Forest Preserve District of Cook County, Illinois
Nature Bulletins
Newton Home Page

Introduction and Instructions

Search Engine

Table of Contents



The Atmosphere
Nature Bulletin No. 542-A   November 2, 1974
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

Until after the time of Christopher Columbus, most people believed that this world was flat, like a table top. Some of the ancient Greeks, however, had reasoned that the earth was round and that the canopy of air above them was part of another sphere surrounding this planet. They used two words to describe it -- atmos (vapor) and sphaira (sphere). We know now that they were right. There is a gaseous envelope which, held by gravity, clings to the earth and follows its every movement. We commonly call it "the air. .

The air we breathe is the commonest thing on earth and, although free, the most precious. There is an old proverb: "A man can live three weeks without food, three days without water, but only three minutes without air. " None of us, nor any of the animals and plants, could exist without our atmosphere. It furnishes us with those elements necessary for all life: oxygen, nitrogen, carbon dioxide and water vapor. It filters and protects us from the killing rays of the sun. We live beneath the roof of a gigantic greenhouse.

Without our atmosphere there would be no winds, no clouds, no rain, no colorful sunrises and sunsets -- in other words, no weather at all and consequently no climate. In daytime, as on the moon, the sky would be black -- not blue -- and the temperature would zoom to 230 F. or more. At night it would plunge to possibly 300 below zero. This would be a lifeless world.

Near the earth's surface, perfectly dry air contains about 78% nitrogen, 21% oxygen, and one percent of argon -- a peculiar inactive gas, small amounts of carbon dioxide and hydrogen, and tiny amounts of five rare gases: neon, krypton, helium, ozone and xenon. Normally, however, air also contains water vapor in quantities varying from a mere trace to about 5 percent on hot humid days, and it is responsible for the clouds, fogs, rain, snow, hail, dew and frost. At altitudes of more than 5 miles there is very little of it because of the low temperatures. In addition, our air contains various amounts of impurities such as dust, soot, pollen, spores, bacteria, salt particles from sea spray and -- especially near industrial areas -- poisonous gases.

The density of the atmosphere diminishes rapidly with altitude. Six miles up it is so thin that a man cannot breathe; at 12 miles there is not enough oxygen to keep a candle burning; at 400 miles, in the almost airless Mesosphere, the main ingredients are probably hydrogen and helium, the two lightest gases.

Data obtained from radio waves, balloons and missiles indicate that, for convenience, the atmosphere may be divided into five layers or concentric spheres around the earth. They are chiefly distinguished by the temperatures in them but each merges gradually into the one above it. The lowest layer, roughly 7 miles high, is the Troposphere where most of our weather is generated and which contains the air we breathe.

Above that is the Stratosphere, extending to an altitude of about 20 miles and then the Chemosphere where the sun's ultraviolet rays are screened from the earth by the ozone gas they produce. The space between altitudes of 50 and 250 is called the Ionosphere. Above it, and extending to possibly 600 miles above the earth, is the Mesosphere. Beyond that is the Exosphere merging into outer space where, like Columbus, men now carry on exploratory work.

To return to the Nature Bulletins Click Here!
Hosted by NEWTON

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Sponsered by Argonne National Labs