THE AGE OF THE EARTH 



By E. JOBLING, A.R.C.Sc, B.Sc, F.C.S. 



The discovery of the embalmed corpse of one of 

 Egypt's ancient kings or the unearthing of some 

 hieroglyphic inscription apparently dating back to 

 Biblical times, are items of information which, when 

 they reach the public ear, awaken at least a transient 

 interest in the probable antiquity of the one or the 

 bearing of the other upon the history of the peoples of 

 the world. The call of the past is an appeal to which 

 few of us are really irresponsive, though in most the 

 receptive faculty gets dulled by inactivity, due in 

 large measure to the lack of that divination 

 which sees interest in objects of almost everyday 

 acquaintance. 



To comparatively few, for instance, has it ever 

 occurred that in the age and life-history of that 

 world upon which they " live and move and have 

 their being " is to be found a problem of keener 

 and more lasting interest than either of the above. 

 The indifference of the many to this question cannot 

 nowadays be attributed to a prevalent unquestioning 

 belief in the Scriptural computation which ascribed 

 to the earth a longevity of between six and seven 

 thousand years; for this form of mental paralysis 

 is happily now a thing of the past. It can only be 

 the absence of any acquaintance with the general 

 trend of scientific thought which debars them from 

 the very real pleasure to be derived from the story 

 of man's endeavours to delve into the unknown. 



After all, to determine the age of the earth is a 

 far more difficult undertaking than to assign the 

 mummified king to his position in the Egyptian 

 dynasties or to unravel the hieroglyphics of a 

 Babylonian column. The presence of a coin or 

 inscription in the one or a scientific deciphering of 

 the other solves the respective problems ; but in the 

 case of the earth the difficulties encountered are not 

 so easily overcome. The shape of the earth has to 

 be determined, its strata have to be laid bare, its 

 oceans weighed, and a thousand and one other 

 investigations satisfactorily completed before even 

 the data are amassed by means of which we hope 

 to realise the vast stretches of time that preceded 

 the very earliest of historians. Stupendous as the 

 obstacles are, however, sufficient is known already to 

 fling into the misty past a beam of light powerful 

 enough to reveal with tolerable certainty the features 

 of the earth as they presented themselves, say, a 

 hundred million years ago, and to dispel to some 

 extent the darkness of an even greater antiquity, if 

 we call to our aid a little justifiable hypothesis. 



Already it has been hinted that only in quite 

 recent times has the question been approached 

 scientifically. Time was when " catastrophism " 

 was the current idea, and men believed that the 

 earth, and indeed the whole solar system, had 

 suddenly sprung full-fledged into being at some 



ridiculously recent date. When, however, the 

 foundations of geology came to be laid by Hutton 

 and Lyell, the immensity of the time required for 

 an orderly deposition of the sedimentary rocks or 

 the elaboration of the organic world laid such hold 

 upon their imagination that " catastrophism " was 

 abandoned for the other extreme, " utilitarianism," 

 which relegated the birth of the earth to the very 

 beginning of time and refused to adopt any smaller 

 chronological standard than an " eternity." 



These somewhat ludicrous extremes are now, of 

 course, replaced by more reasonable views, which 

 owe their conception to the application of the 

 modern scientific spirit and the ever - growing 

 accumulation of experimental data. The iconoclast 

 who assailed and overturned the above extravagant 

 hypothesis was Lord Kelvin, then Sir W. Thomson, 

 who, in the few years following 1862, published 

 papers in which he proceeded by several physical 

 lines of reasoning to an estimate of the earth's age 

 so small comparatively as to make the then-ortho- 

 dox geologists gasp with surprise and indignation. 

 These estimates of his — historically interesting, if 

 now perhaps obsolete — will be briefly dealt with 

 first before attention is turned to other more reliable 

 evidences advanced in recent years. 



It would be as well, however, before discussing the 

 theories if we first obtain a clear idea of the various 

 phases of life-history through which the earth has 

 passed in order that no confusion may subsequently 

 arise as to the relative significance of the numerical 

 values obtained. 



Imagine, then, a vast molten globe — the product, 

 we may take it, of the condensation of a nebular haze 

 — rapidly rotating round the sun. The influence of 

 the latter would be such as to develop vast tides in 

 the liquid magma of the rotating body, one of w hich 

 tidal waves, the late Sir G. Darwin suggested, might 

 conceivably have assumed sufficiently large propor- 

 tions as to disturb the stability of the whole, and to 

 be itself trundled off into space, where it would con- 

 tinue to revolve around the remainder as the infant 

 moon. Sir G. Darwin, by-the-by, has calculated the 

 time which has elapsed since this separation to be 

 fifty-six million years. Its birth-pangs over, what 

 we now know as the " earth " starts upon its career 

 as a separate member of the solar system. Prob- 

 ably soon after the moon's departure the earth had 

 cooled enough to permit of the formation on the 

 sea of magma of floating islands of scoria, which 

 would assume larger and larger dimensions until the 

 outer crust of the earth was entirely solid and what 

 is called in the earth's history its cousistentior status 

 was inaugurated. Further cooling resulted in the 

 condensation of some of the constituents of the 

 atmosphere, which products would collect in 



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