The Atmosphere Can Be Divided Into Four Layers Based on Temperature Variations

Background

The atmosphere can be divided into four layers based on temperature variations. Temperature variations in the four layers are due to the way solar energy is absorbed as it moves downward through the atmosphere. The Earth’s surface is the primary absorber of solar energy. Some of this energy is reradiated by the Earth as heat, which warms the overlying troposphere.

Troposphere

“Tropo” means mix. Air here gets “mixed” up because air is able to rise and fall easily. The troposphere is the layer that is closest to Earth’s surface, staring at the surface and rising to approximately 12 kilometers high. It is the only layer in which life exists and virtually all of the weather occurs. Ninety-nine percent of the water vapor in the atmosphere is in the troposphere. Due to Earth’s gravitational pull, most of the air molecules that make up the atmosphere are found in the troposphere; approximately 75% of air molecules are found here. Therefore, atmospheric pressure is highest here. Temperature also decreases as altitude increases in the lowest layer of the atmosphere.

Stratosphere

“Strato” means layer. The stratosphere starts just above the troposphere and rises to 50 kilometers above Earth’s surface. This part of the atmosphere is dry and much less dense than the troposphere. The ozone layer, which absorbs and scatters solar ultraviolet radiation, is in this layer. Temperatures in the stratosphere generally increase with altitude, due to the absorption of ultraviolet radiation. Approximately 24% of air molecules are located in the stratosphere.

Mesosphere

“Meso” means middle or center, so the Mesosphere is the middle atmospheric layer. The mesosphere stars just above the stratosphere and extends to 80 kilometers above Earth’s surface. Temperatures in this layer drop to approximately -90o Celsius as altitude increases. Molecules are in an excited state here as they absorb energy from the Sun. Meteors or “shooting stars” are burned up in this layer.

Thermosphere

“Thermo” means heat. The thermosphere starts just above the mesosphere and extends to around 500 kilometers above Earth’s surface. Temperatures in this region soar to as high as 1,727o Celsius due to the Sun’s energy. Humans would freeze to death in this layer because the molecules are so far apart, but would burn their skin due to the harmful radiation from the Sun. This layer and the upper mesosphere contain the ionosphere, which is a large number of electrically charged atoms (ions). The ionosphere reflects radio waves, which allows long range communication. Chemical reactions occur much more quickly here than on the Earth. Light displays, called auroras, occur here. The thermosphere is the largest.

Exosphere

“Exo” means outside. The exosphere starts at the top of the thermosphere and continues until it merges with outer space. In this layer, hydrogen and helium are the only gases present at extremely low densities (low amounts). In other words, there are very few molecules. It is the thinnest layer. The space shuttle and other satellites orbit in the exosphere. The exosphere is above 500 kilometers from the Earth’s surface. DIRECTIONS:

Table 1 contains the average temperature readings at various altitudes in the Earth’s atmosphere. Use this data to complete the graph on the following page. Pay close attention to make sure you are graphing the negative temperature numbers correctly. This graph provides a general, average picture of temperature at any given time and place throughout the atmosphere.

TABLE 1. Average Temperature Readings at Various Altitudes

Altitude (km) Temperature (oC) Altitude (km) Temperature (oC) 0 15 52 -2 5 -18 55 -7 10 -49 60 -17 12 -56 65 -33 20 -56 70 -54 25 -51 75 -65 30 -46 80 -79 35 -37 84 -86 40 -22 92 -86 45 -8 95 -81 48 -2 100 -72

Once you’ve completed the graph, complete the following items.

1. On the completed graph, mark the following words in the correct locations:

a. Troposphere d. Thermosphere b. Stratosphere e. Ozone layer c. Mesosphere f. 2. Why are there 4 different layers? a. ______b. 3. Does the temperature increase or decrease with altitude in the: a. b. Troposphere ______d. Mesosphere ______c. Stratosphere ______e. Thermosphere ______f. 4. What causes the temperature to increase with altitude in the stratosphere? a. ______b. ______c. 5. What causes the temperature to decrease with altitude in the mesosphere? a. ______b. ______c. 6. Why does the temperature decrease with altitude in the troposphere? a. ______b. ______c.