CHAPTER V 

 LIFE'S BACKGROUND 



1 LL animals must eat. Therefore in a considera- 



/\ tion of the living world it is important clearly 

 Jl jL to understand the origin of the food which 

 supports the animals. It is essential that we appre- 

 ciate just how the necessary substances are made 

 available for them. It is important that we under- 

 stand the mechanism of the formation of the food of 

 animals. 



Air, water, rocks — from these three ultimate sources 

 do all living things secure those substances which are 

 necessary for their existence and their increase. The 

 energy by means of which these substances are re- 

 leased and through recombination made available for 

 use by living things comes from the sun. This energy 

 radiated from the sun reaches the earth in the form of 

 sunlight and of similar but invisible emanations of 

 wave lengths longer or shorter than those which 

 our eyes are able to perceive. 



The interaction of the water and air upon the rocks 

 which is made possible by the energy provided by 

 the sun is perhaps best understood by the considera- 

 tion of a bleak and desolate mountain top. The 

 exposed summit of a mountain would seem to be the 

 last place in the world in which to contemplate life's 

 mysteries, but from the crags and rough and broken 

 rocks drenched by the rain or covered with snow or 

 ice or wrapped in clouds or mists we may learn first 



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