Notes - The Atmosphere-A - Blanket Of Air
Category : 7th Class
The Atmosphere - A Blanket of Air
The earth is a unique planet, as it is the only planet known to us that supports life in the Solar System There are many reasons why life exists on the earth and one of the reasons is the presence of air Hold your breath tor some time. How do you feel? You feel suffocated. Living beings breathe in air to survive the earth is surrounded by a thick blanket of air called the atmosphere.
If you look down from a spacecraft, you will see the atmosphere as a blue haze that envelopes our planet.
The earth's atmosphere acts like a filter; it allows sunlight to reach us but prevents the dangerous ultraviolet rays of the Sun from reaching us. The atmosphere consists of gases, dust particles and water vapour. The right composition of gases in air also makes life possible here. Thus, the atmosphere provides the necessary conditions for all forms of life to thrive on earth.
COMPOSITION OF THE ATMOSPHERE
Air is a mixture of several gases. The most abundant gas in the atmosphere is nitrogen, followed by oxygen. Carbon dioxide is present in small amount. As seen in the figure given above, air contains about 78 per cent nitrogen and 21 per cent oxygen. The remaining 1 per cent consists of carbon dioxide (0.03 per cent) and traces of other gases like argon, neon, helium, hydrogen, krypton, xenon and methane. Besides these gases, there are water vapour, dust particles, salt particles, etc., in the atmosphere. As we move towards space, the atmosphere becomes thinner and gradually merges with space. All the gases present in air are important to us. Now let us study the constituents of air.
Nitrogen?this is the most abundant gas in the air. Nitrogen neither burns nor helps in burning. Nitrogen is an inactive gas, therefore, it is used in packaged food like chips. This allows the packaged food to remain fresh. Nitrogen is required by plants for growth. Bacteria converts the nitrogen in the atmosphere in forms usable for plants. Recall the nitrogen cycle you read in your science class.
Oxygen-as you know, most of the living beings require oxygen present in air for respiration. Oxygen supports burning. An adequate supply of oxygen is necessary to burn fuels. Oxygen is a heavy gas and most of it is found in the lower layers of the atmosphere. Mountaineers and divers carry oxygen cylinders to help them breathe where the oxygen content is low.
Carbon dioxide?Even though carbon dioxide constitutes only 0.03 per cent of the air, it is an important gas. Plants require this gas to make their food in sunlight by the process of photosynthesis. Oxygen too is produced in this process. Carbon dioxide does not help in burning, hence is used to extinguish fire. It is dissolved in water to make soft drinks. Carbon dioxide is also an important greenhouse gas. Other greenhouse gases are methane and nitrous oxide. Greenhouse gases trap heat in the atmosphere during the day and keep the surface temperature warm at night. This is called greenhouse effect. However, if there is too much carbon dioxide in the atmosphere due to burning of fossil fuel then it will trap too much heat and this will lead to disbalancing in the composition of the atmosphere and leads to global warming.
Activity
You most have heard about the issue of global warming which is considered as a major threat to mankind and cause of many environmental problems like; extinction of plant and animal species, crop failures and change in climatic patterns, etc. Make a collage by using articles, newspaper reports and pictures from various sources to justify that global warming is a serious issue in today?s world and also highlight the measures which can lessen the adverse effect of global warming.
Geography Reveals
Sweden is aiming to be the world's first Fossil Fuel Free Nation. Two-third of its electricity is from renewable energy and it makes extensive use of bio-energy also.
STRUCTURE OF THE ATMOSPHERE
The atmosphere is held in place by the force of gravity. The earth's pull is the greatest near the earth's surface. As a result, the atmosphere is densest near the surface of the earth. The gravity decreases with the increasing distance from the earth. Hence, the atmosphere thins out with height until it finally merges with the outer space.
The atmosphere is broadly divided into five layers. Starting from near the earth's surface, the layers are as follows: troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Layers of the atmosphere
Troposphere?the lowest and the most important layer of the atmosphere is the troposphere. It extends from 8 to 18 kilometre- vertically from the earth's surface. The uneven heating of the regions of the troposphere by the Sun causes convection currents and winds. Moreover, the presence of dust particles and water vapour causes weather phenomena such as clouds, rainfall, storms and lightning in this layer. The temperature in this layer decreases by 1°C with every 166 metres of ascent. This is known as the lapse rate. All the weather conditions that affect us occur in the troposphere. It contains 75 per cent of the atmosphere's mass.
Geography Reveals
Do you know that you can see an explosion in space, but you cannot hear it? Can you imagine why? It is due to the specific composition of our atmosphere that allows us to hear and speak. If we can enjoy soothing music and sound of waves, it is only due to our atmosphere.
The top of the troposphere is marked by the tropopause. This is where the temperature reaches a stable minimum. The tropopause is also known as cold trap. Rising water vapour cannot go higher beyond this point. It changes into ice and is trapped. Had there been no cold trap, the earth would have lost all its water in the form of vapour and there would have been no water cycle.
Q. can you imagine what would happen if there was no water cycle?
Stratosphere-Above the tropopause lies the stratosphere. This is the second layer of the atmosphere and it extends up to 50 kilometres. It gets its name from the Greek word meaning 'stratified layer.' The layer is stratified with the denser, cooler air below the warmer, lighter air. Temperature gradually decreases due to the lapse rate till 20 kilometres but increases thereafter. Temperature increases with altitude here because there is a gas called ozone which absorbs sunlight. This layer is almost free from clouds. High speed winds known as 'jet streams' flow in this layer providing ideal flying conditions for jet planes. The boundary between the stratosphere and the next layer is called the stratopause.
Geography Reveals
Do you know what we actually mean when we say there is a "hole in ozone layer"? It is not literary a hole. It is the thinning of the ozone layer. It is like opening a window through which incoming solar radiation can reach the earth, uniterrupted.
Between 16 and 20 kilometres from the surface of the earth in the stratosphere is a layer of gas called ozone. The ozone layer does not allow ultraviolet rays to enter the earth's surface from the Sun. Ultraviolet rays are harmful to us as they can cause skin cancer, eye problems and other skin diseases. The ozone layer is being depleted, due to pollution and is getting thinner over Europe, Asia, North America and Antarctica.
Geography Reveals
Do you know as solar energy strikes the earth's surface, it is converted into heat. The energy given out by the Sun is called solar radiation. The amount of solar radiation received by the earth is known as "insolation". Again, heat radiates upward from the earth's surface. The energy reflected from the surface of the earth and atmosphere is called terrestrial radiation. The temperature of the troposphere decreases steadily until the ozone layer in the stratosphere. The earth maintains a balance between incoming insolation and outgoing terrestrial radiation.
Mesosphere?the third layer of atmosphere is called the mesosphere, or 'middle layer. This layer extends up to 80 kilometres. The temperature again decreases with altitude in this region and drops to as low as -110°C near the top of the mesosphere bounded by the mesopause. The atmosphere is very rarefied but thick enough to slow down meteoroids and burn them up, leaving fiery trails in the night sky. We call them meteors.
Geography Reveals
The temperature increases in the stratosphere due to ozone layer capturing ultraviolet radiation. The temperature decreases in the mesosphere since there is no ozone and the density of air is less.
Thermosphere-Above the mesopause is the thermosphere, or the 'warm layer.' It extends from above 80 kilometres up to 400 kilometres. In this layer the temperature rises sharply to about 2000°C and then remains steady with increasing altitude. The lower part of this layer is also called the ionosphere. It contains electrically charged particles called ions which help in transmitting radio-weaves back to earth. Communication satellites orbit in this layer, as it helps in transmitting signals back to the earth. The upper limit of this layer is called thermopause.
Exosphere-above the thermosphere lies the exosphere. This is the outermost layer of the atmosphere and extends to about 1600 Km. Temperature in this layer is very high, and can be estimated to be beyond 5500°C. The air is very thin on account of low density. Lighter gases like helium and hydrogen are found here It merges into outer space.
The importance of the atmosphere
The atmosphere is of vital importance for life on the earth,
i. The atmosphere acts as a blanket making the temperature congenial for life here, protecting us from the harmful ultraviolet rays from the Sun.
ii. The atmosphere absorbs heat and keeps temperature on the earth optimum for life to exist,
iii. The presence of different gases such as nitrogen, carbon dioxide and oxygen are helpful for plants, animals and human beings. It gives us oxygen to breathe,
iv. The atmosphere regulates the weather conditions,
v. It helps us in radio communication,
vi. It protects us from meteorites,
vii. It facilitates in navigation of aeroplanes. Thus, we can say that without the atmosphere, life would be impossible on the earth.
Geography Reveals
Heat is on-the average temperature across global land and ocean surfaces was 1.87°F above the 20th century average for January.
Source?Times of India-Feb 20th, 2016
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