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ABSTRACT THE proposal by Urey1 that tektites may originate through Earth–comet collisions has recently been extended to suggest that the energy released may be sufficient to produce periods

of intense geological activity2. But the hypothesis is crucially dependent on the picture adopted for the structure of comets, and Urey assumes that the fundamental permanent heart-and-soul

of a comet is a solid nucleus of kilometric size, with activity of the comet resulting from solar radiation and possibly interaction with the solar wind. If that were so, such an object

impacting the Earth would not produce essentially different effects from those by a meteorite or asteroid of comparable mass. Access through your institution Buy or subscribe This is a

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LONG-PERIOD COMET AS THE ORIGIN OF THE DINOSAUR EXTINCTION Article Open access 15 February 2021 IMPACTS MAY PROVIDE HEAT FOR AQUEOUS ALTERATION AND ORGANIC SOLID FORMATION ON ASTEROID PARENT

BODIES Article Open access 18 May 2021 DELAYED AND VARIABLE LATE ARCHAEAN ATMOSPHERIC OXIDATION DUE TO HIGH COLLISION RATES ON EARTH Article 21 October 2021 REFERENCES * Urey, H. C.,

_Nature_, 197, 228 (1963). Article  ADS  Google Scholar  * Urey, H. C., _Nature_, 242, 32 (1973). Article  ADS  Google Scholar  * Lyttleton, R. A., _Astrophys. Space Sci._, 15, 175 (1972).

Article  ADS  Google Scholar  * Myer, J. A., _Astrophys. J. Lett._, 175, L49 (1972). Article  ADS  Google Scholar  * Lyttleton, R. A., _Proc. R. Soc._, 272, 467 (1963). ADS  CAS  Google

Scholar  * Lyttleton, R. A., _Geophys. J. R. astr. Soc._, 15, 191 (1968). Article  Google Scholar  * Bowen, E. G., _Austr. J. Phys._, 6, 490 (1953). Article  ADS  Google Scholar  Download

references AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Institute of Astronomy, Cambridge R. A. LYTTLETON Authors * R. A. LYTTLETON View author publications You can also search for this

author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE LYTTLETON, R. Encounters of the Earth with Comets. _Nature_ 245, 144–145

(1973). https://doi.org/10.1038/245144a0 Download citation * Received: 14 March 1973 * Issue Date: 21 September 1973 * DOI: https://doi.org/10.1038/245144a0 SHARE THIS ARTICLE Anyone you

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