The Atmosphere and its Layers

How does the atmosphere affect conditions on Earth? What is Earth's atmosphere composed of? How do pressure and density vary with altitude? What are the characteristics of the major layers of the atmosphere? Important Terms atmosphere alarm pressure barometer troposphere weather stratosphere ozone layer mesosphere troposphere Ionosphere aurora At 8848 meters (29,030 feet) above sea level, Mount Everest Is the highest mountain in the world. In 1952 Edmund Hillary, a New Zealand mountaineer, and Tenting

Norway, a mountain guide from Nepal, became the first humans to reach the top. The climb was very dangerous for several reasons, including the extremely low temperature and low level of oxygen at the summit. When they finally made it to the top, the two men cheered and embraced. Then Hillary did something to prove a point ?he took off his oxygen mask. He wanted to show that a person could stay alive while breathing naturally at that high altitude. But after a few minutes, his vision began to fail. When Hillary replaced his mask, his vision improved. Then the two men started back down the mountain.

Why did Hillary and Tenting need to carry oxygen to the top of Mount Everest? And why was It so cold there? The answers to these questions depend on how the alarm around Earth changes with altitude. Earth's Protective Layer What you commonly call air, scientists call the atmosphere. The atmosphere (at mum safer) is the layer of gases that surrounds Earth. The atmosphere forms a protective boundary between Earth and space and provides conditions that are suitable for life. The atmosphere protects Earth's surface from continual pounding by meteoroids, chunks of rock and metal from space.

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The atmosphere also protects Earth from much f the high-energy radiation from space. The atmosphere holds in heat and helps to moderate Earth's temperatures. Without the atmosphere, Earth's surface would be similar to the moon's, boiling hot during the day and freezing cold at night. Earth's relatively constant temperatures allow life to flourish. The atmosphere also provides the gases that are essential for life. Carbon dioxide In the atmosphere Is essential for plants and some other organisms to carry out photosynthesis. Photosynthesis Is the process of capturing the sun's energy to make food.

Oxygen Is produced during photosynthesis and released into the atmosphere. Your body uses oxygen to carry The atmosphere is a mixture of different gases. The composition of the atmosphere is fairly uniform up to an altitude of about 80 kilometers. Earth's atmosphere is a mixture of nitrogen, oxygen, water vapor, and many other gases, in which tiny solid and liquid particles are suspended. As Figure 2 shows, two gases?nitrogen and oxygen?make up more than 99 percent of clean, dry air. The amount of water vapor in air varies from 0. 02 percent in cold, dry air to more than 4. Percent in warm, moist air. Various amounts of water droplets and solid particles are suspended in the atmosphere. Some solid particles can be seen as floating dust, but most particles are microscopic. These solid particles come from various sources, including smoke from fires, ash and dust from volcanic eruptions, and salt from ocean spray. Air Pressure The atmosphere has weight because of Earth's gravity. As a result of this weight, the atmosphere exerts pressure. Recall that pressure is the force exerted on a surface divided by the area over which the force is exerted.

Air pressure is the force exerted by the weight of a column of air on a surface. At sea level, air pressure is about 101 ,325 Newton's per square meter, more commonly expressed as 1013. 5 milliners. One Millard equals 100 Newton's per square meter. Effect of Altitude. Air pressure changes with altitude. The atmosphere is densest near Earth's surface and becomes less dense as altitude increases, as shown in Figure 3. Why is this? Air can be compressed, as it is when you pump air into a tire or a basketball. Near Earth's surface, the column of air includes the entire depth of the atmosphere, so the pressure and density are high.

As altitude increases, the depth of the column of air above decreases, so the pressure decreases. At high altitudes there is very little air in the column above, so air pressure is lower. As altitude increases, air pressure and density decrease. About half of the total mass of the atmosphere is found below an altitude of 5. 6 kilometers. When Hillary and Tenting climbed Mount Everest, they went well above this halfway point. As they climbed, the air became less dense. Hillary had trouble breathing without an oxygen mask because there were fewer oxygen molecules per cubic meter of air at the summit than at sea level.

Measuring Air Pressure. Scientists measure air pressure with an instrument called a barometer. The first barometer was invented in 1643 by the Italian scientist Evangelists Torricelli's. Torricelli's invented a mercury barometer, similar to the one shown in Figure 4. As air pressure increases, the column of mercury in the barometer rises. As air pressure decreases, the column of mercury falls. Thus, a measurement of the height of a column of mercury is a measurement of air pressure. At sea level, the average air pressure is about 760 millimeters of mercury or, more commonly, 29. 2 inches of mercury. An aneroid (an uh rood) barometer is a smaller, more portable type of barometer. The word aneroid means "not using liquid. " Aneroid barometers use a metal chamber that expands and contracts with changes in air pressure. Temperature changes dramatically as you move up from Earth's surface high into the atmosphere. Scientists use variations in temperature to divide the atmosphere into four vertical layers. The four layers of the atmosphere are the troposphere, the stratosphere, the mesosphere, and the troposphere. The Troposphere.

You, along with many other living things, live in the layer of the atmosphere called the troposphere. The troposphere (troth pup safer) is the lowest layer of Earth's atmosphere. This layer contains almost all of the atmosphere's water vapor and suspended particles, which are important in the formation of clouds and reciprocation. Most weather takes place in the troposphere. Weather is the condition of the atmosphere in a particular place at a particular time. The height of the troposphere ranges from about 9 kilometers above the poles to 16 kilometers above the tropics.

The average height of the troposphere is about 12 kilometers. In the troposphere, temperature generally decreases as altitude increases. Though it varies somewhat, the rate of decrease averages about 6. 5 Celsius degrees per kilometer. For example, if it is ICC where you are on Earth's surface, then it is probably about ICC at an altitude of 2 kilometers above you. This characteristic of the troposphere accounts for the extremely low temperatures that Hillary and Tenting had to withstand when they scaled Mount Everest. The Stratosphere. Above the troposphere, as shown in Figure 5, is the stratosphere.

The stratosphere (strata uh safer) extends from an altitude of about 12 kilometers to about 50 kilometers. The temperature of the stratosphere remains nearly the same from the boundary with the troposphere to an altitude of about 20 kilometers. Above that height, temperature increases as altitude increases. The temperature in the lower stratosphere remains about -ICC. Above 20 kilometers, the temperature rises to about COCO. The upper stratosphere is warmer than the lower stratosphere because of the presence of the ozone layer, a region of high ozone concentration.

Recall that ozone is a highly reactive gas whose molecules are composed of three oxygen atoms (03). Most of the oxygen molecules you breathe are composed of two oxygen atoms (02). In the stratosphere, the energy of sunlight is great enough to split 02 molecules into single oxygen atoms (O). When an oxygen atom (O) collides with a molecule of oxygen (02), ozone (03) is formed. Ozone absorbs ultraviolet (XIV) radiation in sunlight and filters such of it out before such radiation can reach Earth's surface. The energy absorbed from UP radiation is converted into thermal energy, warming the upper stratosphere.

Because UP radiation can be harmful to living things, the presence of the ozone layer is extremely important to life on Earth. In humans, I-JP radiation can cause a deadly form of skin cancer. Certain chemical pollutants have been depleting ozone in the stratosphere, permitting more UP radiation to reach Earth's surface. However, the release of such chemicals was limited by international agreements and national policies adopted in the sass. As a result, ozone levels in the stratosphere appear to have stabilized. The Mesosphere. The layer above the stratosphere is the 50 kilometers and extends to about 80 kilometers.

In the mesosphere, temperature decreases as altitude increases. At the top of the mesosphere, the temperature approaches -ICC. The air is very thin in the mesosphere. Studies in the sass discovered that air in this layer may move at speeds of more than 320 kilometers per hour. Most meteoroids that enter the atmosphere burn up in the mesosphere. The Troposphere. The outermost layer of the atmosphere, the troposphere (thru mom freer), begins at an altitude of about 80 kilometers and extends outward into space. No boundary marks the end of the atmosphere.

Instead, the thin air of the troposphere gradually merges with space. In the troposphere, temperature increases rapidly with altitude, from about -ICC to more than 10000C. Recall from physics that temperature is a measure of the average kinetic energy of molecules. Because gas molecules in the troposphere absorb solar radiation and move very fast, the temperature is quite high. The Ionosphere. The ionosphere (eye ann. uh safer) is not a distinct layer of the atmosphere. Rather, it is a region of charged particles, or ions, that overlaps the lower troposphere.

In the ionosphere, molecules of nitrogen and oxygen lose one or more electrons as they absorb high-energy wavelengths of solar radiation. The molecules become positively charged ions. These ions are most dense between the altitudes of 80 and 400 kilometers. At these high altitudes, certain radio waves sent from Earth's surface, such as AM radio waves, bounce off ions and travel back to Earth. You can often hear AM radio stations from very far away at night because the sun's radiation is blocked by Earth. The ions start o recombine at night, allowing AM radio waves to travel farther.

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