Air is as valuable to life as it is invisible to the naked eye. Humans can only live for a few minutes without it. Adult
human beings take in an average of over 800 breaths of air per hour at rest, or 20,000 breaths a day, which amounts to 35
pounds of air. The Earth's atmosphere is responsible for keeping air from escaping into space, while most of the oxygen,
the breathable gas life forms on Earth need, is produced by plants. Air quality can be threatened by air pollution, either from
natural events like volcanoes or by man-made industries and machines that burn fossil fuels. Learning about the nature and the
value of air is essential to understanding its true value.
What is Air?
Air, or more importantly the oxygen that it contains, is the most important resource on Earth for human beings and almost
all species of plants and animals, including fish. Without water, a person can survive for perhaps a few days, but without air,
a person will die in mere minutes, as will most other living things. Despite the fact that it can't be seen, air has mass,
and it exerts pressure, which is called air pressure. Air is made up of primarily nitrogen, at 78 percent, and oxygen, which
makes up around 21 percent, and then other gases, such as carbon dioxide and argon. Living things are sensitive to changes in
the makeup and quality of air. For instance, too little oxygen can result in death by asphyxiation, while too much oxygen means
that the air will become toxic.
Earth's atmosphere is a relatively thin envelope that surrounds the planet and which contains all of the world's
air. The air that living things breathe would have vented into space without the existence of Earth's gravity and its
atmosphere. The boundary of the atmosphere, where it turns into outer space, is commonly accepted as 62 miles above sea level,
a point called the Karman Line. The planet's atmosphere comes in five distinct layers: the troposphere, stratosphere,
mesosphere, thermosphere, and exosphere.
The troposphere, the lowest layer, is where most weather occurs. Most of the air and mass of Earth's atmosphere lies in
the lowest layer, called the troposphere. The stratosphere, at 17 miles above sea level, is the next layer, and is known for
its extremely cold temperatures. The mesosphere starts at an altitude of around 32 miles and is where meteors typically burn up
in the atmosphere. The thermosphere begins at 50 miles above sea level and is extremely hot, but because there are so few gas
molecules, an object could freeze almost instantly. The Earth's gravity at this altitude is so weak that the International
Space Station maintains a stable orbit at the highest reaches of this layer. The thermosphere continues as high as 310 miles.
The Earth's exosphere reaches beyond that, and is occasionally referred to as outer space itself.
Earth's atmosphere has been through three stages of evolution. The stage of evolution occurred during the formation of
the planet. Most of the atmosphere is comprised of hydrogen and helium. Because the planet was still molten, these gases were
hot, escaped gravity, and rose into outer space. Then the atmosphere evolved into its second stage, where carbon dioxide, water
vapor and ammonia were the dominant gases. At this time, about 2.5 billion years ago, life evolved into cyanobacteria
(blue-green algae) which consumed the carbon dioxide and emitted oxygen as a waste by-product. This process, which came to be
known as the Great Oxygenation Event, radically changed the atmosphere by increasing the oxygen level over a period of 200
million years. This caused the atmosphere to evolve to its third and current stage, which is the stage that is required for
almost all known and existing forms of animal and plant life to survive.
Air pollution is defined as gases or particulates that are not a part of Earth's atmospheric composition, or which upset
the balance thereof. Pollution of the air comes in two sets of two categories. The first set of categories is either man-made
or natural in origin, while the second is broken up into indoor versus outdoor pollution. Air pollution can be harmful to
humans, plant life, and other animal life, as it adversely affects respiration, or breathing, and can lead to increased
incidents of diseases such as cancer. Excessive amounts of air pollution can lead to extinction events or irreversible changes
in the weather, such as global warming.
Man-made air pollution is pollution caused by human industries or transportation. Man-made air pollution is primarily caused
by the burning of fossil fuels, the most common of which are oil and coal. It also comes from the burning of other resources
such as chemicals or wood. Common man-made pollutants include smog, carbon dioxide and carbon monoxide from the burning of
fossil fuels. Natural pollution can be caused by soot and particulates from fires, methane from animals, or massive debris
clouds and gas emissions unleashed by volcanic eruptions.
Outdoor air pollution is the most well-known problem as it can affect the entire world's air supply and even its
climate. Indoor air pollution, however, is a problem that threatens the health of both pets and humans on an individual level.
Examples of indoor air pollution include paint fumes, smoke from tobacco, dust and pet dander, and in some cases, a mildly
radioactive gas called radon. Indoor air pollution is highly concentrated, and because humans in urban areas spend over 75
percent of their time indoors, the risk of health problems from indoor pollution is both high and also underestimated. The
problem is made even worse by poor air circulation.
Barometric Air Pressure
While air is invisible, it is a collection of gases which have mass, and as a result are held in place by the Earth's
gravity. Atmospheric pressure results from the weight of the air and the force it exerts upon an object. The density of the air
affects its weight and the level of air pressure. Air pressure is also affected by air temperatures. Because air pressure is
measured by a barometer, it is also referred to as barometric air pressure, and it is measured in either inches of mercury or
by a standard called millibars or hectopascals, the latter of which is more popular among scientists. In the Earth's
troposphere, air pressure and weather patterns are related to each other, with low air pressure leading to cold weather and
storms, while high air pressure is associated with calm skies and warmer weather. Extremely low air pressure, such as what is
encountered at very high altitudes, is potentially deadly to humans because there's too little oxygen available for the
body to survive.