We might live on the Earth, but except for when we go underwater, we live in the air. It is what we move around in; it is what we see through; it is what we breathe. It is also the location where we put a lot of our waste.
While every planet has some form of an atmosphere, our planet has a very unique composition and structure. In our atmosphere, the least, as well as the most, abundant chemical species important for life. We need oxygen for life; yet, we also need ozone to protect us from harmful radiation, and carbon dioxide to keep us warm at night.
Our atmosphere has not always been this way. It has evolved over time, as the interactions between physical and biological components of the Earth have conspired to change it. Today, humans are taking part in this process, and changing the atmosphere in ways and at a rate that have not been seen on the planet for quite some time. Are these changes going to prove to be beneficial to mankind, or are they going to prove to be our downfall? This is one of the most important questions our species faces. To answer it, we need to know more about how our atmosphere works, how it has worked in the past, and what possible changes are due in the future.