this video will introduce you to earth's atmosphere what is the structure of the atmosphere the atmosphere is the thin shell of gases that lies between the solid earth and outer space this layer of gases is a similar thickness to the skin on an apple where the skin of the apple would be the atmosphere and the fruit of the apple would be the solid earth the table shown here shows which gases make up the atmosphere on the left we see the permanent gases these are the gases that make up the vast majority of the air in the atmosphere the top one is nitrogen n2 at 78 percent the second is oxygen o2 at 21 the third is argon at 0.93 percent there is also neon helium hydrogen and xenon on the right side of the table you see the variable gases that make up our atmosphere these are sometimes called trace gases these gases include water vapor carbon dioxide methane nitrous oxide ozone particles like solids that are suspended in the air and chlorofluorocarbons a man-made gas that contributes to the ozone hole these gases may only make up less than one percent of the volume of the atmosphere but some of them can have a large impact on the conditions in our climate for example carbon dioxide which we already started learning about this is a greenhouse gas that has a very large impact on our global temperatures when we look at how the atmosphere is structured we see that 90 percent of the mass of the atmosphere is found in the lowest 10 kilometers this is because of gravity just like everything else air molecules get pulled closer to the surface of the earth by gravity and their density decreases as we rise the graph on the right side is just showing an example of how air pressure decreases with altitude in the atmosphere so on the left side you see numbers in millibars going from a thousand up to a hundred that represents air pressure on the right side we see elevation in meters and in feet let's go a little further in depth on air pressure air pressure always decreases with increasing altitude this is because air pressure is simply a measurement of how much force the air molecules above your head are exerting down on you therefore the more air molecules exist above your head the higher the air pressure will be the less air molecules the lower the air pressure will be so the higher up you are in the atmosphere the less of the atmosphere is contained above your head therefore air pressure is going to be lower on the top of the mountain there's not very much atmosphere above your head so air pressure will be extremely low whereas down in a valley you'll have a lot of atmosphere above your head so a lot of force from those air molecules pushing down on you creating higher pressure as we go up in the atmosphere we see that temperature varies in a more complicated way where temperature has has multiple peaks and valleys as we go throughout the entire altitude of the atmosphere at the surface temperature is relatively warm and it cools as we rise and then at some point it changes and it starts to warm again and then it cools again and then it warms again this is how we designate the different layers of our atmosphere with the lowest layer being the troposphere the second layer being the stratosphere the third the mesosphere and the fourth the thermosphere temperature decreases with altitude in the troposphere it increases with altitude in the stratosphere decreases in the mesosphere and increases in the thermosphere we also see that we can label the boundaries between the layers with the suffix pause therefore the boundary between the troposphere and the stratosphere is called the tropopause the boundary between the stratosphere and mesosphere is the stratopause and the boundary between the mesosphere and thermosphere is the mesopause what are the main characteristics of these layers the troposphere which is the lowest layer is where we live this is also where weather occurs in this layer temperature decreases with height this is also where we find greenhouse gases in the atmosphere the next layer is the stratosphere this layer is above the troposphere and contains the ozone layer in this layer temperature increases with height the layer above that is the mesosphere by the time you get up to the mesosphere it's pretty low air density and temperature decreases with height the final layer is the thermosphere in that sphere there is extremely low air density and very strong solar radiation as we're close to outer space now you have a chance to test yourself take a moment to answering to answer the following three questions before advancing to the next slide number one what are the three most prevalent gases in the atmosphere number two does temperature increase or decrease with height in the troposphere and number three does pressure increase or decrease with height in the troposphere did you get the answers right the answer to number one is nitrogen oxygen and argon number two temperature decreases with height in the troposphere number three pressure decreases with height in the troposphere