Widespread evidence of cosmic impact documented – likely cause of the Younger Dryas cool climate episode

From the University of California – Santa Barbara some paleoclimatology without the need to see hockey sticks.

Comprehensive analysis of impact spherules supports theory of cosmic impact 12,800 years ago

(Santa Barbara, California) –– About 12,800 years ago when the Earth was warming and emerging from the last ice age, a dramatic and anomalous event occurred that abruptly reversed climatic conditions back to near-glacial state. According to James Kennett, UC Santa Barbara emeritus professor in earth sciences, this climate switch fundamentally –– and remarkably –– occurred in only one year, heralding the onset of the Younger Dryas cool episode.

The researchers studied the impact spherules in 18 sites in nine countries on four continents for this study. Credit: YDB Research Group

The cause of this cooling has been much debated, especially because it closely coincided with the abrupt extinction of the majority of the large animals then inhabiting the Americas, as well as the disappearance of the prehistoric Clovis culture, known for its big game hunting.

“What then did cause the extinction of most of these big animals, including mammoths, mastodons, giant ground sloths, American camel and horse, and saber- toothed cats?” asked Kennett, pointing to Charles Darwin’s 1845 assessment of the significance of climate change. “Did these extinctions result from human overkill, climatic change or some catastrophic event?” The long debate that has followed, Kennett noted, has recently been stimulated by a growing body of evidence in support of a theory that a major cosmic impact event was involved, a theory proposed by the scientific team that includes Kennett himself.

Now, in one of the most comprehensive related investigations ever, the group has documented a wide distribution of microspherules widely distributed in a layer over 50 million square kilometers on four continents, including North America, including Arlington Canyon on Santa Rosa Island in the Channel Islands. This layer –– the Younger Dryas Boundary (YDB) layer –– also contains peak abundances of other exotic materials, including nanodiamonds and other unusual forms of carbon such as fullerenes, as well as melt-glass and iridium. This new evidence in support of the cosmic impact theory appeared recently in a paper in the Proceedings of the National Academy of the Sciences.

This cosmic impact, said Kennett, caused major environmental degradation over wide areas through numerous processes that include continent-wide wildfires and a major increase in atmospheric dust load that blocked the sun long enough to cause starvation of larger animals.

Investigating 18 sites across North America, Europe and the Middle East, Kennett and 28 colleagues from 24 institutions analyzed the spherules, tiny spheres formed by the high temperature melting of rocks and soils that then cooled or quenched rapidly in the atmosphere. The process results from enormous heat and pressures in blasts generated by the cosmic impact, somewhat similar to those produced during atomic explosions, Kennett explained.

Younger-Dryas-Boundary-Field-Map

The Younger Dryas Boundary strewnfield shown (red) with YDB sites as red dots and those by eight independent groups as blue dots. Also shown is the largest known impact strewnfield, the Australasian (purple).

But spherules do not form from cosmic collisions alone. Volcanic activity, lightning strikes, and coal seam fires all can create the tiny spheres. So to differentiate between impact spherules and those formed by other processes, the research team utilized scanning electron microscopy and energy dispersive spectrometry on nearly 700 spherule samples collected from the YDB layer. The YDB layer also corresponds with the end of the Clovis age, and is commonly associated with other features such as an overlying “black mat” –– a thin, dark carbon-rich sedimentary layer –– as well as the youngest known Clovis archeological material and megafaunal remains, and abundant charcoal that indicates massive biomass burning resulting from impact.

These are examples of impact spherules collected from different sites. Credit: YDB Research Group

The results, according to Kennett, are compelling. Examinations of the YDB spherules revealed that while they are consistent with the type of sediment found on the surface of the earth in their areas at the time of impact, they are geochemically dissimilar from volcanic materials. Tests on their remanent magnetism –– the remaining magnetism after the removal of an electric or magnetic influence –– also demonstrated that the spherules could not have formed naturally during lightning strikes.

“Because requisite formation temperatures for the impact spherules are greater than 2,200 degrees Celsius, this finding precludes all but a high temperature cosmic impact event as a natural formation mechanism for melted silica and other minerals,” Kennett explained. Experiments by the group have for the first time demonstrated that silica-rich spherules can also form through high temperature incineration of plants, such as oaks, pines, and reeds, because these are known to contain biologically formed silica.

Additionally, according to the study, the surface textures of these spherules are consistent with high temperatures and high-velocity impacts, and they are often fused to other spherules. An estimated 10 million metric tons of impact spherules were deposited across nine countries in the four continents studied. However, the true breadth of the YDB strewnfield is unknown, indicating an impact of major proportions.

“Based on geochemical measurements and morphological observations, this paper offers compelling evidence to reject alternate hypotheses that YDB spherules formed by volcanic or human activity; from the ongoing natural accumulation of space dust; lightning strikes; or by slow geochemical accumulation in sediments,” said Kennett.

“This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event.”

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73 Responses to Widespread evidence of cosmic impact documented – likely cause of the Younger Dryas cool climate episode

  1. omnologos says:

    PNAS, uh? Anybody please check for peer review, if any.

  2. Philip Mulholland says:

    This topic is starting to get interesting.

  3. RoHa says:

    Cosmic collisions! We’re doomed! (Again.)

  4. bueuf1 says:

    The crater..
    Center in Elko, Nevada..
    Diameter form Reno to Salt lake city..
    And form Las Vegas to Boise
    Too Big?

  5. Louis Hooffstetter says:

    The PNAS is publishing studies based on empirical data again?

    Break out the Champagne!

  6. kadaka (KD Knoebel) says:

    omnologos said on May 21, 2013 at 3:53 pm:

    PNAS, uh? Anybody please check for peer review, if any.

    Ahh, FINALLY found it!

    http://www.pnas.org/content/early/2013/05/17/1301760110.abstract

    Twenty eight authors?

    Edited* by Steven M. Stanley, University of Hawaii, Honolulu, HI, and approved April 9, 2013 (received for review January 28, 2013)

    and

    *This Direct Submission article had a prearranged editor.

    Is that anything like an answer?

  7. Allencic says:

    What an interesting article. Does the full article give a hint as to where the impact site is?
    I suppose Barbara Boxer will now want to increase the carbon tax to stop meteorite impacts.

  8. Wilcon says:

    Since it first came out in 2007, the Younger Dryas impact hypothesis has not been supported by other scientists who tried to replicate or test its conclusions. A 2011 review of the evidence concluded

    “In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD. Throughout the arc of this hypothesis, recognized and expected impact markers were not found, leading to proposed YD impactors and impact processes that were novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics. The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public.”

    http://www.sciencedirect.com/science/article/pii/S0012825211000262

  9. OK S. says:

    The Supporting Data makes an interesting read (30 pg PDF):
    http://www.pnas.org/content/suppl/2013/05/20/1301760110.DCSupplemental/sapp.pdf

  10. Pat Frank says:

    I wonder how much safer we’d be, including Jim Hansen’s grandchildren, if all the $ spent over the last 20 years on climate supercomputers and alternative energy tax subsidies had been spent instead on a near-Earth asteroid (NEA) monitoring system, and research into advanced propulsion.

  11. DaveG says:

    Pure science makes paleoclimatology very believable and a very interesting read. about 4 years ago I saw a documentary describing this event in detail – The end of the Clovis age, and is commonly associated with other features such as an overlying “black mat” and abundant charcoal that indicates massive biomass burning resulting from impact.

    See the Nova Doc: End of the Big Beasts
    Who or what killed off North America’s mammoths and other megafauna 13,000 years ago?
    By Peter Tyson
    Posted 03.01.09
    NOVA

    The Program explored many possible aspects of this dramatic climate change the most believable was a sudden asteroid impact Witch caused a mass extinction in most of North and South America.

    The most recent hypothesis, advanced by Kennett and 25 other scientists in a 2007 Proceedings of the National Academy of Sciences paper, concerns the proposed cosmic impact. Right about the time the Younger Dryas began and at least 15 of those 35 extinct mammals and arguably the Clovis culture itself appear to vanish abruptly from the fossil record—that is, right about 12,900 years ago—Kennett et al see markers of a major catastrophe. The markers lie in a thin layer at the base of a “black mat” of soil that archeologists have identified at over 50 Clovis sites across North America.

    Photo of archeologist Vance Haynes, who first discovered the “black mat” in this Arizona riverbed in the 1960s, points it out to geophysicist Allen West. shows the carbon band in the earths layers = Black Mat.

    http://www.pbs.org/wgbh/nova/evolution/end-big-beasts.html

  12. DaveG says:

    Correction: Witch’s nor magic did not change the climate

    : A sudden asteroid impact Witch caused a mass extinction in most of North and South America.

    Should read a sudden asteroid impact Which caused a mass extinction in most of North and South America.

  13. thingodonta says:

    “This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event.”

    Not quite so fast.

    Scientists in the extinction field should stop using language that is ‘either/or’, ‘primary cause’ ‘nearly all’, and should acknowldge that most extinction events as a result of a combination of processes. This sort of thing has plagued the K-T extinction event, for example, where it is known that rates of extinction before the bolide impact 65Ma were already higher than background, with significant volcanism at the time.

    To put it another way, if two detrimenetal ecological effects occur at the same time, doesn’t this make their overall effect larger than just one alone? Of course it does. Most viruses for example hit you harder when you are down, ie. they strike harder when you already weakened by something else. This is how people are killed by AIDS, it weakens resistance. Same, goes for extinction periods.

    So to claim ‘primary cause’ or ‘nearly all’ requires startling good evidence and time correlation. And yes there was in fact, another major factor that was around at the time-hungry humans. Humans like meat, they have a powerful baseball friendly lever to propel missiles from an arm at a safe distance, and they are already long-trained in how to make sharp hand tools to put on them. The large animals have not evolved to counter projectiles from a distance, in fact if anything their size makes them more vulnerable, a larger target is easier to hit, and gets more bang for buck.

    And I dont suppose there were any other minor impacts in all the previous ice ages? Only one thing was different the last time round in America at least-humans.

  14. Billy Liar says:

    The supplementary information for the paper is interesting. They found lots of Clovis artefacts when digging for their spherules.

  15. Looks like the evidence for wildfires is stronger than for a cosmic impact event.

    The real mystery about the YD is, that once it began, the climate was stable for 1300 years. Why didn’t the climate slowly return to the pre-YD event conditions over decades or even centuries?

  16. AnonyMoose says:

    bueuf1, I think the region around Elko, NV, that you’re looking at is the Great Basin. Yes, it’s too big, and geologists have other reasons for it.

  17. Darren says:

    I’ve lost track of the amount of times I have brought this up. This impact was detailed extensively by German Geologist Otto Muck. His book on the subject should be required reading for everyone on the planet. The reason it’s ignored is it’s title – ‘The Secret of Atlantis’. Yes it existed, yes it was the Bermuda Triangle, yes the impact sunk it completely causing a large magnetic disturbance also that lasted for thousands of years. Check out the mating migration of the Sargasso Sea Eels who still behave as if Atlantis was there. None of this is poppycock. Otto Muck used extensive PROOFS.

  18. Michael Cohen says:

    Where are the impact sites? Or were all of them structurally weak comet fragments that airburst? Are the spherules composed of material from the ground at impact sites or from cometary material?

  19. Policy Guy says:

    Based on earlier research into such an occurrence it was then believed to have resulted from collision with soft core (ice) comets that came in over the North Pole and impacted generally in the area of Hudson Bay and further south.

    Those area were completely covered by thousands of feet of thick ice sheets at the time. The theory goes on that the heat of these impacts melted substantial glacial ice and this fresh water proceeded to the Atlantic where is so disturbed the natural conveyor belt currents of the Atlantic that the Gulf Stream shut down.

    Impact into the ice sheets concealed all but trace data that indicate potential impact depressions that can be observed today.

    I don’t have his book in front of me as I write, but as I recall, the lead author of this original work was a scientist at the Lawrence Berkeley Labs, who with colleagues was investigation a sharp shift in atmospheric C13 at about that time that still gives erroneous dating results, if not properly accounted for.

    There is alot more to this current study.

  20. Rob says:

    Looks like a pattern I once saw of the Laacher See eruption . If I’m not mistaken that was around the same time frame.

  21. Max™ says:

    Reminds of the book Stone Spring, they called it the Sky Wolf there.

    http://en.wikipedia.org/wiki/Stone_Spring

  22. Comets cannot selectively kill large mammals (Mastodons, Sabre-Tooth Tigers) and leave small mammals (humans) alive.

    Humans, OTOH, can selective kill large mammals.

  23. Chris @NJSnowFan says:

    There was also a major impact about 5,300 years ago,
    What was in the bible is linked to to that impact..

  24. Wilcon says:

    I know they are not a definitive source but Wikipedia has quite a list of problems that other researchers have raised for this hypothesis. For example, just regarding the extinctions,

    “Since it is assumed the effects of the putative impact on Earth’s biota would have been brief, all extinctions caused by the impact should have occurred simultaneously. However, there is much evidence that the megafaunal extinctions that occurred across northern Eurasia, North America and South America at the end of the Pleistocene were not synchronous. The extinctions in South America appear to have occurred at least 400 years after the extinctions in North America.[19][32][33] The extinction of woolly mammoths in Siberia also appears to have occurred later than in North America.[19] A greater disparity in extinction timings is apparent in island megafaunal extinctions that lagged nearby continental extinctions by thousands of years; examples include the survival of woolly mammoths on Wrangel Island, Russia, until 3700 BP,[19][32][34] and the survival of ground sloths in the Antilles,[35] the Caribbean, until 4700 cal BP.[19] The Australian megafaunal extinctions occurred approximately 30,000 years earlier than the hypothetical Younger Dryas event.[36]”

    http://en.wikipedia.org/wiki/Younger_Dryas_impact_hypothesis

  25. Jeff Alberts says:

    The Program explored many possible aspects of this dramatic climate change the most believable was a sudden asteroid impact Witch caused a mass extinction in most of North and South America.

    Was she riding her Infinite Improbability Broom, powered by a Brownian Motion producer (say, a nice hot cup of tea)?

  26. Walter Dnes says:

    > sunshinehours1 says:
    > May 21, 2013 at 6:06 pm
    > Comets cannot selectively kill large mammals (Mastodons, Sabre-Tooth Tigers)
    > and leave small mammals (humans) alive.

    * Comet landed in, or airburst over, North America.
    * The Clovis culture was wiped out at exactly the same time

    I wouldn’t say it left humans alone.

  27. J.Seifert says:

    The website “The Cosmic Tusk” deals extensively with cosmic impacts and the YDB.
    Our latest paper, out this month, deals with another cosmic impact at 2193BC and the
    impact climate footprint, which always starts with massive global cooling in each and every case.
    JS.

  28. Jeff L says:

    The pattern of the YDB field is interesting – I wonder if you could deduce a likely impact location based on the shape ??

  29. Steve O says:

    Evidence for a near-extinction event within recent times was compiled by Immanuel Velikovsky, whose theories caused great controversy a half century ago. For some very interesting reading I recommend “Earth in Upheaval.”

  30. Dan Harrison says:

    “Since it first came out in 2007, the Younger Dryas impact hypothesis has not been supported by other scientists who tried to replicate or test its conclusions. A 2011 review of the evidence concluded:

    “In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests…”

    This 2011 review is outdated and has been discredited. Note the University of South Carolina, “PNAS: Topper site in middle of comet controversy”
    By Peggy Binette, peggy@mailbox.sc.edu, 803-777-7704.
    http://www.sc.edu/news/newsarticle.php?nid=4706#.UZwgxeDZpSo
    2012 Independent study of micro-spherules related to an extra-terrestrial impact hypothesis is published in the Proceedings of the National Academy of Sciences using Clovis-age sediments from Topper that confirm the original 2007 Firestone study.
    2013 The pre-Clovis occupation of Topper will be presented in October at the international conference on the peopling of the Americas, titled “Paleoamerican Odyssey,” in Santa Fe, N.M. http://www.paleoamericanodyssey.com/

    I first read of a similar impact theory several decades ago, and I once had a very old book with chapters of descriptive data supporting a collision theory on the North American continent causing massive flooding and changing the course of the St. Lawrence River. But I believe the correct date for this is 12,800 BC, not 12,800 years ago. The original theory was about a strike occurring every 5,000 years. In other words a very large comet in a 5,000-year orbit would leave a debris trail through which Earth passed approximately every 5,000 years beginning at least 22,000 years ago. Hence, there would be multiple strikes over a period of years each cycle. I’ve seen articles describing significant impacts in Chad and Chili roughly 5,000 years ago, or approximately 2,800 BC, not just North America. Something tumultuous happened in this timeframe around the world possibly initiating the pyramid building (or rebuilding and expansions) in Egypt and other locations as well as providing the foundations for both pagan and modern religions.

    Note that there is evidence of geological effects in Yellowstone as well in this timeframe. And this is when most of the extinctions occurred (including extinction of “most” human populations in the new World. One apparently remained in New Mexico.) There was also evidence of a strike 18,000 years ago and 22,000 years ago discussed in the book. This timing fits the Maya cyclic calendar and similar Egyptian stories of cyclic destruction of civilizations going back well before 22,000 years ago.

    Did we escape this cycle for good when Showmaker-Levy 9 collided with Jupiter in 1994, or will we see it again after the spectacular comet flyby anticipated this Fall.

  31. Don Easterbrook says:

    There are several compelling lines of evidence showing that the Younger Dryas (YD) was NOT caused by a cosmic impact or other single event. Aside from the fact that cosmic material in YD sediments doesn’t prove a cause-and-effect relationship (correlation isn’t proof of causation), the YD lasted for about 1,300 years, which is far too long for atmospheric dust not to have fallen to the ground. Even more compelling evidence is that the YD is not a simple, single climatic event–it was a series of repeated oscillations of climate each lasting several hundred years. In Scotland, Washington state, and various other places, glaciers advanced and retreated not only during the YD, but also during the preceding late Allerod cold period. The glaciers advanced and retreated as many as 8-12 times during Allerod/YD period and is thus not explainable by a single cosmic event. There were also a number of similar glacial oscillations during the preceding several thousand years. A cosmic event cannot explain the long duration (1,300 years) of the YD nor the multiple oscillations.

  32. Jean Parisot says:

    “Experiments by the group have for the first time demonstrated that silica-rich spherules can also form through high temperature incineration of plants, such as oaks, pines, and reeds, because these are known to contain biologically formed silica.” I hope this part will be released as a stand alone scientific paper that can be replicated and tested.

    As for the rest, I don’t see how we can move beyond the various hypotheses, but I am willing to accept that major cosmic impacts are bad for those under them. Not sure how they change the climate for a millennium, especially when it in a clear phase change.

  33. TimTheToolMan says:

    Don writes “the YD lasted for about 1,300 years, which is far too long for atmospheric dust not to have fallen to the ground. Even more compelling evidence is that the YD is not a simple, single climatic event–it was a series of repeated oscillations of climate each lasting several hundred years”

    There is no need for dust at all. If a number of those collisions were in the ocean (as they appear to have been from the thread’s graphic) then they would have massively stirred up the waters and brought the near freezing water from the bottom up to the surface which would have immediately snap frozen the earth. Then the oceans would have taken a long time to get back to their equilibrium and could easily have involved a number of oscillations. And furthermore impacts into the ocean are going to be very hard to spot and maybe even impossible.

  34. Steven Mosher says:

    J.Seifert says:
    May 21, 2013 at 7:01 pm

    Thanks Nice web site..

  35. Adam says:

    This kind of sudden catastrophic phase change can occur naturally without external stimulus in a suitably chaotic physical system. What we perceive to be a stable state is only a quasi-stable state, it’s dominance ends and is replaced by another state. Only our arrogance leads us to believe that it is a stable state.

  36. edwardt says:

    http://m852.photobucket.com/albumview/albums/etregembo/YDComparison.jpg.html?newest=1

    Maybe the cosmic impact is cyclic and responsible for the abrubt entrance and exit of the warm pulses that are very evident and cyclic in the gisp2 glacial periods? I think we have to understand the origin of the roughly 1200yr pulses before we can discuss the yd event. Unless they share a common origin of course, otherwise we are discussing multiple and simultaneous events, the primary being the 1200 yr cycle, the lesser maybe the impacts discussed above.

  37. bushbunny says:

    The thing is with this argument, is that a lot of mega fauna evolved and adapted. The North American giant buffalo for example. Modern Homo sapiens sapiens, were present in Europe from about 40,000 years ago at the height of the last glacial period. Australian Aborigines were here too possibly for 60,000 from first contact, or subsequent waves of immigrants from SE Asia. In Europe the new genus of humans from Africa, they brought with them better hunting techniques and gathering, possibly fishing techniques, possibly they bred quicker than the Neanderthals. We don’t know for sure. Animals that survived and adapted, they grew smaller from necessity, and also gestation times became shorter aiding survival rates. If a meteor not so much a comet, hit earth we would be in trouble. And asteroids are coming past us every year. The problem is if they are coming from the direction of the sun, we won’t see them until it is almost too late. Space is a big place, but I would be worried if the moon was hit and it changed its orbit. There are many variables involved, but suffice to say, North America was not occupied by humans until 10,000 years ago. And they would have come via the Bering Straights bridge initially. (Not by boat as some have suggested in the past). Oh – I am sure you know this anyway, but don’t wish a mini ice age or ice age on us. Every read, Colleen McCollochs ‘Creed of the Third Millenium’ do – you’ll switch your electric blanket on even in mid summer.

  38. OK S. says:

    J.Seifert says:
    May 21, 2013 at 7:01 pm

    Mosher is right. Nice site:
    http://cosmictusk.com/

  39. Ralph LeVitt says:

    Is this stuff shocked quartz or what? Nothing in the article states what the spherules are composed of.

    Hey, Tony, if you know someone with a helicopter(I thought of rappelling down there, but the knees aren’t what they used to be), check out the “deep hole” just west of Mt. Lassen. Classic signs of an impact crater. Approx. 1km wide by 1/2km deep, flat sandy bottom, with upturned sides… Everyone I ask says it’s a collapsed caldera, but impact craters can happen even in volcanic areas, can’t they? Msg me for map, aerial images, & coords.

  40. denniswingo says:

    Interesting, no one is mentioning the book “World’s in Collision” by Immanuel Velikovsky

    http://en.wikipedia.org/wiki/Immanuel_Velikovsky

    While I don’t agree with his extrapolations regarding planetary collisions I do think that he assembled some pretty interesting evidence that should be investigated related to the YD (possible) impact.

  41. Chris says:

    This is indeed interesting, because we have two groups of scientists slugging it out, with the anti-impact “team” being completely dismissive if not outright abusive of the “team” promoting the impact. (Sound familiar?)

    As alluded to by earlier posters, what will determine the fate of this theory is the finding of an impact crater. With nanodiamonds and impact-produced spherules, there must be a significant impact crater — i.e. this object wasn’t stopped from reaching the ground by mile-thick ice sheets.

    Regarding Velikovsky, I’ve read his book and let’s just say it’s lacking in scientific rigour. There are many grounds that can be used to invalidate his claims. However, it’s interesting to note that his basic interpretation of the universe (catastrophism) is much closer to our current view than the scientific consensus of his time, which posited a pleasant, well-ordered, steady-state universe that didn’t really change much, and where not much bad happened.

  42. vukcevic says:

    Nastapoka Arc?
    http://www.vukcevic.talktalk.net/NArc.htm
    I am not saying that it is, but it must be a leading candidate. Impact was likely to be from a huge ‘lump of iron’ meteorite, slowly sinking into the crust, with sections of it reaching Curie temperature of iron around 770 degrees C, judging by the decline in the magnetic intensity of the area. Distinct coincidence between Magnetic and Gravity anomalies indicates something extraordinary.

  43. Twawki says:

    The Australian megafauna extinctions happened 30,000 years earlier, other countries also at different times

  44. richard verney says:

    Yesterday in the Daily Mail, it was suggested that this episode explained why the Mamouths became extinct. I am somewhat sceptical since the Mamouth was well equipped for the cold and went extinct but other grazing animals that were not so well equipped survived (horses, cattle, elephants etc).

  45. richard verney says:

    sunshinehours1 says:
    May 21, 2013 at 6:06 pm

    Comets cannot selectively kill large mammals (Mastodons, Sabre-Tooth Tigers) and leave small mammals (humans) alive.

    Humans, OTOH, can selective kill large mammals.
    /////////////////////////////////
    Humans are very adaptable, take refuge in caves, keep warm with animal skins/furs, camp fires and the like and can change their diet etc. I can see humans surviving because of their adaptability.

    What surprises me is that some of the animals that were adapated for cold did not survive whereas others which were not so adapted did survive.

    Climatically, the YD is very interesting and we need to understand more about the changes in this period.

  46. John says:

    This controversy, with the attacks on both sides, reminds me a bit of the controversies when younger geologists proposed the plate tectonic theory, and the old boars said it was impossible. When the old boars died off, there were no longer any critics of plate tectonics. The younger scientists had done the new science.

    In this case, it isn’t old boars vs. younger scientists, but it has the same level of intensity. Having read some of the Supporting Data

    (http://www.pnas.org/content/suppl/2013/05/20/1301760110.DCSupplemental/sapp.pdf

    it seems to me that the cosmic impact hypothesis, and not its critics, have the upper hand.

    If the burning of grasslands and forests occurred in fall or winter, megafauna grass eaters would have nothing to eat, and would die. So would their megafauna predators. Maybe in the summer as well, if the burning was complete enough and any regrowth slow or incomplete.

    The megafauna that went extinct almost immediately would be those that lived ONLY in the temperate to steppe habitats of Mexico through almost all of Canada (except the Yukon and Arctic islands). The ones that survived — like mammoths — also lived in Siberia and Alaska.

    Smaller creatures would obviously die as well, but many could survive. For example, when Mt. St. Helens blew, scientists thought that there would be no survivors. But pocket gophers and other creatures that lived in burrows did survive. They had stored food, and the next spring, when things started growing again, there they were.

    And of course, lots of small animals with widespread distribution into Central America could have repopulated North America, as with elk, moose, and bears coming from Siberia during the Younger Dryas.

  47. William Astley says:

    Younger Dryas Burn marks

    Don Easterbrook says:
    May 21, 2013 at 7:35 pm

    A cosmic event cannot explain the long duration (1,300 years) of the YD nor the multiple oscillations.

    William:
    I support your comment. What you point out is one of the facts concerning the Younger Dryas abrupt cooling. There needs to be a mechanism explanation as to what could abruptly cool the planet, 12,900 years ago during a period when insolation at N65 has at maximum for 1,300 years.

    William:
    The following is additional information concerning the burn marks, Heinrich events, abrupt climate change, and the recent discovery of pseudo cyclical geomagnetic excursions.

    Due to the known physics of the atmosphere, confirmed by observations as to how the planet has responded in the past, to step forcing changes: the duration of cooling due to comet or meteoroid impact cooling will be and must be similar in duration to the cooling of a large volcanic eruption: Four, five, at most seven years of cooling. As Dr. Eastbrook points out it is a fact that the Younger Dryas abrupt cooling occurred for 1300 years. The Younger Dryas cooling cannot be explained by cooling due to extraterrestrial object impact.

    The Younger Dryas abrupt cooling event has the same climatic signature as a Heinrich event. Heinrich events are pseudo periodic (with an interval between Heinrich events of 6000 years, 8000 years and 12,000 years) Heinrich events it appears are very, very, strong Dansgaard-Oeschger cycles as they occur in the pseudo cyclical period time of a D-O cycle. The D-O cycles have an interval between events of either 950 years, 1350 years, or 2000 years.

    As the Younger Dryas has the same climatic signature as a Heinrich event, it is often called Heinrich event 0. Heinrich events are abrupt climate change events. It should be noted the past interglacial periods ended abruptly, not gradually. There is a signature in the paleo climatic record of abrupt climate change, including abrupt onset of interglacial periods and abrupt termination of interglacial periods. It appears whatever causes the Heinrich events is the same mechanism that initiates and terminates the interglacial periods.

    In the last decade the geomagnetic field specialists have found that there are either full geomagnetic excursions or suppressed geomagnetic excursions that occur at the same time as the Heinrich events. It has been recently found that there are full geomagnetic excursions that occur at the termination of the past interglacial periods. There is a for example a geomagnetic excursion that occurs at the termination of the last interglacial period the Eemian. The discovery of frequent geomagnetic excursions was not expected as it cannot be explained by a core based geomagnetic field theory: the excursions occur too rapidly and too frequently, it seems the liquid core cannot abrupt change, stop, and 30k years later again abruptly change.

    Astrophysicists have pointed out that a comet or meteoroid impact is a plausible explanation if there were burn marks at one or perhaps two locations on the planet that occurred at the same time. i.e. A comet might break up and strike the earth at one or two locations. An extraterrestrial impact hypothesis cannot however explain burn marks at 18 different locations in the Northern Hemisphere on different continents and at different latitudes on the continents (look at the locations of where the Younger Dryas burn marks occurred). Comets are impacts are very, very, rare. Burn marks on different continents at different latitudes and with regional clustering of burn marks would require multiple comets that are all of the goldilocks size to burn the planet’s surface but not leave an impact mark. That seems unlikely to the point that that it rules out that mechanism as an explanation for what caused the burn marks.

    The burn marks still requires a physical explanation. This paper notes that the burn marks at 18 different locations in the Northern hemisphere require a mechanism that is capable of causing very hot temperature of greater than 2200 Celsius concentrated in 18 different regions to produce what is observed.

    As noted above, there also needs to be an explanation for the recurring geomagnetic excursions. It should be noted that there are other burn marks on the planet surface (Carolina Bay burn marks) which occurred tens of thousands years before the Younger Dryas burn marks.

    http://en.wikipedia.org/wiki/Heinrich_event
    Heinrich event
    Heinrich events, first described by marine geologist Hartmut Heinrich, occurred during the last glacial period, or “ice age”. … ….Heinrich events are global climate fluctuations which coincide with the destruction of northern hemisphere ice shelves, and the consequent release of a prodigious volume of sea ice and icebergs. The events are rapid: they last around 750 years, and their abrupt onset may occur in mere years (Maslin et al.. 2001). Heinrich events are observed during the last glacial period; the low resolution of the sedimentary record before this point makes it impossible to deduce whether they occurred during other glacial periods in the Earth’s history. … ….Heinrich events occur during some, but not all, of the periodic cold spells preceding the rapid warming events known as Dansgaard-Oeschger (D-O) events, which repeat around every 1,500 years. However, difficulties in establishing exact dates cast aspersions on the accuracy—or indeed the veracity—of this statement. Some (Broecker 1994, Bond & Lotti 1995) identify the Younger Dryas event as a Heinrich event, which would make it H0.

    Heinrich estimated dates of occurrence from Hemming (2004)
    H0 ~12kyr BP, H1 16.8kyr BP, H2 24 kyr BP, H3 ~31 kyr BP, H4 38 kyr BP, H5 45 kyr BP, H6 ~60 kyr BP

    William: The author of the next paper appeals to changes to the earth’s inertia to explain the geomagnetic excursions. That hypothesis would requires a separate different mechanism to cause the abrupt change to the ice sheets. The change in mass of the ice sheet is then hypothesized to causes changes to the liquid core that in turn cause the abrupt short duration geomagnetic excursion.

    The author’s hypothesis is not correct. The burn marks cause the geomagnetic excursions. The burn marks are caused by massive electrical charge discharges from the ionosphere to the surface of the planet. The massive electrical charge movement causes the geomagnetic excursion. A geomagnetic excursion is capable by Svensmark’s mechanism of cooling the planet for 750 to 1300 years. When the geomagnetic field recovers after the abrupt external forcing event (the signature of the external forcing function is burn marks on the surface of the planet) the cooling period ends.

    http://en.wikipedia.org/wiki/Heinrich_event
    Heinrich events are global climate fluctuations which coincide with the destruction of northern hemisphere ice shelves, and the consequent release of a prodigious volume of sea ice and icebergs. The events are rapid: they last around 750 years, and their abrupt onset may occur in mere years (Maslin et al.. 2001). Heinrich events are observed during the last glacial period; the low resolution of the sedimentary record before this point makes it impossible to deduce whether they occurred during other glacial periods in the Earth’s history.
    Heinrich events occur during some, but not all, of the periodic cold spells preceding the rapid warming events known as Dansgaard-Oeschger (D-O) events, which repeat around every 1,500 years. However, difficulties in establishing exact dates cast aspersions on the accuracy—or indeed the veracity—of this statement. Some (Broecker 1994, Bond & Lotti 1995) identify the Younger Dryas event as a Heinrich event, which would make it H0.

    Diagnosis of Heinrich events
    Heinrich’s original observations were of six layers in ocean sediment cores with extremely high proportions of rocks of continental origin, “lithic fragments”, in the 180 μm to 3 mm size range (Heinrich 1988). The larger size fractions cannot be transported by ocean currents, and are thus interpreted as having been carried by icebergs or sea ice which broke off from the large Laurentide ice sheet then covering North America, and dumped on the sea floor as the icebergs melted. The signature of the events in sediment cores varies considerably with distance from the source region—there is a belt of ice rafted debris (sometimes abbreviated to “IRD”) at around 50° N, expanding some 3,000 km (1,865 mi) from its North American source towards Europe, and thinning by an order of magnitude from the Labrador Sea to the European end of the present iceberg route.

    http://www.iisc.ernet.in/currsci/apr252003/1105.pdf
    The effect of changes in the Earth’s moment of inertia during glaciation on geomagnetic polarity excursions and reversals: Implications for Quaternary chronology
    Geomagnetic polarity reversals and excursions in the Quaternary correlate well with interglacial-to-glacial transitions and glacial maxima. It is suggested that this relationship results from interactions between the Earth’s mantle and core that accompany decreases in the Earth’s moment of inertia during ice accumulation, which weaken the geomagnetic field in order to try to counter the decrease in differential rotation between the mantle and inner core that is being forced. In the Late Pleistocene, geomagnetic excursions directly correlate with brief phases of rapid ice growth that accompany falls in global sea-level, notably during the Younger Dryas stage, Dansgaard–Oeschger interstadials 5 and 10 that precede the rapid melting events during Heinrich events H3 and H4, and during the transitions between oxygen isotope stages 5c-5b, and 5e-5d. It is proposed that similar relationships between instabilities in climate and the geomagnetic field also typefied the Middle Pleistocene. As a result of the transfer of some of the mass of the oceans into polar ice sheets, the climate instabilities that initiate these rapid ice accumulations redistribute angular momentum and rotational kinetic energy between the Earth’s mantle and inner core. These changes weaken the Earth’s magnetic field, facilitating geomagnetic excursions and also causing enhanced production of cosmogenic nuclides, including 14C. The subsequent phases of rapid ice melting, Heinrich events, reverse this effect: strengthening the field. This explanation, of forcing of geomagnetic excursions by climate instabilities, provides a natural explanation for why, during the Middle-Late Pleistocene, excursions have been numerous but none has developed into a polarity reversal: the characteristic duration of the climate instabilities is too short.

    William:
    This is the geomagnetic excursion that caused the Younger Dryas abrupt cooling. As noted above an geomagnetic excursion cools the planet by Svensmark’s mechanism. Depending on the orbital configuration at the time of occurrence of the burn marks, the massive electrical discharge from the ionosphere to surface of the planet will eventually (the geomagnetic field and charge differential equalize, reaching their normal steady state condition) cause an increase or decrease in the intensity of the geomagnetic field. The geomagnetic field intensity is roughly 3 to 4 greater during the interglacial period.

    The massive ice sheets on the surface of the planet insulate the planet from the ionosphere affecting the location where the charge strikes the earth. This explains why as the planet cooled the glacial/interglacial cycle changed from a cycle of 41 kyrs to 100 kyrs.

    http://www.sciencedirect.com/science/article/pii/003358947790031X
    The Gothenburg Magnetic Excursion
    The Gothenburg Magnetic Excursion in a broad sense ranges from 13,750 to 12,350 years BP and ends with the Gothenburg Magnetic Flip at 12,400−12,350 years BP (= the Fjärås Stadial in southern Scandinavia) with an equatorial VGP position in the central Pacific. The Gothenburg Magnetic Flip is recorded in five closely dated and mutually correlated cores in Sweden. In all five cores, the inclination is completely reversed in the layer representing the Fjärås Stadial dated at 12,400−12,350 years BP. The cores were taken 160 km apart and represent both marine and lacustrine environments. The Gothenburg Magnetic Flip represents the shortest excursion and the most rapid polar change known at present. It is also hitherto the far best-dated paleomagnetic event. The Gothenburg Magnetic Excursion and Flip are proposed as a standard magnetostatigraphic unit.

    http://adsabs.harvard.edu/abs/2004E%26PSL.219..377T

    Geomagnetic moment variation and paleomagnetic excursions since 400 kyr BP: a stacked record from sedimentary sequences of the Portuguese margin

    http://www.esd.ornl.gov/projects/qen/transit.html
    According to the marine records, the Eemian interglacial ended with a rapid cooling event about 110,000 years ago (e.g., Imbrie et al., 1984; Martinson et al., 1987), which also shows up in ice cores and pollen records from across Eurasia. From a relatively high resolution core in the North Atlantic. Adkins et al. (1997) suggested that the final cooling event took less than 400 years, and it might have been much more rapid.

    A paleomagnetic study was performed in clayey-carbonate sedimentary sequences deposited during the last 400 kyr on the Portuguese margin (Northeast Atlantic Ocean). Declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction. The normalized intensity documents a series of relative paleointensity (RPI) lows recognized in other reference records. Three directional anomalies occurring during RPI lows chronologically correspond to the Laschamp excursion (42 kyr BP),the Blake event (115-122 kyr BP) and the Icelandic basin excursion (190 kyr BP). A fourth directional anomaly recorded at 290 kyr BP during another RPI low defines the ‘Portuguese margin excursion’. Four non-excursional RPI lows are recorded at the ages of the Jamaica/Pringle falls, Mamaku, Calabrian Ridge 1,and Levantine excursions. The RPI record is characterized by a periodicity of V100 kyr,paleointensity lows often coinciding with the end of interglacial stages. This record sets the basis of the construction of an authigenic 10Be/9Be record from the same sedimentary sequences [Carcaillet et al.,this issue].

    http://gji.oxfordjournals.org/content/140/1/F1.full.pdf
    Is the geodynamo process intrinsically unstable?
    Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal’ state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30 to 100 kyr; it may not therefore be as stable as we thought.

  48. mogamboguru says:

    Rob says:
    May 21, 2013 at 5:55 pm

    Looks like a pattern I once saw of the Laacher See eruption . If I’m not mistaken that was around the same time frame.
    ——————————————————————————————————————-
    Um, not exactly, Rob.

    The Laacher See volcanic (groundwater/steam) explosions occured around 10,000 BP – i.e. almost 3000 years after the spherule-inducing event in question here.

    I know – because my family is from that Laacher See area – although I must admit that family-records back to 10,000 BP are few and far between – especially during the early years.

    What I can say, though, is that my hunter-gatherer-ancestors seemed to have survided that Lacher See-eruption quite well and lived through it to hunt another deer or horse the next day – because, hey: Here I am, am I not…?

  49. beng says:

    ***
    sunshinehours1 says:
    May 21, 2013 at 6:06 pm

    Comets cannot selectively kill large mammals (Mastodons, Sabre-Tooth Tigers) and leave small mammals (humans) alive.
    ***

    Funny, but that seems (substitute large dinosaurs) exactly what happened 65 million yrs ago.

  50. Bill Illis says:

    Clovis spearpoints are certainly stunning pieces of work and each one of us would like to be able to throw one of those big spears at something.

    But they were abandoned when more efficient hunting techniques like the atlatl / dart system was brought in across the Bering land bridge.

    No human would ever use a Clovis spear again after watching how easy an atlatl worked. It would have spread around the continent very rapidly as happened with all such large technological leaps. Humans have almost always had contact with neighboring groups.

    My guess is this happened in North America right around the YD event naturally.

  51. MarkW says:

    sunshinehours1 says:
    May 21, 2013 at 6:06 pm

    Comets cannot selectively kill large mammals (Mastodons, Sabre-Tooth Tigers) and leave small mammals (humans) alive.
    —————–
    Actually they can, and do. By distrupting the environment.

  52. Heber Rizzo says:

    Well, let’s accept that this was the cause of the Younger Dryas cooling. But then… what was the cause of the subsequent great and rather fast warming. SUVs and damned fosil fuels Clovis technology?

  53. Steve Keohane says:

    As regards a comet selectively killing the large mammals; a massive loss of flora for a single season due to an impact object would have that result. As regards the atlatl making the Clovis culture tools obsolete; the atlatl has been used since the ice ages began, a few 100K years ago. Long enough ago to have been used by the first humans to the Americas, however they arrived.

  54. James at 48 says:

    More excellent work from Los Gauchos.

  55. The Wikipedia artcile debunking this theory linked to this paper claiming that the megafauna were already dying off well before the impact event:

    “Megafaunal populations collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the Bølling-Allerød warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling and the extraterrestrial impact event proposed to have occurred 12,900 years ago.”

    http://adsabs.harvard.edu/abs/2009Sci…326.1100G

    If some argue that the Clovis people also died out, I would suggest they died out for the same reasons the megafauna died or because the megafauna died out ruining food supplies.

    – Part 2 —

    However, what caught my attention and set off my AR5 BS detector was this quote:

    “”Whatever this was, it did not cause the extinctions,” Tankersley says. “Rather, this likely caused climate change. And climate change forced this scenario: You can move, downsize or you can go extinct.” http://phys.org/news/2013-05-mammoth-lament-cosmic-impact-devastating.html

    Sorry, but this is just AR5 “Climate Change Kills” Bull****.

  56. An explanation that rings truer.

    “Northern mammoth populations grew after the Last Glacial Maximum, but then dipped again during the Younger Dryas period about 12,900 years ago. Although there is controversy as to what happened at that time, “there was certainly a very rapid and profound cooling of many regions then, followed by rapid warming,” MacDonald said. “Did this cause the extinction of the mammoth? Absolutely not. They were still present in far northern sites at the end of the Younger Dryas. Right now it’s not quite definitive how great an impact the Younger Dryas had.”

    The last mammoths seen on the continents were concentrated in the north. They apparently disappeared about 10,000 years ago as the climate warmed and peatlands, wet tundra and coniferous forests developed, environments to which mammoths were poorly suited. The long-lasting proximity between mammoths and humans suggested that our species was perhaps a factor in the beasts’ decline, possibly killing off the final island populations of woolly mammoths that went extinct 3,700 years ago.

    Overall, these findings suggest the mammoths experienced a long decline due to many factors.”

    http://www.livescience.com/20894-woolly-mammoths-extinction.html

  57. John another says:

    Jeff L says:
    May 21, 2013 at 7:07 pm

    “The pattern of the YDB field is interesting – I wonder if you could deduce a likely impact location based on the shape ??”
    IIRC, there is a website devoted entirely to hundreds if not thousands of impact craters in West Texas and Northern Mexico from this time. I don’t have the time at the moment to give you more but I do think the YDB event was not a single impact. Rather it was a shotgun blast from a very large object that broke up at some distance from the surface. As for the 1300 years of the remaining YD I do not know the mechanisms involved.

  58. M E Wood says:

    http://en.wikipedia.org/wiki/Ahrensburgian How European tribes coped with the Younger Dryas

  59. E.M.Smith says:

    I’m also going to second the notion of following the Cosmic Tusk site.

    FWIW, one of the major Nickle and Platinum Group Metals mines is in a place in Canada that is the ideal location for the major impact site into the ice field. The land around it evidences “burn through ice” effects. A large incoming bolide with break-up also accounts for the various smaller “burn mark” areas scattered around (and SL-9 into Jupiter showed break up happens outside the atmosphere from near misses of other objects…).

    The ejecta from the Canadian impact landed in S. Carolina making a set of “bays” there with a particular shape and orientation that points back at the primary impact site.

    As per the 1200 – 1300 year disruption: We had a MAJOR flood of water into the oceans from that impact vaporizing megatons of ice. That screws up the ocean cycles until things reorganize. It happened right as we were heading out of a ‘stable cold’ into a ‘stable warm’ pattern and truncated the “stable warm” until things got back on cycle.

    Per Humans and Clovis not being extinct: Um, need I point out that the majority of the Clovis folks DID get extirpated? New folks came over from Asia and repopulated, and a small remnant of Cloves in New Mexico got absorbed into the new population. The (then) largely European type Clovis culture was effectively replaced with an Asian type.

    It is also likely that the impact sent a wall of ice / slush over the pole into Siberia and accounts for the “sudden” burial of mammoths with food still being eaten / digested and the general chaos in the layer of permafrost of that era with all sorts of critters and not so tundra like plants in a jumbled mix. It was a tidal wave of slushy mud that hit them and then set up again.

    (I would expect “interesting things” to be found in Arctic ocean bottom sediments, but doubt folks have looked much due to the ice cover…)

    The impact likely also is the reason that the typical “peak and plunge” shape of other interglacials was, for us, truncated into a “not quite a peak and 10,000 years of flat”. Instead of a heating over shoot, we got ‘truncated’ with a cold spell and more or less stabilized. Now we’ve had our warm duration and the W/m^2 more than 60N degrees is on the edge of falling back into glacial stability mode (we are presently roughly in the ‘metastable’ zone as we leave ‘stable warm’ and the Little Ice Age was the first manifestation of that ‘metastable’… next cold plunge will be non-recoverable, but ought not to come for about 300 more years, IFF we are lucky…).

    The notion of a “Stable pleasant time” like the Holocene is a fantasy. It was entirely an accident of that impact ‘peak clipping’ the usual “Peak and Plunge”. As soon as our 425 W or so drops below about 416 W/m^2 60 N we go cold and stay there. ANYTHING we can do to keep more heat up north gives us more time before the next freeze / glacial cycle. We want and NEED a hotter arctic. More so every century as the orbital mechanics move inevitably toward ever more “unstable to cold” pattern.

  60. milodonharlani says:

    E.M.Smith says:
    May 22, 2013 at 4:24 pm
    ————————————–

    Well reasoned comments based upon discoveries & hypotheses of recent decades.

    IMO it took quite a while before the “European-like” elements were replaced by the Asian. “Caucasoid” Kennewick Man, with an Archaic point in his hip, died c. 9300 BP or earlier, but in any case long after the Younger Dryas.

  61. Big Al says:

    Vukcevic
    I have often wondered about Hudson’s Bay general shape. It seems too circular to be a natural part of the normal earth, the magnetic anomaly really makes it interesting.

  62. E.M.Smith says:

    @milodonharlani:

    The likely impact point is in East Canada, so from that POV, western N. America is far away and “over the top” of the pole for some bits. I would expect that the Clovis folks would have a remnant across the very south west, and potentially up into Washington. Extirpation was likely limited to the center / east arc, but the disruption to big game would have prevented effective repopulation for a long time. Then the added Asian types showed up and did the major repopulation.

    If you look into Native American genetics, it’s a very interesting “mix”. More Asian on the west coast, more European on the east coast (even among those with “pure” ancestry – so not a recent admixture – and visible in the early paintings / photos prior to significant European invasion and colonization. You find specific alleles that only ‘make sense’ if there were an earlier European type population that “blended” with a later Asian type (likely in several waves) and with the locus of Asian arrivals being land bridge down the West Coast. (Oddly, too, there’s a batch of genetic and material goods that indicate a Japanese cluster in South America from folks escaping a volcanic event long long ago; so one of the “tribes” in, IIRC, Peru, is effectively Japanese from early historical times. There may also be a trace of Chinese genetics, but that’s hard to tease out of the general Asian base.) More speculative, there’s some evidence for an African / black genetic component in some of the Maya area / Olmec area; but poorly evidenced at present. What’s very very clear is that the North American genetic type among the various Native Americans is not a simple “out of Asia” type. (There’s even some Polynesian / Australian genetic bits, of unknown mode of arrival. Including some ‘pentagonal’ skull shapes in very small areas of California coastal Indians – a Polynesian marker – and an interesting tooth shape that’s fairly distinctive. )

    It’s all incredibly interesting and a whole lot of fun, except for the hypersensitive folks who want to turn it all into some kind of political statement. It isn’t. It’s just a very interesting and very old long gone history. There’s even some evidence for even earlier occupations of the Americas up to 50,000 years being modestly attested while up to 200,000 years has some “plausible” sites being investigated.

    http://chiefio.wordpress.com/2012/12/22/native-americans-and-european-roots/
    http://chiefio.wordpress.com/2011/11/29/unsettled-age-for-american-early-habitation/

    If folks would be less political about it and just find the stones and history interesting to explore, we would know much more and have a richer past. Oh Well…

    The European genetic mush is even more of a mess. Anyone who thinks they are “pure” anything is just wrong. A “Spaniard” has as much chance of being a German as Phoenician as Celtic as Jewish as Berber genetic ancestry as all have traipsed through the area leaving genes behind. And don’t even get me started on the Roman Empire and the Egyptian history… We have records of Celtic mercenaries in Egypt…

    http://chiefio.wordpress.com/2011/02/20/ramesses-the-red/
    http://chiefio.wordpress.com/2012/09/22/im-hispanic-who-knew/
    http://chiefio.wordpress.com/2011/03/08/galicia-or-galizia-polish-galicja-ukrainian-%d0%b3%d0%b0%d0%bb%d0%b8%d1%87%d0%b8%d0%bd%d0%b0-halychyna/

    So someone from Northern Italy might be a Celt, German, Greek, Slav, or any of a dozen other “genetic types” or ethnicity… so just asking “What is a European type?” is a complicated question.

    Anyway, lots of fun, but not very relevant to how a big rock from space made the Younger Dryas and how that then lead to an abnormally mild Holocene and the rise of modernity…

  63. James Cross says:

    I was enthusiastic about this theory when I first read it but now I don’t know what to make of it. Two separate groups of “experts” come to different conclusions.

    The black mat has been sometimes attributed to fire; however, it is also possible that it could be decayed vegetation arising from heavy flooding. If a comet vaporized a large section of ice, water could have been sent high into the atmosphere and created diluvial precipitation over North America and perhaps the Arctic and Siberia. In the northern areas, this could have fallen as ice and snow and significantly altered the albedo by expanding the area of snow or depositing so much that it might not melt during the summer. Along with a large amount of fresh water falling into the ocean, it seems to me, this could trigger a cooling.

  64. phlogiston says:

    I have always felt that there is “no case to answer” with the Younger Dryas (YD). Glacial periods – in contrast to interglacials such as (and especially) the Holocene, are characterised by rapid, even violent, climate temperature swings up and down, in the context of which the YD is completely unremarkable.

    This view is reinforced even more by literature on the bipolar seesaw (reciprocal oscillation between north and south hemispheres) around the time of the YD and before, leading up to the Holocene. One of the most important such papers is Blunier et al 1997 who show that the YD was just the NH reacting to a warming southern ocean. It was proposed by Tzedakis et al 2012 that sharpened bipolar seesawing marked both the beginning and the end of interglacials. Thus in Blunier we see – in fig. 2 – first a warming in the southern ocean about 16 kYa, then the “Antarctic cold reversal”, a cooling oscillation in the SH, coinciding with sharp NH warming prior to the YD. Then a warming upswing in the SH ending the cold reversal coincides with the abrupt YD. It is noted by Barker et al 2009 that the seesaw is characterised by smooth sinusoidal oscillation in the SH but more abrupt changes in the NH, caused in the latter case by Atlantic meridional overturning circuation (AMOC) regime changes. Then at the Holocene inception both NH (abruptly) and the SH (smoothy) rise in temperature, but the SH again cools slightly in advance of the Holocene optimum.

    One thing that is clear is how Jeremy Shakun, holder of the chair in climate fraud at Oregon SU, has shamelessly exploited the end-glacial bipolar seesaw to concoct a spurious proof of CO2 leading the temperature rise out of the last glacial. Southern ocean temperatures had been rising since 16 kYa and continued to rise during the YD, resulting in a small CO2 increase in anticipation of the Holocene, on the condition that you take the Holocene to begin after the YD. But CO2 was not driving the start of the Holocene, it was merely following the southern ocean established warming. (There is more ocean in the SH than NH.)

    If we demand an atmospheric deus ex machina to explain every upward and downward wiggle of climate history we are falling into the ignorant trap and mental paralysis of AGW believers, who are unable to accept any cause of temperature change other than atmospheric input by humans and are in denial of the existence of the world’s oceans.

  65. talldave2 says:

    The timing is pretty clear.

    It wasn’t a comet, it was super-predator humans. There’s a reason we keep animals in zoos now, you know.

  66. Steve P says:

    It is doubtful that humans were present in N. America in sufficient numbers to account for the extirpation of the mega-fauna. Before they themselves were nearly extirpated, native tribes in N. America took as many buffalo and deer as they could kill at any one time, seemingly without making much of a dent in those populations. It took humans with firearms bent on mass destruction of the native people’s primary food source to very nearly exterminate the bison.

    There remain far too many unknowns surrounding this event, but the black mat was not created by men, of that we can be fairly certain.

  67. Matt G says:

    Comets, asteroids and volcanoes can’t impact the atmosphere for longer than a few years once the event has ended, so this rules out any of these for a 1300 year period, What was found in the fossil record was that the North Atlantic become much colder and the warm water moving North via the Gulf stream was channeled towards Southern Spain instead of between Scotland and Norway. The major change was ocean originated and this initial change would have cooled the northern hemisphere atmosphere considerably. Regions surrounding the North Atlantic would have had the biggest impact with areas other side of the planet hardly affected.

    Temperature estimates from fossils further South towards the sub-tropics and tropics hardly changed. If a comet was responsible for the cooling it would have effected the sub-tropics and tropics too. The sun easily warms the colder ocean temperatures in just 6 months between winter and summer, so a overturning of cooler water with a comet impact in the North Atlantic ocean is ruled out too. A ocean circulation change was certain this caused the cooling over 1300 years with numerous up and downs in between. This event was not a planet atmospheric impact, but an ocean impact.

  68. Ted Clayton says:

    Volcanic eruptions from the early Holocene (say, 12,800 years ago) put down ash-layers which we readily find & identify at large numbers of locations. We commonly map the fallout-pattern from old eruptions at close grid-spacing, with high accuracy.

    If the continent had been devastated by a huge blast at the beginning of the Younger Dryas, the tell-tale black layer would be commonplace in every corner of the land. It would be easily found at the 12,800 year horizon, wherever it has remained stable.

    We would all be able to get in the car and take a short drive out to cuts & exposures, and have a look for ourselves at the black-layer signature of the stupendous cataclysm that befell early Native Americans, ravaged the environment & ecosystem from top to bottom, and radicalized the climate for more than a millennium.

    But we don’t & can’t go out and look at this remarkable layer at the 12,800 year horizon, because it isn’t there. And the fact that there is no such widely-distributed layer, means there was no such widespread cataclysm. If there had been, we would know of thousands, or 10s of thousands of sites at which it had been documented.

  69. Steve P says:

    If the continent had been devastated by a huge blast at the beginning of the Younger Dryas, the tell-tale black layer would be commonplace in every corner of the land.

    Not if a flood followed an impact.

  70. Ted Clayton says:

    There are many known & identified layers & horizons within the soil & sediment record, from both before & after the 12,800 year horizon. These deposits have been stable & undisturbed, since before the Younger Dryas. The entire Holocene soil & sediment record is continuous.

    There have been certain cataclysmic floods, such as those that passed through Washington state, as ice-dams holding back large melt-water lakes in the Rockies periodically gave way. From these examples, we know well what such mega-floods do to the landscape. The great majority of the continent shows no such effects. There has been no continent-scale flooding during the Holocene.

    Had there been a continent-scale flood 12,800 years ago, it would have left its own very dramatic horizon-signature – exposures of which we would likewise drive out to in the car and gawk at, the hair rising up on our necks as the gargantuan spectacle whispers to us from across the ages.

    But again, we don’t go out to observe and study this tremendous flood-mark left in the sediment-record, because it too does not exist.

  71. Steve P says:

    I take it then that the remains of mammoths found in the semi-frozen muck of Siberia were not overwhelmed by flood, but by some other unknown force that killed them suddenly, and preserved them perfectly.

    And I suppose that the New Siberian Islands of the Russian far north are not really comprised largely of the shattered bones of extinct megafauna, because there is no record of a flood that could have transported them there?

  72. Ted Clayton says:

    There is a lot of boggy terrain in the high north, which grows rich browse, but it doesn’t have enough solid ground for a mammoth to move around on it … when it’s thawed. This would be their winter-pasture, after if froze-over good ‘n firm.

    Many tundra-ponds are active ‘compost-piles’, generating heat down-deep, well after the landscape looks like a deep-freeze. Mammoths pushing their luck for fresh feed, deceived by concealing snow-layers, or just drawing the short-straw with a warmer & thinner-frozen pond … broke through into these deep mucky bog-pits in large numbers, and died quickly, often drowning in the liquid goo as their own body-weight forced it up around them & over their head.

    This terrain and these conditions are hazards to smaller animals too, and to smaller (and of course large) machines as well, still today.

    It was winter and cold, when the mammoth stepped into its doom, and the struggling beast entombed itself in the excellent preservative of bog-mire, which then often froze solid.

    Dating of bones & frozen tissue on the New Siberian Islands shows they have steadily accumulated over a span of 200,000 years, at least. During the Ice Ages, these are a nice piece of hill-country, out on a vast, flat plain … and this of course about 90% of the time.

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