Publications

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In this paper we review the evidence for the Younger Dryas impact hypothesis (YDIH), which proposes that at ∼12.9k cal a BP North America, South America, Europe and the Middle East were subjected to some sort of extraterrestrial event. This purported event is proposed as a catastrophic process responsible for: terminal Pleistocene environmental changes (onset of YD cooling, continent-scale wildfires); extinction of late Pleistocene mammals; and demise of the Clovis 'culture' in North America, the earliest well-documented, continent-scale settlement of the region. The basic physics in the YDIH is not in accord with the physics of impacts nor the basic laws of physics. No YD boundary (YDB) crater, craters or other direct indicators of an impact are known. Age control is weak to non-existent at 26 of the 29 localities claimed to have evidence for the YDIH. Attempts to reproduce the results of physical and geochemical analyses used to support the YDIH have failed or show that many indicators are not unique to an impact nor to ∼12.9k cal a BP. The depositional environments of purported indicators at most sites tend to concentrate particulate matter and probably created many 'YDB zones'. Geomorphic, stratigraphic and fire records show no evidence of any sort of catastrophic changes in the environment at or immediately following the YDB. Late Pleistocene extinctions varied in time and across space. Archeological data provide no indication of population decline, demographic collapse or major adaptive shifts at or just after ∼12.9 ka. The data and the hypotheses generated by YDIH proponents are contradictory, inconsistent and incoherent. © 2014 John Wiley & Sons, Ltd.

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Because of complications associated with temperature heterogeneities in shocked metal powders, time-resolved radiation pyrometer measurements of shock temperatures in powders with particle sizes greater than a few tens of microns cannot be made under normal laboratory conditions with uniaxial loading durations limited to about one microsecond. Fortunately, for highly porous, reactive powders, the difference between shock and postshock temperature is negligible. For loading conditions similar to those that have yielded reaction products in recovery experiments, there is no evidence of any chemical reaction in a coarse (-325 mesh) nickel/aluminum powder mixture within the first 6 μs of shock arrival, based on constraints on postshock temperatures provided by thermal radiation measurements. This result is in contrast to that for a micron-sized nickel/aluminum mixture, for which there is evidence of significant reaction on a time scale of 100 ns under similar shock loading conditions.

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Climate change, through drought, flooding, storms, heat waves, and melting Arctic ice, affects the production and flow of resource within and among geographical regions. The interactions among governments, populations, and sectors of the economy require integrated assessment based on risk, through uncertainty quantification (UQ). This project evaluated the capabilities with Sandia National Laboratories to perform such integrated analyses, as they relate to (inter)national security. The combining of the UQ results from climate models with hydrological and economic/infrastructure impact modeling appears to offer the best capability for national security risk assessments.

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