The Earth and its Early History 



of rock from numerous sources shows that in all prob- 

 ability the radium in the Earth yields enough heat to 

 compensate for the loss by radiation into space, and that 

 therefore the Earth may not be cooling at all; it may 

 be indeed slowly rising in temperature. 



Thus the Geologist is no longer bound by beliefs in 

 a high internal temperature involving a gaseous or liquid 

 centre, nor is he strictly limited to a calculated duration 

 of geological time, which has long been thought utterly 

 inadequate either for the working out of the enormous 

 changes through which the rocks have passed or for the 

 evolution of plants and animals from primeval types. 



Though, as has been stated, these matters belong to 

 the domain of the Astronomer and Physicist, Geologists 

 may not ignore them, as they affect profoundly many 

 purely geological matters. 



Many of the older Geologists believed that mountain 

 chains were produced by the shrinking of the liquid or 

 gaseous interior of the Earth as the result of cooling, 

 and the consequent wrinkling of the hard crust, and 

 that volcanoes were supplied with molten lava from the 

 great liquid interior. 



Clearly, if there is good reason to believe that the 

 great mass of the Earth is solid, other means must be 

 found of accounting for these phenomena. Again certain 

 very ancient crystalline rocks, known as gneiss, were at 

 one time considered to be parts of an original crust 

 formed on the surface of a molten sphere much as ice 

 is formed on the surface of a lake in winter, but if the 

 Earth was formed by the accumulation of cold and solid 

 planetesimals, it is obvious that some modification of 

 this view is necessary. 



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