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Letters to Nature
Nature 242, 32 - 33 (02 March 1973); doi:10.1038/242032a0

Cometary Collisions and Geological Periods

HAROLD C. UREY

Chemistry Department, University of California at San Diego, La Jolla, California 92037

SOME fifteen years ago, I suggested that tektites were produced by collisions of comets with the Earth1–3. Many detailed investigations of these objects have added much to our knowledge, and these, together with the lunar investigations, have proved this hypothesis to be very probably correct. I have also suggested that the geological periods were terminated by such collisions, but this was published in the Saturday Review of Literature, and no scientist except me, so far as I know, reads that magazine. The energy of such collisions and their frequency was roughly estimated at that time, and the number of these collisions has been reviewed again by Durrani4.

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References

1. Urey, H. C., Nature, 179, 556 (1957).
2. Urey, H. C., Nature, 197, 228 (1963).
3. Urey, H. C., Science, 137, 746 (1962).
4. Durrani, S. A., Nature, 235, 383 (1972).
5. Russell, H. N., Dugan, R. S., and Stewart, J. Q., Astronomy, 446 (Ginn and Co., New York, 1945).
6. Whipple, F. L., in Moon, Meteorites and Comets (edit. by Middlehurst, B. M., and Kuiper, G. P.), chapter 19 (Chicago Univ. Press, 1963).
7. Lin, S. C., J. Geophys. Res., 71, 2427 (1966).
8. Laurence Kulp, J., Science, 133, 1106 (1961).
9. Durrani, S. A., Phys. Earth Planet. Int., 4, 251 (1971).
10. Storzer, D., and Wagner, G. A., Earth Planet. Sci. Lett., 10, 435 (1971).



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