ON THE ASTRONOMICAL DATING OF THE 
EARTH’S CRUST? 
By Harlow SHAPLEY 
Harvard University, Cambridge, Mass. 
These notes on cosmogony are only minor contributions in an im- 
portant and expanding theme. Over the years a considerable num- 
ber of scientists are gradually developing a fairly complete and satis- 
fying cosmogony. When the hypotheses settle down into accepted 
laws, and the skimpy observations grow into “facts of the world,” my 
present contribution will avail little; but at this particular moment, 
it may show the trend of our thinking and planning. 
Until recently, the word cosmogony generally implied, astronomi- 
cally, the study of the origin of the earth and of the other planets;? 
scientific thoughts about the universe had of necessity been restricted 
closely to the planetary system, with an occasional vague adventure 
into the unexplored realm of stellar bodies. But as our knowledge 
of stars and nebulae increased, this vagueness diminished; and, with 
a fine disregard for our impotence, we have now tackled the origins 
of stars, star clusters, nebulae, galaxies, and space-time itself. Cos- 
mogony has appropriately expanded beyond the bounds of the solar 
system, and now includes the description and theory of the whole 
knowable material universe. As something of a digression, it ex- 
amines the riddles of the origin of planetary systems. But perhaps 
this appearance of implied condescension toward earthly affairs is 
inappropriate, for the more we look into the problems of the origin 
of the earth, the more we find that its genesis involves operations that 
are universal. The earth’s crust, it appears, has an age not at all 
insignificant compared with the duration of stellar processes; and the 
chemistry of the earth’s crust is a convenient and comprehensive 
sample of the chemistry of the universe. 
1Paper No. 90, published under the auspices of the committee on research in experi- 
mental geology and geophysics and the division of geological sciences at Harvard University. 
Reprinted by permission from the American Journal of Science, vol. 243—A, Daly Volume, 
1945. 
2To many writers, cosmoiogy is a preferred synonym, notwithstanding its frequent dis- 
coloration with metaphysics ; and cosmography is a proper and modest substitute when sim- 
ple description of cosmic matters is concerned. 
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