THE CHILDHOOD OF THE EARTH 



a thin solid crust was all that covered the molten interior 

 of the globe. It was too thin always to contain the 

 boiling liquid, and Titanic explosions, followed by 

 enormous overflows of lava, continually broke up the 

 crust. The pressure was relieved by these explosions, 

 and gradually the earth would settle down again to its 

 process of consolidation. Another explosion would follow ; 

 again a great flow of lava; and again the effects of 

 the catastrophe would subside. After each explosion 

 and outflow the earth's crust would grow a little thicker. 

 All this time, and for long succeeding ages, the earth 

 was attracting to itself, as a magnet attracts iron filings, 

 all the small bodies which it encountered on its path 

 round the Sun. These little rocks or masses of matter, 

 some great and some small, would each add something 

 to the size of the earth, and, by the shock of collision 

 with it, something to the earth's heat just as a bullet 

 flattening itself against a target melts in the heat of 

 collision. Just also as the bits of matter which we call 

 " shooting-stars " are set on fire by friction as they rush 

 into the earth's atmosphere. These meteorites, as they 

 are called when they are comparatively small bodies, 

 or " planetismals," as they are called when they are 

 large, still exist. But the earth, in the millions on 

 millions of years which it has been coursing round the 

 Sun, has swept up all the large ones that are likely to 

 fall into it, and there remain only the small ones which 

 occasionally cross its path. These are called " Leonids " 

 or "Lyrids" or "Perseids," and these meteor showers 

 occur at nearly the same time every year when the 



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