362 



GEOLOGY 



to the effects of radioactivity springing from the spontaneous 

 decomposition of uranium, thorium, and some other substances, 

 on the temperature of the earth. The heat thus generated is even 

 held to be sufficient to account for the heat that is lost from the 

 earth's surface, and for the rise of temperature below the surface. 



Pressures in 

 million Megadynes. 



Temperatures 

 in degrees C. 



3.1 



32000 



.1 .2 .3 .4 .5 .6 .7 . .8 .9 1. 



Fig. 288. Diagram illustrating the distribution of temperature in the in- 

 terior of the earth under the accretion hypothesis (neglecting the heat 

 from infall and other external sources). The divisions of the base-line 

 'represent fractions of the earth's radius. The vertical divisions repre- 

 sent both pressure in megadynes per sq. cm., nearly the same as atmos- 

 pheres per sq. in., at the left, and temperatures in degrees C. at 

 the right. The upper curve at the left, PC, is the pressure curve. The 

 middle curve, DC, is the density curve, beginning at 2.8 at the surface 

 and reaching nearly 11 at the center. The lower curve, TC, is the tem- 

 perature curve, rising from the surface temperature, O C., at the right. 

 to 20,000 C. at the center. It is to be noted that the portion of this 



grad 



radius, and then decreases, and that between .8 radius and the surface -. 

 a distance of about 800 miles, the decrease is notable. This means that 

 with an equal co-efficient of conductivity, the flow from the center out- 

 ward to .6 or .7 radius will bo faster than the flow from .S to (lie surface. 

 neglecting the immediate surface effects of cooling. In other words, the 

 heat will be increasing between .8 and 1. Curves worked out by Dr. Lunn. 



