How Much Oxygen is in the Air?

Well hopefully there is enough, or else we’d all be extinct. Currently there is 21% oxygen in our air and atmosphere. I believe it will not deplete because we have trees and plants that have respiration. They take our carbon dioxide and produce oxygen. Next time you feel light headed from the lack of air, stand next to a tree. If the atmosphere was made up of 100% oxygen, and someone was to light a match, poof! Look here for more information: