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W. Bruce Masse, Los Alamos National Laboratory (United States)
Dallas H. Abbott, Lamont Doherty Earth Observatory of Columbia University (United States)
Mike Baillie, Queen's University (Ireland)
Gustavo Barrientos, Universidad Nacional de La Plata (Argentina)
Kord Ernstson, University of Wurzburg (Germany)
Richard B. Firestone, Lawrence Berkeley National Laboratory (United States)
Viacheslav K. Gusiakov, Institute of Computational Mathematics and Mathematical Geophysics (Russian Federation)
Simon K. Haslett, Bath Spa University (United Kingdom)
Michael A. Rappengluck, Institute for Interdisciplinary Studies (Germany)
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Planetary scientists suggest that globally catastrophic impacts by asteroids and comets capable of killing one quarter or more of Earth's human population-currently estimated at 106 megatons (roughly 5,000,000 times the energy release of the Hiroshima and Nagasaki atomic weapons)-occur on average once every million years. Since the Holocene period represents only around 1% of this time, conventional wisdom implies that it is highly unlikely that such impacts, or even smaller regionally catastrophic impacts (ca. 104-105 megatons) have occurred during this short time interval. Indeed, most members of the near Earth object (NEO) planetary science community doubt that there are any demonstrable records during the past 5,000 years of anyone being killed by a cosmic impact, and likewise think it highly unlikely that impacts have played a role in any of the periods of rapid climate change in the paleoclimatic record of the past 15,000 years. This paper focuses on the record of recent validated cosmic impacts, such as Campo del Cielo and Rio Cuarto in Argentina, but also on several hypothesized impacts that have drawn recent attention, often negative, in scientific and media circles. The authors are part of a consortium of more than two dozen scientists from at least eight countries who are currently evaluating the Earth's physical record to determine if one or more major cosmic impacts may have occurred during the past 15,000 years.
We focus on sites where catastrophic cosmic impacts may have been responsible for (1) the beginning of the Younger Dryas climatic ordeal at 12,900 bp; (2) the boundary between the middle and late Holocene at around 4800-5000 bp; (3) climatic disruption during the period of 3200-2800 bp (4) the "Years without summer" climate downturn shortly after 1500 bp; and (5) the beginning of the Little Ice Age at around 700 bp. Each of these potential impacts is linked to a still poorly understood recent period of rapid environmental and climate change where the hypothesis of catastrophic impact can be well tested. These provide a robust test of impact flux and the physical products of impact. Regardless of the actual nature of each hypothesized impact event, we recognize that our most immediate task and obligation is to collect sufficient high quality physical evidence, which when coupled with dynamic modeling can provide the necessary data and tests to validate or disprove each impact claim. We will summarize the current status of our research, and highlight recent positive findings as well as problems and issues demanding greater attention. If any one of these hypothesized impacts were to be eventually validated, the knowledge to be learned from such an event would be of considerable value for our understanding of cosmic impact and rapid climate change.
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