Air and Atmosphere

arth is surrounded by a blanket of air called the atmosphere. Air is a mixture of gases. It supports life, soaks up energy from the Sun, and moves water around the planet. The atmosphere protects us from harmful rays from space.

Gases and Gravity

Air is made mainly of nitrogen and oxy­gen with small amounts of other gases. The weather, winds, and air currents keep the gases mixed up together. The gases in dry air are 78 percent nitrogen, 21 percent oxygen, and 0.9 percent argon. The remaining 0.1 percent is a mix of carbon dioxide, neon, helium, methane, krypton, hydrogen, and all other gases. The atmosphere also con­tains varying amounts of water vapor.

Gravity pulls the atmosphere down toward the ground, which means the atmosphere has weight. In fact, the atmosphere weighs about 5,500 trillion tons (about 5,000 trillion metric tons).

This great weight presses down on Earth’s surface. At sea level, it presses against everything with a force of about 14.22 pounds on every square inch (98 kilopascals). This pressure is known to scientists as “1 atmosphere.”