250 day: geophysical research 



loss of heat by radiation into space is more than compensated by 

 heat received from the sun. Obviously, the earliest portions of 

 this history are and must remain dependent upon inference but 

 the formation of a solid crust cannot advance far before portions 

 of it become fixed in a form such that further disturbance does not 

 destroy their identity. From this point on the history of the 

 earth is a matter of record and can be interpreted if only we have 

 sufficient knowledge of the mineral relations thru all the stages 

 of their development. 



It must have been a very turbulent sea, the molten surface of 

 our earth upon which the rocky crust began to form. The first 

 patches of crust were probably shattered over and over again 

 by escaping gases and violent explosions of which our waning 

 volcanic activity is but a feeble echo. If the earth was first 

 gaseous, and the outer surface gradually condensed to a liquid, 

 its outer portions at least must have been whirled and tumbled 

 about sufficiently, even in a few thousand years (which is a very 

 small interval in the formation of an earth), to mix its various 

 ingredients pretty thoroly. It has accordingly been hard to 

 see just how it came to separate into individual rocks of such widely 

 different appearance and character. Of course the number of its 

 ingredients was large. We have already discovered eighty or 

 more different elementary substances in the earth, and there is an 

 almost endless number of more or less stable compounds of these. 

 The freezing of an earth is therefore different from the freezing 

 of pure water, but the freezing of salt water offers a clue to the 

 explanation of the way in which the earth solidified as we find it. 

 When salt water freezes, the salt is practically all left behind. 

 The ice contains much less salt and the remaining water relatively 

 more salt than before freezing began. Applying this familiar 

 observation to the supposed molten surface of the earth as it 

 begins to solidify, we have a suggestion of order and reason in its 

 separation into so many kinds of rocks. 



Now, it happens that in the recent development of chemistry 

 much attention has been given to the study of solutions of vari- 

 ous kinds, and a great body of information has been gathered and 

 classified of which our observation upon the freezing of salt water 



