A cataclysmic event of a certain age

[knocker]

 

At the end of the Pleistocene period, approximately 12,800 years ago­ -- give or take a few centuries -- a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.

 

New research by UC Santa Barbara geologist James Kennett and an international group of investigators has narrowed the date to a 100-year range, sometime between 12,835 and 12,735 years ago. The team's findings appear today in the Proceedings of the National Academy of Sciences.

 

http://www.eurekalert.org/pub_releases/2015-07/uoc--ace072715.php

 

Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

http://www.pnas.org/content/early/2015/07/21/1507146112

[Yarmy]

This is interesting as the Younger Dryas is usually attributed to the freshening of the North Atlantic following a huge outburst flood from glacial Lake Agassiz.

 

http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr

 

I suppose if the impact theory is true someone needs to find a great big hole as 12000 years isn't that long ago in geological terms.

[knocker]

Yes this is interesting because it has been much debated. From your link

 

 

Lake Agassiz's eastern outlet history also presents an issue, as the most recent study suggested that the outlet remained closed until well after the start of the Younger Dryas, with the lake having no outlet for much of the Younger Dryas (Lowell et al., 2009). In contrast, a simple consideration of Lake Agassiz's water budget requires an outlet for the lake during the Younger Dryas (Carlson et al., 2009). This ongoing debate over the ultimate cause of the Younger Dryas has led to a search for other potential forcing mechanisms, such as an abrupt discharge of meltwater to the Arctic Ocean (Tarasov and Peltier, 2005) and a bolide impact (Firestone et al., 2007).

 

Does this latest paper support the Firestone paper from the above link?

 

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

 

Abstract

A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

 

http://www.pnas.org/content/104/41/16016.abstract?ijkey=fa63250befe1e15daabd83d5626a3852ab70b3aa&keytype2=tf_ipsecsha

Edited July 28, 2015 by knocker

[Yarmy]

There certainly seems plenty of evidence for an impact and thinking about it the Tunguska event demonstrates that a large crater need not necessarily be formed. The extended duration of the YD suggests some kind of secondary effect would have been required and the final link hints at that.

[knocker]

Just noticed a blog by Richard Telford on the subject that should be interesting (haven't had a chance to read it yet)

 

From the Journal of Younger Dryas Impact Hypothesis Studies

[Nouska]

Thanks for posting - very interesting read.

 

With conditions as hypothesised in the Firestone paper it would be hard to envisage the humans surviving to relocate as seems to be suggested in the latest study. Is there anything else that could explain the complex 'carpet' of elements though?

 

 

Environmental Effects.

The YD event would have created a devastating, high-temperature shock wave with extreme overpressure, followed by underpressure, resulting in intense winds traveling across North America at hundreds of kilometers per hour, accompanied by powerful, impact-generated vortices (50–52). In addition, whether single or multiple objects collided with Earth, a hot fireball would have immersed the region near the impacts and would have been accentuated if the impact angles were oblique (46, 53). For comparison, Svetsov (48) calculated that a Tunguska-sized airburst would immerse the ground with a radiation flux severe enough to ignite 200 km² of forest within seconds. Thus, multiple, larger airbursts would have ignited many thousands of square kilometers. At greater distances, the reentry of high-speed, superheated ejecta would have induced extreme wildfires (53), which would have decimated forests and grasslands, destroying the food supplies of herbivores and producing charcoal, soot, toxic fumes, and ash. The number of ET airbursts or impacts necessary to induce the continent-wide environmental collapse at 12.9 ka is unknown.

[Gray-Wolf]

And what if the impactor landed in the glacial lake? If you want a sudden collapse of a glacial dam and massive glacial lake outpourings that'd do it? Add in the torching of the North American Forests ......