THE EVOLUTION OF THE EARTH 



In the second place, the following chapter 

 will show that the chief circumstance which has 

 favoured terrestrial heterogeneity has been the 

 continuous supply of molecular motion from 



by Professor Winchell, entitled *« The Geology of the Stars." 

 " The zoic age of the moon," says the author, " was reached 

 while yet our world remained, perhaps, in a glowing condition. 

 Its human period was passing while the eozoon was solitary 

 occupant of our primeval ocean. ' ' More careful reflection will 

 probably convince us that, with such a rapid succession of geo- 

 logic epochs, the moon can hardly have had any human period. 

 For the purposes of comparative geology, the earth and the 

 moon may be regarded as of practically the same antiquity. 

 Now, supposing the earliest ape-like men to have made their 

 appearance on the earth, say during the Miocene epoch, we 

 must remember that at that period the moon must have ad- 

 vanced in refrigeration much farther than the earth. Supposing 

 organic evolution to have gone on with equal pace in the two 

 planets, it might be argued that the moon would be fast becom- 

 ing unfit for the support of organic life at about the time when 

 man appeared on the earth. Still more, it is a fair inference 

 from the theory of natural selection, that upon a small planet 

 there is likely to be a slower and less rich and varied evolution 

 of life than upon a large planet. On the whole, therefore, it 

 does not seem likely that the moon can ever have given rise 

 to organisms nearly so high in the scale of life as human beings. 

 Long before it could have attained to any such point, its sur- 

 face is likely to have become uninhabitable by air-breathing 

 organisms. Long before this, no doubt, its surface air and 

 water must have sunk into its interior, and left it the mere 

 lifeless ember that it is. The moon would thus appear to be 

 not merely an extinct world, but a partially aborted world ; 

 and the still smaller asteroids are perhaps totally aborted worlds. 

 Nevertheless, from the earth down to the moon, and from the 



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