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Title: Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis.

Abstract

Abstract not provided.

Authors:
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1124374
Report Number(s):
SAND2010-1280C
493184
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the 2009 AGU Fall Meeting held December 14-18, 2009 in San Francisco, CA.
Country of Publication:
United States
Language:
English

Citation Formats

Boslough, Mark Bruce Elrick. Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis.. United States: N. p., 2010. Web.
Boslough, Mark Bruce Elrick. Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis.. United States.
Boslough, Mark Bruce Elrick. 2010. "Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis.". United States. doi:. https://www.osti.gov/servlets/purl/1124374.
@article{osti_1124374,
title = {Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis.},
author = {Boslough, Mark Bruce Elrick},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2010,
month = 3
}

Conference:
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  • The YDB impact hypothesis of Firestone et al. (2007) is so extremely improbable it can be considered statistically impossible in addition to being physically impossible. Comets make up only about 1% of the population of Earth-crossing objects. Broken comets are a vanishingly small fraction, and only exist as Earth-sized clusters for a very short period of time. Only a small fraction of impacts occur at angles as shallow as proposed by the YDB impact authors. Events that are exceptionally unlikely to take place in the age of the Universe are 'statistically impossible'. The size distribution of Earth-crossing asteroids is well-constrainedmore » by astronomical observations, DoD satellite bolide frequencies, and the cratering record. This distribution can be transformed to a probability density function (PDF) for the largest expected impact of the past 20,000 years. The largest impact of any kind expected over the period of interest is 250 m. Anything larger than 2 km is exceptionally unlikely (probability less than 1%). The impact hypothesis does not rely on any sound physical model. A 4-km diameter comet, even if it fragmented upon entry, would not disperse or explode in the atmosphere. It would generate a crater about 50 km in diameter with a transient cavity as deep as 10 km. There is no evidence for such a large, young crater associated with the YDB. There is no model to suggest that a comet impact of this size is capable of generating continental-wide fires or blast damage, and there is no physical mechanism that could cause a 4-km comet to explode at the optimum height of 500 km. The highest possible altitude for a cometary optimum height is about 15 km, for a 120-m diameter comet. To maximize blast and thermal damage, a 4-km comet would have to break into tens of thousands fragments of this size and spread out over the entire continent, but that would require lateral forces that greatly exceed the drag force, and would not conserve energy. Airbursts are decompression explosions in which projectile material reaches high temperature but not high pressure states. Meteoritic diamonds would be vaporized. Nanodiamonds at the YDB are not evidence for an airburst or for an impact.« less
  • Abstract not provided.
  • no abstract
  • Previous work in Nova Scotia and New Brunswick, Canada has proven that a late-glacial climatic oscillation expressed itself in North America. Despite physical and palynological evidence in Canada for an event centered on the Alleroed-Younger Dryas chronozones, little conclusive evidence has been found for an equivalent oscillation in Maine. The only physical evidence for an Alleroed-Younger Dryas event so far in Maine is a deformed peat layer within a diamicton near Oxbow. Newman et al. reported ages on the peat ranging from 10,395 [plus minus] 85 to 11,760 [plus minus] 145 [sup 14]C yrs B.P. New excavation of the sitemore » in 1992 did not reveal the peat. Newman et al. reported a strong NNW-SSE stone fabric in the diamicton, which is consistent with regional flow directions and suggests that the diamicton may be a till. Regional basal organic [sup 14]C dates suggest that the area was ice-free by Younger Dryas time. The authors strategy for trying to solve this problem has been to investigate the stratigraphy of the Oxbow region, in conjunction with ice-flow directions as determined by bedrock striae and till fabrics. Ongoing fieldwork has shown that the direction of strongest bedrock erosion records a Late-Wisconsin ice flow event which occurred along a mean trend of s26E, based on 261 striation measurements at 36 localities. The NNW-SSE-trending striae cross-cut a W-E set at some localities. Faint striation sets which cross-cut the NNW-SSE-trending striae have no consistent orientation. This is in agreement with the striation data. A major drag fold found at the contact between the surface till and underlying gravel also indicates ice flow from the NNW (fold axis trend:s66W). The surface till has not been dated directly. The genesis of the diamicton at Oxbow and its relationship to the regional surface till remains unclear.« less