ORIGIN AND NATURE OF THE MOON — TJRET 265 



density is lack of iron, this would indicate that the moon has a com- 

 position similar to that of the sun, and that the earth and the other 

 planets acquired increased amounts of iron during their formation. 

 This bears on two important problems, namely, the origin of the 

 elements and the origin of the solar system. 



The rigidity could be determined by seismographs and gravimeters 

 placed on the surface, and these could be flown to and landed on the 

 moon. Such measurements will show whether the moon is now 

 molten in the deep interior and give much information about its 

 internal temperature. 



The determination of the age of the moon's surface, by radioactive 

 dating methods, will tell us definitely the time at which the events 

 described in this paper occurred. The surface materials — particu- 

 larly at the poles, which have remained cool during geologic time — 

 will give us a record of cosmic-ray intensities during the time that the 

 solar system has existed. For such studies it is necessary to extract 

 the inert gases from the surface materials. Knowing how rapidly 

 they are produced by cosmic rays, we can calculate the time of expo- 

 sure if the intensity of the rays has been constant. If the age so 

 calculated agrees with the radioactive ages, we should then know that 

 the cosmic rays have been constant in intensity, at least on the aver- 

 age. Disagreement would require another explanation. 



The moon has been an object for astronomical study for centuries. 

 We are now entering a period when physical and chemical studies will 

 supplement the astronomical ones. Certainly the petrologists will 

 have a field day if at some time samples of the moon can be secured. 

 However, if the story of the moon as presented here is correct, the 

 usual processes of geology — the mountain uplift, volcanology, erosion, 

 sedimentation, and formation of the fossil record — will have little 

 application to selenology. 



REFERENCES 



1. Gilbert, G. K. Bull. Philos. Soc. Washington, vol. 12, p. 24, 1893. 



2. Baldwin, R. B. The face of the moon. University of Chicago Press, 1949. 

 2a. Urey, H. C. ; Elsasser, W. M. ; and Rochester, M. G. Astrophys. Journ., 



vol. 129, p. 842, 1959. 



3. Urey, H. C. Boundary conditions for the origin of the solar system. In 



Progress in physics and chemistry of the earth, vol. 2. Pergamon Press, 

 London, 1957. 



4. Kelvin, Lord. Trans. Roy. Soc. Edinburgh, vol. 23, p. 157, 1862. 



5. DiETZ, R. S. Journ. Geol., vol. M, p. 359, 1946. ' 



6. Gold, T. Monthly Not. Roy. Astron. Soc, vol. 115, p. 585, 1955. 



7. Opik, E. J. Contr. Armagh Observ., No. 6, p. 186, 1951. 



8. Kozyrev, N. Sky and Telescope, vol. 18, p. 184, 1959. 



9. KuiPER, G. P. The exploration of the moon. In Vistas in astronautics, voL 



2, p. 286. Pergamon Press, London, 1959. 

 10. Salisbury, J. W. (In press.) 



