Air refers to the Earth‘s atmosphere.
It is a mixture of many gases and tiny dust particles.
Air is the clear gas in which living things live and breathe.
It has an indefinite shape and volume. It has mass and weight, because it is matter.
The weight of air creates atmospheric pressure.
There is no air in outer space.
Air is a mixture of about 78% of nitrogen, 21% of oxygen, 0.9% of argon, 0.04% of carbon dioxide, and very small amounts of other gases.
Air is invisible – it cannot be seen by the eye, though a shimmering in hot air can be seen.
Water vapor in the air is sometimes visible as clouds. Water enters the atmosphere through the water cycle. The water cycle also brings molecules in the air into oceans, lakes, and rivers.
Animals live and need to breathe the oxygen in the air. In breathing, the lungs put oxygen into the blood, and send back carbon dioxide to the air. Plants need the carbon dioxide in the air to live. They give off the oxygen that we breathe. Without it we die of asphyxia.
The air is different as you move higher and higher into the atmosphere. The air gets “thinner” as elevation climbs because there are fewer air molecules up there. Mountain climbers often have to use canisters of oxygen as they climb above 3,800 meters (12,500 feet) because there is not enough oxygen in the atmosphere for most people to breathe. High mountains such as Mount Everest (8,848 meters or 29,035 feet), in Nepal and China, are littered with empty oxygen canisters that climbers discard when they are used up.
Air can be found everywhere on earth exept where there is water. Air is even located in the surface layer of the earth – in the soil.
Air is not only located on earth, it is also located around the earth in an air layer called the atmosphere. The atmosphere can be divided up in separate layers depending on temperature and height. These lines are not clearly separated by straight borders – they gradually overflow one another.
The first layer of air, which is located closest to the earth is called the troposphere. This layer is 11 kilometres (7 miles) in height. When moving up in the troposphere temperatures fall 6 or 7 degrees per kilometre.
The second layer of air above the troposphere is called stratosphere. Temperatures stop decreasing in the lower part of this layer. The temperature is around -55 °C (-67 °F) here.
The third layer of air is called the mesosphere. This layer can be found over 52 kilometres (32 miles) above the earths’ surface. The upper part of the mesosphere is called the mesopause. Within the mesosphere, temperatures are decreasing once more. Mesosphere temperatures are around -90 °C (-130 °F).
The fourth layer of air, the thermosphere is located over 90 kilometres (56 miles) above earth. Temperatures rise enormously in this layer, causing the highest temperature to be above 1,000 °C (about 1800 °F). The density of air is very low in this layer, therefore the forces between molecules nearly vanish. The lightest molecules can escape through the lowest layer of the thermosphere, the exosphere. The exosphere does not have a clear border, because it fades into space.
Air can be polluted by some gases (such as carbon monoxide, hydrocarbons, and nitrogen oxides), smoke, and ash. This air pollution causes various problems including smog, acid rain and global warming. It can damage people’s health and the environment.
Since early times, air has been used to create technology. Ships moved with sails and windmills used the mechanical motion of air. Aircraft use propellers to move air over a wing, which allows them to fly. Pneumatics use air pressure to move things. Since the late 1900s, air power is also used to generate electricity.
Air is one of the four classical elements along with water, earth and fire in ancient Greek philosophy and in Western alchemy.
According to Plato, it is associated with the octahedron – air is considered to be both hot and wet.
The ancient Greeks used two words for air: aer meant the dim lower atmosphere, and aether meant the bright upper atmosphere above the clouds.