Air

Air is the Earth's atmosphere. Air is a mixture of many gases and tiny dust particles. It 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.

Earth's atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases.

Animals live and need to breathe the oxygen in the atmosphere. 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 animals die of asphyxia.

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. There are debates about whether or not to act upon climate change, but soon enough the Earth will heat up too much, causing it to become too hot and not support life. Some say fewer people would die of cold weather, and that is true but there is already a huge amount of people dying from heat and that number is and will keep increasing more and more.

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 invisible: it cannot be seen by the eye, though a shimmering in hot air can be seen.^[1]

Air is one of the 4 classical elements (water, air, earth and fire).

1. ↑ "Why is air invisible?".