Green Science 10 Final PDF (2076)

The seeds produced by red-flowered pea were collected and sown. The plants produced in this generation were called the plants of F1-generation. He found that all plants obtained in F1-generation produced red-flowers. These red-flowered pea plants obtained in 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 produced red flowers and other produced white flowers in the ratio of 3:1. The seeds obtained in F3-generation were collected and sown again. They were allowed to self-pollinate to obtain F3-generation. In F3-generation, Mendel found that white flowered plants of F2-generation produced white flowers. Out of red-flowered pea of F2-generation, one-thirds were pure red-flowered and two-thirds were hybrid red-flowered. Pure red- flowered plants of F2-generation produced pure red flowers in F3-generation. The diagrammatic representation of Mendel's experiment is given below: Parents Pure red-flowered pea plant × Pure white flowered pea plant Genotype RR rr Gametes R r Cross-pollination All hybrid tall Rr F1-generation Cross for F2-generation Rr Rr Gametes R rR r Possible gametes Fig. RR Rr Rr rr F2-generation Pure red Hybrid red Pure white flowered pea flowered pea 19.9 flowered pea If F2-generation are bred together, The result of f3-generation of Mendel's experiment can be summarized as follows: i. Pure red-flowered pea plants produced red-flowers. GREEN Science (Biology) Book-10 351

ii. Hybrid red-flowered pea plants produced red-flowers as well as white flowers in the ratio of 3:1. iii. Pure white flowered pea plants produced white flowers. Mendel's laws of inheritance On the basis of the result of his experiment on pea plants for eight years, Mendel formulated three laws of inheritance which are as follows: 1. Law of dominance 2. Law of segregation or law of purity of gametes 3. Law of independent assortment In this unit, we will study law of dominance and law of segregation. 1. Law of dominance Mendel's law of dominance states that, 'In a crossing between two pure organisms for contrasting characteristics of a pair, only one characteristic of the pair appears in F1- generation, i.e. first filial generation'. In Mendel's experiment, when two pure organisms were crossed for contrasting characteristics of one pair, only one characteristic of the pair appeared in F1-generation by suppressing the another characteristic. The characteristic which appears in successive generation is called dominant characteristic and the characteristics that remains hidden or unexpressed in F1-generation is called recessive characteristic. For example, when a pure tall pea plant is crossed with a pure dwarf pea plant, all plants become tall in F1-generation. The dwarf characteristic remains hidden in F1-generation. So, tall is a dominant characteristic and dwarf is a recessive one. Law of dominance can be explained as follows: When a pure black guinea pig (BB) is crossed with a pure white guinea pig (bb), all guinea pigs becomes black (actually hybrid black) in F1-generation. In this cross, black coat is a dominant characteristic as it appears in F1-generation and 'white coat' is a recessive characteristic as it remains hidden in F1-generation. Parents Pure black guinea pig × Pure white guinea pig Genotypes BB bb Fig. Gametes B Bb b Crossing Bb Bb Bb Bb F1-generation 19.10 All hybrid black 352 GREEN Science (Biology) Book-10

Mendel's laws are equally applicable in plants and animals. Like pea plants, guinea pigs can also be taken as an experimental material because of the following reasons. i. It is easy to tame guinea pigs as they are small animals. ii. They have a short life cycle. So we can study several generations of guinea pigs within as few years. iii. They contain many contrasting characteristics in pairs. Genetic characteristics in human beings have a large number of dominant as well as recessive characteristics. The major dominant and recessive characteristics of human beings are as follows: Dominant characteristics Recessive characteristics 1. Curly hair 1. Non-curly hair 2. Dimpled cheek 2. Non-dimpled cheek 3. Free ear-lobe 3. Attached ear-lobe 4. No hitcher's thumb 4. Hitcher's thumb 5. Rolling of tongue 5. Non-rolling of tongue 6. Bending of thumb 6. Straight thumb Activity 1 Study the above table and observe dominant and recessive characteristics of the students in your class. Note down the dominant and recessive characteristics and prepare a short report on it. GREEN Science (Biology) Book-10 353

2. Law of segregation or law of purity of gametes Mendel's law of segregation states that, “The hybrids obtained in F1-generation contain two contrasting characteristics of dominant and recessive nature. These characteristics remain together in hybrids but do not mix with one another and separate or segregate at the time of gamete formation in such a way that each gamete gets only one characteristic, either dominant or recessive.” The gametes of hybrid organism get purified in successive generations. Therefore, law of segregation is also called law of purity of gametes. Law of segregation can be explained as follows: Let us consider a pure tall pea plant having genotype (TT) and a pure dwarf pea plant having genotype (tt). These plants are first cross-pollinated and then self-pollinated. The result obtained upto F2-generation is given below: Parents Pure tall pea plant × Pure dwarf pea plant Genotypes TT tt Gametes T Tt t Tt Tt Cross- Tt F1-generation pollination (All hybrid tall) Tt Gametes T tT t Self-pollination Fig. TT Tt Tt tt F2-generation 19.11 Pure tall Hybrid tall Pure dwarf In F1-generation, all pea plants become tall (hybrid tall) with dominant characteristic (T) and recessive characteristic (t). Both ‘T’ and ‘t’ characteristics remain together in hybrids but do not mix with one another. Finally, ‘T’ and ‘t’ get separated during gamete formation resulting in the formation of two pure gametes T (tall) and t (dwarf). In F2-generation, the phenotypic ratio of tall : dwarf pea plants is 3:1. Similarly, the genotypic ratio of pure tall: hybrid tall : pure dwarf pea plants is 1:2:1. This result is possible only due to purity of gametes. T.H. Morgan performed this experiment on drosophilla (a fruit fly). He crossed a long- winged drosophilla with a short-winged drosophilla upto F2-generation. In F1-generation, all drosophilla were long-winged, when the drosophilla obtained in F1-generation were crossed, long-winged and short-winged drosophilla were obtained in the ratio of 3:1 by phenotype and 1:2:1 by genotype. 354 GREEN Science (Biology) Book-10

Fig.Variation When you observe the body structure of your own family members, you find many differences. Similarly, there are many differences among the students of your class. They differ in height, complexion, shape of face, shape of nose, colour of hair, colour of eyes and so on. The children of the same parents also differ in many characteristics. The structural differences which provide individuality to every member of a species is called variation. The members of the same family differ from each other due to variation. Types of variation There are two types of variation. They are as follows: 1. Heredity (genetic) variation 2. Environmental variation 1. Heredity variation The variation that occurs due to variation in genes is called heredity (genetic) variation. This type of variation is found in the offspring produced by sexual reproduction. Meiosis cell division that occurs during gamete formation plays a great role to bring out heredity variation. When two gametes having different characteristics fuse together, it leads to genetic variation. Genetic variation also depends on parental characteristics. This process helps in evolution of organisms. 19.12 Variation in dogs 2. Environmental variation The variation that occurs in genotypically similar organisms due to effect of environment is called environmental variation. Living beings are affected by the environment in which they live. Variation may occur gradually or suddenly. The variation that occurs gradually or continuously called continuous variation. This type of variation transmits from one generation to another. Various factors like environment, crossing over during meiosis cell division, food, habitat, etc. are responsible for continuous variation. Difference in height, colour of eyes, colour of hair, shape of nose, shape of face, etc. are the examples of continuous variation. GREEN Science (Biology) Book-10 355

The sudden heritable change in the genetic material of an organism is called discontinuous variation. It is also called mutation. It may not transmit from one generation to another. A newborn baby with extra limb, a calf with two tails, a puppy with extra limb and a baby with extra tail are some examples of mutation or discontinuous variation. X-various factors like X-ray, UV-rays and harmful chemicals are responsible for mutation. Fig. 19.13 A person with extra fingers A boy with tail Differences between Variation and Mutation Variation Mutation 1. It gives individuality to a member of 1. It is a sudden heritable change. a species. 2. It is called continuous variation. 2. It is called discontinuous variation. 3. It is seen in every generation. 3. It is seen only in some generation. 4. Factors like food, parental features, 4. X-ray, UV-rays, gamma rays and habitat, etc. bring out variation. harmful chemical cause mutation. Key Concepts 1. Heredity is the phenomenon by which living beings transmit parental characteristics to their offspring. 2. Genes determine physical, anatomical and physiological characteristics of organisms. 3. A gene is a segment of DNA (deoxyribo nucleic acid) which can form exact copies by the process of replication. 4. The characteristics of the parents which are transmitted to their offspring are called hereditary characteristics. 5. The branch of biology in which we study about genes and heredity is called genetics. 6. Gregor Johann Mendel conducted experiment on hybridization of garden pea plants. On the basis of his research, he formulated the laws of inheritance. These laws are popularly known as Mendel’s laws of inheritance. 356 GREEN Science (Biology) Book-10

7. The structural differences which provide individuality to every member of a species is called variation. The members of the same family differ from each other due to variation. 8. The variation that occurs due to variation in genes is called heredity (genetic) variation. 9. Meiosis cell division that occurs during gamete formation plays a great role to bring out heredity variation. 10. The variation that occurs in genotypically similar organisms due to effect of environment is called environmental variation. 11. Variation may occur gradually or suddenly. The variation that occurs gradually or continuously called continuous variation. 12. The sudden heritable change in the genetic material of an organism is called discontinuous variation. It is also called mutation. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. The branch of science which deals with the study of genes is called ............ biology genetics ecology geology b. Which is the following is the Mendel's material for his experiment? garden pea mustard guinea pig drosophilla c. What is the phenotypic ratio of the offspring obtained in F2-generation? 2 : 1 3 : 1 1 : 3 1:2:1 d. Which of the following factor is responsible for mutation? food light X-ray climate e. Which of the following is an example of mutation? variation in complexion variation in shape of face extra finger in hand variation in skin colour GREEN Science (Biology) Book-10 357

2. Answer the following questions. a. What is heredity? b. What are hereditary characteristics? Give any two examples. c. What is genetics? Who is considered as the father of genetics. d. What is Mendel's material for his experiment? e. Why did Mendel selected pea plants for his experiment? Give any four reasons. f. Can we apply Mendel's laws for animals? g. What is variation? Write its types. h. What is mutation? Write any three factors responsible for mutation. i. What is environmental variation? 3. State Mendel's law of dominance and explain it. 4. State and explain law of segregation. Why is this law also called law of purity of gametes? 5. When black and brown dogs were bred together, all offspring in F1-generation were found to be black. Why weren't there any brown dog? Show it with a chart. 6. What is monohybrid cross? According to Mendel's experiment, draw a chart to show the types of offspring produced in F1 and F2-generation after crossing a pure tall pea plant with a pure dwarf pea plant. Also, write down phenotypic and genotypic ration of F2-generation. 7. Study the given table and answer the following questions. i. Which filial generation does this result belong to? Male ii. What is hybrid? What is the percentage of hybrids Female R r in this generation? RR Rr iii. Which pair of genotype indicates pure red- R flowered pea plant? r Rr rr 8. Differentiate between: a. Dominant characteristic and recessive characteristic b. Mutation and Variation 358 GREEN Science (Biology) Book-10

Grid-based Exercise 2 Group ‘A’ (Knowledge Type Questions) (1 Mark Each) 1. What is heredity ? Write. 2. Who is considered as the father of genetics ? Why ? 3. What is dominant characteristic? 4. What is recessive characteristic? 5. Define genotype. 6. What is hereditary characteristic ? Give one example. 7. What is monohybrid cross ? Give one example. 8. What is dihybrid cross ? Give one example. 9. What is a hybrid ? 10. Write any two recessive characteristics seen in human beings. (Ans: (i) Non-curly hair (ii) (Non-dimpled cheeks) 11. Write down the full form of DNA and RNA. 12. What is variation ? 13. What is environmental variation ? 14. What is mutation ? 15. State Mendel’s law of dominance. Group ‘B’ (Understanding Type Questions) (2 Marks Each) 16. Write any two reasons for selecting pea plants by Mendel for his experiment. 17. Write any two differences between dominant and recessive characteristic. 18. The characteristic of having red flower is called dominant characteristic and that having white flowers is called recessive characteristic, why? 19. Write any two differences between variation and mutation. 20. What is a hybrid ? Write with an example. 21. Every living being reproduces its own kind offspring, why ? 22. Explain the reason that only one characteristic is found expressed in F1 generation of Mendel’s experiment. 23. Mating of black and brown dogs takes place and all the offspring produced in F1– generation are black. Why isn’t there brown offspring ? 24. Define dominant characteristics with an example. 25. How is hybrid produced? Write. Group ‘C’ (Application Type Questions) (3 Marks Each) 26. Show the genotype and phenotype of offspring produced by crossing Drosophila with long wings and short wings upto second filial generation. GREEN Science (Biology) Book-10 359

27. Write a name of sex-linked disease seen only in male. Draw a chart to show first and second generation offspring obtained by crossing between black coloured mother (BB) and white coloured father (bb). Also, write phenotypic and genotypic ratio of second generation offspring. (Ans: Baldness) 28. Every living being reproduces its own kind of offspring, why ? A hybrid tall pea (Tt) plant is crossed with a dwarf pea (tt) plant to get F1–generation. Show it with genotype and phenotype. 29. 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 genotypic ratio of this process. 30. Draw a chart to show the F1–generation and F2-generation resulted due to the fusion of gametes of long-winged housefly (HH) and short-winged housefly (hh). Group ‘D’ (Higher Abilities Type Questions) (4Marks Each) 31. A tall (T) pea plant and a dwarf (t) pea plant were first cross-pollinated and then self- pollinated. The given table shows the result of this experiment. Answer the following questions with the help of the table. Tt i. Which filial generation does this result belong to ? ii. What is a hybrid ? What is the percentage of pea plants T Tt Tt having hybrid character in this generation ? iii. Which pair of genes indicate the pure tall plant ? t Tt tt 32. The result obtained by crossing pure red flowering pea plant (R) and pure white flowering pea plant (r) is shown in the given checker board. i. Which filial generation does this result belong to? ii. What is the ratio of the plant having dominant and recessive character? iii. Which one is pure red flowering plant ? 33. The result obtained by crossing a black rat with a white rat is Bb shown in the given checker board. On this basis, answer the following questions. i. Which filial generation does this result belong to? B BB Bb ii. Write down the ratio of dominant and recessive characteristics. b Bb bb iii. Which one is pure black rat? 34. Write a short note on: ii. Environmental variation i. Heredity variation 35. Describe Mendel’s law of dominance with one example. 360 GREEN Science (Biology) Book-10

Environmental UNIT Pollution 20 and Management Weighting Distribution Theory : 7 Practical: 2 Before You Begin The totality of the physical and biological factors including their chemical interactions that affect an organism or a group of organisms is called environment. Natural environment includes both living beings and non-living things in our surroundings. The introduction of contaminants into the natural environment that causes adverse impacts on its various components is called environmental pollution. Environmental pollution degrades living and non-living components of natural or physical environment. For example, introduction of contaminants in water degrades natural quality of water and polluted water has adverse impacts on living beings and non-living things. Environmental management refers to an attempt to control adverse impacts on natural environment in order to preserve natural resources. In this sense, environmental management focuses on maintaining natural environment and the improvement in degraded environment for the welfare of present and future generations. Learning Objectives Syllabus After completing the study of this unit, • Air pollution students will be able to: • Sources of air pollution (Reduction in visibility, Greenhouse effect, Inhibition i. list the causes and effects of air pollution, water pollution and in biological growth of plants, Adverse effect on human land pollution. health, Depletion of ozone layer, Acid rain, Destruction of historical monuments, change in climate) ii. explain the measures to reduce • Measures to control air pollution air pollution, water pollution • Water pollution and land pollution. • Sources of water pollution (Sewage water, contaminated water, from industries, Agricultural, wastes, obstruction iii. explain the methods in flow of water, oily pollution, Heat, Radioactive of conservation and substances) managements of forests. • Measures to control water pollution • Soil pollution • Sources of soil pollution (Domestic wastes, Excessive use of pesticides, Industrial wastes, Use of chemical fertilizers, Municipal wastes, Acid rain) • Measures to control soil pollution • Conservation and management of sources of water Glossary: A dictionary of scientific/technical terms pollution : the action or process of making land water, air, etc. dirty and not safer or radiation suitable to use sewage monuments : a type of dangerous and powerful energy that is produced by radioactive, substances : waste material that is carried away from homes and other buildings in a system of pipes : a building, statue, etc. that honors a person or event GREEN Science (Biology) Book-10 361

Environmental Pollution The degrading condition of one or many components of natural environment is called environmental pollution. The condition of losing natural quality of air is an example of environmental pollution. Environmental pollution Fig. is a burning issue of the present world that creates difficulty in the lives of all 20.1 living organisms including Environmental pollution human beings. In other words, environmental pollution disturbs natural ecosystem by degrading the natural quality of air, water, soil, etc. The imbalance of natural ecosystem and degradation of natural quality of various environmental components has adverse impacts on various organisms. The major negative effect of environmental pollution is spreading various diseases due to air pollution, water pollution, etc. The natural environment has been degrading rapidly day by day due to industrialization, rapid population growth and unmanaged urbanization. There is more pressure on environmental components in the present world. If the present rate of environmental pollution continues, the amount of carbon dioxide increases in atmosphere in near future. As a result, the whole living world will be affected adversely. Thus, the immediate actions should be taken in order to maintain environmental balance by preserving various environmental components. In this context, the causes and impacts of air pollution, water pollution and soil pollution are discussed along with the measures of controlling these pollutions. Also, conservation and management of forest as well as sources of water is also discussed briefly. Air Pollution All living beings need fresh air for respiration. Such air is found in atmosphere of natural environment. Fresh air is polluted due to introduction of various contaminants in the atmosphere. Such contaminants are dust particles, smoke, micro-organisms, etc. The condition of degrading natural quality of air due to mixing of different pollutants in atmosphere is called air pollution. On the basis of production, air pollutants are classified into primary pollutants and secondary pollutants. The air pollutants that introduce in atmosphere immediately after their production from sources are called primary air pollutants. The major source of such pollutants is burning of petro-products. Burning of petro-products produces minute and rough particles, stink, nitrogen, compounds of oxygen, materials related to halogen group, radioactive rays, etc. The immediate introduction of these pollutants pollutes fresh air of atmosphere. Secondary air pollutants are produced by the simple reaction of two or more primary pollutants. Secondary pollutants pollute air of atmosphere indirectly. The sources of secondary air pollutants are formaldehyde, peroxyl, acetile nitrates, etc. 362 GREEN Science (Biology) Book-10

The major causes o air pollution are: i. Dust and smoke emitted form various industries, construction works and domestic activities ii. Burning of bio-materials iii. Stink produced from rotten materials iv. Smoke emitted from means of transportation Sources of Air Pollution Broadly, the sources of air pollution are classified into natural sources and artificial sources. Natural resources The sources of air pollution that are produced from nature are called natural sources of air pollution. For example, volcanic eruption, forest fire, soil erosion, Fig. Fig. steam produced from plants, etc. 20.2 Artificial sources Air pollution The sources of air pollution produced due to the human activities are called artificial or man-made sources of air pollution. The artificial source of air pollution are pollutants produced by burning materials, by products of industries, materials produced due to atomic test, smoke emitted from vehicles, materials produced from agro-related activities, etc. Carbon monoxide (CO), Carbon dioxide (CO2) , Nitric oxide , (NO), Nitrogen dioxide (NO2), Sulphur dioxide (SO2), Chlorine (Cl2), Ammonia (NH3), etc are air pollutants produced from artificial sources. Effects of Air Pollution Air pollution has short term and long term adverse impacts on local environment, climate, ecosystem and human health. Some of the negative impacts of air pollution are described below briefly. 1. Reduction in Visibility The direct effect of air pollution is reduction in visibility. Atmosphere becomes unclear due to mixing of 20.3 minute dust particles in environment. Reduction of visibility due to air pollution GREEN Science (Biology) Book-10 363

As a result, things remaining at far distance cannot be seen clearly. Air pollution causes fog in winter and smoky atmosphere in spring. It causes disturbance in catching sight of scenery and accidents of vehicles and aeroplanes. 2. Reduction in solar radiation The pollutants of air pollution absorbs solar radiation and disperse sun rays. It causes reduction in solar radiation on the earth surface. It also creates negative impact on atmosphere by increasing temperature. 3. Greenhouse effect Fig. Air pollution increases various greenhouse gases in 20.4 atmosphere. Air pollution creates greenhouse gases like Reduction in solar radiation due to air pollution carbon dioxide (CO2), nitrogen dioxide (NO2) methane (CH4), sulphur dioxide (SO2), water vapour, etc. The increment of these gases in atmosphere obstructs the reflection of solar radiation from earth surface. As a result, the temperature of the earth increases. The increment of the temperature of the earth is the impact of greenhouse effect. Various statistics have shown that the level of oceans has been raised due to the melted snow of poles. The snow of poles of the earth melts due to greenhouse effect. 4. Inhibition in biological growth in plants Increasing amount of pollutants in environment causes reduction in solar radiation in atmosphere. The stomata of green plants do not open well due to the reduction in solar radiation. It obstructs entry of carbon dioxide into green plants and hence it disturbs photosynthesis. As a result, physical activities and growth of green plants is inhibited resulting in poor biological growth and development of plants. 5. Adverse impact on human health Human being has a direct relation to atmosphere. It is found that human being inhales oxygen approximately 22,000 times on day. Breathing in polluted air causes various respiratory diseases as well as other diseases related to air. Such diseases cause pain in wind pipe, diseases of nose and eyes, bronchitis, heart diseases, cancer, etc. Besides, polluted air causes the problems like sleeplessness, laziness, etc. 6. Depletion of ozone layer Air pollution creates various chemicals that are harmful to ozone layer. Such chemicals and gases are chlorofluorocarbons (CFCs), methyl chloroform, carbon tetra chloride, methyl bromide, etc. The presence of these compounds in atmosphere for a long time creates elements like nascent chlorine, bromine, etc. These elements cause depletion of ozone layer. 364 GREEN Science (Biology) Book-10

7. Acid rain The gases emitted from industries, vehicles, etc. produce sulphur dioxide, nitrogen dioxide, etc. in atmosphere. These oxides combine with rain water and produce sulphuric acid, sulphurous acid, nitric acid, etc. It causes acid rain on the earth. As a result, the constructions of metals and calcium carbonate get destructed. 8. Destruction of historical monuments Polluted air destructs historical monuments, statues and buildings. The negative impacts on the structures of historical and cultural importance have been seen day by day due to polluted air. 9. Change in climate Fig. The impact of greenhouse effect has been seen due to 20.5 polluted air in atmosphere. It causes change in natural Acid rain corrodes historical monuments pattern of climate in environment. Change in climate refers to change in natural pattern of climate and weather. Extreme cold in winter, extreme hot in summer, hailstones, drought, etc. are some of the results of climate change. Measures to control air pollution Some of the measures of controlling air pollution air mentioned below: i. Establishing industries far from human residential areas and sending poisonous gases by filtering them ii. Reducing the impacts of smoke and poisonous gases in local environment by establishing high chimneys in industrial areas iii. Controlling rapid population growth iv. Banding in the use of atomic kilns v. Afforestation and conservation of green forests vi. Using alternative sources of energy (e.g. solar energy, wind energy, hydroelectricity, etc.) to operate industries and vehicles vii. Curtailing the production and use of various air polluting gases viii. Generating awareness and campaign for controlling air pollution GREEN Science (Biology) Book-10 365

Water Pollution Water is a colourless and odourless compound. Water is polluted due to various natural causes and human activities. The contaminants produced due to natural causes and man made activities mix into natural water. The mixing of such contaminants degrades Fig. Fig. natural and original quality of water resulting in water pollution. Water pollution 20.6 refers to change in actual and Water pollution original quality of water due to contamination in it. Polluted water has adverse impacts on human health, health of living organisms and other materials present in environment. Sources of water pollution Although natural cause as well as man-made activities are responsible for water pollution, human activities are major causes of water pollution. The contamination of water due to introduction of dust particles, micro-organisms, stink, etc. causes destruction of natural quality of water. The major causes that are responsible for degrading natural and original quality of water are mentioned below briefly. 1. Sewage water The water of river, stream, pond, lake, etc. gets polluted when it is mixed with human and animal excreta, discharged water and other materials from domestic works. The mixing of such contaminants in fresh water causes destruction in the natural quality and freshness of pure water. The mixing of excreta of 20.7 human and animals in fresh Sewage water pollutes river water produces various microorganism in it. As a result, fresh water gets polluted. The use of polluted water can escalate various water borne epidemic diseases. 366 GREEN Science (Biology) Book-10

2. Contaminated water from industries Various unuseful materials are produced from industries as byproduct during the production of useful goods. Various chemicals, solid wastes, stinking water, radioactive materials, etc. are discharged from industries. The mixing of these various contaminants in water degrades natural quality and Fig. freshness of pure water. It makes water unsuitable for 20.8 drinking and polluted water Industrial wastes thrown in river is not suitable for aquatic animals. Polluted water also causes different types of water borne diseases. 3. Agricultural wastes In the course of modernization of agriculture, various types of chemicals, insecticides and pesticides are used to carry out agricultural activities. The chemicals like DDT, BHC, Aldrin, Dialdrin, chemical fertilizers, etc. are used in agricultural farms. Such chemicals are mixed with the sources of water due to rain, flow of water, human activities, etc. The mixing of these chemicals in water pollutes natural water and it causes imbalance in water ecosystem due to the destruction of aquatic animals. 4. Obstruction in flow of water The obstruction in flow of water due to various reasons causes water pollution. Ultimately, it causes negative impacts in the life process of aquatic animals. 5. Spilling of oil in water resources The mixing of various oily materials in the sources of water pollutes water of river, pond, lake, stream, etc. The leakage of oil from tankers and oozing of oil from various materials get mixed with water sources. As a result, fresh water gets polluted with oil and oily water in not suitable for aquatic animals. Such type of water destructs various aquatic organisms. It creates imbalance in aquatic ecosystem. 6. Heat Industries discharge various materials like pieces of metals, petro-products, electric energy, etc. The mixing of these materials in water produces heat in pure water and such water is destructive for aquatic organisms. GREEN Science (Biology) Book-10 367

7. Radioactive Substances Various atomic kilns discharge radioactive substances. The mixing of such substances in water causes water pollution. The polluted water is destructive for aquatic animals. The destruction of aquatic organisms creates imbalance in water ecosystem. Measures to control water pollution Some of the measures that can be adopted for controlling water pollution are mentioned below: i. Managing sewage water discharged from domestic activities properly ii. Disposing dead bodies of animals and rotten materials properly iii. Maintaining sanitation around water resources iv. Afforestation and conservation of forest around water resources v. Emphasizing on the use of compost manure and discouraging the use of chemical fertilizers, insecticides, pesticides, etc. vi. Protecting water resources by stopping the movement of domesticated animals near water resources vii. Generating awareness regarding conservation of water resources viii. Implementing rules and regulations for protecting water resources strictly. Soil Pollution Soil is a fundamental material for all living beings for their livelihood. All plants and animals get their food from soil. Green plants absorb various raw materials from soil for photosynthesis. Animals get their food from the plants grown in the soil. Thus, soil is an important abiotic component of environment for all living beings including micro- organisms. Human beings conduct various agricultural activities in soil to produce crops, vegetables, fruits, etc. They use different types of insecticides, pesticides, chemical fertilizers, etc. for modernization of agriculture. Mixing of various chemicals and poisons in soil degrades natural quality of soil. Similarly, over-pressure of animals and encroachment of human beings in soil to conduct various activities is also responsible for reducing natural quality of soil. Thus, soil pollution refers to degradation in original quality of soil due to various natural processes and man-made activities. Natural disasters like earthquake, landslide, flood, etc. and various human activities are major causes of soil pollution. Polluted soil is not suitable for proper growth of plants and it is harmful for various organisms. Sources of soil pollution Various natural processes as well as human activities are major sources of soil pollution. Some of the major sources of soil pollution are described below briefly. 368 GREEN Science (Biology) Book-10

1. Domestic wastes Different types of materials and food stuffs are used for domestic purposes at our home. Various wastes are produced during the use of these materials. Such wastes include unused parts of food materials, dust, excreta pieces of broken utensils, plastics, rotten agricultural Fig. products, papers, etc. The introduction of such materials in soil causes 20.9 production of various Household wastes thrown on land harmful microorganisms in soil. Such micro-organisms create favorable condition to spread various diseases. Besides, these organisms diminish fertility of soil by degrading original quality of soil. 2. Excessive use of pesticides Various pests and insects attack agricultural products like crops, vegetables, fruits, etc. Farmers use different types of insecticides and pesticides to protect their agricultural products from various diseases and insects. The use of such poisons in soil degrades natural quality of soil. Insecticides, pesticides, fungicides, weedicides, chemical fertilizers, etc. are major sources of soil pollution. Generally, the chemicals like DDT, dialdrin, aldrin, parathion, etc. are responsible for reducing original quality of soil. 3. Industrial wastes Various useful products are produced in industries. Along with the production of such products, various harmful materials are produced from industries as byproducts. Such materials are chemicals, pieces of metals and non-metals, organic and inorganic wastes, etc. The mixing of such harmful materials in soil causes soil pollution by destructing natural quality of soil. Polluted soil is poor in fertility and it has negative impact in the health of various organisms, animals, plants, etc that live on the earth. 4. Use of chemical fertilizers Various chemical fertilizers are used to increase the production of agricultural products. Such major soil pollutants of chemical fertilizers are As, Ba, B, Ca, Cu, Zn, Hg, Pb, etc. These components pollute soil by destructing original quality of soil. Also, mixing of these materials in soil imbalances nutrients of soil by destructing various useful microorganisms. GREEN Science (Biology) Book-10 369

5. Municipal wastes Rapid growth in urbanization has become major source of soil pollution. It is a challenge to manage wastes in city areas due to the pressure of over population. Different types of organic and inorganic wastes are thrown in soil due to lack of proper disposal of such wastes. Fig. The introduction of such wastes causes soil pollution 20.10 Municipal wastes in urban and city areas. The mixing of municipal wastes in soil reduces fertility of soil and it also harms various animals living on the earth. 6. Acid rain Generally, the mixing of acidic materials in rain water is called acid rain. The chemicals like sulphur dioxide (SO2), nitrogen oxide (N2O), etc. are responsible for acid rain. These chemicals are mixed with air in atmosphere and react with water during rain. As a result, rain water falls on the earth in the form of acid rain. The acid rain increases acidity of soil resulting in degradation of fertility of soil. Measures to control soil pollution The following measures can be adopted to control soil pollution. i. Discouraging excessive use of insecticides and encouraging the use of biological methods to control insects and diseases in agriculture sector ii. Replacing the use of chemical fertilizers with organic and compost manure to increase agricultural products iii. Managing and disposing domestic wastes properly iv. Discouraging irrigation with polluted water v. Disposing radioactive waste produced from atomic kilns and laboratories properly in safe places vi. Managing and disposing human and animal excreta properly vii. Generating awareness for conserving soil and land and implementing laws regarding it strictly viii. Conducting agricultural activities by agro-forest system. ix. Protecting soil degradation from soil erosion, flood, landslide, etc. x. Discouraging the use of unbiodegradable materials 370 GREEN Science (Biology) Book-10

Conservation and Management of Forest Forest plays a vital role in maintaining environmental balance of a particular place. Forest is the habitat of various wild animals, birds and micro-organisms. It also provides various useful materials to human- beings for various purposes. The plants and other bio Fig. -remains of forest help increase fertility of soil. Forest plays a great role in 20.11 maintaining water resources Forest and it also helps maintain water cycle. Different types of herbal and medicinal plants are available in forest. Therefore, it is necessary to conserve and manage forest for well being of living beings by maintaining environmental balance. The major ways that have been adopting worldwide for conservation and management of forest are mentioned below: i. Cutting and planting trees by making a plan in advance ii. Control in forest fire iii. Afforestation and conservation of forest iv. Implementation of laws for conservation of forest v. Proper utilization of forest products vi. Plantation in bare, spare and slope lands Conservation and Management of Sources of Water Water is a natural resource. The quantity and proper use of water resources has a great contribution in economy of a nation. Water is an essential component to operate our daily activities. Similarly, water is used to operate various industries and water tourism, to produce hydroelectricity and to irrigate agricultural farms. Thus, it is necessary to conserve and manage sources of water for the existence of living beings on the earth. Some of the ways that can be adopted to conserve and manage water resources are mentioned below: i. Conducting campaign for conserving watersheds and snow lake. ii. Banning fishing with the use of poisons and electricity. iii. Afforestation to protect land from soil erosion, flood, landslide, etc. iv. Generating awareness to control misuse and wastage of water. v. Adopting scientific ways for storing and distributing water. vi. Proper management for controlling water pollution, storing and transforming surface GREEN Science (Biology) Book-10 371

water in order to conserve water resources vii. Recycling and reusing of polluted water for various purposes. Fig. Do You Know 20.12 Water occupies approximately 71% part of the total earth. Oceans occupy River 97% of total water and the remaining 3% water can be found in other forms. Key Concepts 1. The degrading condition of one or many components of natural environment is called environmental pollution. 2. Environmental pollution is a burning issue of the present world that creates difficulty in the lives of all living organisms including human beings. 3. The condition of degrading natural quality of air due to mixing different pollutants in atmosphere is called air pollution. 4. The air pollutants that introduce in atmosphere immediately after their production from sources are called primary air pollutants. 5. Air pollution creates various chemicals that are harmful to ozone layer. Such chemicals and gases are chlorofluoro carbons (CFCs), methyl chloroform, carbon tetra chloride, methyl bromide, etc. 6. Change in climate refers to change in natural pattern of climate and weather. Extreme cold in winter, extreme hot in summer, hailstones, drought, etc. are some of the results of climate change. 7. Water pollution refers to change in actual and original quality of water due to contamination in it. Polluted water has adverse impacts on human health, health of living organisms and other materials present in environment. 8. The contamination of water due to introduction of dust particles, micro-organisms, stink, etc. causes destruction of natural quality of water. 9. The use of polluted water can escalate various water borne epidemic diseases. 10. Soil is an important abiotic component of environment for all living beings including micro-organisms. 11. Soil pollution refers to degradation in original quality of soil due to various natural processes and man-made activities. 372 GREEN Science (Biology) Book-10

12. Polluted soil is poor in fertility and it has negative impact in the health of various organisms, animals, plants, etc that live on the earth. 13. Rapid growth in urbanization has become major source of soil pollution. It is a challenge to manage wastes in city areas due to the pressure of over population. 14. The mixing of municipal wastes in soil reduces fertility of soil and it also harms various animals living on the earth. 15. Generally, the mixing of acidic materials in rain water is called acid rain. The chemicals like sulphur dioxide (SO2), nitrogen oxide (N2O), etc. are responsible for acid rain. 16. The acid rain increases acidity of soil resulting in degradation of fertility of soil. 17. Forest plays a vital role in maintaining environmental balance of a particular place. 18. It is necessary to conserve and manage forest for well being of living beings by maintaining environmental balance. 19. Water is an essential component to operate our daily activities. Similarly, water is used to operate various industries and water tourism, to produce hydroelectricity and to irrigate agricultural farms. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. What is called the condition of changing the original structure of fresh air with the introduction of external contaminants? air pollution water pollution soil pollution sound pollution b. What is the major cause of reduction of visibility and solar radiation? water pollution air pollution soil pollution sound pollution c. In which category does the vapour produced from plants fall in environmental pollution? primary source secondary source tertiary source artificial source GREEN Science (Biology) Book-10 373

d. Besides the major chemical chlorofluorocarbon, which one among the following is responsible for depletion of ozone layer? methyl chloroform methyl chloroform, methyl bromide carbon tetrachloride methyl chloroform, carbon tetrachloride, methyl bromide e. Among the following, for which the use of chemicals and chemical fertilizers in agricultural farm is more responsible? water pollution air pollution soil pollution sound pollution 2. Answer the following questions. a. What is environmental pollution? What does environmental management mean? b. Define air pollution. Mention any four causes of air pollution. c. Explain the sources of air pollution. d. Mention any six effects of air pollution. What is green house effect? e. Mention any six effects that are created due to polluted air in your locality. f. Which measures can we adopt to control air pollution? Mention any six. g. \"Control in air pollution is necessary to conserve our atmosphere.\" Justify this statement with appropriate examples. h. What is water pollution? What are the effects of water pollution in your locality? i. Make a list of any four measures that can be adopted to control water pollution in your locality. Why is it necessary to control water pollution? Explain. j. What do you mean by soil pollution? Mention any four effects of soil pollution. 3. Suppose that there is rapid pace of polluting soil due to the human activities in your locality. Suggest some of the measures to people in your locality that can be adopted to control the soil pollution of the place. 374 GREEN Science (Biology) Book-10

4. Explain the importance of forest. Also, mention any six points that can be adopted to conserve and manage forest. 5. \"Water is an essential environmental component for all living beings.\" Justify this statement with logical reasons. 6. How does environmental pollution create imbalance in ecosystem? Explain with suitable examples. Project work Make a study of air pollution in your locality. Prepare a report by including control measures of air pollution and present it in your classroom. Collect the water during rainy season and test it to find out whether is it acid rain or not. Make a list of any five contaminants of air pollution, water pollution and soil pollution each and discuss it in your classroom. Grid-based Exercise 2 (1 Mark Each) Group ‘A’ (Knowledge Type Questions) 1. What is environmental pollution ? 2. Write any two effects of air pollution. 3. What is meant by oily pollution ? 4. What is acid rain ? Write. 5. Write any two sources of soil pollution. 6. Name any two natural sources of air pollution. 7. What is water pollution? 8. What is soil pollution? 9. Write any two effects of water pollution. 10. Write any two artificial sources of air pollution. 11. What is air pollution? 12. Write any two causes of air pollution. 13. What is greenhouse effect? GREEN Science (Biology) Book-10 375

14. What percentage of the total part of the earth is occupied by water? (Ans: 71%) 15. What percentage of total area of Nepal is always covered with snow? (Ans: 15.5%) Group ‘B’ (Understanding Type Questions) (2 Marks Each) 16. What is meant by environmental management? Write in brief. 17. How does air pollution deplete ozone layer? 18. Air pollution causes acid rain, how? 19. How does sewage water cause water pollution? 20. What is meant by oil pollution? 21. Industrial wastes cause soil pollution, how? 22. Soil pollution is caused due to excessive use of chemical fertilizers, why? 23. How does acid rain cause soil pollution? 24. What is meant by conservation and management of forests? 25. What is meant by conservation and management of water? Group ‘C’ (Application Type Questions) (3 Marks Each) 26. Mention three effects on human health due to air pollution. 27. Mention any three control measures of air pollution. 28. Mention any three effects of water pollution. 29. Write any three measures to control soil pollution. 30. Write any three measures of conservation and management of forests. Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each) 31. How does air pollution increase greenhouse effect? Describe. 32. How does air pollution cause climate change? Describe in brief. 33. Write the main sources of soil pollution and describe any two of them. 34. Human being is the main cause of environmental pollution. Justify this statement. 35. Mention the role of human beings for environment conservation and management. 376 GREEN Science (Biology) Book-10

Geology and Astronomy UNIT History of the Earth 21 Weighting Distribution Theory : 4 Practical: 1 Before You Begin The earth is the common habitat of all living beings. It is the third planet from the sun. The earth lies in the universe. People have curiosity regarding the origination of universe and solar system. There are eight planets in solar system. Among them, the earth is suitable for the survival of living organisms due to its climatic condition. The history of the earth is very old and people have different views regarding the origin of the earth. Various scientists have come up with various opinions regarding the origin of the earth. But it is difficult to pin point the certain opinion as the final answer of the origin of the earth. Similarly, evolution of different species and other components on the earth are also related to the history of the earth. In this unit, brief description of the history of the earth, evolution of life and other components on the earth is presented briefly. Learning Objectives Syllabus After completing the study of this unit, • Some hypothesis about the origin of the students will be able to: earth (George Wofan's Hypothesis, Nebular hypothesis, Tidal hypothesis) i. describe history of the earth on the basis of rocks and fossils. • Geological Time Line (Cenozoic era, Mesozoic era, Palaeozoic era, Precambrian era) ii. describe the evolution of life on the basis of evidences obtained • Evolution of Life from fossils. • Fossils (Formation, Identification and iii. identify fossils and explain process Importance) of formation of fossils. • Fossil Fuels (Coal and Mineral oils) iv. explain the importance of fossil fuels. • Formation and Importance of Coal and Mineral oils • Utility of some major petroleum products Glossary: A dictionary of scientific/technical terms eon : the largest duration in geological time scale in which major events occurred era : the division of an eon in the geological history in which major events fossil occurred carbonization : the remnants of organisms which are buried in the earth crust : the formation of coal from plants due to high temperature and pressure under the ground GREEN Science (Geology and Astronomy) Book-10 377

Some Hypotheses About the Origin of the Earth The earth is a member of solar system. If revolves around the sun in elliptical orbit. Thus, the origin of earth is closely related to the origin of solar system. It is difficult to pin point the date of origin of the earth because age of human beings is negligible in comparison to the time of origin of the solar system and the earth. Different scientists have come up with different opinions regarding the origin of the earth. There is not an unanimity among different scientists regarding the date of origin of the earth. Thus, there is not an actual fact and universal theory related to the origin of the earth. There are different hypotheses put forward by different scientists regarding the origin of the solar system and the earth. Some of the hypotheses in this regard are presented in this context. George Wofan's Hypothesis or Planetesimal Hypothesis In 1745 AD, a French scientist George Wofan put forward his hypothesis regarding the origin of the earth. This hypothesis is called George Wofan's hypothesis. According to this hypothesis, the earth along with other planets and satellites were formed millions of years ago when a huge comet struck the huge round mass of hot gases while revolving around the universe. The broken pieces of the round mass are planets and satellites and the remained central part of that mass is the sun. This hypothesis is also called planetesimal hypothesis. Nebular Hypothesis or Kant Laplace Nebular Hypothesis Nebular hypothesis of origin of the earth was put forward by a German philosopher and scientist Immaneul Kant in 1755AD. Later, it was modified by a French mathematician Laplace in 1796AD. Thus, nebular hypothesis is also known as Kant Laplace nebular hypothesis. According to this hypothesis, extremely large masses or nebulae were formed out of large mass of gases and dust in the sky. Such nebulae were cooled and contracted due to their own gravity during their revolution in their own orbits. During this process, an outer ring was detached from the central core and started to revolve around the central core due to the effect of gravitation. The large masses began to break into small masses due to their collision and started revolve around the central mass. This central mass is the sun and other revolving small masses are planets including the earth and satellites. Tidal Hypothesis or Jeans and Jeffrey Hypothesis This hypothesis was put forward by British scientists James Jeans and Harold Jeffrey in 1917AD. Thus, this hypothesis is also called Jeans and Jeffery's hypothesis. According to this hypothesis an extremely big star approached the sun during its revolution around the sun and it produced a mass of gas from the sun due the tidal effect. The tidal matter fragmented into various small pieces in the course of cooling and resulted in forming planets, satellites, etc. including the earth. Different geologist and zoologists have studied the rocks and fossils with their radioactivity to estimate the age and structure of the earth. But they have different views and opinions regarding the age and structure of the earth. Some of the important statistic data recorded in The World Book Encyclopedia regarding various aspects of the earth are presented below. 378 GREEN Science (Geology and Astronomy) Book-10

Estimated age : 4.5 billion years Total surface area : 509, 700, 000 sq.km Diameter : 12756.3km Approximate relative density : 5.5 g/cm3 Mass : 6 × 1021 metric ton Land : 148,400,000 sq.km Water body : 361,300,000 sq.km Number of satellites : 1(moon) Major gases : N2, O2, CO2 Source: The World Book Encyclopedia Geological Time Line Different geologists have come up with various opinions regarding the geological history of the earth and the age of various layers of rocks. The total time period from the origin of the earth to till date is called geological time scale. On the basis of existence of living beings, the geologist have divided the whole geological history into four parts. They are eon, era, period and epoch. Eon is the largest unit of geological time scale. Eon is further divided into Phanerozoic, Proterozoic, Archean and Hadean. Similarly, eon is divided into era, era into period and period into epoch. Thus, the largest section of geological time scale is eon and the smallest section is epoch. The whole geological time scale is divided into four eras. They are Cenozoic era, Mesozoic era, Palaeozoic era and Precambrian era. 1. Cenozoic Era (Between 6 crore 50 lakh years to present) The duration of Cenozoic era is in between 6 crore 55 lakh years ago to present. It is also called era of human beings or era of mammals. The major events of this era are: i. Expansion and breaking of rocks and formation of mountains ii. Volcanic eruptions iii. Climate change due to heat and freezing of water due to extreme cold iv Abolution of ancient animals v. Evolution of new animals vi. Evolution and development of mammals including human beings. vii. Dominance of human beings 2. Mesozoic Era (Between 25 crore years ago to 6 crore 50 lakh years ago) The duration of this era was in between 25 crore years ago to 6 crore 50 lakh years ago. The study of rocks found in this era shows the formation of various hills and peaks. Mesozoic era is also known as the golden era of reptiles due to the evolution of large quantity of reptiles in this era. The major events of this era are given below: GREEN Science (Geology and Astronomy) Book-10 379

i. Formation of hills and peaks ii. Creation of adaptable environment for land, aquatic and areal animals iii. Evolution of reptiles in large quantity iv. Evolution, dominance and extinction of dinosaurs Fig. 21.1 Different types of dinosaurs 3. Palaeozoic Era (Between 57 crore years ago to 25 crore years ago) The duration of Palaeozoic era was between 57 crore years ago to 25 crore years ago. The major events of this era are given below: i. Evolution and development of animals and plants ii. Change in climatic condition in atmosphere iii. Evolution of terrestrial and aquatic vertebrates and invertebrates 4. Precambrian Era (Before 57 crore years) The duration of 57 crore years ago is called Precambrian era. In the beginning of this era, there was not the existence of living beings. The major events of this era are given below: i. Existence of bacteria before around 3.8 billion years and existence of moss before 3.2 billion years. ii. Formation of rocks like gneiss and granite iii. Existence of invertebrates at the end of this era Brief Description of Geological and Biological History of the Earth Era Duration Origin or organisms Cenozoic Between 6 crore 50 lakh – Different mammals like elephants, whale years ago to present and fish, owl – Sharp teethed cats and monkeys – Herbivorous animals – Human beings of stone age – Modern human beings and other mammals – Dominance of human beings 380 GREEN Science (Geology and Astronomy) Book-10

Mesozoic Between 25 crore years – Evolution of dinosaurs, birds, tortoise, ago to 6 crore 50 lakh reptiles and coniferous plants years ago – Existence of reptiles, dinosaurs and other animals and their development – Origin of different insects, extinction of large reptiles and dinosaurs – Evolution of flowering plants Palaeozoic Between 57 crore years – Development of aquatic animals in ago to 25 crore years ago oceans – First vertebrates, aquatic animals in oceans – Evolution and development of first green terrestrial plants and fish – Evolution and development of insects with wings, fish and plants – Evolution of reptiles and amphibians, evolution and development of plants of fern family – Extinction of various vertebrates and invertebrates, development of the first reptile Pre-cambrian Between 57 crore years – Existence of bacteria before about 3.8 ago to the origin of the billion years and moss before 3.2 billion earth years ago – Evolution of unicellular organisms, development of multicellular animal (Source: The ICS's Geologic Time Scale, 2012) Evolution of Life In the beginning of origin of the earth, there was no favourable environment for the evolution and development of organisms in the earth. In the course of time the earth became the favorable place for the evolution and development of organisms before 4 billion years due to the various climatic changes on the earth. In the course of evolution of life, innumerable organisms evolved on the earth, but all of them did not existed. These organisms have left various evidences of their existence, development and destruction. These organisms have left their hard organs on stones and soil. The dead parts animals and plants can be found safe in the layers of sedimentary rocks. These dead remnants of animals and plants are called fossils. Scientists have found out the history of evolution of life on the earth by studying and analyzing fossils. After creating the favorable environment for origin and development of organisms, the origin of bacteria took place before 3.8 billion years and moss before 3.2 GREEN Science (Geology and Astronomy) Book-10 381

billion years. With the development of various multicellular animals, various terrestrial and aquatic invertebrates and vertebrates evolved. In this era, various types of terrestrial and aquatic plants evolved. In mesozoic era, different terrestrial and aquatic animals evolved rapidly. Various plants and coniferous plants evolved in the earth surface. Various flowering plants evolved and developed in this era. This ara is called the era of reptiles due to the development of various terrestrial and aquatic reptiles. The development of tortoise and huge dinosaurs took place in this era and it is believed that destruction of dinosaurs took place at the end of mesozoic era. In Cenozoic era, there was climatic change in atmosphere due to the reduction in temperature. Expansion and breaking down of rocks took place in this era. Many organisms got destructed in this era. With the evolution and development, different types of birds and mammals flourished in this era. This era is also known as the era of mammals. Fossils Fossils are dead remains or impressions of Do You Know animals and plants that are burried in the earth crust over a long period of time. Fossils The word fossil is originated form can be found in stones, soil or rocks in the the Latin word 'fossils', which means form of remains or impressions or cast. extracting by digging up. Generally, all Generally, fossils are present in sedimentary fossil are extracted form the layers of rocks. The branch of science which deals sedimentary rocks. with the process of fossil formation is called Palaeontology. There are several processes of fossil formation. Fig. 21.2 Fossil Process of Fossil Formation The process of fossil formation is called fossilization. In fossilization, the whole body or some parts of organisms and plants decay in the soil and burried in mud, sand, rocks, etc. The impressions or skeleton of such materials are preserved in the rock. In general, fossils are found in sedimentary rocks. 382 GREEN Science (Geology and Astronomy) Book-10

Fig. 21.3 Process of fossil formation Natural disasters like earthquake, volcanic eruption, flood, landslide, etc. destruct organisms or plants. The destructed animals or plants may be covered inside the earth's surface. The hard remains of these materials are pressed down in the ground. These remains or their impressions are found in the form of fossils over a long period of time. Identification of Fossils Fossils can be identified from the remains or impressions of dead animals or plants that are preserved in rocks, stones, mud, etc. There are various methods of identifying fossils. Some of them are mentioned below. i. Fossils can be identified by studying the remains or impressions of dead animals or plants preserved in hard ground, stone or rocks. ii. Fossils can be identified by studying the structures of the whole skeleton of animals or plants found in rocks in pressing condition. iii. They can be identified by the study of the morphology of the hard parts of animals like skeletons, bones, teeth, etc. and study of shoots of plants. Importance of Fossils Do You Know In Paleontology, the importance of fossils is Generally, there is no bone in the fossil of presented in the following points. bone. Fossil is found in the structure of dead body or remains but in the form of i. The study of fossils helps find out hard rock in chemical form. evolutionary trend of animals and plants on the earth. ii. It is important to investigate the deposits of minerals like petroleum, coal, etc inside the ground. iii. The study of fossils helps know geological history, organic evolution and age of rocks on the earth. GREEN Science (Geology and Astronomy) Book-10 383

Fossil Fuels Fossil fuels are fuels that are formed in nature by the decomposition and preservation of organic materials under high temperature and pressure over a long time period. The most important fossil fuels are coal, petroleum and natural gases. A brief description of these fossil fuels is given below. Coal Coal is an important fossil fuel which is found in the form of sedimentary rocks. It is a hard black mineral found below the ground. It comprises of hydrogen, oxygen and some free carbon. Coal is burnt to produce heat energy. Coal is found between stones or sedimentary rocks with thickness of about one inch to some feets. Fig. Fig. 21.4 Different types of coal Formation of coal Natural disasters like earthquake, volcano, floods, etc. are responsible for forming coal. In ancient time, destroyed animals and plants got covered under the ground due to various geological phenomena like natural disasters. The remains of dead bodies and plants were pressed under high pressure and temperature under the ground for a long time in the form of fossils. Over 21.5 a long period of time, these fossils are Formation of coal converted into coal. The major parts of plants are cellulose and lignin. Cellulose and lignin are formed from oil, protein and organic acid. Thus, cellulose and lignin play and prominent role in the formation of coal. The process of forming coal from plants due to the high pressure and temperature under the ground is called carbonization. Since, carbonization is a slow and gradual process, it takes about thousand years to form coal form fossils. Importance of coal i. Coal is an important source of fuel. ii. It is used to generate electricity. 384 GREEN Science (Geology and Astronomy) Book-10

iii. It is used in railway transportation, industries, brick and iron factories, etc. iv. It is used to manufacture petrol, natural gas, coke, etc. v. It is used to make various organic compounds like phenol, benzene, etc. Mineral Oil Mineral oil (or mineral fuel) is a black coloured viscous liquid with foul smell. It is the mixture of hydrocarbons and other materials like oxygen, sulphur, nitrogen, etc. About 90% hydrocarbons are found in mineral oil. Mineral oil is found in nature between rocks on the earth crust. Generally, carbon and hydrogen are the prominent components of mineral oil. Unprocessed mineral oil is called crude oil. Fig.21.6DieselKerosene Fig. Petrol Formation of mineral oil In nature, mineral oils are formed by the decomposition of animals and plants that are burried under the ground for a long period of time. The hard parts of animals and plants are pressed by sedimentary rocks under high pressure and temperature for a long time. As a result, various chemical reactions take place and crude oil is formed from the Mine of mineral oil hydrocarbons. After purification of 21.7 crude oil, mineral oils are obtained. The crude oils are obtained by drilling the holes on the earth's surface. The crude oil contains water, mineral salts, rocks, etc. The crude oil is processed by fractional distillation and various petroleum-products are extracted from it. GREEN Science (Geology and Astronomy) Book-10 385

Utility of Some Major Petroleum Products Petroleum Products Utility Petroleum gas In the form of gas fuel Petroleum ether A good solvent, for the purpose of cleansing Petrol (gosoline) Fuel in small vehicles Diesel Fuel in large vehicles Kerosene Domestic fuel Lubricating oil, greese, vaseline Lubrication, for the purpose of reducing friction Paraffin wax Materials used for making candles, matches, etc. Petroleum coke Smokeless fuel Importance of mineral oil i. Mineral oil is a major source of fuel. ii. It is used to operate vehicles, industries, factories, etc. iii. It is used to generate electricity. iv. It is used for domestic purpose (e.g. kerosene is used for cooking food) v. It is used to make various types of chemicals like fertilizers, insecticides, plastics, medicines, explosives, etc. Key Concepts 1. It is difficult to pin point the date of origin of the earth because the age of human beings is negligible in comparison to the time of origin of the solar system and the earth. 2. The total time period from the origin of the earth to till date is called geological time scale. On the basis of existence of living beings, the geologist have divided the whole geological history into four parts. They are eon, era, period and epoch. 3. The largest section of geological time scale is eon and the smallest section is epoch. The whole geological time scale is divided into four eras. They are Cenozoic era, Mesozoic era, Palaeozoic era and Precambrian era. 4. The duration of Cenozoic era is in between 6 crore 50 lakh years ago to present. It is also called era of human beings or era of mammals. 5. Mesozoic era is also known as the golden era of reptiles due to the evolution of large quantity of reptiles in this era. 6. The duration of Palaeozoic era was between 54 crore years ago to 25 crore years ago. 7. In the beginning of origin of the earth, there was no favourable environment for the evolution and development of organisms in the earth. 8. Fossils are dead remains or impressions of animals and plants that are burried in the earth crust over a long period of time. 386 GREEN Science (Geology and Astronomy) Book-10

9. The word fossil is originated form the Latin word 'fossils', which means extracting by digging up. Generally, all fossils are extracted form the layers of sedimentary rocks. 10. The branch of science which deals with the process of fossil formation is called Palaeontology. 11. Coal is an important fossil fuel which is found in the form of sedimentary rock. It is a hard black mineral found below the ground. 12. The process of forming coal form plants due to the high pressure and temperature under the ground is called carbonization. 13. In nature, mineral oils are formed by the decomposition of animals are plants that are burried under the ground for a long period of time. 14. The crude oil contains water, mineral salts, rocks, etc. The crude oil is processed by fractional distillation and various petroleum-products are extracted from it. 15. Mineral oil is a major source of fuel. It is used to operate vehicles, industries, factories, etc. It is also used to generate electricity. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. Which one is the nebular hypothesis of origin of earth from the following? The tidal matter fragmented into various small pieces and formed the sun, planets and satellites in the course of cooling. The large masses began to break into small masses due to their collision and started to revolve around the central mass. A huge star struck the huge round mass of hot gases while revolving around the universe. All of the above b. In how many parts the geologist have divided the history of the earth? 2 3 4 5 c. Which one is the most important era for the evolution and development of organisms? Palaeozoic, Precambrian Palaeozoic Mesozoic Palaeozoic, Mesozoic and Cenozoic Precambrian GREEN Science (Geology and Astronomy) Book-10 387

d. What is called the branch of science that studies with fossils? Palaeontology Cosmology Ecology Zoology e. Among the following, which elements are found in coal? Hydrogen, oxygen Carbon, oxygen Carbon, hydrogen Carbon, hydrogen, oxygen 2. Answer the following questions. a. Name three hypotheses about the origin of the earth. Explain briefly George Wofan's hypothesis. b. Differentiate between nebular hypothesis and tidal hypothesis of origin of the earth. c. What does geological time line mean? Mention the four divisions of the entire geological history. d. Mention the major events of Cenozoic era. e. Compare and contrast between Mesozoic and Palaeozoic era. f. Mention any four events of Precambrian era. g. In which era did the following events occur? i. Evolution and development of fishes ii. Evolution of dinosaurs iii. Evolution and development of fern plants iv. Evolution of flowering plants v. Evolution and development of elephant, whale and fish vi. Evolution and development of human beings vii. Dominance of reptiles viii. Dominance of conifers ix. Dominance of human beings x. Formation of rocks like gneiss and granite h. Write a short note on evolution of life on the earth. i. What is fossil ? Explain the process of fossil formation. j. \"Fossils are important in Palaeontology.\" Justify this statement with suitable reasons. 388 GREEN Science (Geology and Astronomy) Book-10

k. What are fossil fuels? Name any three important fossil fuels. l. What is coal? Explain the process of coal formation. m. What is mineral oil? Mention any three importance of mineral oil. 3. Write the utility of the following petroleum products. i. Petroleum ether ii. Kerosene iii. Petroleum gas iv. Vaseline v. Paraffin wax 4. Give reason: i. Tidal hypothesis of origin of the earth is called Jeans and Jeffery's hypothesis. ii. Mesozoic era is considered as the golden era of reptiles. iii. The study of fossils helps discover history of evolution of animals and plants on the earth. iv. Diesel and kerosene are called fossil fuels. v. Petroleum ether is a good solvent. 5. On the basis of which evidences the scientist have come up with the opinion that the earth and human beings have not come into existence at the same time? Explain. Project work Collect some rocks which can be found around your school or home and classify them with the help of your subject teacher. Select land or forest or river in your locality for study. Make a study regarding its present situation and find out its past situation by consulting with old members in your family or locality. Now, prepare a report on it by comparing its present situation with its past one and present it in your classroom. Grid-based Exercise 2 Group ‘A’ (Knowledge Type Questions) (1 Mark Each) 1. Define eon and era. 2. Which is the largest unit of the geological history? 3. What is geological epoch? 4. What is the duration of Mesozoic era? 5. List any two events that occurred in Mesozoic era. 6. What is the duration of Cenozoic era? 7. What is the duration Precambrian era? GREEN Science (Geology and Astronomy) Book-10 389

8. What is a fossil? 9. What is mineral oil ? 10. Name the main elements found in the mineral oil. 11. In which period did following organisms evolve? i. Insects with wings ii. Fern 12. In which era did evolution of modern human being take place? 13. In which era did evolution of fish and dinosaur take place? 14. In which era did evolution of monkey and flowering plants take place? 15. In which geological period did following events occur? i. Evolution of human being ii. Evolution of horses Group ’B’ (Understanding Type Questions) (2 Marks Each) 16. Why is mesozoic era called golden era of dinosaurs? 17. Write any two differences between palaeozoic era and cenozoic era. 18. State the hypothesis propounded by George Wofan about the origin of the earth. 19. Write down the hypothesis propounded by Jeans and Jeffery about the origin of the solar system. 20. Describe in brief the Kant-Laplace nebular hypothesis about the origin of the earth. 21. Write any two differences between cenozoic era and mesozoic era. 22. Cenozoic era can be called golden era for human beings, why? 23. Living beings were evolved very long after the earth was created, why? 24. Write any two differences between palaeozoic era and mesozoic era. 25. why did dinosaur evolve earlier than man? Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each) 26. Explain the process of formation of fuel in mine and explain its importance in points. 27. Write any three hypotheses regarding the origin of the earth and describe any one of them. 28. Write short notes on: i. Cenozoic era ii. Palaeozoic era 29. Mention the similarities and dissimilarities between Mesozoic era and Cenozoic era regarding the evolution of life. 30. i. The origin of the earth and evolution of human beings did not occur at the same time. Justify this statement with facts. ii. Write short note on geological time scale. 390 GREEN Science (Geology and Astronomy) Book-10

UNIT Climate Change and 22 Atmosphere Weighting Distribution Theory : 4 Practical: Before You Begin Most days are sunny, some are cloudy and other may be rainy or foggy. Similarly, some days are hot and other days are cold. It may be sunny in the morning, cloudy in the noon and rainy in the evening. Weather and climate both refer to the condition of the atmosphere in a certain place. The condition of the atmosphere at a particular place and time is called weather. Sunny, cloudy, foggy, rainy, hot, cold, etc. are some states of weather. The weather of a place keeps on changing from time to time. Similarly, the weather varies from place to place. Climate is the average atmospheric condition over a long peroid of time. The totality of existing temperature, atmospheric pressure, humidity, rainfall, etc. is called climate. The thick layer of air that surrounds the earth's crust is called atmosphere. The atmosphere consists of different gases like nitrogen, oxygen, carbon dioxide, argon, neon, water vapour, etc. the atmosphere exist on the surface of the earth due to gravity of the earth. The temperature and composition is being changed day by day due to environment pollution. In this unit, we will study about climate change, effects of climate change, methods for reducing effects of climate change, layers of atmosphere, ozone layer depletion and industrial gases. Learning Objectives Syllabus After completing the study of this unit, students will be able to: • Introduction to climate i. introduce climate change and give brief account of change national and international efforts for adaptation and • National and international reduction of climate change. efforts for reduction and adaptation of climate change ii. explain the various layers of atmosphere including ozone layer. • Layers of atmosphere iii. explain the effects of chlorofluorocarbon on ozone • Ozone layer, ozone layer layer. depletion and importance of ozone layer iv. describe the harmful effects of industrial gases. • Industrial gases Glossary: A dictionary of scientific/technical terms planet : the heavenly body that revolves around the sun hydrosphere : the part of water present on the earth lithosphere : the part of land present on the earth plateau : the plain surface at the top of a mountain, e.g. Tibetan plateau crust : the outermost solid and hard layer of the earth. mantle : the layer of the earth between the crust and the core GREEN Science (Geology and Astronomy) Book-10 391

A. National and International Efforts for Reduction and Adaptation of Climatic Change Climate change is a global problem. Its adverse effects are increasing throughout the world. Climate change affects nature and living beings adversely. If climate change is not reduced, it may create difficulty in existence of living beings on the earth. All people throughout the world should work together for reduction and adaptation of climate change. United Nations Organization also has taken initiation to solve the problem caused by climate change. Institutional as well as organized effort help to solve the problem of climate change. Among many efforts, inclusion of curriculum related to climate change in schools, colleges and universities also plays a great role to generate awareness for reduction and adaptation of climate change. Some national and international efforts for reduction and adaptation of climate change are given below: 1. National efforts The efforts that are paid in Nepal for reduction and adaptation of climate change are called national efforts. Such efforts are mentioned below: a. National communication report b. Climate change policy , 2067 c. Climate change adaptation strategic programme d. National adaptational programme e. Local adaptational programme related to climate change f. Other programmes a. National Communication Report Nepal submitted its first report to the COP of United Nations Organization Protocol related to climate change. The things included in this report are (i) the adverse effect of climate change in Nepal and measures of its adaptation (ii) required strength and policy, rules and (iii) plans for reducing the effects of climate change. National communication report also includes the importance of research in the sectors like agriculture, forests, health, industries, transportation, waste materials, etc. that are affected by climate change. This report also emphasizes to the development of a certain mechanism to reduce the effect of climate change on the basis of scientific study. b. Climate change policy, 2067 The atmospheric temperature increased due to climate change has many adverse effects on various sectors like biodiversity, public health, forests, agriculture, socioeconomic aspects, etc. We should develop awareness and adopt measures for reduction and adaptation of such type of effects. We should generate the capacity of many people at different levels to cope with climate change. To meet these objectives climate change policy, 2067 has been introduced in Nepal. 392 GREEN Science (Geology and Astronomy) Book-10

c. Climatic change adaptation strategic programme Climate Investment Fund invited Government of Nepal in May, 2009 AD to join the worldwide programme related to adaptation of climate change. Global climate model programme provides economic support to poor countries to adopt various measures for reduction and adaptation of climate change. Climate change adaptation strategic programme has been divided into following five sectors. i. Adaptation to risks induced by climate change ii. Climatic adaptation of water sheds that lie in hilly ecosystem iii. Mainstream flow of \"Climate change risk management\" in development projects iv. Building a capable community for climate change adaptation in active participation of private sectors v. Promotion of climate change adaptation for vulnerable species d. National adaptation programme The Government of Nepal prepared National adaptation programme in September, 2010. This programme evaluates the climate change and its risks. National adaptation programme conducts 250 programmes under nine integrated programmes. e. Local adaptational programme related to climate change This programme is conducted in rural and community level. Four theories, viz. progressive, inclusive, capability and flexibility are kept in mind while selecting the adaptational programmes related to climate change in local level. This programme prepares and co- ordinates local and national programmes related to climate change adaptation. Under this programme, various activities are conducted to reduce adverse effects in local level due to climate change. These programmes develop environment to provide service to endangered communities, area and families. f. Other programmes Other programmes related to climate change reduction adaptation include programmes related to brick industries, improved cooking stove, biogas programme, encouragement to store carbon, rainwater harvesting, pre-information system regarding natural hazards, seminars and conferences. 2. International efforts The efforts paid at international level for adaptation and reduction of climate change are called international efforts. The major international efforts for adaptation and reduction of climate change are as follows: a. United Nations Framework Convention on Climate Change b. The UNFCCC Conference of the Parties c. Agenda 21 GREEN Science (Geology and Astronomy) Book-10 393

d. Intergovernmental Panel on Climate Change e. Kyoto Protocol f. Measures of reducing emission of greenhouse gases according to Kyoto Protocol g. Reduction of emission due to deforestation a. United Nations Framework Convention on Climate Change The UN Framework Convention on Climate Change (UNFCCC) is an intergovernmental Do You Know treaty developed to address the problem of climate change. The convention, which sets The main objective of UNFCCC is to out an agreed framework for dealing with the stabilize greenhouse gas concentrations issues, was negotiated from February 1991 to in the atmosphere at a level that would May 1992 and opened for signature in June prevent dangerous anthropogenic 1992. UN Conference on Environment and interference with the climate system. Development (UNCED) also known as the Rio Earth Summit. The UNFCCC entered into force on 21 March 1994, ninety days after 50th country's ratification had been received. By December 2007, it had been ratified by 192 countries. UNFCCC addressed the issue of increasing environment pollution, sustainable development programme, effect of climate change, etc. The government of Nepal signed this treaty in June, 1992. The Fig. parliament of Nepal adopted this treaty in 1994 AD. Since then the articles of the treaty came into 22.1 action in Nepal. b. The UNFCCC Conference of the Parties Parties to the UNFCCC continue to adopt decisions, review progress and consider further action through regular meetings of the conference of parties (COP). The conference of parties is the highest decision making body of the convention and usually meets annually. According to the treaty of UNFCCC in 1992, the member countries should inform the programmes conducted in their countries to the other member countries. Nineteen conferences related to climate change have been conducted till 2013 AD. In 2014 AD, the UNFCCC conference of the parties was held in Peru. On the basis of the treaty of UNFCCC, Nepal has prepared climate change policy in 2011 AD. c. Agenda 21 Agenda 21 is a non-binding voluntarily implemented action plan of the united nations with regard to sustainable development. It is a product of the earth summit (UN Conference on Environment and Development) held in Rio de Janerio, Brazil, in 1992. It is an action agenda for the UN, other multilateral organizations, and individual governments around the world that can be executed at local, national and global levels. The \"21\" in Agenda 21 refers to the 21st century. The action plan of Agenda 21 was formulated on the basis of a slogan \"Think 394 GREEN Science (Geology and Astronomy) Book-10

globally and act locally.\" to conserve environment and ensure sustainable development. It has been affirmed and had a few modifications at subsequent UN conferences. Agenda 21 is a 350 page document divided into 40 chapters that have been grouped into 4 sectors. Section I : Social and Economic Dimensions Section II : Conservation and Management of Resources for Development Section III : Strengthening the role of Major Groups Section IV : Means of Implementation The full text of Agenda 21 was made public at the UN Conference on Environment and Development (Earth Summit), held in Rio de Janerio on June 13, 1992, where 178 governments voted to adopt the Fig. programme. The final text was the result of drafting,Fig. consultation (IPPC) and negotiation beginning in 1989 22.2 and culminating at the two week conference. d. Intergovernmental Panel on Climate Change The international Panel on Climate Change (IPCC) is a scientific and intergovernmental body. The IPCC developed from an international scientific body, the Advisory Group on Greenhouse set up in 1985 by the International Counsil of Scientific Unions, the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) to 22.3 provide recommendation based on current research. The IPCC was established in 1988 AD. The principles that the IPCC operates under are set out in the relevant WMO Executive council and UNEP Governing Council resolutions and decisions, as well as on actions in support of the UNFCCC process. The aims of the IPCC are to assess scientific information relevant to: i. Human-induced climate change ii. The impacts of human-induced climate change iii. Options for adaptation and mitigation e. Kyoto Protocol The Kyoto Protocol was historical agreement in which many of the world's industrial nations concluded a verifiable agreement to reduce their emissions of six green house gases in order to prevent global warming. The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force on 16 Ferbuary 2005. 184 parties of the convention have ratified its protocol to date. GREEN Science (Geology and Astronomy) Book-10 395

It is an international agreement linked to the United Nations Framework Convention on Climate Change. Nepal ratified Kyoto Protocol in 16 September 2005 AD. The major feature of Kyoto Protocol is that it sets binding targets for 37 industrialized countries and the European community for reducing emissions. These amount to an average 5.25% again 1990 levels over the five year period 2008-2012 AD. A second commitment period started in 2012 AD, known as the Doha Amendment to the protocol, in which 37 countries have binding targets. As on July 2016, 66 states have accepted Doha Amendment, while entry into force requires acceptances of 144 states of the 37 countries with binding commitments, 7 have ratified. Negotiations were held in the framework of the yearly UNFCCC climate change conferences on measures to be taken after the second commitment period ends in 2020 AD. This resulted in the 2015 adoption of the Paris Agreement. The Kyoto Protocol implemented the objective of the UNFCC to fight global warming by reducing green house gas concentrations in the atmosphere to \"a level that would prevent dangerous anthropogenic interference with the climate system. f. Measure to Reduce Greenhouse Gases According to Kyoto Protocol Developed countries consume a large amount of mineral fuel to operate their industries and factories. As a result, a large amount of greenhouse gases are released into the atmosphere by the developed countries. It is not easy to reduce their emission too. Therefore, Kyoto Protocol has encouraged the developed as well as developing countries to conduct three additional means, viz. (i) International Emission Trading, (ii) Joint Implementation and (iii) Clean Development Mechanism to meet their emission targets. g. Reduction of emission due to deforestation Carbon plays a prominent role in climate change. Forest is an important natural resource that absorbs and stores carbon in a large amount. Therefore, developed countries should reduce deforestation and conduct afforestation programmes. On the other hand, developed countries that produce a large amount of industrial gases should provide economic aids to developing and underdeveloped countries for conservation and proper management of forests. Layers of Atmosphere Fig. Atmosphere is the thick layer air that Different layers of atmosphere surrounds the earth's surface. The atmosphere consists of various types of gases such as nitrogen, oxygen, carbon dioxide, neon, argon, etc. Dust particles and water vapour are also present in atmosphere. The layer of atmosphere becomes thinner as the altitude increases. Thus, the atmospheric pressure reduces 22.4 in the higher altitude. Solar heat is stored 396 GREEN Science (Geology and Astronomy) Book-10

in atmosphere due to the presence of various gases in it. The atmosphere is divided into five layers according to the altitude, temperature and atmospheric pressure. These layers of atmosphere are given below. i. Troposphere (0-16 km) ii. Stratosphere (16-50 km) iii. Mesosphere (50-80 km) iv. Thermosphere (80-720 km) v. Exosphere (above 720 km) i. Troposphere The lowermost layer of atmosphere is called troposphere. It extends upto 16km from the earth's surface. The troposphere lies at about 8 to 10 km from the poles and about 16km from the equator. It contains gases like nitrogen, oxygen, carbon dioxide. It also contains water vapour and dust particles. It is estimated that about 95% of the atmosphere lies in the troposphere. The uppermost part of troposphere which separates troposphere and stratosphere is called tropopause. On increasing altitude, around 6.5°C temperature falls per kilometer in this layer and it happens upto tropopause. Troposphere is also called changeable layer since temperature keeps on changing in this layer on increasing the altitude. Various weather related activities such as cloud formation, fog formation, rain, wind, lightening, hail stone, etc. take place in troposphere. Thus, weather forecasting is done by studying this layer. Troposphere has been adversely affected by the dust particles and smoke produced due to the various human activities. ii. Stratosphere The layer of atmosphere situated above troposphere and below mesosphere is called stratosphere. It extends about 16km to 50km vertically upward from the surface of the earth. The major gases present in this layer are ozone, nitrogen, oxygen, etc. The uppermost part of stratosphere is called stratopause. The temperature in this layer increases on increasing altitude. It keeps on upto the stratopause. This layer contains negligible amount of humidity. Stratosphere consists of ozone layer at its upper surface. Thus, stratosphere is also called ozonosphere. In the presence of solar radiation, the formation and destruction of ozone gas layer takes place in stratosphere at the altitude of 20km to 30km. Stratosphere absorbs about 99% solar radiations. As a result, the harmful solar radiations cannot enter the earth. The absence of harmful solar radiations in the earth creates favorable condition for existence of living beings in it. iii. Mesophere The layer of atmosphere which is situated above stratosphere and below thermosphere is called mesosphere. It extends approximately upto 50km to 80km from the surface of the earth. The thin layer of air is found in mesosphere. The temperature of mesophere decreases on increasing the altitude. Mesosphere is the coldest layer of atmosphere. The streaks of hot gases released from meteores are found in mesosphere. The uppermost layer of mesosphere is called mesopause. The strong wind blows in mesopause. Such wind blows from the west to east during winter and from the east to the west during summer. GREEN Science (Geology and Astronomy) Book-10 397

iv. Thermosphere The layer of atmosphere situated above mesosphere and below exosphere is called thermosphere. It extends upto 80km to 720km from the surface of the earth. Less amount of air and thin layer of air is found in the thermosphere. The temperature of this layer increases on increasing altitude due to the more effect of solar radiation in this layer. The upper part of thermosphere contains the gases like hydrogen and helium. Similarly, the lower part of this layer contains the gases like nitrogen, oxygen, etc. In this part, the molecules of nitrogen and oxygen undergo ionization and give ions due to the effect of UV-radiation of the sun. Thus, thermosphere is also called ionosphere. The uppermost layer of thermosphere is called thermospause. It separates thermosphere and exosphere. v. Exosphere The uppermost layer of the atmosphere is called exosphere. It extends about 720km above from the surface of the earth. Exosphere is the outermost layer of the atmosphere. This layer is also called fringe region. Air is negligible in this layer, but air molecules and atoms blow at high speed in this region. There is no effect of gravity in this layer since it is very far from the surface of the earth. Similarly, there is no effect of gravity on the molecule and atoms of air due to their high speed. Thus, air molecules and atoms enters the space since they are free from the effect of gravity. The major gases found in exosphere are hydrogen and helium. Ozone layer Ozone (O3) is formed by the chemical reaction of three atoms of oxygen. In atmosphere, solar radiation decomposes molecule of oxygen into atom of oxygen. Ozone is formed by the combination of one atom of oxygen and one molecule of oxygen. The compound of ozone stores in huge amount of stratosphere and thick layer of ozone is formed in the atmosphere. Ozone layer extends upto 25km to 40km from the surface of the earth. Ozone layer is present in the stratosphere in the form of the layer of pale-blue gas. It absorbs about 99% harmful solar radiations like UV-rays, X-rays, gamma rays, etc. Ozone layer protects living organisms on the earth from harmful UV-radiations. Thus, ozone layer is called protective layer. Ozone layer plays a key role in balancing weather and temperature on the earth. Formation of ozone layer O2 Solar radiation O + O (Nascent oxygen) O2 + O UV-rays O3 (Ozone) O3 UV-rays O2 + O Ozone is formed by the combination of three oxygen atoms due to influence of ultraviolet radiation through the natural process. When a molecule of oxygen absorbs high energy solar radiation, it dissociates into nascent oxygen. The highly reactive nascent oxygen combines with oxygen molecule and one molecule of ozone is formed. In troposphere, ozone gas is formed by the combination of oxygen gas with the gases like methane and 398 GREEN Science (Geology and Astronomy) Book-10

carbon monoxide but the amount of ozone is very less in troposphere. In stratosphere, large amount of ozone is found. Thus, ozone is found in both troposphere and stratosphere. Importance of ozone layer Ozone layer is a very important layer for living beings as it protects the earth from the harmful ultraviolet radiations by absorbing them. It not only absorbs the ultraviolet radiations but also absorbs the radiations of wave length less than 3 × Fig. 10–7m. As a result, radiation cannot reach the surface of 22.5 the earth. Ozone layer helps Ozone layer maintain terrestrial and aquatic ecosystem in the earth. It prevents various disease like cataracts (blindness), skin cancer, deficiency of immune system that may be caused due to the over exposure of radiations on living beings. It also helps balance temperature and weather of the earth. Depletion of ozone layer The major chemical responsible for depleting ozone layer is chlorofluorocarbons (CFCS). Besides methyl chloroform, carbontetrachloride and methyl bromide also cause depletion of ozone layer. Ozone layer depletion refers to decreasing the thickness of ozone layer or formation of hole in it. The chemicals like CFCs and other gases like oxides of nitrogen, exposure to the atmosphere due to the effect of air. After a long time, these compounds decompose into the elements like chlorine, bromine, etc. and they deplete ozone layer. CFCl3 UV-rays CFCl2 Cl + O3 ClO + O2 2ClO 2Cl + O2 Similarly, NO + O3 NO2 + O2 2NO2 + O3 N2O3 + 2O2 Chloroflurocarbon was discovered by Thomas Midgley, Junior in 1928 AD. It is used as a solvent, cooling agent, etc. CFCs is a chemical compound which contains carbon, hydrogen, chlorine and flourine. It has not any natural source since it is an industrial chemical. CFCs is a stable, non-poisonous, non-inflammable and cheaper chemical. This gas is cheaper than ammonia gas. Thus, it has been using as a cooling agent since 1955AD. In 1974 AD, CFCs was discovered in atmosphere. GREEN Science (Geology and Astronomy) Book-10 399

The chemical substances produced due to the human activities are also responsible for depletion of ozone layer. For example, the equipment formed by CFC like refrigerator, aerosol spray can, air conditioners, etc. CFC gas is also produced due to the burning of plastics. The various gases produced on the earth slowly enter the stratosphere of atmosphere and cause depletion of the ozone layer. Although, CFCs is mainly responsible for depletion of ozone layer, it does not destruct ozone layer itself. CFCs produces atomic chlorines in the presence of ultraviolet radiations released from the sun. These atomic chlorines deplete ozone layer. A single atomic chlorine has strength of damaging more than one lakh ozone molecules. The strength of damaging ozone molecule depends upon the strength of atomic chlorine molecule and amount of CFC in atmosphere. Thus, the process of decreasing of thickness of ozone layer in stratosphere is called depletion of ozone layer. CFC is responsible for greenhouse effect and depletion of ozone layer in the atmosphere. In the middle of 1980s, the depletion of ozone layer over the Antarctica continent was discovered. Along with CFC, the gases like hydroxide ions and nitric oxides also cause the depletion of ozone layer in the atmosphere. Effects of depletion of ozone layer The solar ultraviolet radiations reach the surface of the earth due to the depletion of ozone layer. As a result, it affects physical and biological aspects of the earth. The major adverse impacts of ozone layer depletion are given below. i. Adverse impacts on health • UV-rays cause various diseases like cataract (blindness), skin cancer, breast cancer, sun burn, eye burn, leukaemia, etc. in human beings. • UV-rays cause skin burn, skin rupture, skin cancer of animals. • UV-rays adversely affect reproductive system of living beings. • UV-rays are responsible for deficiency of immune system of human beings. ii. Adverse impacts on plants • UV-rays cause retardation in growth and development of plants. • UV-rays disturb photosynthesis of green plants. • UV-rays cause reduction in agricultural products. • UV-rays disturb reproduction of plants. iii. Adverse impacts on temperature of the earth • The presence of large amount of UV-rays on the earth causes greenhouse effect. • Greenhouse effect is responsible for increasing the temperature of the earth. • Increasing of the temperature of the earth causes melting of snow. iv. Adverse impacts on ecosystem • UV-rays are responsible for creating imbalance in terrestrial and aquatic ecosystem by degrading various aspects of ecosystem. 400 GREEN Science (Geology and Astronomy) Book-10