What is the atmosphere?

<v ->Today, we’re going to talk about the atmosphere</v> and what is it? And I really like this section of the class because I really like the atmosphere. We live in it. The majority of, well, the majority of our lives, unless you’re a scuba diver and you love scuba diving, we live in the atmosphere. We breathe it, we work in it, we play in it and we sleep in it. But what is the atmosphere? In essence, the atmosphere is this collection of gases that envelop the earth. A thin layer. And in it is about 78% nitrogen, 21% oxygen, a little, almost a percent argon.

And then lots of other trace gases in there as well, like helium, water vapor and carbon dioxide. And interesting fact, carbon dioxide in 1850 was at a level and we measure it in parts per million by volume, which is one molecule per other for every million molecules. CO2 was at a level of 285 parts per million by volume in 1850. With the advent of fossil fuels and the heavy use of fossil fuels and the carbon emissions they entail today global atmospheric CO2 values are over 400 parts per million by volume. And they’ll never go back down again in your lifetime. It’s very unlikely. And so we are able to impact and have an impact on our atmosphere.

And the reason is because it’s such a fragile and delicate part of our earth. Now we’ve talked about what’s in the atmosphere. Let’s talk about how that’s structured. And this is one of the really interesting things about the atmosphere. The atmosphere is structured into many layers. The layers we’ll talk about today are the four layers closest to the surface of the earth. Starting from the surface we have the troposphere. Above that we have the stratosphere. And then the mesosphere and the thermosphere. And there’s lots of really interesting things going on in all of those. But where we live and the layer that’s most important to us and the one we have the most impact on is the troposphere.

And it’s from the surface of the earth to about 12 kilometers in altitude. Now, 12 kilometers is not very much. In fact, it’s a vanishingly short distance. I can drive 12 kilometers in about 10 minutes. And if you look behind me there, the top of that mountain on Magnetic Island is 13 kilometers away. And what’s really important to remember is that within 13 kilometers of the surface of the earth, 13 kilometers up is almost 85 to 90% of our atmosphere by mass. That means everything that protects us from the vacuum of space is within that 12 to 15 kilometers from the surface of the earth.

Now I know if I were in the space station, I wouldn’t open the door without a space suit on, but every day we walk out of our house depending on the atmosphere to protect us from the vacuum of space and the cold dark expanse that it is. One of the things I challenge you guys to do is to get on Google Earth. And there’s a cool little ruler tool on Google Earth, and you can actually measure 12 kilometers or 15 kilometers from your home to another place around your town or city. And that’ll give you the sense when you turn that distance vertically of how thin our atmosphere is.

In fact, when you look up at the sky and you see an airplane flying over with a contrail that airplane is almost at the top of our troposphere. Okay, they’re usually flying at about 10 kilometers high. There’s very little of that atmosphere left above that level. So today we’ve talked about what’s in the atmosphere and how that is structured. And I think what I really want you to take away is the fragility of that atmosphere and how thin it really is. Like a layer of plastic wrap on a bowling ball. There’s not that much there and yet it’s so incredibly important for keeping us alive and keeping our environment healthy.