CHAPTER X 



THE GEOSPHERES 



The earth is the only pUmot of our soh\r 

 system having oceans on its rocky surface. 

 Mars and the moon had apparently 

 at one time hu'i^e bodies of water on their 

 surfaces, but tl^ese seem now to have dis- 

 appeared. The same fate is possibly in store 

 for our oceans. We look back on a past when 

 the crust of the earth was in a molten condi- 

 tion with a temperature of lOCV"" F.. when what 

 is now the water of the ocean existed as water- 

 vapour in the atmosphere. We can imagine 

 a future when the waters of the ocean will, 

 because of the low temperature, have become 

 solid rock, and over this will roll an ocean of 

 liquid air about forty feet in depth. The 

 earth is at present in the terraqueous phase 

 of its evolution, that is to say, its surface is 

 occupied by continents and islands, oceans, 

 seas, lakes and rivers. 



If we regard our earth as it is s^^1mg in space 

 at the present time, we may see, with the 

 mind's eye, that it is composed of concentric 

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