

THE CHILDHOOD OF THE EARTH 



waters began to ebb and flow in tides. (Another con- 

 sequence of this constant ebb and flow was that the 

 friction of these movements began to diminish the speed 

 of the earth's rotation -just as a string that was placed 

 round the circumference of a spinning-top would, if 

 constantly pulled backwards and forwards, gradually 

 help to slow down the top.) Then oceanic waves and 

 currents would begin to eat a way into the land that 

 was on their borders, or which was emerging from their 

 depths. Rivers would begin to arise, and they would 

 carry on the work of erosion. Other causes tending to 

 break up the rocks would be the gases in the air the 

 excessive quantities of carbonic acid and oxygen would 

 be active chemical agents in this work. Before the 

 close of this era the limestones and iron carbonates 

 began to form ; sediments arose in the lifeless oceans, 

 and thus began the first formation of those sedimen- 

 tary rocks and strata which have been dealt with in 

 the earlier chapters. 



After the lifeless era began the age when the lowest 

 forms of life came into existence. The initial stage was 

 perhaps the Era of the First Plants, Algae, and later 

 still aquatic fungi or bacteria. This began when the 

 general temperature of the ocean may have been as high 

 as 150 F. (some water plants can now live in waters up 

 to and above 180 F.). Limestones began to form from 

 the secretions of plants, and deposits of silica from silica 

 secretions. Also where the conditions were favourable 

 there were large sedimentary deposits and accumulations. 

 In the second part of this aeon the earth, still continuing 



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