Relations of tfic Life 'A one. 555 



water-sphero, (3) and outside of all is the gas or air 

 sphere. These have been named 



1. Geosphere. 



2. Hydrosphere. 



3. Atmosphere. 



701. Interpenetration of the Three Spheres. The mate- 

 rials of the three spheres are neither entirely separated from 

 one another nor stationary. Beneath the oceans and be- 

 neath the surface of the continents the solid earth is per- 

 meated by water. Even under desert skies there may be 

 wells and the soil contains moisture. With the water, too, 

 goes more or less of air from the atmosphere ; the fishes 

 of the oceans and lakes find air to breathe wherever they go 

 and the spaces in rock and soil not occupied by water are 

 filled with air. Floating in the water and drifting in the 

 atmosphere even at great hights are solid particles of silt 

 and dust broken from the earth-sphere, and nowhere is air 

 so dry that it contains no moisture. 



Drifted by the currents of air and water on land and at 

 sea solid particles are continually being moved from place 

 to place. The w^ter of the ocean, of the lakes or of the at- 

 mosphere is never at rest, neither is that which has pene- 

 trated tho solid crust of the earth. So, too, the air of the 

 atmosphere, of the water and of the soil is continually 

 changing and upon the rate of these changes depends the 

 well being of plant and animal life. 



702. Relation of the Life Zone to the Three Spheres. Tho 

 living forms of the earth make their homes in the bottom 



O 



of the atmosphere and in the top of the water sphere or of 

 the earth sphere. This relation is necessitated by the fact 

 that all living forms derive their food from the air, from 

 tho water, and either from the earth or from other forma 

 which take their ash inTe<li'iits from the earth. This re- 

 lation is further necessitated by the fact that all living- 

 forms must dwell where they can have a certain nmounr 01 

 direct sunshine or else where they ?\\\\ live upon .tlu i 



