DATING THE EARTH’S CRUST—SHAPLEY 145 
Several years ago, despairing of our finding an acceptable orderly 
theory of the origin of the planets, I proposed an alternative that can- 
not be easily disproved.” It might be called the hypothesis of the 
chaotic origin of the solar system. It ties in earth-birth with the 
genesis of stars. We should remember that the hardest problems of 
cosmogony would not necessarily be disposed of even if we should 
get a satisfactory theory of the origin of the earth. For we would 
ask at once concerning the origin of the sun and of galaxies, and even- 
tually be driven back to the deeper puzzles of the origin of matter, 
origin of space, of time, and of origins. Planetary genesis is there- 
fore only a decoy, leading to universal processes. 
One working hypothesis of the origin of stars prescribes that they 
have come disruptively from an original all-encompassing mass 
(Lemaitre’s cosmic atom), perhaps through several shattering explo- 
sive stages. Other cosmogonies also require high concentrations of 
matter at some past time, perhaps at “the beginning of things.” 
On the chaos hypothesis we assume that whatever collisional or 
explosive event produced the sun also simultaneously produced a very 
large number of fragments. Much of the debris has subsequently been 
lost—diffused or driven off as gases, or as particles dynamically 
ejected. If, in this confusion, the great fragments that are now Jupi- 
ter and Saturn moved in the same direction around the gravitationally 
controlling primitive sun, and moved in practically the same plane, 
they together might in time set the tune for the surviving fragments 
(planets and asteroids). We must visualize a long cleaning-up proc- 
ess, in which bodies with highly elliptic orbits were rejected or cap- 
tured, and those with other-direction motions likewise subjected to 
dynamical elimination. The bodies with essentially circular orbits, 
rightly spaced and oriented, revolving in the correct direction, are 
the only natural survivors of the cleaning-up and regularization. 
There are, of course, difficulties even with this generous chaotic 
hypothesis—for instance, the present nonexistence of orbits of high 
inclination (except cometary). But its greatest weakness, of course, 
is that it represents a council of despair—it is the antithesis of “orderly 
procedure” at the time of the system’s origin. Nevertheless the hypoth- 
esis would certainly suffice to end our search, because in the primitive 
star-making violences, and in the confusion of bodies, motions, and 
explosive processes, almost any detail can be specified. The momen- 
tum puzzle could be bypassed, and the other difficulties resolved by 
appeal to forces of varied and irregular fragmentation. 
My suggestion” really amounts to saying that the planets and 
10facts and fancy in cosmogony. Annual Sigma Xi address, Atlantic City, December 
28, 1932. 
11The Sigma Xi address was not published. Somewhat later H. N. Russell independently 
made a similar suggestion, and probably others have also, 
