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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The atmosphere is the layer of air that surrounds the Earth and is comprised mainly of Nitrogen and Oxygen. The atmosphere also contains traces of gases like carbon dioxide, neon, helium, etc. There are 5 main layers of the atmosphere: the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.

Right now I'm swimming in the atmosphere because it's all around me, it's the air around us, it's the oxygen we inhale and it's the CO2 that we exhale. It's something that we are dependent on everyday. So let's take a closer look at what the atmosphere is. So it's this thin layer of air above the surface of the earth? The majority of it despite what everybody thinks is actually not oxygen most of it is actually nitrogen gas.
Now roughly 20 percent of the atmosphere is oxygen gas the air that we inhale, we're doing that to take in oxygen gas. When we exhale out comes the CO2 and other gases that make up maybe one percent or less of the atmosphere depending on. I was surprised to find out that almost one percent of the atmosphere; I'm just a little bit shy of it, it's actually noble gases, things like argon and neon and xenon.
Now there's multiple layers of the atmosphere stacked up and we always think well I'm in the atmosphere but actually we exist way down here on what's called the troposphere. The outer most that kind of slowly merges into space is called the exosphere and it starts at roughly 600 kilometers but these are very vague numbers because as you guys know, if the air heats up it expands and so these layers between the different parts of the atmosphere can bulge up and down.
As you go a little bit deeper you ultimately get to what is called the thermosphere, and this is where the international space station and space shuttle are located. That starts at about 85 kilometers going up towards the exosphere. And it's called the thermosphere because you get very high temperatures but weirdly enough you got really low density. And I read something that indicated that it may take an oxygen molecule; it may fly an entire kilometer before it hits another air molecule. That's incredibly spread out. So yeah it's really hot and so then that one molecule hits you it's really hot, but there is so few molecules up there. Its kind of crazy.
Next as you get a little bit deeper, you start getting into the mesosphere, and its much cooler than the thermosphere but this is where you starting to get densities of air that are thick enough that they can generate enough friction so this is where microscopic little rocks and other chunks of outer extra terrestrial materials start burning up. And those are what you call meteors, the are burning up the meteorites in the air. And this extends from about 50 kilometers on up to the thermosphere.
Next is the Stratosphere, and this is where the ozone layer is. The ozone layer being a layer of O3 molecules that helps protect us against ultraviolet radiation. And that starts at about 20 kilometers up.
Finally down at the bottom is the Troposphere, and this is starting at the surface moving up and here the majority of the warmth of the air is being caused by the surface, the lithosphere, the rock that we are standing on right now shedding off its heat and the hot air then rises. This rising hot air is what causes air currents and wind.
If we take a look at how the atmosphere keeps cycling materials, this is primarily what's going on down at that bottom troposphere. What happens basically is hot air rises. So as hot air rises and where it would be hottest? The equator. The hot air starts to rise well that's sucks in cooler air from nearby and that starts to generate what I call convection cells of rising and cooling air. And you get typically three of these convection cells happening. And that causes both circulation up and down in the atmosphere but because the earth itself is rotating underneath it as the earth moves this way the air is being left behind in this causes a spiraling either in the clockwise or counterclockwise direction based on where you're located and that's how the atmosphere works.