Air
. Air, mixture of gases that composes the atmosphere surrounding Earth . These gases consist primarily of the elements nitrogen, oxygen, argon, and smaller amounts of hydrogen, carbon dioxide, water vapor, helium, neon, krypton, xenon, and others. The most important attribute of air is its life-sustaining property. Human and animal life would not be possible without oxygen in the atmosphere. In addition to providing life-sustaining properties, the various atmospheric gases can be isolated from air and used in industrial and scientific applications, ranging from steelmaking to the manufacture of semiconductors. This article discusses how atmospheric gases are isolated and used for industrial and scientific purposes. GASES IN THE ATMOSPHERE The atmosphere begins at sea level, and its first layer, the troposphere, extends from 8 to 16 km (5 and 10 mi) from Earth’s surface. The air in the troposphere consists of the following proportions of gases: 78 percent nitrogen , 21 percent oxygen...