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Alexander Tollmann's bolide, proposed by Kristan-Tollmann and Tollmann in 1994,〔Kristan-Tollmann, E. and A. Tollmann, 1994, ''The youngest big impact on Earth deduced from geological and historical evidence''. Terra Nova. v. 6, no. 2, pp. 209–217.〕 is a hypothesis presented by Austrian geologist Alexander Tollmann, suggesting that one or several bolides (asteroids or comets) struck the Earth at 7640 BCE (±200), with a much smaller one at 3150 BCE (±200). If true, this hypothesis explains early Holocene extinctions and possibly legends of the Universal Deluge.〔 The claimed evidence for the event includes stratigraphic studies of tektites,〔Glass, B.P., 1978, ''Australasian Microtektites and the Stratigraphic Age of the Australites'' Bulletin of the Geological Society of America. v. 89, no. 10, pp. 1455–1458.〕〔Izokh, E.P., 1988, ''Age-paradox and the Origin of Tektites'' in J. Konta, ed., 2nd international conference on natural glasses'' Abstracts – International Conference on Natural Glasses-Prague, Czechoslovakia, 1988. v. 2, pp. 379–384.〕〔Prasad, N.S. and P.S. Rao, 1990, ''Tektites Far and Wide''. Nature. v. 347, no. 6291, pp. 340.〕 dendrochronology, and ice cores (from Camp Century, Greenland) containing hydrochloric acid and sulfuric acid (indicating an energetic ocean strike) as well as nitric acids (caused by extreme heating of air). Christopher Knight and Robert Lomas in their book, ''Uriel's Machine'', argue that the 7640 BCE evidence is consistent with the dates of formation of a number of extant salt flats and lakes in dry areas of North America and Asia. They argue that these lakes are the result remains of multiple-kilometer-high waves that penetrated deeply into continents as the result of oceanic strikes that they proposed occurred. ==Scientific evaluation== Quaternary geologists, paleoclimatologists, and planetary geologists specializing in meteorite and comet impacts have rejected the Tollmann bolide hypothesis.〔Deutsch, A., C. Koeberl, J.D. Blum, B.M. French, B.P. Glass, R. Grieve, P. Horn, E.K. Jessberger, G. Kurat, W.U. Reimold, J. Smit, D. Stöffler, and S.R. Taylor, 1994, ''The impact-flood connection: Does it exist?'' Terra Nova. v. 6, pp. 644–650.〕 They reject this hypothesis because: # The evidence offered to support the hypothesis can more readily be explained by more mundane and less dramatic geologic processes # Many of the events alleged to be associated with this impact occurred at the wrong time (i.e., many of the events occurred hundreds to thousands of years before or after the hypothesized impacts); and # There is a lack of any credible physical evidence for the cataclysmic environmental devastation and characteristic deposits that kilometer-high tsunamis would have created had they actually occurred.〔 First, many pieces of evidence used by the Tollmann bolide hypothesis to argue for catastrophic Holocene impacts can be just as well, in most cases even better, explained by more pedestrian geological processes. For example, the chemical composition of and the presence of volcanic ash with the specific acidity spikes in the Greenland ice cores presents clear evidence that they are volcanic, not impact, in origin.〔Hammer, C.U., H.B. Clausen, and W. Dansgaard, 1980, ''Greenland ice sheet evidence of post-glacial volcanism and its climatic impact''. Nature. v. 288, no. 5788, pp. 230–235.〕〔Zielinski, G.A., P.A. Mayewski, L.D. Meeker, S. Whitlow, and M.S. Twickler, 1996, ''A 110,000 year record of explosive volcanism from the GISP2 (Greenland) ice core''. Quaternary Research. v. 45, no. 2, pp. 109–118.〕 Also, the largest acidity spikes found in Antarctica ice cores are far too old, from 17,300 to 17,500 BP, to be associated with any Holocene impacts.〔Hammer, C.U., H.B. Clausen and C. Langway, Jr., 1997, ''50,000 years of recorded global volcanism''. Climatic Change. v. 35, no. 1, pp. 1–15.〕 The formation of modern salt lakes and salt flats is readily explained by the concentration of salts and other evaporite minerals by the evaporation of water from stream-fed lakes lacking external outlets, called "endorheic lakes", in arid climates. The composition of the salts and other evaporate minerals found in these lakes is consistent with their precipitation from dissolved material continually input into the lakes by rivers and streams and concentration by evaporation instead of evaporation of sea water.〔Eugster, H.P., 1980, ''Geochemistry of Evaporitic Lacustrine Deposits''. Annual Review of Earth and Planetary Sciences. v. 8, pp. 35–63.〕〔Spencer, R.J., Eugster, H.P., and Jones, B.F., 1985, ''Geochemistry of Great Salt Lake, Utah II: Pleistocene-Holocene evolution''. Geochimica et Cosmochimica Acta. v. 49, no. 3, pp. 739–747.〕〔Hart, W.F., J. Quade, D.B. Madsen, D.S. Kaufman, and C.G. Oviatt, 2004, ''The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system''. Geological Society of America Bulletin. v. 116, no. 9–10, pp. 1107–1119.〕 Whether a lake becomes salty or not simply depends on whether the lake lacks an outlet and the relative balance between water flowing into the lake and leaving the lake via evaporation.〔 Ocean water dumped into a lake as the result of a single catastrophic event, as suggested above, would contain an inadequate amount of dissolved minerals to produce, when evaporated, the vast quantities of salts and other evaporites found in the salt lakes, flats, and pans cited as evidence of a mega-tsunami by this hypothesis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tollmann's hypothetical bolide」の詳細全文を読む スポンサード リンク
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