What is air and where does it come from?
Many children when talking about the air would simultaneously mention oxygen and air as the same thing. Our next discussion of the air should help to clear this up. At this point we have established that all humans and animals breathe. When we take in air what part or parts are we using and what are we exhaling? Is air the same as oxygen?
An ocean of air surrounds the earth. The air we breathe is a mixture of several different gases. The three most important that are needed for survival are oxygen, nitrogen, and carbon dioxide. We breathe in oxygen that combines with sugars in our body cells and releases heat energy. Students may believe that the air is pure oxygen. While we can breathe pure oxygen for short periods of time, too much pure oxygen is poisonous to our system and we would die.
Oxygen makes up about 21% of the air, and nitrogen 78%. There is really only a small amount of carbon dioxide in the air – about 3/100 of 1%. There are less than 1% of other gases such as argon, krypton, helium, neon, radon, and xenon. All the gases get mixed by the wind and are covering cover the earth in a five to six mile deep layer. Of course this mixture of gases is not all we breathe. There are other substances in the air like pollens, dust, smoke, salt particles, water vapor, chemicals, spores, bacteria and viruses.5
Billions of years ago when the earth was first developing the air around the earth was made up of gases that evaporated from water that seeped out of the soil and escaped from the hot lava that came from beneath the earth’s crust. The first atmosphere that the earth had would not have been able to sustain life, as we know it. When the first living organisms appeared in the water there was still no oxygen in the air. When the first plants appeared they changed the air by using up carbon dioxide and giving off oxygen. Over the subsequent years the atmosphere as we know it developed.6
Doing Experiment #47 in Appendix A will demonstrate to the class that air is composed of more than one gas. In this experiment the oxygen combines with the steel wool to make rust. Water comes in to replace the air but the tube will still have air in it. Most of the oxygen has been removed so what is in the air that remains? There must be gases that do not react with the wool. Therefore there is more than oxygen in the air.