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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I’m sitting here this morning reading this in Sierra Vista, with the Murray Springs Clovis site about 10 miles out of town. Both the Science article and the journal abstract refer to 3 sites that are appropriately dated to the Younger Dryas. Unfortunately, they don’t name them. My impression is that Murray Springs is well dated, including with Clovis artifacts, and I would guess it is one of the three. If I remember correctly, the Murray Springs black mat layer (with alleged nano-diamonds) was correlated with other sites some distance away–like thousands of miles. One suggestion was that there may have never been an actual impact, only a disintegration causing huge damage along the object’s trajectory. Seems to this layman that 3 well-dated sites that far apart showing (if true) identical geological anomalies, is significant evidence for impact, even if all the others are irrelevant.
PS. Could someone with access, bring back the names of those three sites?
: > )
Listen to vukcevic , above.
The warming at number 7 on the chart, “Warming at end of Younger Dryas” looks unprecendented to me – the mother of all hockey sticks, for sure.
– – – – – – – – – –
Science in very blunt self-correction mode with that assessment of “conjured up “out of thin air” “.
I am also starting to enjoy the blunt scientific self-correction mode increasingly applied to the observation contradicting theory of significant AGW by fossil fuel.
John
The most telling evidence against the impact theory of the cause of the Younger Dryas (YD) is not the dating of impact craters–that just shows that a particular crater didn’t happen during the YD. Far more significant is that (1) we now know that the YD was a multiple event (I’ve mapped 9 YD separate moraines) not a single unique event, (2) the YD lasted 1000 years and you can’t keep dust in the air that long, (3) the YD ended just as suddenly as it began, and (4) the abrupt warm/cool climate changes near the end of the last Ice Age are not restricted to the YD (it’s the biggest one, but there are many others). You would need to have a lot of impacts for a long time.
If you want to see the geologic evidence for these, see “Multiple, intense, abrupt, late Pleistocene warming and cooling: Implications for understanding the cause of climate change” posted June 2, 2013 on WUWT and “The intriguing problem of the YD–what does it mean and what caused it?” posted June 19, 2012 on WUWT.
The abrupt and intense climate changes that occurred 10-15,000 years ago near the end of the last Ice Age are called Dansgaard-Oeschger Events, named after the scientists who discovered them in the first Antarctic ice cores and since found in the Greenland ice cores and in the glacial record. Dansgaard and Oeschger referred to them as ‘flickering’ of climate. No one has come up with really convincing evidence for their cause, but they are well documented. Broecker suggested changes in global ocean circulation, but that doesn’t work because climate changes in the Southern Hemisphere should lag the Northern Hemisphere by hundreds of years and we now know that these climate changes were simultaneous in both hemispheres. Understanding the cause is really important because if we knew that, we would be in a much better position to understand what causes major ice ages.
There is some similarity between the politics of the CO2 and asteroid impact debates, with the asteroids being the “consensus”, defended almost to the death by zealots against what are seen as attacks by a few souls brave enough to suggest problems with it.
I believe that careers have been ended by the asteroid zealots, but now it appears that that particular consensus was wrong, and volcanism may have been more significant.
Some commenters here asked for the alternative explanation for the cooling. Seems likely to me to have been just a rerun of the main ice age cooling event.
richard says:
May 13, 2014 at 4:29 am
what caused the rapid warming?
take that away and you get the rapid cooling.
——————————–
Exactly.
There are 28 of these rapid warming and rapid cooling events during the last ice age in the Greenland ice cores. Older, Younger and Oldest Dryas events were just one of these 28 phases.
The megafauna were adapted to live in an environment which had 2 km high glaciers covering the Earth down to 50N. The glaciers melted away, the environment changed, the grass turned into bushland, humans arrived on the scene and the megafauna died out at different intervals. Not a nice tidy story but its not hard to imagine how it all happened.
Any experts here? What happens when you freeze water? Does the O18 go with the ice or stay in the liquid water. If it stays behind (in the liquid), what happens when you melt the ice, lots of it? Would you get an anomalous dO18 as the melt water blankets the surface and would this anomaly be picked up in the ice cores?
My best estimate is that warming of the post glaciation period around 14300 BP was interrupted by a series( 4 to 5 separate major periods as shown by the blue lines) of global volcanic activity which put a lot of gas and particulate matter into our atmosphere. It took until 12000 BP for the atmosphere to clear and the warming to resume. People had to flee to caves and underground places for safe air in many regions
what caused the rapid warming? take that away and you get the rapid cooling.
Milankovitch cycles will have caused the warming. And that certainly can’t have caused the cooling.
Speaking of 2 km high glaciers melting in a short few thousand years, can you imagine how big the floods were and how wide the rivers flowing south got in the summer melt season. The Mississippi would have been impossible to ford unless your species could build good boats.
Don Easterbrook says:
May 13, 2014 at 7:06 am
“The most telling evidence against the impact theory of the cause of the Younger Dryas (YD) is not the dating of impact craters–that just shows that a particular crater didn’t happen during the YD. Far more significant is that (1) we now know that the YD was a multiple event (I’ve mapped 9 YD separate moraines) not a single unique event, (2) the YD lasted 1000 years and you can’t keep dust in the air that long…”
————————————————-
It seems unlikely (as Don mentions above) that an impact could have such a long term effect in such a discontinuous way. Same for volcanoes. Both would have immediate effect from which the Earth would recover quickly (maybe not so much the life forms). But to switch the Earth from warm to cold for 1,000 years and then quickly back to warm (from an asteroid or volcano) doesn’t seem logical.
Also these events are described as being world-wide and yet life flourished in Siberia and Alaska throughout this time period. Such as the Alaskan wolf (45,000 to 10,000 years ago) which survived the ice age, then the YD, but then disappeared. Their extinction is blamed on rapid global warming, which also makes no sense to me. At a time when humans were hunting caribou in record numbers the wolves went hungry?
The above pictured graph is not exactly to scale because it is intended to be a “reference diagram” for the author’s commentary. Here is the .jpg link to it:
http://wattsupwiththat.files.wordpress.com/2012/06/clip_image0021.jpg
If you want to see the above referenced central Greenland temperature proxy “to scale” …… then click on this .png link to this “Holocene Temperature Variations” graph ….. http://commons.wikimedia.org/wiki/File:Holocene_Temperature_Variations.png …. and observe the “light blue” line on said graph, which is the Greenland proxy data as per, to wit:
(light blue) GISP2 ice core, interpreted paleotemperature, Greenland: Alley, R. B.. Quaternary Science Reviews. doi:10.1016/S0277-3791(99)00062-1
And if you are interested in the relationship between the Holocene Temperature Variations proxies and the Post Glacial Sea Level Rise proxies ….. then click this link:
http://i1019.photobucket.com/albums/af315/SamC_40/HoloceneInterglacialmeltwatertemperatureMediumWebview.jpg
This very obviously is not a scientific study. It is speculation fronted by scare tactics just as the majority of CAGW articles are. Here in the states this whole exercise beginning with the creation of this study is a transparent attempt by the administration to divert attention from the colossal mistakes and misuse of power practiced by modern American politics. I not only disbelieve in this tactic but am appalled by the ignorance of those who take it seriously.
If this portrays contempt of the IPCC and it’s supporters in your mind…..congratulation you got it right.
Doug
johnmarshall says:
May 13, 2014 at 4:25 am
The conclusion was it wasn’t an impact. Beyond what the data and any given analysis shows, science has to leave room for “I don’t know”.
All things being equal :), as water freezes, O18 tends to concentrate in the remaining “liquid” water resulting in a relative increase in the ratio between O18/O16. Conversely, the O16 tends to concentrate in the “ice”. This process is readability observable as precipitation from sea level to higher altitudes (and latitudes {both high and low]) show strong fractionation between O16 and O18. As such large volumes of high (or very low) latitude ice, if rapidly melted and flooded the oceans may result in anomalous O16/O18 ratios for a limited time, but likely under a residence time unrecordable in the sediment record. For ice cores, I would believe that any significant melt would be discernible as a anomalous “missing” section mostly based on other distinguishing features besides stable oxygen isotope rations.
A bit annoying when reading a study raises more questions than it answers.
Don E
It seems to me the most likely influence on the YD would be a sudden change in the heating source. Has there been studies that show any solar factor in convincing ways? Being a geologist I have, of course some familiarity with proxy evidence, but do not recall such studies concerning the YD. I am quite sure however, it has nothing to do with carbon, or man, so in essence this issue being used to promote AGW, is pure obfuscation. A growing trend in the face of hypothesis failure.
My justification for considering this topic fraudulent rests primarily on the fact that I have never seen a hypothesis supported after such obvious lack of correlation to observed reality.
Many sketchy attempts to prop up this idea, including adjustment to the past records, ignoring evidence, and general anger from those who don’t appreciate our resistance to using pre-modern science to show that the emperor has no clothes, goes beyond science and towards religion.
In religion everything must be based on faith, thus providing wealth and power tp adherents, and pesky facts are considered heresy.
The climate issue is far closer to the religious system than the scientific one, and unlike many true believers I am still a scientist not an alchemist.
Doug
,
Whenever astrophysicists,geologists, warmists or some other body of ‘science’ does not know anything, they always invoke a rogue rock as the culprit. Lame. Maybe blame Hawking’s phantom spacemen from the ‘multiverse’. At least this paper tries to delve into some other reasons as to why an ice age occurred so quickly.
I’m going with too many mammoth BBQ pits causing soot in sky and blocking the sun – – Yup, man-made climate change!!
“pochas says:
May 13, 2014 at 7:24 am
Any experts here? What happens when you freeze water? Does the O18 go with the ice or stay in the liquid water. If it stays behind (in the liquid), what happens when you melt the ice, lots of it? Would you get an anomalous dO18 as the melt water blankets the surface and would this anomaly be picked up in the ice cores?”
Glacial melt water is depleted in 18O not because it froze but because the water had to EVAPORATE to be transported from the ocean to land. Evaporation rejects heavy isotopes similarly (and probably for the same reasons) as biological processes. Evaporative rejection is the basis for using 18O as a temperature proxy. It measures the amount of water stored as ice with higher concentrations of 18O being colder periods when more 16 is stored in ice.
The concept works well for periods when there is ice on the planet as there has been for the last 20 million years or so. The approach gets dicey when it is applied to the majority of the last half billion years when there has been no ice. During ice free times biological rejection may be seriously skewing the results, especially during extinction events.
Bottom line: They didn’t really “study” anything. Re-hashing existing data does not come under theheading of doing science. It’s just an excercize in statistics. If you give the same data set to ten different statisticians, you’ll get ten different results. And anyone who claims they can resolve a date thirteen thousand years ago to a resolution better than +/-100 years is living in a fantasy world anyway. So what the paper really illustrates is the sad state of the science of radiometric dating.
I’m not familiar with radiometric dating but I have heard that geochronologists can “do it for ages”.
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.
The name of the three sites:
Big Eddy, Missouri
Daisy Cave, California
Sheriden Cave, Ohio
These are listed in Figure 1 of the paper as “Sites with supposed YDB layer dated to 12.8 +/- 0.15 k cal BP”.