The Atmosphere – We learned that commercial planes fly at about 10,000 m because the air at that altitude is less dense which causes less drag and requires less fuel. The air is also less turbulent above the clouds. We learned that the air we breathe is mostly nitrogen. We learned that observers report hearing a crackling noise when watching the Aurora. Scientists believe that the electromagnetic effects of the Aurora affect the human nervous system and cause it to generate this noise in the human brain, but it doesn’t really exist. Next, we learned that the ozone in the stratosphere protects life on earth by reducing the amount of damaging UV radiation that can reach the Earth’s surface.