564 



GEOLOGY, 



3. Thermal distribution under the accretion hypothesis. — The accre- 

 tion hypothesis assumes that the internal heat was gradually developed 

 from the center outwards as the earth grew and the internal compres- 

 sion was progressively developed. The heat, therefore, continued to 

 rise at the center as long as compression continued, or at least as long 

 as the compression was sufficient to generate heat faster than it was 

 conducted outwards. As the conduction of heat through rock is exceed- 

 ingly slow, the central heat may be assumed to have continued to rise 

 so long as the infall of matter caused appreciable compression. In 

 the same way, heat was generated progressively in the less central parts, 



COMPUTED PRESSURES, DENSITIES, AND TEMPERATURES WITHIN THE 



EARTH BASED ON 



LAPLACE S LAW. 



Distance 









from center 



Pressure 





Temperature 



in terms of 



in megadynes 



Density. 



in 



ra(.1ius. 



per sq. cm.i 





degrees C. 



1.00 







2.80 







.95 



97,000 



3.37 



320 



.90 



215,000 



3.95 



1,110 



.85 



353,000 



4.54 



2,190 



.80 



510,000 



5.13 



3,470 



.75 



684,000 



5.71 



4,880 



.70 



874,000 



6.28 



6,350 



.65 



1,077,000 



6.84 



7,860 



.60 



1,289,000 



7.38 



9,360 



.55 



1,507,000 



7.90 



10,830 



.50 



1,727,000 



8.39 



12,250 



.45 



1,944,000 



8.84 



13,590 



.40 



2,154,000 



9.26 



14,840 



.35 



2,353,000 



9.64 



15,980 



.30 



2,535,000 



9.98 



17,000 



.25 



2,698,000 



10.27 



17,880 



.20 



2,836,000 



10.51 



18,610 



.15 



2,947,000 



10.70 



19,190 



.10 



3,029,000 



10.84 



19,610 



.05 



3,078,000 



10.92 



19,870 



.00 



3,095,000 



10.95 



19,950 



and these parts also received the heat that passed out from beneath. 

 It is assumed under this hypothesis that the degree of interior com- 

 pression stands in close relation to interior density, for while there 

 would probably be some segregation of heavier matter toward the center 

 and of lighter toward the surface by means of volcanic action and internal 

 rearrangement under stress differences, the interior density is regarded 

 as due mainly to compression. The distribution of internal pressure 

 and density generally accepted is that of Laplace, who assumed that the 

 ^ Essentially the same as atmospheres. 



