The troposphere is the layer that's in contact with Earth's surface where we live and climb mountains and fly in planes. Everything we do unless you're an astronaut or a very specialized type of pilot is going to be in the troposphere.

Above the troposphere is the stratosphere, then the mesosphere, and then finally the thermosphere. And I do want to make a point to say that there is not some distinct line up here that's like this is the thermosphere and this is our atmosphere and then this is space. It's not a hard boundary. It's very much a gradient and the thermosphere just sort of dissolves into space eventually.

Chemically, the atmosphere is made up of 70% Nitrogen, 21% Oxygen, like 0.93% Argon, and then after that you've got water vapor, and carbon dioxide, and methane and "NOx" and all of the other trace gases.

But of all of those trace gases, water vapor is going to vary the most. It can be up to like 5% of the atmosphere's makeup if you're over like the equator or a jungle or the ocean or something like that and it can get just almost nothing over say a desert region.

And that is in a nutshell what the atmosphere is made of.