About 12,800 years ago, the last Ice Age was coming to an end, the planet was warming up. Then, inexplicably, the planet plunged into a deep freeze, returning to near-glacial temperatures for more than a millennium before getting warm again. The mammoths disappeared at about the same time, as did some Native American cultures that thrived on hunting them. That climatic event is known as The Younger Dryas.
Many explanations for the event point to the impact of a comet or an asteroid, but now there is a new study suggests the driver/trigger was all from terrestrial based events.”
According to the article in Science Magazine, they find no evidence for an impact:
The study “pulls the rug out from under the contrived impact hypothesis quite nicely,” says Christian Koeberl, a geochemist at the University of Vienna. Most evidence for the extraterrestrial impact hypothesis, he says, was conjured up “out of thin air.”
The notion was popularized in television documentaries and other coverage on the National Geographic Channel, History Channel, and the PBS program NOVA.
…
Now comes what some researchers consider the strongest attack yet on the Younger Dryas impact hypothesis. In a paper published online this week in the Proceedings of the National Academy of Sciences, a team led by David Meltzer, an archaeologist at Southern Methodist University, Dallas, in Texas, looks at the dating of 29 different sites in the Americas, Europe, and the Middle East in which impact advocates have reported evidence for a cosmic collision.
Only three of the 29 sites actually fall within the time frame of the Younger Dryas onset
http://news.sciencemag.org/archaeology/2014/05/what-caused-1300-year-deep-freeze
From the publication:
A key element underpinning the controversial hypothesis of a widely destructive extraterrestrial impact at the onset of the Younger Dryas is the claim that 29 sites across four continents yield impact indicators all dated to 12,800 ± 150 years ago. This claim can be rejected: only three of those sites are dated to this window of time. At the remainder, the supposed impact markers are undated or significantly older or younger than 12,800 years ago. Either there were many more impacts than supposed, including one as recently as 5 centuries ago, or, far more likely, these are not extraterrestrial impact markers.
Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago
David J. Meltzer, doi: 10.1073/pnas.1401150111
David J. Meltzera, Vance T. Holliday, Michael D. Cannon, and D. Shane Miller
Abstract
According to the Younger Dryas Impact Hypothesis (YDIH), ∼12,800 calendar years before present, North America experienced an extraterrestrial impact that triggered the Younger Dryas and devastated human populations and biotic communities on this continent and elsewhere. This supposed event is reportedly marked by multiple impact indicators, but critics have challenged this evidence, and considerable controversy now surrounds the YDIH. Proponents of the YDIH state that a key test of the hypothesis is whether those indicators are isochronous and securely dated to the Younger Dryas onset. They are not. We have examined the age basis of the supposed Younger Dryas boundary layer at the 29 sites and regions in North and South America, Europe, and the Middle East in which proponents report its occurrence. Several of the sites lack any age control, others have radiometric ages that are chronologically irrelevant, nearly a dozen have ages inferred by statistically and chronologically flawed age–depth interpolations, and in several the ages directly on the supposed impact layer are older or younger than ∼12,800 calendar years ago. Only 3 of the 29 sites fall within the temporal window of the YD onset as defined by YDIH proponents. The YDIH fails the critical chronological test of an isochronous event at the YD onset, which, coupled with the many published concerns about the extraterrestrial origin of the purported impact markers, renders the YDIH unsupported. There is no reason or compelling evidence to accept the claim that a cosmic impact occurred ∼12,800 y ago and caused the Younger Dryas.
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Steve Garcia says:
May 13, 2014 at 9:38 pm
The glacial meltwater lakes & seas formed during the retreat of the Laurentide Ice Sheet on the last glaciation have been pretty well studied:
http://dspace.usc.es/bitstream/10347/3757/1/pg_049-074_xeografica7.pdf
It’s from a Spanish language journal, so its English is a little rough in places, but the graphics reflect state of the art understanding of the geology & geography of the melting process. Two graphics bracket the YD.
@Retired Engineer John at 9:17 am:
“There was a period of extreme instability in the Earth’s climate starting about 11,500 years ago and extending back some 3,000 years. Those are extreme temperature changes that require big changes in the Earth’s balance of energy for an extended period of time. Singular events such as volcanos or comet impacts could not produce lasting effects sufficient to make these changes. Any explanation should be accompanied by calculations of the changes in accumulated energy required to make the temperature changes along how much change a proposed event could possibly make. I suspect that only an instability in the Sun could cause such large variations.”
It is hard to draw solid conclusions, because the Greenland ice cores show NUMEROUS monumentally huge changes – Down AND up – called Dansgaard-Oeschger events. The YD onset apears to dovetail with ONE of those. 1300 years later a reversal of that occurred, and that one no one knows enough about yet to tackle it. The YD onset has been noted in various sciences – biology, climatology especially – and MANY people have been REALLY wanting to get to the bottom of it. The climate really DID shift -a LOT. After several thousand years of temps not far from ours today (and which was the first real warm period in a very LONG time), the YD put the planet right back in the cooler. Not just in Greenland, but everywhere. But Greenland, being Arctic, is, like most arctic regions, more sever in the ups and downs that happen when the climate changes. So the ice cores may be representing the most severe changes at the YD onset (as well as those other D-O downturns).
YES, you are correct about the energy losses – they DO need to be explained. The duration of the YD of 1300 years – it DOES need to be explained. The equally sudden rebound from the YD glacial/stadial DOES also need to be explained.
Be aware that nothing so far within the closed system of the Earth that has been suggested as the cause has come anywhere NEAR being feasible as an explanation. They invoke gradualism, and all its know internal mechanisms simply are inadequate in the extreme.
Firestone himself did not set out to look for the YD cause. He ran across some weird numbers in radiocarbon dating. As he kept turning up other weird stuff – iron balls imbedded in mammoth tusks and other megafauna tusks, magnetic grains in certain layers that kept on showing up at different sites (now extended to four continents), mammoth bones lying with the mysterious “black mat” literally ON the bones, staining them and imparting radioactivity and magnetism to the bones. He orignally thought it was from a supernova somewhere nearby, because he ruled out (based on the evidence he was uncovering) any terrestrial causes. By the time he got into it a bit, others were joining in trying to figure out WTF was going on – or had GONE on. The impact scenario was not the first idea in their heads, but it was always a possibility, once they found out how FAST those iron balls had to be traveling. The bottom SURFACE of that black mat turned out to be consistently carbon dated to 12,900 years ago (calibrated – and then not long ago adjusted down to 12,800). THAT put the mammoth extinction not only AT the YD onset by date, but also PHYSICALLY.
The Holliday-Melzer tandem have addressed all of these points in a 2010 paper that didn’t get NEARLY this much attention. They don’t have any answers, either. And they don’t DO any original work on this – all theydo is snipe at those doing the work. “Those who can, DO; those who CAN’T teach.” With Melzer and Holliday if could finish with “..; those who CAN’T, snipe.”
IMHO, there IS sufficient evidence of a forensic type – properly taken samples, tested in labs, providing much quantitative data, pointing at X, Y, or Z possible causes, and of sufficient BREADTH of evidence types (impact materials, ammonium spikes in the atmosphere (e.g.), to collectively point at an impact as the most likely suspect. It is possible to point at individual data and snipe at that one – while ignoring ALL the other types of data – and then turn around and tell the world, “NOPE. That one thing is kind of weak, so the whole thing is crap.” That is what is done here. The Holliday-Melzer group (including Boslough, Daulton, Pinter, van Hoesel and few others) conveniently pretend that the other line of evidence do not exist – and they hope that no one will ask them about it all.
It would actually not be laughable if any of them actually did any field work themselves. But they are like Monday morning quarterbacks – you know, really someone we should all listen to (snarc).
milodonharlani says:
May 13, 2014 at 10:45 am
“The previous interglacial, the Eemian lasted 16,000 years by the most common way of dating its onset & demise. It was also warmer than the Holocene, which, by the same dating system, is about 11,400 years old.”
——————–
My personal opinion is, ….. if one is calling the current period the “Holocene Interglacial” then one has to date it at being about 21,000 years old as defined by the “start” of the post-ice age melting of the glacial ice.
To wit, proxy graph of Post-Glacial Sea Level Rise
http://withfriendship.com/images/e/22018/another-graph-of-the-holocene.gif
Sea levels had already risen by 70 meters (230 feet) by 12,000 years ago, …. stalling at the start of the Younger Dryas, ….. and then re-starting their rise 1,000 years later at 11,000 years ago at the end of the YD. Glacial ice melting also stalled at about the 14,000 year date and re-started 1,000 years later.
Thus, the question is, …. why two (2) identical “1,000 year periods” of non-melting ….. right in the middle of a 15,000 year period of extremely quick melting of glacial ice? Could not the “freshwater” influx into the North Atlantic be a likely culprit for causing both?
Anyway, global temperatures had to have started rising long time before sufficient melt water could have been detected via said Sea Level Rise proxies.
If you have never seen the Illinois surface topography map produced by the Illinois State Geological Survey, go to their website and check out their online version. I don’t know of many other maps which so clearly show the power of melting glaciers. Much of the topography of NE Illinois (and really much of the state) was produced by the Kankakee Torrent–a sudden release of a vast amount of glacial melt water released about 15,000 years ago–which pushed the Mississippi river to its current position from the present Illinois River valley. It is so stunningly beautiful that it graces my office wall.
Steve Garcia
“The timing of the retreat of the Laurentide simply was too late. The serachd for outlet for the ice dam failure on Lake Agassiz had to be aborted. The timing killed the idea, and Wally accepts that.”
The timing was not so bad. Geological evidence of major outbreak of Lake Agassiz 13,000 yrs ago. Younger Dryas began 12,800 yrs ago. Off by 200 years. You need time for fresh water to travel from Beaufort sea to North Atlantic.
“the proponents have shifted to an outlet via the Mackenzie River north, across the Yukon, to the western Arctic – about as FAR away from the Atlantic as you can get in Canada”
Yes but the Bering Strait had a land bridge 12,000 yrs ago. Fresh water cannot flow to Pacific Ocean. It went under the frozen Arctic Ocean to Greenland Sea to North Atlantic. That took 200 years.
Dr. Strangelove says:
May 15, 2014 at 1:57 am
“Yes but the Bering Strait had a land bridge 12,000 yrs ago. Fresh water cannot flow to Pacific Ocean. It went under the frozen Arctic Ocean to Greenland Sea to North Atlantic. That took 200 years.”
——————
Great point about the land bridge but …… I have to question whether the Arctic Ocean was frozen over at that time and I’m inclined to believe that it wasn’t, as per, to wit:
=====================
“Holocene Treeline History and Climate Change Across Northern Eurasia
Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P.
Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern.
The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation.
http://www.sciencedirect.com/science/article/pii/S0033589499921233 ”
Thanks, Dr. Easterbrook.
I have a new article my climate pages showing an older version your “Temperature fluctuations over the past 17,000 years” graphic.
Samuel C Cogar says:
May 14, 2014 at 10:06 am
I’m with you on meltwater as the likeliest explanation for Dryas Events.
Dating the onset of not just the Holocene but previous interglacials is always open to discussion. The beginning of Holocene has most recently (JOURNAL OF QUATERNARY SCIENCE, 2009) been dated to ~11,700 calendar years BP (where “present” means AD 1950), rather than some other point, based upon Greenland ice core & “selected auxiliary records”.
http://www.stratigraphy.org/GSSP/Holocene.pdf
Upon reading my own source, I see that the definition of BP its authors used has been moved up to AD 2000 from 1950.