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 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.
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.
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.”
Was she riding her Infinite Improbability Broom, powered by a Brownian Motion producer (say, a nice hot cup of tea)?
> 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.
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.
The pattern of the YDB field is interesting – I wonder if you could deduce a likely impact location based on the shape ??
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.”
“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.
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.
“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.
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.
J.Seifert says:
May 21, 2013 at 7:01 pm
Thanks Nice web site..
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.
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.
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.
Mosher is right. Nice site:
http://cosmictusk.com/
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.
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.
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.
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.
The Australian megafauna extinctions happened 30,000 years earlier, other countries also at different times
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).
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.
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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.
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.
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.
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.
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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…?
***
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.