Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
04 The Nature of the earth and space By the end of this chapter, you will be competent to... • investigate the constituents of the atmosphere, in order to make human affairs effective. • contribute to maintain optimum composition of the atmosphere. • use natural resources obtained from the earth effectively For free distribution 1 4.1 Main layers of the atmosphere and their features Think of an occasion when you observed the night sky. You may have thought that there was nothing between you and the stars. Actually, you observed the stars through a layer made up of invisible gases which is the earth’s atmosphere. The layer of air over the surface of the earth is called the atmosphere. It can be considered as a protective layer which supports life. The air that we inhale is also a part of the atmosphere. Atmosphere is mainly composed with two gases, oxygen and nitrogen. The atmosphere extends to a height of about 1000 km above the surface of the earth. Do you know how the earth’s atmosphere was created? One of the theories regarding its origin is given below; At the time the earth was first formed, it was a ball of molten substances. This substance was cooled down and the outer surface condensed to form a thin layer called the crust. The inside of the earth protected by this crust is still in liquid form. The activities within this liquid produce various types of gases. These gases that are at extremely high temperatures can seep out through the crust, and sometimes by volcanic eruptions. The atmosphere is formed out of the gases that were formed over millions of years. Fig 4.1 - Eruption of volcanoes 2 For free distribution Main layers of the atmosphere Considering the nature of the atmosphere, it is composed of five main layers. They are troposphere, stratosphere, mesosphere, thermosphere and exosphere. 600km Troposphere This is the lowest layer of the atmosphere. It is about 15 km thick around the equator. Near the poles it gets reduced to about 8 km. 90% of the total air content is confined to this layer. Highest air pressure is found on this layer. All of the climatic changes we experience originate at this layer. Some examples of climatic changes that occur in the troposphere are formation of wind, flow of wind at various speeds in various directions, formation of clouds and production of rain. Helicopters, parachutes and planes fly in this layer. Main gases in the troposphere are nitrogen and oxygen, together with small amounts of argon, carbon dioxide, and a few other gases. A composition of air suitable for respiration of organisms, at suitable pressures is found only in the troposphere. Further, conditions suitable for photosynthesis and burning are also found only in this layer. The temperature of the troposphere reduces as we go higher above the sea level, and at the highest level temperature is about -44 oC. Stratosphere This layer found above the troposphere and stretches up to about 50 km above sea level. The composition of the air in this layer differs only a little from that of the troposphere. This layer contains the ozone layer which prevents the harmful ultra-violet rays from the sun reaching the earth. Jets fly in the lower layers of the stratosphere. For free distribution 3 15km Fig 4.2 - Layers of the atmosphere There is a rise in the temperature as you go up the stratosphere. The ozone layer is found here and at the highest level. Of this layer, the temperature is around +15 oC. The reason for this is the generation of heat due to absorption of ultra violet rays. Mesosphere This is above the stratosphere and stretches up to about 80 km above sea level. The lowest atmospheric temperature of -120 oC is found in this layer. The burning off of the meteors which travel towards the earth from space begins here. Thermosphere The layer above the stratosphere, that is stretching from 50 km to 600 km is called the thermosphere. The temperature rises gradually as you go up. Since The gases present here absorb heat radiations, the temperature is at a higher value. Some of the radio waves emitted from the earth get refracted back to earth at this layer. This activity makes communication between far distant places on earth Fig 4.3 - Aurora possible in a very short time. The man made satellites too revolve round the earth in this layer, at the level of the thermosphere. This layer too absorbs the harmful ultraviolet rays and prevent them reaching the earth. The ‘Aurora’ clouds which give off light at midnight visible in the polar regions also originate at the thermosphere. Exosphere This is the outermost layer of the atmosophere. It is about 600 km above sea level. Assignment - 1 • • Prepare a poster showing the various layers of the atmosphere, using suitable materials. Exhibit it in the classroom. 4 For free distribution 4.2 Maintaining the composition of the atmosphere at optimum level 4.2.1 Composition of the atmosphere The table and figure below show the composition of the atmosphere near the surface of the earth. Others 1% Table 4.1- Composition of the air Component Nitrogen Oxygen Argon Carbon dioxide Other Gases Percentage according to volume 78% 21% 0.93% 0.03% Trace (Helium,Neon) Water vapour Not definite } 1% Oxygen 21% Nitrogen 78% Fig 4.4 - Composition of the air Atmosphere is made up of a mixture of gases. The figure above shows that its main components are oxygen and nitrogen. Carban dioxide, water and nobel gas such as argon, neon, helium etc compose approximately 1% of the composition of air and the composition of the water vapour varies with time and location. All of the above components of the atmosphere are colourless and odourless. 4.2.2 Function of the atmosphere Respiration is one of the most essential activities of organisms on earth. Oxygen gas needed for this purpose is provided by the atmosphere. Hence, this can be considered as the most important function of the atmosphere. In addition, there are many other functions of the atmosphere. Rain, wind, lightning etc occur at the lower layers of the atmosphere, this layer is involved in the maintenance of the water cycle, which ensures the conditions needed For free distribution 5 for life on earth. Another function is the controlling activity of solar rays which reach the earth as well as those which leave the earth, and thereby control the temperature of the earth. You already know about the protection offered by the atmosphere from the harmful rays of the sun. The meteors from space, which can do enormous harm if they fall on earth are also burnt off into ashes by the atmosphere. Do you know ? The huge crater of circumference 1.2 Km and depth of 180 m in Winslow in Arizona is believed to have been caused by a meteor which fell about 50,000 years ago. Crater in Winslow The refraction of waves by the atmosphere also helps in radio communication activities. This activity allows us to listen to radio services from other countries as well. The atmosphere also helps to disperse the various gases, smoke and dust that are discharged to the atmosphere, thus maintaining suitable conditions for survival of life. Let us now consider the function of the different gaseous components of the atmosphere. Nitrogen Under normal conditions nitrogen is a fairly inactive gas. Many of the tissues of organisms are composed of proteins. A major component of proteins is nitrogen. Nitrogen is essential for plant growth. The nitrogen essential for plant growth is obtained from nitrogenous fertilisers. Atmospheric nitrogen undergoes many chemical reactions and produce compounds which enter the plants. An initial step in this process is the combination of nitrogen and oxygen in the presence of lightning. 6 For free distribution Oxygen Oxygen is essential for plant and animal respiration. Hence oxygen is an essential factor for survival of life. This is the reason why persons travel into regions deficient in oxygen have to carry their oxygen. Some such examples are deep sea divers, mountain climbers and astronauts. Burning of substances, decaying of dead plant and animal tissues and rusting of metals are all activities that take place with the contribution of atmospheric oxygen. Carbondioxide Carbondioxide is an essential raw material for the process of photosynthesis that takes place in plants. It helps to maintain the temperature of earth at an optimum level. Water Vapour Water vapour is important in maintaining the water cycle as well as the moisture content of the earth. 4.2.3 Factors affecting the optimum composition of the atmosphere. Many reactions that take place in the environment help to maintain the composition of the atmosphere at an optimum level. This helps for the well being of organisms. Forests play a major contribution in this process. This optimum composition of the environment may change by the addition of excess of carbon dioxide, other harmful gases, solid and gaseous particles to the atmosphere. This condition is called atmospheric pollution. The factors that contribute to pollution are called pollutants. Gases such as carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide and particles such as carbon, lead and dust are examples of some pollutants. Human activities are mainly responsible for pollution (Fig 4.6). Some natural phenomena too may contribute to air pollution. For free distribution 7 Fig 4.6 - Some human activities responsible for air pollution Given below is a list of various components that are added to the atmosphere which change its composition in a harmful manner. Table 4.2 Component How it is added Carbon dioxide • Factories, vehicles, thermal power generators, houses etc. where a large amount of fossil fuels is used to get energy. e.g.: Petrol, diesel, kerosine oil, coal etc. Carbon monoxide • Incomplete combustion of fuels in motor engines. Sulphur dioxide • Burning of coal containing a high percentage of sulphur. Volcanic eruptions Oxides of nitrogen • Combination of atmosphere nitrogen with oxygen during lightning and in vehicle engines. Particles of solid and liquid wastes e.g. carbon particles, lead particles, dust • Construction activities, activities in factories and burning of fuel. e.g. Cement industry, phosphate fertilizer industry, asbestos industry Addition of excess carbondioxide to the atmosphere causes a rise in atmospheric temperature. It has been reported that this would result in melting of glaciers, rise of ocean water level and change of climatic and weather patterns. Carbon monoxide is a poisonous gas. It is harmful to organisms. It may cause various respiratory diseases and even death at some instances. 8 For free distribution Gases such as sulphur dioxide, nitrogen dioxide dissolve in rain water and produce an acidity in the rain water. This condition is known as acid rain. Acid rain causes harm to organisms, water bodies and to buildings. The particulate pollutants cause respiratory diseases. The increase of such diseases at present is basically due to the increase of pollutant particles in the atmosphere. Another harmful result is the reduction of the transparency of the atmosphere. 4.2.4 Maintaining the composition of the atmosphere at an optimum level. If we can control the addition of the above harmful substances to the atmosphere, we can maintain the levels of each constituents at an optimum level. Some strategies for such an action are stated below; 1. Preventing destruction of forests and taking steps for re-forestation. (Fig 4.8) 2. Minimize the use of fossil fuels as much as possible. e.g. use public transport instead of private vehicles. 3. Use energy sources that emit minimum amount of harmful substances to the environment. Example: Hydro power, wind power, tidal power. 4. Use fossil fuel free of harmful substances. e.g. Sulphur free coal, lead free petrol. 5. Removing harmful substances from factory effluent before they are released to the atmosphere. (Fig. 4.7) 6. Recycling of garbage instead of burning those. Fig 4.8 - Re forestation Fig 4.7 - Smoke tower directed high into the air Assignment - 2 Make a list of activites, your family members and you can do to control addition of harmful substances to the environment. For free distribution 9 4.3 Natural resources from the earth 4.3.1 Minerals and rocks Observe a newly broken piece of granite and quartz. (Better observations can be made using a hand lens) You can notice that there are different coloured parts in the piece of granite, while the quartz is even in colour. Did you observe that there is a resemblance between some parts of the piece of granite and the quartz? Fig 4.9 - Granite Fig 4.10 - Quartz A substance which exists as a solid and is made up of one type of element or a single compound is known as a mineral. Quartz is a mineral made up of a single compound. Diamond, graphite, gold silver and sulpher are minerals made up of elements. A mineral is a substance in crystal form which has a definite composition and composed with one type of element or a single compound. Diamond Gold Graphite Fig 4.11 - Minerals made up of elements A piece of granite is made up of a mixture of three different types of minerals. A solid substance made up of a number of minerals is called a rock. Therefore, granite is an example for a rock. It is a mixture of feldspar, quartz and mica. Granite taken from different places will have different percentages of mineral components. Therefore their colours will be different. This observation suggests the composition of rocks may differ from place to place. However, the composition of minerals do not change according to the location, because a mineral consists of a single pure substance. 10 For free distribution Table 4.3 shows a comparison between rocks and minerals. Table 4.3 Minerals • • • Pure substance Homogenous Fixed composition Rock • • • Mixture of two or more pure substances. Heterogeneous Composition varies 4.3.2 Minerals and rocks of Sri Lanka. Sri Lanka is rich in minerals. These minerals and rocks are used in a variety of industries. Some minerals are also exported. Let us learn more about some rocks and minerals found in Sri Lanka. Fig 4.12 - Limestone Limestone : Apatite : Iron ore : Mineral sands: For free distribution Fig 4.13 - Apatite Fig 4.14 - Iron ore (Heamotite) Limestone is abundantly found in areas such as Puttalam, Kankasanthurai, Matale and the southern coast of the island. Limestone is used as a raw material in manufacturing cement and in the lime industry and manufacturing toothpaste. The Eppawela area has a large ore of apatite. It is used to produce phosphate fertiliser. Finely crushed apatite can be used directly as a fertiliser for long term crops such as tea, rubber and coconut. Apatite has a low water solubility. Therefore it is essential to increase the solubility, if it is used for short term crops. There are various chemical methods to improve its solubility. All containing iron are called iron ores. Iron is manufactured using iron ores. eg. haemotite magnetite. Various types of iron ores are found in Seruwila, Kahawatta, Kalawana and Rakwana. Mineral sands are commonly found in some coastal areas of Sri Lanka, Black coloured Illemenite is found in northern beaches such as Pulmudai. In Hambantota and Tangalle areas a red coloured mineral sand garnet is common. Some common types of mineral sands and their uses are stated in the table below. (Table 4.4) 11 Table 4.4 - Some mineral sands and their uses Type of mineral sand Illemenite Rutile Zircon Monosite Clay : Use For production of paints, titanium metal for aero plane parts. For production of paints, Welding rods. Production of crockery, Porcelain items. Polishing of lenses, production of gas mantles. Clay is formed by the weathering of rock. Many kinds of clay are found in different parts of Sri Lanka. When clay is mixed with water it can be moulded into many shapes. This property of clay is called plasticity. Ordinary clay is suitable for manufacturing tiles and bricks. Clays with special properties are used for other types of productions. Different types of clay and their uses are given in table 4.5. Fig 4.15 - Ordinary Clay Fig 4.16 - Kaolin Table 4.5 - Various types of clay, their properties and uses Type of clay Kaolin Properties White when burnt. Resistant to high temperature. Plasticity is less. Uses Production of porcelain Ball clay Grey in colour. Hard. High Plasticity Crockery, ornaments. Fire clay Ordinary clay Resistant to high temperature. Production of hearths, Tiles, bricks and pots etc. Very fine. Red when burnt. Assignment - 3 Indicate the distribution of various kinds of minerals and rocks in a map of Sri Lanka in a creative manner. 12 For free distribution Fig 4.17 - Ornaments made out of clay Excercise 1 Select suitable words from those within brackets and fill the blanks in the following paragraph. (atmosphere, nitrogen, troposphere, covering, layers, ultra violet rays oxygen, ozone, heat, meso, exo) Note : some words may be used more than once. The ……………….. on the earths ……………… acts as a layer for protecting organisms. In this the layer closest to the earth is known as the …………....……. . The main components in it are ………………. and ……………. . ……...…….. sphere is found outside the ………………. sphere. The ……………… sphere that prevents harmful rays from the sun reaching the earth is found here. The …………. sphere where the lowest temperatures are recorded is found outside this layer as ……....…. and ………........... in order. 2. Prepare an article for a science magazine describing the ill effects that will have to be faced by man if the atmosphere is not available. 3. Describe the way you would try to identify rocks from minerals by observing through the naked eye or through a hand lense. For free distribution 13