Tables 71 7 and 71 8 cyi 



TABLE 717.— Age of Earth, Moon, and Strata 



(See The Earth, by Jeffreys, 1929.) 



The age of the earth is probably from (1.3 to 3) X io 9 years (radioactive data). Its 

 liquefaction was probably complete within 5000 years, solidification within 15,000 years 

 from start. The age of the earth's crust may be taken as roughly 2000 million years. 



Ages of Geologic Strata 



Note (Science 73 (Suppl.), 10, Mar. 13, 1931) : An age of the earth of at least 

 2,000,000,000 years was adopted by a committee (Kovarik, Holmes, Knopf, Brown, Lane) 

 appointed by the National Research Council ; the age of the oldest rock, a uranite from 

 Sinyaya Palo, Carelia, Russia, 1,852,000,000. 



TABLE 718(a). — Geologic Age Determinations Based on the Lead Method 



(Knopf, Nat. Res. Council Bull. 80, 1931.) 



Age 

 (Millions of years) 



Based on Based on 



Tu =4.56x10* Tn=4-56XI0 9 

 Geologic age. Mineral. Locality. TTh = 1.28X io 10 TTh=i.6sx io 10 



Paleozoic; Devonian or Thorite Norway 224 310 



Carboniferous. 



Latest Cambrian Kolm Sweden 450 



Pre-Cambrian Broggerite ..Norway 915 910 



Pre-Cambrian Cleveite Norway 067 964 



Pre-Cambrian Cleveite Norway 986 965 



Pre-Cambrian Uraninite . . . S. Dakota . . . 1,465 1,462 



Pre-Cambrian Uraninite ...Russia 1,852 1,852 



TABLE 718(b).— The Age of the Earth 

 (Taken from Nat. Res. Council Bull. 80, 1931.) 



Radioactive disintegration presents the only reliable measure. No trace of a beginning 

 can yet be found. " The oldest rocks have everywhere been made from preexisting and 



therefore still older materials of which no other relics now survive The earth is 



older than the oldest granitic intrusion. It is impossible with the data available to know 

 whether the highest reliable lead ratio so far obtained (Keystone uraninite, Black Hills, 

 S. Dak.) represents the oldest granitic rocks. Accepting a ratio of 0.216 as an index of its 

 age this is 1460 million years old. Before the oldest granites were intruded into the crust 

 at least one cycle of denudation and sedimentation occurred indicated by the rocks into 

 which the granites were injected. To the 1460 we should add perhaps 140, giving as the 

 age some 1600 million years, as indicated by above mean. An upper limit assuming all 

 rock lead of radioactive origin is 1600 million. The estimate of the total life of the earth 

 (Russell, Holmes, loc. cit. p. 8) is some 3000 million years. 



Strata accumulated : Max. since beginning of Cambrian from America data — 260,000 ft. ; 

 111,000 of this deposited during Paleozoic time, 86 are Mesozoic, 61,000 during Cenozoic. 



Smithsonian Tables 



