In Chapter 1 we discussed the organization of the 

 earth's surface into four zones: atmosphere, hydro- 

 sphere, hthosphere, and biosphere. The next several 

 chapters will discuss in some detail the composition 

 and characteristics of each of these major zones. In 

 the present chapter we will examine the equilibrium, 

 zonation, and phenomena of the atmosphere. 



The characteristics and phenomena of the atmos- 

 phere are intimately related to those of the land, 

 water, and living organisms. Two atmospheric phe- 

 nomena, weather and climate, have a profound effect 

 on living organisms and are therefore discussed at 

 length in this chapter. 



THE ATMOSPHERE 



THE ATMOSPHERIC CYCLE 



Although the composition of atmosphere is much 

 the same now as it has been for the past 2 billion 

 years, this "sameness" is, paradoxically, the result 

 of constant change. Many factors, especially living 

 organisms, work independently to produce the atmos- 

 phere's dynamic equilibrium (Figure 2. 1 ). 



Most life uses oxygen to burn food for energy; in 

 this life process of oxidation, carbon dioxide is re- 

 leased as a waste product. During the day plants, as 



Figure 2.1 The Atmospheric Cycle, a summary of chemical inter- 

 changes between organisms and their environment. H^ (hydrogen), Oj 

 (oxygen), Nj (nitrogen), COj (carbon dioxide), H^O (water), NH3 

 (ammonia). 



a part of photosynthetic activity, use carbon dioxide 

 to produce basic foodstuffs and give off oxygen as a 

 waste product. Night and day plants use oxygen for 



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