TIME SCALE OF OUR UNIVERSE OPIK 207 



time scale is definitely won by the former, although the latter did 

 not yield without a struggle. 



In the course of the controversy, arguments based on subordinate 

 time scales were produced. These subordinate time scales — of the 

 earth, the radioactive elements, stellar evolution, stability of binaries 

 and star clusters — all fell below a not too large multiple of one thou- 

 sand million years; as, moreover, some were obvious overestimates, 

 they were considered as supporting the short time scale of the universe 

 itself. An early, apparently the first, synoptic account of the evidence 

 relating to the age of the universe concludes as follows (1) ^: "the 

 combined evidence presented by meteorites, by statistical data relating 

 to wide double stars, by the distribution of stellar luminosities in 

 globular clusters . . . , and by the observed recession of spiral 

 nebulae . . . points to an age of the stellar universe of the same 

 order of magnitude as the currently accepted age of the solar system : 

 not much more than 3,000 million years." In this account stress was 

 laid on radioactive age determinations of meteorites by Paneth (whose 

 results were later greatly changed), and on the abundance of lead 

 isotopes in the earth's crust as testifying to the age of the radioactive 

 elements (results which have been corroborated since). Subsequent 

 synoptic reviews invariably arrived at practically similar conclusions, 

 formulated sometimes more, sometimes less cautiously, although, with 

 the changing aspect of our knowledge and different personal approach, 

 the emphasis was on different phenomena : radioactivity and the age 

 of the earth, and stellar evolution with a hydrogen-helium source 

 of energy (2) ; galactic dynamics (3) ; the stability of star clusters 

 and binaries (4, 5) ; the red shift of nebulae and the radioactive age 

 of the earth's crust (6). 



The survival of the idea of the short time scale over two decades of 

 intense astronomical and physical research is in itself a measure of its 

 worth; it serves now as a generally accepted working basis in widely 

 different fields of study. 



In the following an attempt is made to draw an up-to-date balance 

 for the problem of the time scale or age of the universe. 



THE AGE OF THE EARTH 



The continental shields of northeastern Europe, Canada, South and 

 Central Africa, and others, where mountain building ceased at an 

 early age of our planet's history, represent the oldest undisturbed 

 portions of the earth's crust. All these regions are lowlands or pla- 

 teaus devoid of mountain chains, and are free from earthquakes which 

 are the sign of continuing upheavals. The age of these old formations 



* Numbers in parentheses are references to the literature cited at end of text. 



