Air is the mixture of gases that surround the Earth. Air is often called the atmosphere. Air covers the land and sea and reaches far above the Earth's surface. We cannot see, smell or taste it, yet air is as real as land or water. When the wind blows, you feel the air against your body.
Without air, there could be no life on Earth. All living things need air to stay alive. You are breathing air now. You must breathe air to live.
Air also shields the Earth from harmful rays from the sun and other objects in outer space. At the same time, it holds the heat that comes from the sun. In this way, air helps keep the Earth warm enough to support life. Clouds that form in the air bring us water in the form of rain and snow.
The main gases in air are nitrogen and oxygen. Nitrogen makes up almost four-fifths of the air. Oxygen makes up about one-fifth. The air contains tiny amounts of other gases too, especially argon.
Some gases in the atmosphere are especially important. When people and animals breathe, they take in oxygen from the air and give off a gas called carbon dioxide. Green plants do just the opposite. They take in carbon dioxide and give off oxygen.
The Earth has plenty of air, but some of the things people do have make the air dirty, or polluted. Air pollution is a serious problem in most big cities. Polluted air is bad for our health and it hurts plants and animals, too. It damages buildings and it can even change the weather. For example, carbon dioxide gets into the atmosphere when coal and other fuels are burned. Scientists believe that this carbon dioxide acts like a blanket to keep heat near the Earth. They think that the Earth is getting warmer. This is called global warming. Source: NASA
|