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The Birth and Life of Our Atmosphere
Nature Bulletin No. 554-A February 15, 1975
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
THE BIRTH AND LIFE OF OUR ATMOSPHERE
In Bulletin No. 542-A we described the atmosphere that surrounds the
earth, held there by the pull of gravity, including the canopy of air
immediately above us. That canopy is responsible for our weather and
climates, shields us from the killing rays of the sun, and furnishes
substances necessary for all life: oxygen, nitrogen, carbon dioxide, and
water vapor.
Astronomers believe that none of the other planets -- excepting Mars,
perhaps -- has an atmosphere anything like ours. The principal
elements, free nitrogen (78 percent) and free oxygen (21 percent),
apparently are rare in the universe. On the other hand, the earth's
atmosphere contains only traces of free hydrogen and helium -- the two
lightest gases -- whereas they are by far the most common elements
elsewhere in the universe.
Originally, those two gases must have been present here in vast
quantities. What happened, and what was the origin of our atmosphere?
The answer, according to modern theory, is that the earth has had other
atmospheres which escaped; and that the latest one was slowly
accumulated during eons of time.
Most scientists believe that this planet condensed from a whorl of star
dust and gases into a naming ball where the heaviest elements
gravitated inward and lighter ones rose to the surface. Fiery spouts of
gases, especially hydrogen and helium, jetted away into space. As the
earth lost that heat, its surface gradually cooled and became a fluid crust
with hardening islands of granite and basalt which eventually formed
continents. Torrents of naming lava erupted through innumerable weak
spots in the crust, and also terrific jets of gases more complex and
heavier than hydrogen and helium: water vapor (as steam), carbon
dioxide, and probably other compounds such as ammonia and methane.
Those gases formed enormous hot clouds that grew and grew until they
were many miles high, shutting out sunlight and shrouding the earth in
perpetual darkness for perhaps millions of years. From their upper
reaches into cold atmosphere, wave after wave of rains fell but boiled
and became rising steam before they reached the earth's hot crust.
Thus, each rainfall sapped the earth of some of its heat energy and
carried that upward into the clouds where it radiated into outer space.
Other losses of heat and energy resulted from the awful lightning that
must have been continual, and from the tremendous jets of fiery gases.
The earth cooled until at last there came a time when the rains fell and
did not boil away. Meanwhile the crust had heaved and wrinkled. When
the clouds thinned and those deluges ended, the sun shone upon
glittering seas collected in the depths.
Life apparently began, somehow, in shallow waters warmed by
sunshine. Green plants developed until some emerged and grew along
the beaches. Later, others invaded higher ground. Primitive animals
developed in the seas and their descendants crept out to live on land.
Green plants, in daytime, take in carbon dioxide and give off oxygen.
At night the process is reversed. Animals consume oxygen and exhale
carbon dioxide. As dead plants and animals decay, carbon dioxide is
released into the air and nitrogen into the soil. However, because plants
give off far more oxygen than they consume and take in far more
carbon dioxide than they give off, the supply of oxygen in the air
increased and that of carbon dioxide gradually dwindled.
The dust, smoke, fumes and nuclear explosions produced by modern
civilization threaten to disrupt that vital cycle of use and renewal.
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Update: June 2012
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