The Structure of the Atmosphere

I well remember a brilliant red balloon which kept me completely happy for a whole afternoon, until, while I was playing, a clumsy movement allowed it to escape. Spellbound, I gazed after it as it drifted silently away, gently swaying, growing smaller and smaller until it was only a red point in a blue sky. At that moment I realized, for the first time, the vastness above us: a huge space without visible limits. It was an apparent void, full of secrets, exerting an inexplicable power over all the earth’s inhabitants.

I. The Function of the Atmosphere A. Earth’s atmosphere allows for life to exist by: Regulating temperature Providing protection from harmful solar radiation Providing space for water and nutrient cycles II. The Composition of the Atmosphere 78% Nitrogen Gas 21% Oxygen Gas (O 2 ) 1% other-- water vapor, carbon dioxide, argon, helium, hydrogen, ozone, particles (dust, soot), chlorofluorocarbons, etc. CO 2 and H 2 O vapor play a critical role in regulating the amount of heat energy the atmosphere absorbs.

III. The Structure of the Atmosphere A. In order from the top down: Exosphere Thermosphere Mesosphere Stratosphere Troposphere *The Sky Makes Thunder Emphatically! Figure 11.2

B. Characteristics of the Troposphere Contains most of the atmospheric mass (mass of air in our science classroom is about 1000 lbs!). Weather occurs in this layer. Pollution and smog collect in this layer. Temperature decreases as altitude increases. The amount of heat absorbing molecules (CO 2, H 2 O) decrease as the distance from Earth’s surface increases. The layer closest to the Earth’s surface. Bottom boundary: 0 km (sea level) Top boundary: 9-16 km, varying from equator to poles Approximate Thickness: 9-16 km

C. Characteristics of the Stratosphere Contains ozone gas (O 3 ), making the ‘Ozone Layer’. Jet planes fly here because of steady weather conditions. Temperature increases as altitude increases. Ozone gas absorbs ultraviolet radiation from the sun. Bottom boundary: ranges from 9-16 km Top boundary: 50 km Approximate Thickness: km

C. Characteristics of the Mesosphere Air molecules are less concentrated in this layer. Temperature decreases as altitude increases. With the absence of ozone, temperature again decreases as the number of heat absorbing molecules decrease. Bottom boundary: 50 km Top boundary: 80 km Approximate Thickness: 30 km

D. Characteristics of the Thermosphere Gas molecules are sparse and widely spaced. Temperature increases as altitude increases. Molecules are heated faster because they are closer to the sun and absorb intense solar radiation. Temperatures are high (up to 1000 °C!), but heat is low. Bottom boundary: 80 km Top boundary: 500 km Approximate Thickness: 420 km

E. Characteristics of the Ionosphere (part of the thermosphere) This layer is made of electrically charged particles called ions. At the poles, ions interact with air molecules to form auroras. Radio waves from earth reflect off the ionosphere back to Earth. Ranges from 65 km -500 km above sea level.

F. Characteristics of the Exosphere Air molecules are very sparse in this layer. Only light gases (Helium & Hydrogen) are found here. Temperature increases as altitude increases. Temperatures are high, but heat is low. Bottom boundary: 500 km Top boundary: ??? There is no clear distinction between the top boundary and outer space.

Summary Diagram