Chapter 7: Composition and Structure of Atmosphere - Class 11 Geography Extra Notes
Q. 1 Describe the composition of atmosphere.
Answer Key Points: -
1) The air is an integral part of the Earth’s mass and 99 per cent of the total mass of the atmosphere is
confined to the height of 32 km from the Earth’s surface.
2) The atmosphere is composed of gases, water vapour and dust particles. Nitrogen constitutes 78.8%, oxygen contributes 20.94% and argon contributes 0.93% in atmosphere.
3) Nitrogen and oxygen together constitute 99% of the atmosphere. Neon, krypton, xenon are scarce gases.
4) Other gases include carbon dioxide, helium, ozone, methane, hydrogen, krypton, xenon and neon, etc.
5) The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the Earth.
Q. 2 What is the importance of different gases of atmosphere?
Answer Key Points: -
1) Nitrogen 78%: - It is fifth most abundant element in the universe. Nitrogen is essential to life on Earth as it is helpful in the growth of living beings. It is a component of all proteins, and it can be
found in all living systems. Nitrogen compounds are present in organic materials, foods, fertilizers, explosives and poisons.
2) Oxygen 21%: - Oxygen is essential for respiration because the body uses it to 'burn' food molecules. Human and animals take in oxygen when inhaling and give off carbon dioxide when exhaling.
3) Carbon dioxide 0.04%: - Carbon dioxide plays an important part in vital plant and animal process, such as photosynthesis and respiration. Green plants convert carbon dioxide and water into food compounds, such as glucose, and oxygen which is required for their survival.
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4) Other Gases: - All other minor gases such as Argon, Ozone, Neon, Helium, Methane, Krypton, Hydrogen etc. along with Carbon dioxide are considered as the greenhouse gases as these are the primary cause of global warming. At ideal levels, greenhouse gases play an important role in keeping our planet warm enough for us and other organisms to live comfortably.
Q. 3 Write a short note on water vapours.
Answer Key Points: -
1) Water vapour is a principal element in the thermodynamics of the atmosphere as it contributes to transport and absorption of heat.
2) It condenses into clouds that reflect and adsorb solar radiation and also leads to precipitation that directly affects the climate of a place on the Earth.
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3) It preserves the Earth’s radiated heat and thus acts as a blanket by allowing the Earth neither to become too hot nor too cold.
4) It plays a dominant role in the hydrological cycle.
5) The amount of water vapour decreases with the altitudes. In warm and wet tropics, it accounts for 4% of the air by volume whereas in dry and cold areas of deserts and Polar Regions, it may be less than 1% of the air.
6) It also decreases from the equator towards the poles.
Q. 4 Explain about dust particles.
Answer Key Points: -
1) Dust particles are concentrated in the lower layers of the atmosphere but sometimes conventional currents take them to the higher altitudes.
2) Dust particles include sea salts, fine soil, smoke, ashes, pollens, dust, and disintegrated particles of meteors.
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3) Dust particles and salt particles act as hygroscopic nuclei around which water condenses into water vapour to produce clouds.
4) Dust particles produce optical phenomenon which makes the sky look beautiful at dawn and dusk.
5) Sky looks blue due to the presence of dust particles and water vapour which are scattered in the atmosphere.
6) Higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and Polar Regions.
Q. 5 Draw a suitable diagram for the structure of the atmosphere and label it and describe it. Or
Why is troposphere the most important of all the layers of the atmosphere?
Answer Key Points: -
The atmosphere consists of different layers with varying density and temperature. Density is highest near the surface of the Earth and decreases with increasing altitude. The atmosphere is divided into five different layers depending upon the temperature condition these are: -
1) Troposphere: - The troposphere is the lowermost layer of the atmosphere. Its average height is 13
km and extends roughly to a height of 8 km near the poles and about 18 km at the equator. Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convectional currents. This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer. The air never remains static in this layer. Therefore this layer is called ‘changing sphere’ or troposphere. The temperature in this layer decreases at the rate of 1°C for every 165m of height. The upper limit of the troposphere is known as Tropopause.
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2) Stratosphere: - The stratosphere is found above the troposphere and extends up to a height of 50 km. This layer is free from clouds and other weather related activities as air blows horizontally here, so this layer is considered ideal for flying of aircraft. The temperature remains almost the same in the lower part of this layer up to the height of 20 km. After this, the temperature increases slowly with the increase in the height due to the presence of ozone gas. One important feature of the stratosphere is that it contains the ozone layer. This layer absorbs ultra-violet radiation and protects life on the Earth from intense, harmful VU rays of the Sun. The upper limit of the stratosphere is known as Stratopause.
3) Mesosphere: - The mesosphere lies above the stratosphere, which extends up to a height of 80 km. In this layer, temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km. Meteors or falling stars occur in this layer. The upper limit of the mesosphere is known as Mesopause.
4) Thermosphere/Ionosphere: - The ionosphere is located between 80 and 400 km above the Mesosphere. It contains electrically charged particles known as ions, and hence, it is known as ionosphere. Radio waves transmitted from the Earth are reflected back to the Earth by this layer. Temperature here starts increasing with height.
5) Exosphere: - The uppermost layer of the atmosphere above the thermosphere is known as the exosphere. Gases are very thin in this sphere due to the lack of gravitational force. Therefore, the density of air is very less here and the atmosphere merges into outer space. Temperature starts increasing in this layer as it is composed of very widely dispersed particles of hydrogen and helium. Lower boundary of Exosphere is called Exobase.
Q. 6 Why different boundaries are there in the layers of Atmosphere? Give the brief description of boundaries of different layers of Atmosphere of the Earth.
Answer Key Points: -
There are 4 boundaries in between the 5 layers of the atmosphere showing constant temperature called "pauses". Each pause is composed by different physical and chemical phenomena.
1) Tropopause: - The zone separating troposphere from the stratosphere is known as tropopause.
It is a thermodynamic gradient stratification layer, marking the end of the troposphere. It lies, on average, at 17 km above equatorial regions, and about 9 km over the Polar Regions. The air temperature at the tropopause is about minus 80° Celsius over the equator and about minus 45° Celsius over the poles. The temperature here is nearly constant due to convection, (the process of mixing and transporting heat between boundaries of the troposphere and stratosphere) and hence, it is called tropopause.
2) Stratopause: - The stratopause is the boundary in the Earth's atmosphere between the stratosphere and the Mesosphere. The stratopause is the region where a maximum in the temperature occurs and remains constant. On Earth, the stratopause is 50 to 55 km high above the Earth's surface. The temperature in the stratopause is minus 15° Celsius.
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3) Mesopause: - The mesopause is the point of minimum temperature at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling (process by which a body loses heat) from carbon dioxide, the mesosphere is the coldest region on Earth with temperatures as low as -100 °C (-148 °F or 173 K)
4) Thermopause: - It is the atmospheric boundary of Earth's energy system, located at the top of the thermosphere. The temperature of the thermopause could range from nearly absolute zero to 987.548 °C. Below this, the atmosphere is defined to be active on the insolation received, due to the increased presence of heavier gases such as monatomic oxygen. The solar constant is expressed at the thermopause. As a lower boundary for the exosphere, this boundary is also called the Exobase.
Q. 7 What would happen if there is no Ozone in the atmosphere?
Answer Key Points: -
1) It is the special variety of oxygen gas which is found in small quantity in atmosphere between 10 and 15 km above the Earth surface.
2) It acts as a filter and absorbs UV radiation from the sun and prevents them from reaching the Earth surface.
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3) If ozone is not there, then UV rays will reach the surface of the Earth and which can damage the DNA of plants and animals.
4) There will be extreme skin problems, instances of cancer and in all probabilities life would not have been possible on the Earth.
Q. 8 Write about elements of weather and climate in detail.
Answer Key Points: -
1) The main elements of atmosphere which are subject to change and which influence human life on Earth are temperature, pressure, winds, humidity, clouds and precipitation.
2) These elements determine the direction and speed of wind, amount of sunlight received, cloud formation and amount of rainfall which in turn affect weather and climate.
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3) These factors behave differently in different places.
4) All these elements are affected by a number of factors in turn. For example, temperature is affected by latitude and height; humidity is affected by distance from the sun and pressure is affected by height from sea level.
