

LIBRARY 



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CHAPTER 2 



EARLY HISTORY OF LIFE 



If we are to understand living things on 

 the earth today, even in the most rudimen- 

 tary way, we must have some understand- 

 ing of the physical world in which they 

 came into being. It must be remembered 

 that the physical world was here first, and 

 that all living things have sprung from it, 

 using the materials and forces that are 

 present in it. There can be no life without 

 a surrounding world, an environment in 

 which it resides. In a sense they must 

 always be considered together, for the en- 

 vironment can exist without the living 

 organism, but the reverse is not true. Since 

 the environment was here first, it is well to 

 consider some of the fundamental charac- 

 teristics of this environment, so that when 



we study life later it will have more 

 meaning. 



THE SETTING-THE PHYSICAL 

 WORLD 



The earth was born two or three billion 

 years ago. Along with the other planets of 

 our solar system, it was probably formed 

 out of a very large, flattened, and highly 

 rarefied mass of gas and dust that sur- 

 rounded the sun and rotated about it. As 

 the rotation proceeded, with the regions 

 near the sun moving faster than the outer 

 regions, whirling eddies must have formed 

 in different parts of this tenuous nebula. 

 Although most of the gas and dust probably 



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