Saturday, August 2, 2008
"Last Ice Age happened in less than year say scientists"
According to a release by the German Research Center for Geosciences (cited in The Scotsman) the shift from post glacial warming in Europe, 12900 years ago, back into a glacial freezing pattern called the Younger Dryas happened during the course of a single year.
Dr Achim Brauer, of the GFZ (GeoForschungs Zentrum) and colleagues determined through analysis of annual layers of sedimentation from a crater lake in Germany that the onset of re-glaciation was a sudden event. In essence winter came and simply stayed.
It is theorized that the abrupt freezing was caused by a disruption in Atlantic Ocean currents and atmospheric circulation.
"The Younger Dryas stadial, named after the alpine / tundra wildflower Dryas octopetala, and also referred to as the Big Freeze, was a brief (approximately 1300 ± 70 years) cold climate period following the Bölling/Allerød interstadial at the end of the Pleistocene between approximately 12,800 to 11,500 years Before Present, and preceding the Preboreal of the early Holocene.
The Younger Dryas (GS1) is also a Blytt-Sernander climate period detected from layers in north European bog peat. It is dated approximately 12,900-11,500 BP calibrated, or 11,000-10,000 BP uncalibrated." (Wikipedia)
A paper entitled "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling" can be downloaded in PDF format at: http://www.pnas.org/cgi/reprint/0706977104v1.pdf
This paper deals with a suspected cause of the YD cooling and its abrupt onset.
The paper leads off with the following provocative introduction and develops a case for accepting an ET impact event as the cause for several troublesome anomalies:
"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..."
"Increasing evidence suggests that the extinction of many mammalian and avian taxa occurred abruptly and perhaps catastrophically at the onset of the YD, and this extinction was pronounced in North America where at least 35 mammal genera disappeared (3), including mammoths, mastodons, ground sloths, horses, and camels, along with birds and smaller mammals.
At Murray Springs, AZ, a well known Clovis site, mammoth bones and Clovis-age stone tools lie directly beneath the black layer where, as described by Haynes: ‘‘[T]he sudden extinction of the Pleistocene megafauna would be dramatically revealed by explaining that all were gone an instant before the black mat was deposited.’’
The cause of this extinction has long been debated and remains highly controversial due, in part, to the limitations of available data but also because the two major competing hypotheses, human overkill (5) and abrupt cooling (6), fall short of explaining many observations.
For example, Grayson and Meltzer (7) summarized serious problems with the overkill hypothesis, such as the absence of kill sites for 33 genera of extinct mammals, including camels and sloths. In addition, although abrupt cooling episodes of magnitudes similar to the YD occurred often during the past 80 ka, none are known to be associated with major extinctions..." © 2007 by The National Academy of Sciences of the USA
Should this information be correct it will finally lay to rest the attribution of wholesale fauna extinctions in the Americas, North America especially, to early indigenous humans.
The article in "The Scotsman" is a bit Euro-centric, if that's an acceptable construction, and expresses concern that the sudden cooling of Europe might be repeated soon. The writer did not make any reference to a suspected cause for the observed abrupt freezing.
Dr. Firestone's (and many others) paper from PNAS indicates that the evidence strongly suggests one or more large low-density ET objects exploded over northern North America, towards the end of the last ice age. This caused two main effects: First a huge disruption to the atmosphere, including a reduction of the ozone layer, massive injection of particulates (from fires caused by the impact) and sulphur and nitrogen compounds, as well as water vapor into the upper atmosphere. Second, the impact destabilized the Laurentide ice sheet releasing huge quantities of ice and fresh water into the North Atlantic causing the thermohaline circulation in the northern Atlantic to weaken. This caused the sudden onset of re-glaciation in Europe and sustained the cooling for 1,000 years or so until the feedback mechanisms restored ocean circulation.
So, while another abrupt cooling might well occur soon, the trigger mechanism would probably not go unobserved and the cooling might prove to be the least troublesome effect experienced...
Just one more reason to step up the process of cataloging near Earth objects and Earth-orbit crossing objects in space. It's possible that we may soon develop technologies which will allow us to deal with such ET objects before they become "an event"...