Glarenae King — Age of the Earth. 5 



importance in any attempt to determine the earth's thermal 

 age or to delimit the period of active geological dynamics. 



Pressure and Temperature Tables. 



The following tables offer figures for the construction of the 

 pressure and some of the temperature gradients on both Plates 

 I and II. Data for the distribution of earth-pressure may be 

 obtained either from the formula of Laplace or that of Gr. H. 

 Darwin for radial earth density, combined with the known 

 decrease of terrestrial gravitation from center to surface. 



In table 1, Laplace's law is used as giving the most conserva- 

 tive values of density at great depths. For the superficial "2 of 

 radius, however, the two density laws are near together, and 

 as the thermal phenomena which determine the earth's age 

 are probably wholly in the surface tenth, either law might 

 be applicable to the present purpose. As, however, Darwin's 

 law requires a surface density of 8*7, while Laplace only 2*75, 

 the latter accords better with the average specific gravity of 

 superficial rocks and is, therefore, here preferred. 



Tables 2, 3 and 4 give data for three temperature gradients 

 derived by mechanical quadrature from the well known Fourier 

 equation in the manner given by Lord Kelvin, and are con- 

 sidered as sufficient in number and variety to indicate the 

 character of the data ; figures for the other gradients shown on 

 Plate II are therefore omitted. 



Table 2 presents data for the Kelvin gradient, 3,900° C. 

 initial excess, surface rate "03600 in degrees Centigrade per 

 meter of depth, and secular cooling lOOxlO 6 years. Earth 

 temperatures in ° C. are given for depths that are expressed 

 both in miles and fractions of radius and extend to 250 miles 

 or about *06 of radius. Surface rate appears both in ° Fahr. 

 and feet, and ° C. and meters. Tables 3 and 4 exhibit similar 

 data for earths of lower initial excess and shorter periods of 

 secular cooling. Table 3 is computed for an earth of 1,740° C, 

 20xl0 9 secular cooling, and table 4 for 1,230° C, 10x10° cool- 

 ing. 



Table No. 1. 



Estimated Earth Pressures (Laplace's densities) n being radial distances from the 



center of the earth and p being the pressure corresponding to 



n expressed in atmospheres. 



n. 

 Earth Ead. 



Atm. 



n. 

 Earth Rad. 



Atm. 



n. 

 Earth Rad. 



Atm. 



1-000 







•94 



116000 



•5 



1680000 



•995 



8600 



•92 



162000 



•4 



2100000 



•990 



17400 



•90 



199000 



•3 



2470000 



•985 



26400 



•80 



497000 



•2 



2770000 



•980 



35600 



•70 



852000 



•1 



2950000 



•960 



74500 



•60 



1260000 







3020000 



