Composition and Structure of Atmosphere - Chapter 8 Geography NCERT Class 11

so this video is on chapter 8 composition and structure of atmosphere now what do we mean by the word atmosphere the atmosphere surrounds us wherever we go and it is necessary for a survival it has layers of gases surrounding the earth while it may just look one vast blue sky when we look up in the sky but there's a lot that goes there then atmosphere is divided into five layers about which we will read as we go forward so basically it is essential to the survival of all organisms because it contains life-giving gases like oxygen for humans and animals and carbon dioxide for plants so the air that we need has no color it has no smell it can only be felt when the wind blows and ninety-nine percent of the total mass of the atmosphere is confined to the height of 32 kilometers from Earth's surface which means the first and little bit of the second layer of atmosphere falls into this 32 kilometers inch again about which we will read in detail as we go forward alright so that was a little introductory part now let's read about the first topic of this chapter composition of the atmosphere meaning what is the atmosphere made of if you look at this table you can see the different gases we have in our atmosphere always remember nitrogen oxygen and argon are the three major constituents of Earth's atmosphere you can remember it as Noah and Oh a pause the video and take a look at their respective percentages now here it says carbon dioxide and water vapor are found only up to ninety kilometers from the surface of the earth let me just pull up these five different layers of the atmosphere here's the pegs and you can see the first layer which is closest to the Earth's surface is troposphere which exists up to ten kilometers from the surface of the earth after that we have stratosphere that Meisel says after that thermosphere and finally exhaust finish so here when it says carbon dioxide and water vapor are found only up to 90 kilometer from the surface of the earth it means that carbon dioxide and water vapor exists till the initial boundary of thermosphere I hope this part is clear now now let's read about this topic gaseous carbon dioxide is an important gas remember this point I'll get back to this it is transparent for the incoming sunrays but it is opaque to the outgoing terrestrial radiation alright let me just explain this line what I just said now you must be aware of this phenomena that differential heating of land and water is the reason behind rainfall and precipitation now having said that we now clearly know that Earth's surface just gets heated up due to sun rays and because Earth's surface heats up due to the incoming sun rays and that heat has to go somewhere it is because of carbon dioxide the heat is trapped within the Earth's atmosphere this is what is causing climate change now you must have heard about greenhouse gases they are methane nitrous oxide sulfur dioxide ozone carbon dioxide so these are a bunch of gases in the atmosphere that blocks the Earth's radiation from going out in the space now these greenhouse gases trap the heat within the Earth's atmosphere and makes the earth warmer now the interesting part to notice that the volume of other gases is constant but the volume of carbon dioxide has been rising in the past few decades mainly because of the burning of fossil fuels since the Industrial Revolution that is from the mid 18th century the amount of carbon dioxide has increased machines on daily basis are using fossil fuels like diesel petrol and that's emitting more and more carbon in the atmosphere which is increasing the overall carbon content now ozone is another important component of the atmosphere that is found between 10 and 15 kilometer above the Earth's surface basically it's located in these stratosphere what ozone layer does is it acts as a filter and absorbs the ultraviolet rays that comes from the Sun so UV rays are very harmful if taken in excess it can cause sunburn skin cancer etc in a nutshell they're harmful rays now ozone layer is protecting the UV rays from coming directly basically it's filtering it but this layer is depleting it is purely due to man-made activities ozone layer depletion is one of the most serious problems faced by our planet Earth's now we will read about this topic water vapor so basically water vapor is the amount of moisture that is present in the atmosphere when we think of water it is a liquid state with vapor it becomes a gas so water vapor means liquid and gaseous state so as I said the amount of moisture that is present in the atmosphere is called water vapor similarly the amount of water vapor present in the atmosphere is called humidity and if I were to ask you in India which place is more humid that would be coastal areas you go to go watch any any coastal place it's humid because there's a lot of water vapor in the air due to the sea in front of you and it's not the same case everywhere on earth the point that I'm trying to make is that water vapor decreases from equator towards the poles so equatorial region is known for warm as well as wet temperature because direct sun rays hit only at the equator therefore evaporation is high in this region this is what increases the water vapor level in the atmosphere now as you go towards the pole area you will not find moisture no moisture means no water vapor and no humidity that's why when you go to a cold region your skin will be try and your lips may crack due to dryness so this is what is water vapor now the role of water vapor is to absorb parts of the sun rays and not make the earth surface too much warm likewise it also blocks some heat of the sun rays and it does not allow it to escape out of the atmosphere because we don't want the entire heat of the earth to escape without these sun's heat we would have frozen to death so we need heat but not too much and it's the water vapor that sets the right temperature for us to live it acts like a blanket on the earth which doesn't make the earth too cold not too hot and this line over here is absolutely true water vapour also contributes to the stability and instability in the air let me just explain this in a simple and straightforward way the amount of water vapor in the atmosphere exists in direct relation to the temperature in other words higher the temperature higher will be the water vapor content in the atmosphere just like how water vapor decreases as we go away from the equator towards the poles similarly with increase or decrease in temperature water vapor also increases and decreases now let's assume that I increase the temperature on earth in a more funny or relatable sense I push the earth a little closer to the Sun that would increase the temperature reasonably now more water will evaporate from oceans right which means evaporation process creates water vapor now imagine this when something else causes an increase in temperature I'm talking about extra carbon dioxide from burning of fossil fuels so you see here the trigger has changed now instead of me pushing the earth closer to the Sun increase in carbon dioxide in the atmosphere is causing the temperature to rise now that the trigger has changed but the mechanism remains the same that is due to increase in temperature more water evaporates when more water vapor evaporates more vapor is formed in the atmosphere and increase in water vapor causes humidity when there is humidity we feel warm likewise the air in humid region is warm and the warm air rises and that's how it comes in contact with the cool air when warm air comes in contact with the coolest turbulence rainfall and precipitation occurs so I hope you see the chain effect and you're understanding how water vapor contributes to the stability and instability in the air I hope you're comprehending as to what I'm saying so far now let's talk about dust particles so far we saw that the tons of water vapor in the atmosphere but I want you to know that atmosphere has a sufficient capacity to keep small solid particles now what are these particles these are dust particles that originated from sea salts fine soil smoke from incomplete burning ash pollen dust and disintegrated particles of meteors since dust particles are fairly heavier than water vapor therefore they are generally found in the lower layer of the atmosphere which are troposphere and stratosphere now it is the air movement that takes these dust particles to create a height and a longer distance now I want you to remember this point the higher concentration of those particles is found in subtropical and temperate regions due to dry winds I'll show you sub tropical and temperate regions on this world map so here the veins are try remember moments back we read that water vapor decreases as we go away from the equator towards the poles that means at equatorial region the moisture content in the atmosphere does not allow the particles to rise but then as we go away from the equatorial region moisture content in the atmosphere decreases and drivin carries the dust particles and as we go further away at poles area I'm talking about North Pole and South Pole there you will hardly find any dust particle you will mostly see ice crystals I don't know if that can be called as dust particle another important point is that dust particles are a major component behind cloud formation now if you see there is water around us all the time in the form of tiny gas particles which is also known as water vapor then there are also tiny dust particles floating around in the air now if you look closely at a black background you can see the dust particles so the combination of this water vapor and dust particles together form the cloud obviously you must have heard that cloud is a result of condensation where the water vapor turns into visible water droplets but then if there isn't anything to hold them up in the air how will a cloud form otherwise droplets will fall and it will simply drain so to hold this condensed water droplet floating dust particles come into picture these are called aerosols these aerosols attract the condensed water droplets and large combination of these forms a cloud so that's the role of dust particles now let's get to know quickly about different layers of the atmosphere so this is the picture of different layers of the atmosphere from low most layer to the outermost layer overall there are five layers remember this order now these layers have different density and temperature now density is highest near the surface of the earth because of the gravitational pull of the earth and as we go higher the density decreases now coming to the temperature part the lowest layer that is the troposphere is hotter because it's nearer to the Earth's surface so heat from the earth warms up the air of this layer as the height increases the number of air molecules decreases and that certain pressure decreases and this continues till the end of measles fires now this place is also called as me so pause this is the coldest part of Earth's atmosphere temperature falls up to minus 90 degree Celsius now after me so says we have thermosphere by the word thermo you can relate the word thermal and which means heat here the temperature goes up to 500 to 2,000 degrees Celsius now after this we have exhaust air it is also the first layer to come into contact and protect the earth from meteors asteroids comets basically after this layer space starts the temperature here varies from zero to over 1700 degrees Celsius that means it is colder at night and much hotter during day and I also remember watching some NASA astronauts interview where he said that when an astronaut goes on a spacewalk that spacesuit they are wearing it is like the mini spaceship it protects them from the heat of Sun and he said something which I will always remember he said when they face decide where the Sun is that side is illuminated by the Sun as a result that front part of the suit is so much hot and the back side of the suit is freezing cold I hope you are getting what I'm saying of course the spacesuit has the temperature control mechanism which keeps the astronauts safe but I hope you're getting the relevance of the extreme sides of the atmosphere I'm going to make a separate video on different layers of the atmosphere I mean right now I just explained you the entire structure of the atmosphere in a simple and easy manner but then I intend to make a separate video for those of you who just wants to understand the structure of the atmosphere without going through this entire video so I hope you found this video useful as usual thanks for watching and I'll see you in the next one

Channel: Amit Sengupta

Views: 282,814

Keywords: upsc, ssc, ias, cds, cgl, amit sengupta geography, ncert geography, ncert, Composition and Structure of Atmosphere, Atmosphere, Chapter 8 Geography NCERT Class 11, class 11 ncert geography, water vapour, dust particles, diferent layers of the atmosphere, Earth, troposphere, stratosphere, mesosphere, exosphere, ionosphere, thermosphere, atmosphere layers, atmospheric gases, 5 layers of atmosphere, atmosphere structure and composition, geography atmosphere, geography class 11 ncert

Id: yIlF8DjXH88

Length: 12min 34sec (754 seconds)

Published: Mon Aug 21 2017