scientific, technical
and socio-economic information relevant to understanding scientific basis of the risk
of human induced climate change, its potential impacts and options for adaptation and
mitigation.

5. Kyoto Protocol

The Kyoto Protocol is an international agreement linked to the United Nations Framework
Convention on Climate Change, which commits its parties by setting internationally
binding emission reduction targets.

Recognizing that developed countries are principally responsible for the current high
levels of greenhouse gases emissions in the atmosphere as a result of more than 150 years
of industrial activity, the protocol places a heavier burden on the developed nations un-
der the principle of common but differentiated responsibilities.

The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered
into force on 16 February 2005. The detailed rules for the implementation of the proto-
col were adopted at COP 7 in Marrakesh, Morocco, in 2001, and are referred to as the
"Marrakesh Accords". Its first commitment period started in 2008 and ended in 2012. Till
2008, 36 developed and 137 developing countries had adopted this protocol. In Doha,
Qatar on 8 December 2012, the Doha Amendment to the Kyoto Protocol was adopted.
The amendment includes Kyoto:

i. New commitments for Annex-I parties to the Protocol who agreed to take on
commitments in a second commitment period from 1 January to 31 December 2020.

386 Oasis School Science - 10 Geology and Astronomy

ii. A revised list of greenhouse gases (GHG) to be reported by parties in the second
commitment period, and

iii. Amendments to several articles of the Kyoto Protocol which specially, referenced
issues pertaining to the first commitment period and which needed to be updated
for the second commitment period.

On 21 December 2012, the amendment was circulated by the Secretary General of
the United Nations acting in his capacity as the Depositary, to all parties to the Kyoto
Protocol in accordance with articles 20 and 21 of the Protocol.

During the first commitment period, 37 industrialized countries and the European
Community committed to reduce GHG emissions to an average of five percent against
1990 levels. During the second commitment period, parties committed to reduce GHG
emissions by at least 18 percent below 1990 levels in the eight year period from 2013 to
2020. However, the composition of parties in the second commitment period is different
from the first.

6. Measures to reduce GHG on the basis of Kyoto Protocol

Under the Kyoto Protocol, countries must meet their targets primarily through national
measures. However, the protocol also offers them an additional means to meet their tar-
gets by way of three market based mechanisms. They are:

i. International Emissions Trading

ii. Clean Development Mechanism

iii. Joint implementation

These mechanisms help to stimulate green investment and help parties meet their emis-
sion targets in a cost-effective way.

7. Reduction of emission due to deforestation
Forests are the most important natural resources for the absorption and storage of car-

bon. For this, deforestation should be reduced by developed countries which emit a
large amount of greenhouse gases and these countries should help underdeveloped and
developing countries in forest conservation and management providing financial as
well as technical support. In this regard, both developed and developing countries have
agreed.

Geology and Astronomy Oasis School Science - 10 387

SUMMARY

• The layer of air that surrounds the earth is called atmosphere.

• In the atmosphere, there are five different layers. They are the troposphere,
stratosphere, mesosphere, thermosphere and exosphere.

• Troposphere is also called living sphere, stratosphere is also called ozonosphere
and thermosphere is also called ionosphere.

• The layer of O3 which is present in the stratosphere and prevents the entry of
harmful solar radiation to the earth’s surface is called ozone layer.

• Decreasing the thickness of the ozone layer or formation of a hole in it is called
ozone layer depletion.

• CFC is the main gas responsible for ozone layer depletion.

• The mixture of different industrial gases like CO2, CH4, CFCs, water vapour, etc.
present in the troposphere are called greenhouse gases.

• Our earth is surrounded by a mixture of various gases which allows solar
radiation to enter but does not allow them to escape after reflection. As a result,
the temperature of the earth increases. This phenomenon is called greenhouse
effect, or global warming.

• Various toxic gases like CO2, SO2, SO3, NO, NO2, N2O5, etc., which are released
by industries, are called industrial gases.

• Industrial gases in reaction with water give acids. Those acids when they fall in
the form of rain are called acid rain.

• Climate change is the change in the statistical distribution of weather patterns
when that change lasts for an extended period of time, i.e decades to millions of
years.

• Certain human activities like deforestation, industrialization, excessive use of
chemical fertilizers, etc. play a significant role in climate change.

• Various studies and research have shown that the escalation of rapid climate
change may create a crisis in the existence of living beings. Therefore, it is the
need of the time to adopt various ways to minimize climate change.

• The Kyoto Protocol is an international agreement linked to the United Nations
Framework Convention on Climate Change, which commits its parties by
setting internationally binding emission reduction targets.

• The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and
entered into force on 16 February 2005.

388 Oasis School Science - 10 Geology and Astronomy

Exercise

Group-A

1. What is atmosphere?
2. Name the different layers of atmosphere.
3. What is troposphere?
4. What is tropopause? Write the average temperature of this layer?
5. In which layer of the atmosphere is the ozone layer found?
6. Name the main chemicals that deplete ozone layer.
7. Write any two characteristics of chlorofluorocarbon.
8. Write down the full form of CFCs and name the scientist who discovered this gas.
9. Where is ozone hole found?
10. What is stratopause? What is the average temperature of this layer?
11. What is mesosphere?
12. What is mesopause? Write down its average temperature.
13. What is thermosphere?
14. Write down two main features of thermosphere.
15. What is exosphere?
16. What is a greenhouse?
17. Name any two greenhouse gases.
18. What is climate change?
19. Write down the main cause of climate change.
20. Write any two national efforts for reduction and adaptation of climate change.
21. When was climate change policy come into practice in Nepal?
22. When did Government of Nepal prepare National Adaptation Program?
23. Write any two international efforts for reduction and adaptation of climate change.
24. When was Kyoto Protocal entered into force?

Group-B

1. Which layer of the atmosphere is responsible for the change in weather? Why?
2. Troposphere is also called variable layer, why?
3. The temperature of troposphere decreases as the increase in height, why?
4. Ozone layer is called a protective layer, why?

Geology and Astronomy Oasis School Science - 10 389

5. Human being is the prime cause of ozone layer depletion, why?
6. The temperature of stratosphere increases as the increase in height, why?
7. The temperature of the thermosphere is very high, why?
8. Exosphere is also called fringe region, why?
9. Write any two differences between mesopause and stratopause.
10. Write any two differences between tropopause and mesopause.
11. Write any two differences between natural greenhouse and artificial greenhouse.
12. What is meant by greenhouse effect?
13. What would happen if the greenhouse gases were not present in the atmosphere?
14. The temperature inside an artificial greenhouse is comparatively more than that of out-

side, why?
15. Atmosphere is called a protective umbrella, why?
16. In troposphere, temperature goes on decreasing while going up. Give reason.
17. The use of chlorofluorocarbon in refrigerator is not good, why?
18. Statisticial data shows that the average temperature in Nepal is increased by 0.06 0C

every year. Write one main cause and one effect of it in Nepal.
19. What would happen if greenhouse gases were not present in the atmosphere?
20. The temperature inside an artificial greenhouse is comparatively more than that of

outside, why?
21. In artificial greenhouses, summer vegetables can be grown even in winter, why?
22. Climate change is a global problem, why?
23. Climate change can be reduced in some extent by conserving forest. Justify.
24. What is meant by climate change adaptation?

Group-D

1. How is ozone layer depleted? Describe in brief.
2. Describe the importance of ozone layer for living beings.
3. How do industrial gases increase the temperature on the earth? Describe.
4. How do industrial gases cause acid rain? Describe in brief.
5. Explain how excess deposition of greenhouse gases in atmosphere may cause natural

disaster like flood?
6. What is the effect of increasing production of chlorofluorocarbon to the atmosphere?

Give its one disadvantage.

390 Oasis School Science - 10 Geology and Astronomy

7. Consequences like skin burn and skin cancer were observed when sunbathe is taken on
the earth surface. Answer the following questions on the basis of it.

i) What is the cause of it?

ii) What is to be done to control this situation?

iii) What happens to the environmental temperature at this condition ?

8. Following are the findings in a study done on the earth environment.

The temperature of respective environment is increasing. The number of amphibians is
decreasing. Human beings are suffering from cataract and skin cancer. Answer the fol-
lowing questions on the basis of above facts:

i) What is the cause of above findings?

ii) What is to be done to be safe from above conditions?

iii) Write down its one more harmful effect to the health.

9. Chlorofluorocarbon is responsible for greenhouse effect and depletion of ozone layer.
Justify.

10. Describe in brief the climate change, its causes and effects.

22. List the national efforts for reduction and adaptation of climate change and describe any
one of them.

12. Write short notes on:
i) National Communication Report

ii) Climate Change Policy, 2067

13. Describe in brief the climate change adaptation strategic program.

14. List any four international efforts for reduction and adaptation of climate change and
explain any one of them.

15. Write short notes on: ii) Intergovernment Forum
i) Agenda 21

16. Explain in brief about Kyoto Protocol.

Geology and Astronomy Oasis School Science - 10 391

UNIT 23 Estimated teaching periods

Theory 4

Practical 1

THE UNIVERSE

Milky-way galaxy

Objectives

After completing the study of this unit, students will be able to:
• describe the structure and shape of the solar system with necessary diagram.
• describe artificial and natural satellites.
• describe comet and meteors.
• explain galaxy with its figure.
• describe zodiacs with figures.
• evaluate scientific facts regarding zodiacs.

23.1 Introduction

The universe is all of spacetime and everything that exists therein including all planets,
satellites, stars, galaxies, constellations, comets, dust particles, matter, energy, etc. In short, the
vast surrounding space is called the universe. The sun is one of the stars among billions of
stars in the universe. The earth on which we live is only a tiny speck of the universe. Billions
of stars in the universe are not distributed uniformly. They occur in the form of clusters or
group of stars called galaxies.

Our solar system is located in the Milky Way
galaxy. This galaxy consists of more than
one billion stars. Among them, the sun is a
medium sized star. The width of the universe
is about 100,000 light years. The solar system
is located about 30,000 light years away from
the centre of the Milky Way galaxy.

Different studies about the universe were

carried out with the help of powerful Fig. 23.1 Universe

telescopes. The study of the universe is called

astronomy. To know about the universe, it is important to discuss the heavenly objects, like

galaxies, stars, the sun, planets, satellites, comets, etc.

392 Oasis School Science - 10 Geology and Astronomy