WHAT IS THE ATMOSPHERE?
Earth is surrounded by a blanket of air, which we call the atmosphere. The atmosphere describes all the air surrounding Earth. This applies to the air at the bottom of the deepest cave to the very edge of outer space. Until recently, the atmosphere could only be studied by observation. Scientists could only hypothesize based on weather trends. Today, using the space shuttle, satellites and other technology, scientists can much more effectively observe the atmosphere in action.
According to NASA, the Earth's atmosphere is about 375 miles (600 km) thick. Most of the atmosphere (about 80%) is within 10 miles (16 km) of the surface of the Earth. It may seem like a lot, but compare it to an apple. If the apple core is the core of the Earth and the flesh and skin are the mantle and crust, the atmosphere would be the thin layer of wax they put on apples to preserve them.
The atmosphere is composed of several layers. The transitions between the layers are gradual, and despite new technologies, there isn’t a definitive height for when a layer ends or even when space begins. There are only good estimates. Therefore, the layers of the atmosphere have been identified using a combination of four different characteristics: chemical composition, movement, density and temperature change. The four layers are: the Troposhere, the Stratosphere, the Mesosphere and the Thermosphere. The Thermosphere is further divided into the Ionosphere and the Exosphere.
Life on Earth might not be possible without the atmosphere. The atmosphere collects and stores energy from the sun. It does this by absorbing infared radiation. The infared radiation gets captured by water and carbon dioxide in the atmosphere. These liquids and gases are trapped on Earth by gravity but are not dense enough to sink into the crust. Instead, they surround the surface of the Earth and act like a blanket to trap the warmth near the ground. Just enough energy is trapped to allow water to exist as a liquid. Liquid water is needed for living things, at least the living things we know of!
Speaking of water, the atmosphere recycles water. Water on the surface of the Earth evaporates into the sky, condenses into clouds and falls back to the surface as precipitation. This process is known as the Hydrologic (water) Cycle. The Hydrologic Cycle is a huge factor in the establishment of climatic zones on Earth. It can be said that climate is created in the atmosphere.
The thin layer of gases surrounding Earth also serves as protection from high-energy radiation and the frigid vacuum of space. In the darkest regions of space, the temperature is a chilly -450° Fahrenheit. That is dangerously close to Absolute Zero. Nothing known can live at such an extreme temperature. On the other hand, radiant energy from the sun also produces extremely high temperatures. Without the protection of the atmosphere, the surface of the Earth facing the sun could heat up to hundreds of degrees Fahrenheit.
The atmosphere also protects life by absorbing harmful ultraviolet radiation. Ultraviolet radiation is what causes sunburns and has been proven a cause of skin cancer and eye damage. Most ultraviolet radiation is absorbed in the upper stratosphere by the ozone layer.
THE COMPOSITION OF THE ATMOSPHERE
All planets have at least some sort of atmosphere. Venus and Mars have atmospheres made almost entirely of the compound carbon dioxide. Jupiter’s atmosphere is much like the sun’s, with both consisting of 80% hydrogen, 19% helium and traces of the rest of the elements. Shortly after its formation, Earth probably had an atmosphere very similar to the Gas Giants. However, beneath the surface, Earth was cooking and above, it was getting bombarded.
Gases like carbon dioxide, water vapor, sulphur dioxide and nitrogen were released from the interior of the Earth by constant volcanic activity in aprocess called degassing. This radically changed the composition of the atmosphere. In addition, meteors carrying many other elements pelted the surface delivering new molecular possibilities.
Most geologists believe Earth’s original atmosphere was hardly the life-sustaining blanket of air that it is today. It is far more likely that its main constituents then were nitrogen and carbon dioxide.
Notice
how oxygen is not mentioned. By looking at the fossil record, scientists have
determined that there is no evidence for free oxygen in the atmosphere until
about 2 billion years ago. At about that time the first bacteria appeared and
began taking in atmospheric carbon dioxide and releasing oxygen. Since then,
the amount of oxygen in the atmosphere has risen steadily. Life has altered
the atmosphere dramatically. Today, t he atmosphere
on Earth is composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon
dioxide, and trace amounts of other gases.
ATMOSPHERIC PRESSURE
At sea level, the air pressure is about 14.7
pounds per square inch. What that means is that a one inch square column of
air that starts on the ground and extends to space weighs 14.7 pounds. When
the fact that 80% of the atmosphere’s density occurs in the first ten miles
is considered, it is understandable that the density of air is greatest near
the surface of the Earth. Consequently, as your altitude increases the air pressure
decreases. At an altitude of 10,000 feet, the air pressure is 10 pound per square
inch; at 20,000 feet it is 7.4 pounds; and, if a person was to climb Mt. Everest,
a pressure of about 4.9 pounds would be exerted on them.
Why do so many people die climbing Mt. Everest ? Is it because of the cold or do they fall? No! They simply cannot breathe. As altitude increases, oxygen molecules are less concentrated and become scarce. This makes breathing more work, because more air must be inhaled to get enough oxygen molecules. The added burden of inhaling and exhaling more frequently is compounded by the fact that the lungs must work harder. Why? Normal lungs are used to handling 14.7 pounds of pressure pushing into them. When the pressure decreases, lungs tend to try to collapse. Keeping your lungs inflated at 1/3 the pressure is a tricky thing to do! That is why planes pressurize the cabin.
