THE EARTH 145 



power at the end of seventeen million years, and 

 could not have been effectual for more than ten 

 million years back. Now, geologists required at 

 least twenty-six million, and possibly as much as 

 a thousand million, years to account for the sedi- 

 mentary strata. Accordingly, there must have 

 been some other source of heat, and this other 

 source of heat is now believed to be explosive 

 compounds or atoms in the Sun, which explode 

 with a force comparable to the energy of decom- 

 position of radium. " We may therefore imagine," 

 says Arrhenius, " the interior of the Sun charged 

 with compounds which, brought to the surface 

 of the Sun, would dissociate with an enormous 

 evolution of heat and an enormous increase of 

 volume. These compounds have to be regarded 

 as the most powerful blasting agents, in comparison 

 with which dynamite and gun-cotton would appear 

 like toys. ... It thus becomes conceivable that 

 the solar energy — instead of holding out for four 

 thousand years, as it would if it depended upon 

 the combustion of a solar sphere made out of 

 carbon — will last for something like four thousand 

 million years. Perhaps we may further extend 

 this period to several billions." Even in four 

 thousand million years a good deal may happen. 



As soon as the Earth obtained a suitable crust, 

 a suitable atmosphere, and a suitable temperature, 



10 



