The Atmosphere: Properties and composition

One of the most unique features of Earth is the presence of a stable atmosphere. The atmosphere is the layer of gas that surrounds the earth. Earth’s atmosphere shapes our weather, climate, and vegetation patterns and makes life possible. Without air there would be no day-to-day weather changes. It would be extremely hot during the day and very cold at night. And, there would be no colour, no weather, no fire, no sound. Without air nothing on earth could live. This ocean of gases rises upward for hundreds of miles. It can be heavy or thin, calm or stormy, hot or cold. More than 98 percent of the gases that make up the atmosphere, are found within 26 kilometers of the earth’s surface. Farther above the earth, the gases gradually thin out. And the composition of the atmosphere changes with the distance from the earth’s surface.

Air in its natural state is a colorless, odorless, tasteless mixture, which has weight. Anything that takes place has weight and exerts pressure by pushing. An Italian scientist, Evangelista Toricelly, was the first person to show that pressure of air could be measured. The body of an average man has a surface of 2, 300 square inches.¹ At sea level this body will support air pressure of 34,500 pounds.² We are not crushed by this enormous weight because the air inside of the bodies presses out just as strongly as the air outside presses in. The atmospheric pressure is measured by a barometer, and is normally registered in millibars.

Scientists speak of the atmosphere as divided into layers. The layer near the surface – the troposphere – contains the air we breathe, which is 78 percent nitrogen (N₂), 21 percent oxygen (O₂), 0.03 percent carbon dioxide (CO₂), and 1 percent inert gases such as argon. There are tiny quantities of other gases such as helium, ozone (O₃), nitrous oxide (N₂ O), and methane (CH₄). Water vapour is also present but to a variable extent, ranging from nearly none to about 4 per cent. The lower atmosphere also contains a considerable quantity of small solid particles of different kinds, such as soot, bits of rock and soil, salt, salt grains from the evaporation of seawater droplets, and spores, pollen, and bacteria. The troposphere we live in varies in thickness from 10 miles high at the equator to five miles high at the North and South Poles. All our weather is formed in this layer, as well as clouds, the blue colour of the sky and the winds.

The blue colour of the sky is due to the scattering of sunlight by gas molecules and dust particles in the atmosphere. Blue light is scattered most; hence skylight, which consists of scattered sunlight, is predominantly blue, and the sun itself appears a little more yellowish or reddish than it would if there were no atmosphere, the scattering is greatest, and the sun may be a brilliant red.

From 15 to 80 kilometeres above the earth is the stratosphere, an upper portion of the atmosphere. It contains thin, cold air with less oxygen and no dust or water vapor. The ionosphere contains very thin air and electrically charged particles which reflect electromagnetic waves. We use the ionosphere to send radio signals around the earth.

The lower part of the stratosphere contains a band of warm gas called the ozone layer (between 15 and 40 kilometers above sea level). Ozone absorbs very shortwave ultraviolet radiation – that is, the harmful, burning rays from the sun. These rays kill plants and cause burns, skin cancer, and cataracts in animals and man. The ozone layer protects us from these damaging effects.

Notes:

1. inch – дюйм (=2,5 см)

2. pound – фунт (=453,6 г)