Air

A fan moves 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 we 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 to much, causing our home 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 at a frighting height.

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)

Main history

Original atmosphere

At first it was mainly a hydrogen atmosphere. It has changed dramatically on several occasions—for example, the Great Oxygenation Event 2.4 billion years ago, greatly increased oxygen in the atmosphere from practically no oxygen to levels closer to present day. Humans have also contributed to significant changes in atmospheric composition through air pollution, especially since industrialisation, leading to rapid environmental change such as ozone depletion and global warming.

Second atmosphere

Out gassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids, produced the next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases.^[2]

Third atmosphere

Oxygen content of the atmosphere over the last billion years^[3]^[4]

The constant re-arrangement of continents by plate tectonics influences the long-term evolution of the atmosphere. Carbon dioxide was transferred to and from large continental carbonate stores. Free oxygen did not exist in the atmosphere until about 2.4 billion years ago. The Great Oxygenation Event is shown by the end of the banded iron formations.

Air Media

View of the crescent moon through the top of the Earth's atmosphere. Photographed above 21.5°N, 113.3°E by International Space Station crew Expedition 13 over the South China Sea, just south of Maca
Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations). Numbers are mainly from 2000, with Template:CO2 and methane from 2019, and do not represent any single source.
Earth's atmosphere. Lower four layers of the atmosphere in three dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.
Afterglow of the troposphere (orange), the stratosphere (blue) and the mesosphere (dark) at which atmospheric entry begins, leaving smoke trails, such as in this case of a spacecraft reentry
A picture of Earth's troposphere with its different cloud types of low to high altitudes casting shadows. Sunlight is reflected off the ocean, after it was filtered into a redish light by passing through much of the troposphere at sunset. The above lying stratosphere can be seen at the horizon as a band of its characteristic glow of blue scattered sunlight.
Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on NOAA weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:
Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light
Distortive effect of atmospheric refraction upon the shape of the sun at the horizon
Animation shows the buildup of tropospheric Template:CO2 in the Northern Hemisphere with a maximum around May. The maximum in the vegetation cycle follows in the late summer. Following the peak in vegetation, the drawdown of atmospheric Template:CO2 due to photosynthesis is apparent, particularly over the boreal forests.