THE HEAT OF THE EARTH 67 



48. THE HEAT OF THE EARTH 



We realize that the earth is very hot inside when we think 

 of volcanoes or even hot springs. In most mines the tempera- 

 ture increases one degree every fifty or sixty feet. If this 

 were continued, the temperature at the center of the earth 

 would be enormously high, but it is probable that at a depth 

 of one hundred and fifty miles the maximum is reached. This 

 is estimated to be seven thousand degrees F. The heat of the 

 earth is probably maintained, to a certain extent, by radium. 



Since we know that anything which is hot gradually loses 

 its heat, we can reckon backwards and conclude that the 

 earth once must have been extremely hot. We cannot be 

 sure, however, just how hot the earth has been. Neverthe- 

 less, we can believe that it was once in a molten condition. 

 References : 



1. 1002 : 133-135. The Condition of the Interior of the Earth. 



2. 1205 : 277-280. Conditions of the Interior of the Earth. 



3. 1304 : 17-18. The Earth's Interior. 



4. 1601 : 16. The Earth Cooled by Water. 



a. 1001 : 66. Constitution of the Earth's Interior. 



6. 1207 : 88-90. The Result of the Cooling of the Earth's 

 Interior. 



c. 1302 : 28-29. Temperature of the Center of the Earth. 



d. 1303 : 16-17. Underground Temperatures. 



e. 1305 : 41-42. Interior of the Earth and its Crust. 

 /. 1306 : 11-12. Temperature of the Earth. 



g. 1306 : 205-206. Interior Condition of the Earth. 



h. 1309 : 40-45. Evidences of Internal Heat. 



i. 1311 : 4. The Earth Within and Without. 



