CREATION BY EVOLUTION 



planets will be broken up and another one born. This rhythm 

 may go on forever, so far as we can tell, for there appear to 

 be no agencies tending to put an end to it. 



Each star or sun, apart from these incidents associated with 

 the origin and evolution of planets, has a long, slow evolution 

 of its own. Each is at first a young sun, very tenuous, rela- 

 tively cool, and blue-white in color. As it grows older it 

 becomes hotter, denser, and yellowish in color. With increas- 

 ing age it becomes progressively denser and cooler and 

 changes in color from lighter to darker red. With this pro- 

 gressive increase in density the constitution of its atmosphere 

 undergoes remarkable changes. In the young suns the atmos- 

 phere consists of numerous lighter elements and compounds 

 that can exist at relatively low temperatures; in the somewhat 

 older suns, which are intensely hot, the atmosphere contains 

 only the lightest and simplest atoms, such as hydrogen and 

 helium; in the old, red suns the atmosphere includes not only 

 atoms of the heavier elements, but various compounds. The 

 density of some of these aged suns is amazing. Astrophysicists 

 estimate that a cupful of material from one of these old red 

 suns, if weighed on the surface of our earth, would scale 

 twenty-five tons. 



A sun endures so long and changes so slowly that an 

 ephemeral being like a man can observe no change in it. We 

 know, however, that our own galaxy is made up of suns of 

 all grades of brightness and density, and we therefore infer 

 that suns have a regular course of existence — an evolution. 

 Our own particular sun is middle-aged, verging on senility. 

 To an observer living on a planet in another solar system it 

 would appear as a reddish-yellow star, relatively a dwarf as 

 compared with many of the giant suns in our galaxy. 



A sun is at all times giving off enormous amounts of 

 energy. This activity alone would cause it to change pro- 



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