So today I'm going to talk about the atmosphere. You have four basic sections of the atmosphere; the troposphere, the stratosphere, the mesosphere, and the thermosphere. Together, they start at the surface and they continue for 350-800 kilometres above the surface of the Earth, with variations due to solar activity. I will now breakdown and thoroughly explain each.
As you can see from the lovely diagram obtained from Wikipedia, the troposphere is the closest layer to the Earth. The stratosphere is the second closest; the mesosphere third; and finally, the thermosphere is last. Now, there is one more layer above the troposphere, it's called the exosphere. I won't be talking about it because it doesn't really behave like the rest of the atmosphere, mainly because it has very few particles (mostly hydrogen and helium) that are so spread out that they could travel hundreds of kilometres before colliding with each other. If you think of the Earth as an orange, and the atmosphere as it's skin, then the exosphere is the thin layer of dust on the surface of the orange.
The Stratosphere extends from the tropopause to a height of about 51 kilometres. This layer of the atmosphere is where the ozone layer is located. The temperature in the stratosphere actually increases as you get higher! This is due to the absorption of ultra-violet energy by the ozone layer. It is the highest layer of the atmosphere that life can still survive unprotected. Birds will sometimes fly in it, and bacterial life makes it their habitat. The stratosphere is separated from the mesosphere by the stratopause.
The Mesosphere starts at the stratopause and continues to a height of 80-85 kilometres. Here, the temperature again decreases as the height increases. The top part of the mesosphere, called the mesopause can be considered the coldest, naturally occurring place on Earth. With temperatures as low as -100° Celsius, it's easy to see why one can't book trips to the mesosphere. ;) Seriously though, out of all the layers of the atmosphere, the least is known about the mesosphere. This is because the mesosphere is between the maximum height for aircraft and the minimum height for orbital spacecraft. Thus, all we know about it is gained from launching sub-orbital "sounding" rockets into it.
The Thermosphere is the fourth and final layer of the atmosphere (other than the exosphere). It begins at the mesopause and continues to about a height of 500 kilometres. The temperatures here rise the higher you go, but they are largely dependent on solar activity. The temperature can get as high as 2,500° Celsius, but since the energy lost by thermal radiation would be higher than the energy gained by infrequent collisions with sparsely located particles the actual temperature one would feel would be below 0° Celsius.
For a more detailed description on the atmosphere, check out Wikipedia or the video below.