Extraterrestrial impact caused Younger Dryas?

[Andre]

Some earlier threads have been dedicated to the Younger Dryas and a possible connection to an impacter. Here is the full paper about it.

Firestone et al 2007 (http://www.pnas.org/cgi/reprint/104/41/16016), Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021

A carbon-rich black layer, dating to ~12.9 ka, has been previously identified at ~50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ~12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period.....

Firstly I'm interested in the dating ~12,9 ka:

example, the end-Clovis stratum (theYDB)is well dated at Murray Springs,AZ, (eight dates averaging 10,890 14Cyr or calendar 12.92 ka) and the nearby Lehner site (12 dates averaging 10,940 14C yr or 12.93 calendar ka). Haynes (2) correlated the base of the black mat (the YDB) with the onset of YD cooling, dated to 12.9 ka in the GISP2 ice core, Greenland (see GISP2 chronology in SI Fig. 6) (18). Therefore, we have adopted a calendar age of 12.9 ~ 0.1 ka for the YD event.

That's pretty clear. Open and shut case? Let's have a look here (http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/index.html).

This picture (http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/bilder/MFM) clearly shows this transition. Consequently:

Lücke, A.; Brauer, A. 2004 Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany),Palaeogeography, Palaeoclimatology, Palaeoecology, 211, 1-2, 139-155 p.

Abstract

The response of a lacustrine ecosystem to climatic changes from 13,500 to 10,800 BP was studied in a varve dated sediment profile of Lake Meerfelder Maar, western Germany. Bulk biogeochemical parameters, stable carbon and nitrogen isotopes of sedimentary organic matter and micro-facies analysis are used for a detailed investigation of the lake's development from the Allerød interstadial (AL) to the Younger Dryas stadial (YD) and into the early Holocene (Preboreal). Varve micro-facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones. The respective responses of bulk proxy parameters (bi-decadal resolution) indicate different sensitivities to diverse climatic changes. A prominent transition took place within two decades at the AL/YD boundary (12,690–12,670 BP). Increased flux of nutrients released from redeposited littoral sediments and shorter YD summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13C. High lacustrine primary production was further favored by relatively warm YD summer temperatures......


So what is it? 12,9 ~ 0.1 Ka or 12,690-12,670 counted years BP and what are those relatively warm YD summer temperatures doing there?

[Andre]

So how about getting the ice cores here to see when the Younger Dryas started.

We plot the stable isotope data of the three main cores, the European NGRIP (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/ngrip/isotopes/ngrip-d18o-50yr.txt), GRIP (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/grip/isotopes/gripd18o.txt) and the American GISP-2 (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gispd18o.txt).

So if we plot those for the time frame of interest, we get this (http://gallery.myff.org/gallery/127389/YD-start.GIF).

Note NGRIP is a bit curious giving two values per 50 years (grey). So I averaged that (blue). Even more curious is that the timescale started at 2000AD, while the standard is 1950, which would have caused a mismatch. So I corrected for that.

Now, if we assume that the Younger Dryas started halfway the last spike down then NGRIP (blue) and GRIP (black) agree nicely between 12,650 and 12,700 counted annual ice layers. GISP2 (red) is definitely the outlier around 12,850 years ago.

How about yet another source, Isarin and Bohncke 1999 (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPN-45GMY00-K&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0ee4aa48735bf2947d58e5657d00e9c3) have made an extensive compilation of paleo flora records in Europe and wrap it up thus:

Abstract

We estimated minimum mean July temperatures in northwestern and central Europe during the Younger Dryas (10,950–10,150 14C yr B.P.) (start date calibrates to 12,875 cal BP, Andre) from distributions of climate indicator plant species, which were reconstructed from 140 pollen and plant macrofossil diagrams. Paleobotanical records, mainly from the central and eastern part of the study area, show that the coldest conditions occurred early in the Younger Dryas (before 10,550 14C yr B.P.) C (calibrates to 12,640 Cal BP, Andre). For this phase, mean July temperatures at sea level of around 10°C are suggested for the northern part of the British Isles and for ice-free Scandinavia. We estimated a mean July temperature of 12°C for central England, The Netherlands, and northern Germany. The 13°C mean July isotherm—largely based on the modern distribution of Typha latifolia—was most probably located in southern England, Belgium, central Germany, and Poland. The reappearance of thermophilous elements in the records after 10,550 14C yr B.P. suggests a summer warming, at least temporarily, of 1° to 2°C in the study area. The reconstructed temperatures are comparable with temperature estimates based on beetle data. However, they appear rather high when compared with estimates based on glaciological evidence....

For carbon dating calibrating is used the INtcal04 calibration tabel (http://www.radiocarbon.org/IntCal04%20files/intcal04.14c)

It's starting to look like we have two Younger Dryases, one phase starting around ~12,850 calendar years BP according to the American and European carbon dating and the GISP-II ice core and one starting around 12,670 calendar years BP according to European annual layer counted records and the GRIP and GISP-II ice cores, the latter with warm summers? What is going on here?

[Andre]

Not interesting? Nagging about a mere 200 years dating discrepancy on a scale thousands of years? It should be though, when it appears to challenge one of the most important fundamentals of climate science.

Let's see what is the likely correct time frame of that isotope spike going down, the supposed start of the Younger Dryas. it seems that the mentioned number of records suggesting a time frame of 12,900 - 12,850 are at par with the records for the 12,700 - 12,650 time frame. However this is only optical, since all the calibrated carbon dates are now reflecting the age of the counted layers, as the INTCAL04 calibration table is generated from comparing the annual layer count with the carbon date of the same specimen.

Note also here (http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/bilder/MFM_corr.png) that the stable isotope records (d18O) from the Ammersee in Germany and lake Gosciaz in Poland concur with high accuracy with GRIP. There is very little doubt that the isotopes dropped in the period 12,700 - 12,650 Cal BP.

That would mean that the single outlier is now the GISP-2 ice core only.

But what about all those reports on the cold starting at 12,900 cal BP. Take this one for instance:

Van’t Veer R., G.A. Islebe, H. Hooghiemstra, 2000; Climate change during the Younger Dryas chron in Northern South America: a test of the evidence. Quartenary Science Review Vol 19 (2000) pp 1821 - 1835

(all carbon date calibrations and emphasis mine)
Abstract

New AMS and palynological data are presented from the Colombian Andes to assess vegetational and climatic change during the Lateglacial-Holocene transition, with special emphasis on the Younger Dryas (YD) chronozone. The new evidence is compared and discussed with other Colombian cores and with data from other countries in the region. The Lateglacial climatic reversal in Colombia, known as the El Abra stadial, has an estimated lower boundary of 11,200 (conventional) and 10,900 (interpolated) 14C yr BP, respectively (13,100 and 12,870 cal BP) .

Although the El Abra stadial is assumed to be the equivalent of the European YD, the present data suggest that the El Abra stadial is a biostratigraphical signal representing both the YD chronozone and the earliest Holocene (11,000-9000 14C yr BP - 12,910 - ~ 10,195 Cal BP). On the basis of new AMS dates and a re-evaluation of the pollen zones, we divided the Colombian El Abra biozone into two phases. From ca. 11,000 to ca. 10,500 14C yr BP (12,910-12,590 Cal BP) there is a sharp increase of subparamo and paramo pollen, reflecting a relatively cool phase during the YD chronozone (zone Y1). After ca. 10,500 14C yr BP (12,590 Cal BP), a slight increase of arboreal pollen and the presence of Cactaceae (zone Z1) point toward a relatively milder but drier phase extending to ca. 9000 14C yr BP (10,195) in the earliest Holocene. Our conclusions add detail to the concept of astronomical forcing of contrasting rainfall changes in northern South America between 12,400 and 8800 14C yr BP. (14,260 - 9790 Cal BP)


We propose an environmental drought during the El Abra biozone, with subsequent erosion of the sediments deposited during that period, as a major factor explaining the poor presence of YD evidence in northern South America. We conclude that at hydrologically sensitive sites without a clear lithological change around 11,000-9000 14C yr BP, a hiatus during the YD chronozone can only be detected if other cores are available with bracketed time control.

We state that the start of the temperature decline in Central America and northern South America is related to the global YD cooling event. However, much work is still required to understand the duration and amplitude of the climatic reversal during the YD chronozone in this part of the globe..

To me that's a wow! So they seem to see the same cold period in Columbia as Isarin and Bohncke 1999 in Europe as mentioned before and also some warming after 12,590 Cal BP versus 12,640 Cal BP respectively. Pretty close to the 12,700 - 12,650 Cal BP d18O isotope drop.

So we tested the hypothesis if the Extraterrestrial impact did cause the Younger Dryas and the result is that it would depends on your definition of when the Younger Dryas started, the North American events around 12,900 Cal BP could be related to the widespread cooling noted around that period. But it does not concur with the 12,700 Cal BP drop in the stable isotopes ratio (d18O).

But we seem to have tested also another hypothesis here (http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.html).

Alley R.B. 2000, The Younger Dryas cold interval as viewed from central Greenland
Quaternary Science Reviews Volume 19, Issues 1-5, 1 January 2000, Pages 213-226.

As said, it appears that the comparison of relevant records is showing that the summer temperature in Europe and the general temperature in Colubia rose in about the same period that the stable d18O isotopes of the European lakes and the GRIP-2 ice core dropped. So if the European lake isotopes did not reflect the rise in summer temperatures why would the Greenland isotopes do so?

[Andre]

okay, let's see if we can wrap this up in reasonable English.

early research of all kind of geologic records, mostly based on remains of plants, shows that there was a sudden cold period not too lang ago, an apparant return to ice age conditions, which was named the Younger Dryas after abundant pollen of the near arctic Dryas flower. As soon as carbon dating was invented the period was determined to be between 11,000 and 10,000 years Before Present - BP - (=1950).

But with the maturing of counting techniques like annual tree ring series (dendrochronology) and annual individually visible sediment layers in lake sediments annual coral growth it became apparant that something was wrong with the carbon dating technique, notably the start concentration of radioactive carbon isotopes. But this problem could be solved by comparing carbon dating with counting. This meant that the radiocarbon dates of 11,000 - 10,000 BP calibrated to 12,910 cal BP and about 11,400 Cal BP counted years

Parallel to those devellopments there was the research to the ice cores of Greenland and Antarctica, which also allowed for layer counting to determine age to a certain extend. Moreover using the heavy to light isotope ratios of the ice it was thought that the temperatures could be reconstructed. So the Dye cores and the GISP cores made the news by showing the distinct isotope ratio drop, the younger dryas, concurring with the geologic records of plant remains?

So things looked like a pretty convincing proof that isotopes are indeed a good paleo thermometer. There had been several challenges to that assumption.

But there was a glitch. several counted records insisted that the Younger Dryas begun after 11,700 cal BP while the plant remains and the GISP-2 ice cores suggested before 11,850 cal BP. So with the evidence suggesting an extra terrestrial impactor, emphasis was given again to the return to cold conditions around 11,900 Cal BP. However, several individually and independently counted records agreed on the isotope drop after 11,700 Cal BP. But -I did not mention this before- the cooling of 11,900 years ago concurs with the rise of the isotopes in the ice and European lake cores, suggesting that it warmed.

Meanwhile the plant remains of the different geologic records suggest that after 11,650 the climate in Europe and in the north part became drier and warmer in summer time but this concurs with the drop in isotope values which suggest a drop in temperature.

Hence

12,900
Isotopes: warming
geologic record: cooling and wet

12,700:
Isotopes: Cooling
geologic record: warmer summers and arid.

So which records do you want to believe?

To confirm the confusion have a look here:

http://www.geol.lu.se/personal/seb/Geology.pdf.pdf

ABSTRACT

The first late-glacial lake sediments found in Greenland were analyzed with respect to a variety of environmental variables. The analyzed sequence covers the time span between 14 400 and 10 500 calendar yr B.P., and the data imply that the conditions in southernmost Greenland during the Younger Dryas stadial, 12 800–11 550 calendar yr B.P., were characterized by an arid climate with cold winters and mild summers, preceded by humid conditions with cooler summers. Climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and Fohn effects. It shows that regional and local variations of Younger Dryas summer conditions in the North Atlantic region may have been larger than previously found from proxy data and modeling experiments.

[Andre]

Another player in this field not mentioned before is the Laacher see (http://www.laach.de/en/?Laacher+See) in Germany. It's actually a Maar (http://www.ux1.eiu.edu/~cfjps/1300/igterms.html), A low-relief explosion crater the walls of which consist largely or entirely of loose fragments of country rock and possibly some ejecta.

This eruption was the largest of the late Pleistocene in Europe and produced an ash or tephra layer which is widely visible in Europe. It's eruption date? 12,900 years ago (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGS-3YDGB93-6&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4b9a7f99693375cf9aa22e3cd391058b) as dated by several independant method. Litt et all (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-433W7C4-6&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0a0fa70d08fcf94a43a179f48f00e88e) count the Laacher See tephra at 12,880 annual sediment layers (varves) in the sediments of the Meerfelder Maar but that is also 200 varve years before the onset of the Younger Dryas.

See in the OP that Firestones extraterestrial event is also dated at 12,900 years ago. How big is the coincidence of an extreme rare big impact event codating within a few years with an extreme rare mega eruption? Could the eruption of the Laacher see be responsible for any of the evidence that Firestone finds or could the impact have triggered the eruption of the Laacher See?

[Andre]

meanwhile, today Science magazin, features an article, debunking the comet impact.

Kerr R.A 2008 Experts Find No Evidence for a Mammoth-Killer SCIENCE VOL 319 7 MARCH 2008

It looked impressive as slide after data-laden slide flashed on the screen last spring. Nearly a dozen debris markers, found at 26 sites from the U.S. West Coast to Belgium, testified to a huge impact followed by a continent-spanning wildfire. The catastrophe had taken place a geologic instant ago—closely coinciding with the disappearance of North America’s mammoths and the continent’s earliest human culture (Science, 1 June 2007, p. 1264).

The article claims that the comet related phenomena can be explained differently.

[John L]

Andre, you will have to travel to ai-Jane to read my reply to your astute thread. Unfortunately the moderator/admin here is not open minded enough to allow me to make my 15 posts in order to link to important sites.

Sorry, but I am gone, to find some other venue.

John

[Andre]

Meanwhile a new paper has been publised in PNAS:

Buchanan, Briggs, et al 2008 Paleoindian demography and the extraterrestrial impact hypothesis, PNAS August 19, 2008 vol. 105 no. 33 pp 11651–11654

Abstract

Recently it has been suggested that one or more large extraterrestrial (ET) objects struck northern North America 12,900 +/- 100 calendar years before present (calBP) [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104: 16016–16021]. This impact is claimed to have triggered the Younger Dryas major cooling event and resulted in the extinction of the North American megafauna. The impact is also claimed to have caused major cultural changes and population decline among the Paleoindians. Here, we report a
study in which ~1,500 radiocarbon dates from archaeological sites in Canada and the United States were used to test the hypothesis that the ET resulted in population decline among the Paleoindians.

Following recent studies [e.g., Gamble C, Davies W, Pettitt P, Hazelwood L, Richards M (2005) Camb Archaeol J 15:193–223), the summed probability distribution of the calibrated dates was used to identify probable changes in human population size between
15,000 and 9,000 calBP. Subsequently, potential biases were evaluated by modeling and spatial analysis of the dated occupations. The results of the analyses were not consistent with the predictions of extraterrestrial impact hypothesis. No evidence of a population decline among the Paleoindians at 12,900 +/- 100 calBP was found.
Thus, minimally, the study suggests the extraterrestrial impact hypothesis should be amended.

That's surprise as it was generally assumed that the Clovis culture disappeared without a trace to be replaced by the Folsom several centuries later with distinct differences in fluted points.

Well,...

When the facts change, I change my mind. What do you do, sir?

John Maynard Keynes (http://en.wikiquote.org/wiki/John_Maynard_Keynes)

[Mammo]

Some earlier threads have been dedicated to the Younger Dryas and a possible connection to an impacter. Here is the full paper about it.

Firestone et al 2007 (http://www.pnas.org/cgi/reprint/104/41/16016), Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021


I saw a programme on TV about the Rick Firestone suggestion of a comet airburst event around 12.9 ka and the evidence of a black mat and magnetic sphericules etc. http://www.newscientist.com/article/dn11909. However, I found the explanation of the resultant dramatic cooling very unconvincing. Also the absence of impact craters was explained by laboratory test firings into sheets of ice, but even these showed some shallow craters. It seemed to me that the evidence pointed towards that of a supervolcano, especially the drop in temperature due to the release of SO2 gas. An underwater supervolcano would explain the unusual sphericules perhaps? What do you think?

Here is an extract from the 2007 book 'Supervolcano' by John Savino and Marie D. Jones:

"While extremely active, there are no known supervolcanoes on the mid-ocean ridge system or in the deep ocean basins. The reason for this is the relatively thin oceanic crust, as opposed to the thicker continental settings and rhyolitic compostions for the land-based volcanoes." (emphasis is mine)

The oceanic supervolcano seems a better fit for a mass extinction than a comet event in my opinion.

[Andre]

It seemed to me that the evidence pointed towards that of a supervolcano, especially the drop in temperature due to the release of SO2 gas.

The oceanic supervolcano seems a better fit for a mass extinction than a comet event in my opinion.

If there was a release of SOx, then that must be visible in volcanic sulfate tracers in the Ice Cores (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/chem/volcano.txt). We see a spike (369 ppb) at 12,932 yrs but a bigger spike (524 ppb) at 13,033 years. However we know that one of the biggest Volcanic events at that time was the Laacher See Eruption (http://sp.lyellcollection.org/cgi/content/abstract/213/1/307), and there is something strange with the timing of that event. It's counted 200 annual sediment layers (varves) years in the Meerfelder maar before the onset of the Younger Dryas (Lücke and Brauer 2004) (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6R-4CWBMMN-2&_user=10&_coverDate=08%2F19%2F2004&_alid=846600555&_rdoc=2&_fmt=high&_orig=search&_cdi=5821&_sort=d&_docanchor=&view=c&_ct=4&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e6dd0460e10c436cdbcb5302973e7801)

[Mammo]

However we know that one of the biggest Volcanic events at that time was the Laacher See Eruption (http://sp.lyellcollection.org/cgi/content/abstract/213/1/307)

Was this the size of a supervolcano event? How could the ash deposits reach the North American great lakes area? In the same TV series I mentioned above, it was shown that the Indian subcontinent was covered in ash and caused a mass extinction around 74,000 years ago by the Mt Toba eruption which lasted for days. This was a supervolcano event bigger in size than Yellowstone. Due to the wind direction the debris drifted over India. They reported that the human population must have been reduced to something like 600, to account for their low genetic diversity. They estimated that the emission of SO2 reduced the temperature by 5-6 degrees for several years. The North American cause for the estimated 10 degree temperature drop and continental mass extinction implies an eruption even larger than this. The evidence of such an event from Laacher See would be obvious if this was the case. The size of the eruption makes me dubious because of this.

[Andre]

Was this the size of a supervolcano event? How could the ash deposits reach the North American great lakes area? In the same TV series I mentioned above, it was shown that the Indian subcontinent was covered in ash and caused a mass extinction around 74,000 years ago by the Mt Toba eruption which lasted for days. This was a supervolcano event bigger in size than Yellowstone. Due to the wind direction the debris drifted over India. They reported that the human population must have been reduced to something like 600, to account for their low genetic diversity. They estimated that the emission of SO2 reduced the temperature by 5-6 degrees for several years. The North American cause for the estimated10 degree temperature drop and continental mass extinction implies an eruption even larger than this. The evidence of such an event from Laacher See would be obvious if this was the case. The size of the eruption makes me dubious because of this.

The Mt Toba event appears to be visible in the aforemention GISP-II volcanic sulpor tracers at 71058 years with 466 ppb Volcanic sulphur, alternately it could be concealed in the frequent volcanic tracers between 72.5 Ky and 74 Ky. An unusual active period.

About the Laacher see eruption, this is the crater of the explosion, the Laacher See, a volcanic "maar", not a small boy, the biggest in the Eifel in Germany:

http://www.esys.org/rev_info/laachsee.jpg

The ashes (Tephra) did not reach America but the aerosols disperse world wide of course.

[Mammo]

About the Laacher see eruption, this is the crater of the explosion, the Laacher See, a volcanic "maar", not a small boy, the biggest in the Eifel in Germany:

The ashes (Tephra) did not reach America but the aerosols disperse world wide of course.

I'm feeling a bit confused Andre, are you suggesting that the Laacher See eruption is responsible for the evidence Rick Firestone attributes to a comet impact/airburst event? I presume not of course.

Incidentally, I've suddenly woken up to the significance of the Allerød dramatic warming event of around 14,000 B.P. Although interstadials are defined by region, the Allerød period is not, being global in its effects; that is, the temperature and sea level rose everywhere, not just in north Europe. The Greenland ice core graph shows this was a sudden increase in temperature by around 10 degrees! What could have caused that? This is the first event before the YD climate variations and therefore could be the most influencial, with the following millenia of climate change still being connected to this initial event. I tentatively propose that an oceanic supervolcano eruption could cause such a rise in temperature by the emission of CO2 gas into the atmosphere. Similarly, an oceanic supervolcano could be the cause of the Devils Hole sudden warming signature. These huge events could be the cause of ice age terminations in general. Perhaps only the gases escape to be released from the surface, whereas the ash is absorbed by the ocean, hence the lack of signatures in the ice cores?

[Andre]

I'm feeling a bit confused Andre, are you suggesting that the Laacher See eruption is responsible for the evidence Rick Firestone attributes to a comet impact/airburst event? I presume not of course.

Incidentally, I've suddenly woken up to the significance of the Allerød dramatic warming event of around 14,000 B.P. Although interstadials are defined by region, the Allerød period is not, being global in its effects; that is, the temperature and sea level rose everywhere, not just in north Europe. The Greenland ice core graph shows this was a sudden increase in temperature by around 10 degrees! What could have caused that? This is the first event before the YD climate variations and therefore could be the most influencial, with the following millenia of climate change still being connected to this initial event. I tentatively propose that an oceanic supervolcano eruption could cause such a rise in temperature by the emission of CO2 gas into the atmosphere. Similarly, an oceanic supervolcano could be the cause of the Devils Hole sudden warming signature. These huge events could be the cause of ice age terminations in general.

No the idea was that a super volcano with cooling sulphur would have left Volcanic tracers in the ice cores. But we see only the Meerfelder maar eruption which may have been in the same order of magnitude of the Tambora eruption (http://vulcan.wr.usgs.gov/Volcanoes/Indonesia/description_tambora_1815_eruption.html) that caused the year without summer.

Also there is something strange about the Bolling Allerod warming as narrated here (http://www.physicsforums.com/showpost.php?p=2006433&postcount=2)

[Mammo]

No the idea was that a super volcano with cooling sulphur would have left Volcanic tracers in the ice cores. But we see only the Meerfelder maar eruption which may have been in the same order of magnitude of the Tambora eruption (http://vulcan.wr.usgs.gov/Volcanoes/Indonesia/description_tambora_1815_eruption.html) that caused the year without summer.

Also there is something strange about the Bolling Allerod warming as narrated here (http://www.physicsforums.com/showpost.php?p=2006433&postcount=2)

Okay, you're saying the Meerfelder maar eruption could be responsible for the year without summer. But we still need to explain the Allerod warming and the black mat/extinction event of North America.

I'm still confused, Andre. With regard to mid-ocean ridge supervolcanoes, I propose that any SO2 gas emissions could be mostly absorbed by the overlying ocean to form sulphuric acid. CO2 emissions could be much greater for a particular supervolcano and therefore be the only significant outpouring. This seems a plausible explanation for dramatic global warming periods in the order of 10 degrees. Do you not think so?

[Andre]

Okay, you're saying the Meerfelder maar eruption could be responsible for the year without summer. But we still need to explain the Allerod warming and the black mat/extinction event of North America.

I'm still confused, Andre. With regard to mid-ocean ridge supervolcanoes, I propose that any SO2 gas emissions could be mostly absorbed by the overlying ocean to form sulphuric acid. CO2 emissions could be much greater for a particular supervolcano and therefore be the only significant outpouring. This seems a plausible explanation for dramatic global warming periods in the order of 10 degrees. Do you not think so?

You don't see it, the other evidence as linked to, do not support that dramatic warming. What you actually see is a deamatic shift in isotope ratios, isotope ratios are dependent on temperature, but is the conclusion logically correct that hence there was warming?

See the affirming the consequent fallacy (http://www.fallacyfiles.org/afthecon.html)

[Mammo]

You don't see it, the other evidence as linked to, do not support that dramatic warming. What you actually see is a deamatic shift in isotope ratios, isotope ratios are dependent on temperature, but is the conclusion logically correct that hence there was warming?

See the affirming the consequent fallacy (http://www.fallacyfiles.org/afthecon.html)

So what is your explanation for the dramatic shift in isotope ratios then? The earlier link to the 'list' wasn't very convincing, more confusing. Perhaps you could go through each example a bit more slowly. I want to be on your side, but the temperature proxies of the ice cores have a good record, I believe. They won't be perfect of course. Are you saying the Devils Hole proxy data isn't registering an abrupt temperature increase either?

[Mammo]

The Mt Toba event appears to be visible in the aforemention GISP-II volcanic sulpor tracers at 71058 years with 466 ppb Volcanic sulphur, alternately it could be concealed in the frequent volcanic tracers between 72.5 Ky and 74 Ky. An unusual active period.


Interestingly, here is an article which states that Yellowstone caldera erupted 70,000 years ago Yellowstone article (http://news.yahoo.com/s/ap/20081230/ap_on_sc/yellowstone_quakes). This is a likely candidate for the 71058 date of the volcanic sulphur tracer.

[Andre]

So what is your explanation for the dramatic shift in isotope ratios then? The earlier link to the 'list' wasn't very convincing, more confusing. Perhaps you could go through each example a bit more slowly. I want to be on your side, but the temperature proxies of the ice cores have a good record, I believe. They won't be perfect of course. Are you saying the Devils Hole proxy data isn't registering an abrupt temperature increase either?

Here is an early warning sign that isotopes do more than tracking temperatures:

Edwards T.W.D, B.B. Wolfe 1996 (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPN-45N44H3-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=ae66745c7a8de15eccc7a6c43b8d56c9) Influence of Changing Atmospheric Circulation on Precipitation d18O–Temperature Relations in Canada during the Holocene, Quartenary Research 46, 211–218 (1996)

with as key sentence:

Summer Relative Humidity was evidently closely coupled to changing d18Op

Anyway that doesn't say that there was not a comet: Fresh from the press:

Kennett D.J, et al 2009 Nanodiamonds in the Younger Dryas Boundary Sediment Layer, Science 2 January 2009: Vol. 323. no. 5910, p. 94

Brevia

....We report that nanometer-sized impact diamonds are abundant at multiple locations across North America in YDB sediments dating to 12.9 ± 0.1 thousand cal. yr B.P. Nanodiamonds (NDs) are associated with known impacts, during which they may arrive inside the impactor or form through shock metamorphism (6). We found subrounded, spherical, and octahedral crystallites, ranging in size from 2 to 300 nm, distributed within carbon spherules, suggesting crystallization from the amorphous carbon matrix...

[Mammo]

Here is an early warning sign that isotopes do more than tracking temperatures:

Edwards T.W.D, B.B. Wolfe 1996 (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPN-45N44H3-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=ae66745c7a8de15eccc7a6c43b8d56c9) Influence of Changing Atmospheric Circulation on Precipitation d18O–Temperature Relations in Canada during the Holocene, Quartenary Research 46, 211–218 (1996)

Very interesting. It shows that changes in oxygen isotopes aren't necessarily measuring a temperature change. The Allerod period is recognised as being a global warming though. Do you dispute this conclusion?


Anyway that doesn't say that there was not a comet: Fresh from the press:

Kennett D.J, et al 2009 Nanodiamonds in the Younger Dryas Boundary Sediment Layer, Science 2 January 2009: Vol. 323. no. 5910, p. 94

If nanodiamonds can arrive in an impactor, I don't see how anyone can categorically say they can't arrive from mid-ocean ridge highly explosive volcanic eruptions.

[Mammo]

If there was a release of SOx, then that must be visible in volcanic sulfate tracers in the Ice Cores (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/chem/volcano.txt). We see a spike (369 ppb) at 12,932 yrs but a bigger spike (524 ppb) at 13,033 years. However we know that one of the biggest Volcanic events at that time was the Laacher See Eruption (http://sp.lyellcollection.org/cgi/content/abstract/213/1/307), and there is something strange with the timing of that event. It's counted 200 annual sediment layers (varves) years in the Meerfelder maar before the onset of the Younger Dryas (Lücke and Brauer 2004) (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6R-4CWBMMN-2&_user=10&_coverDate=08%2F19%2F2004&_alid=846600555&_rdoc=2&_fmt=high&_orig=search&_cdi=5821&_sort=d&_docanchor=&view=c&_ct=4&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e6dd0460e10c436cdbcb5302973e7801)

Is it not logical to assume that the smaller spike at 12,932 yrs is from Laacher See and that the bigger spike at 13,033 years is from the 'black mat/extinction' event? There may be a dating error somewhere of only around a 100 years.

[Xnn]

If nanodiamonds can arrive in an impactor, I don't see how anyone can categorically say they can't arrive from mid-ocean ridge highly explosive volcanic eruptions.

Diamonds come from 3 sources:

Cratons
Detonation
and Extra-terrestrial.

Cratons are found in the interior of continents where the crust is thick.
They are not found mid-ocean where the crust is thin.

Detonation diamonds can be formed by impact events (meteorites or comets) or human actions (TNT, lasers and ultrasound). They can be distinguished from craton formed diamonds.

True extra-terrestrial diamonds are those that were created outside of earth and arrive from outer space as opposed to being formed during the impact event.

[Mammo]

Diamonds come from 3 sources:

Cratons
Detonation
and Extra-terrestrial.

Cratons are found in the interior of continents where the crust is thick.
They are not found mid-ocean where the crust is thin.

Detonation diamonds can be formed by impact events (meteorites or comets) or human actions (TNT, lasers and ultrasound). They can be distinguished from craton formed diamonds.

True extra-terrestrial diamonds are those that were created outside of earth and arrive from outer space as opposed to being formed during the impact event.

Am I definitely wrong then? The underwater eruption was looking as if it had potential. I don't mind, I'd rather know one way or another for definite.

[Gokul43201]

Am I definitely wrong then? The underwater eruption was looking as if it had potential. I don't mind, I'd rather know one way or another for definite.The article is a Brevia, so has limited details, but here are the portions (and references) relevant to your query:
Selected area electron diffraction patterns (SADPs) display d-spacings typical of cubic diamonds (2.06, 1.26, and 1.08 Å) and often produce additional "forbidden" reflections indexed at 1.78, 1.04, and 0.796 Å, consistent with the n-diamond polymorph (7) known to occur in meteorites (8).
...
Cubic diamonds form under high temperature-pressure regimes, whereas n-diamonds crystallize under lower temperature-pressure conditions (7). Both form outside the range of Earth's surficial processes but may crystallize during cosmic impacts (6). These data support the hypothesis that a swarm of comets or carbonaceous chondrites produced multiple air shocks and possible surface impacts at (approx)12.9 ± 0.1 thousand cal. yr B.P. (2).

References:

# 2. R. B. Firestone et al., Proc. Natl. Acad. Sci. U.S.A. 104, 16016 (2007).
# 6. R. M. Hough, I. Gilmour, C. T. Pillinger, F. Langenhorst, A. Montanari, Geology 25, 1019 (1997).
# 7. B. Wen, J. J. Zhao, T. J. Li, Int. Mater. Rev. 52, 131 (2007).
# 8. M. M. Grady, M. R. Lee, J. W. Arden, C. T. Pillinger, Earth Planet. Sci. Lett. 136, 677 (1995).

[Evo]

The article is a Brevia, so has limited details, but here are the portions (and references) relevant to your query:


References:

# 2. R. B. Firestone et al., Proc. Natl. Acad. Sci. U.S.A. 104, 16016 (2007).
# 6. R. M. Hough, I. Gilmour, C. T. Pillinger, F. Langenhorst, A. Montanari, Geology 25, 1019 (1997).
# 7. B. Wen, J. J. Zhao, T. J. Li, Int. Mater. Rev. 52, 131 (2007).
# 8. M. M. Grady, M. R. Lee, J. W. Arden, C. T. Pillinger, Earth Planet. Sci. Lett. 136, 677 (1995).Firestone et al has been pretty much debunked. A friend of mine, an expert on Clovis culture, is one of the many debunkers. The article below is not by him, although his work is cited.

Just as close scrutiny of the Holocene impacts belies an extraterrestrial source, an impact on the southeastern Laurentide ice sheet at 12.9 ka proposed at the 2007 American Geophysical Union Joint Assembly (Firestone et al., 2007a, 2007b) engenders similar doubts. This purported impact is cited as a trigger for the Younger Dryas climate event, extinction of Pleistocene mega-fauna, demise of the Clovis culture, the dawn of agriculture, and other events (Firestone et al., 2007a, 2007b). Evidence of the 12.9-ka impact includes magnetic grains, microspherules, iridium, glass-like carbon, carbonaceous deposits draped over mammoth bones, fullerenes enriched in 3He (Becker et al., 2007), and micron-scale “nanodiamonds” (Firestone et al., 2007c). We suggest that the data are not consistent with the 4–5-km-diameter impactor that has been proposed, but rather with the constant and certainly noncatastrophic rain of sand-sized micrometeorites into Earth's atmosphere.

The 12.9-ka impact story has struggled to bring its disparate evidence under a single umbrella. The impact story originated in Firestone and Topping (2001) and the Firestone et al. (2006) book, both of which contain observations and claims so wild that other work by these authors invites careful scrutiny. The nature of the 12.9-ka event changes radically with each iteration, from a supernova-generated “cosmic ray jet” (Firestone et al., 2006) to a massive atmospheric airburst (Firestone et al., 2007a, 2007b) to “multiple ET airbursts along with surface impacts” (Firestone et al., 2007c). Airbursts are a convenient explanation, given the lack of an impact crater, tektites, shocked quartz, or high-pressure minerals. Airburst events are associated with small impactors, perhaps <160 m diameter (e.g., Chapman and Morrison, 1994). Furthermore, the 12.9-ka event is identified as an oblique strike with “high-speed projectile material” (Firestone et al., 2007a) creating the elliptical “Carolina Bays” of the southeastern United States. Yet, of all impacts in the solar system, only a handful represent strikes capable of generating visibly elliptical forms (Pierazzo and Melosh, 2000). No meteorite material has ever previously been recovered from the Carolina Bays. Firestone and colleagues return to an impact origin for the Bays, ignoring a half-century of mainstream research focused on geomorphic mechanisms and age control documenting formation over extended time (Grant et al., 1998; Ivester et al., 2007). Similar elliptical depressions in Argentina, once claimed as an oblique impact swarm, were recently debunked and are now recognized as eolian (Bland et al., 2002).

http://www.gsajournals.org/perlserv/?request=get-document&doi=10.1130%2FGSAT01801GW.1&ct=1

[Gokul43201]

From your link: The suggestion that some of the material identified as 12.9 ka represents extraterrestrial input is consistent with its reported iridium content (Firestone et al., 2007a, 2007c), but we suggest that these levels simply represent the expected composition of micrometeorite ablation fallout. “[F]ullerenes enriched in 3He” (Firestone et al., 2007c; Becker et al., 2007) are consistent with micrometeorite ablation fallout, although it must be noted that the fullerene and helium signals have been repeatedly characterized as nonreproducible (e.g., Taylor and Abdul-Sada, 2000; Farley and Mukhopadhyay, 2001; Buseck, 2002; Farley et al., 2005). Nanodiamonds may represent a true extraterrestrial signature, but this material was identified only obliquely and requires rigorous corroboration.

Well isn't that what the new observation does? In any case, I don't know if this sufficiently distinguishes between micro-meteorite showers and (Tunguska-sized) chondrite showers. And like I said before, it's only a very short one-page (brevia) report - we would have to wait for the full article to come out to see if there is more to it.

Also, the article doesn't directly claim that this event had caused the YD - but it does make oblique references to it - so I think the authors are being a little more cautious.

PS: I have no bone to pick here. I'm just a layman observer, and my previous post was only meant to address the question about a super-volcano eruption. I leave the debunking of peer reviewed work to other peer reviewed work.

[Evo]

Mainly it was their claims This purported impact is cited as a trigger for the Younger Dryas climate event, extinction of Pleistocene mega-fauna, demise of the Clovis culture, the dawn of agriculture, and other events (Firestone et al., 2007a, 2007b).that caused a backlash. Apparently evidence doesn't support it.

[Andre]

As said before, there is a big problem with 12,900. The Laacher See eruption is dated at 12,900 years (http://www.google.com/search?hl=en&q=laacher+see+tephra+date+12900&btnG=Search&meta=) with several methods with an error margin much less than 100 years. Extensive research (http://www.informaworld.com/smpp/content~db=all~content=a713782812~tab=content) to the chronology of the Younger Dryas in Europe with counting techniques (Dendrochronology, lake sediment varves) puts it on <12,700 years, 200 counted years. Curiously enough we find the same dating conflict back in the Greenland ice cores between GISP-II (http://www.agu.org/revgeophys/mayews01/node3.html) versus GRIP and NGRIP (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/ngrip/gicc05-20yr.txt).

So whether or not there was a comet, this still challenges the claim that it caused the Younger Dryas.

[Gokul43201]

The article by Kennett et al doesn't directly claim an extraterrestrial cause for the YD, but neither does it make any mention of possible ambiguity in the dating of the YD onset. It unreservedly asserts that the YD began at 12.9KY BP and it cleverly lets the reader make the connection.

Incidentally, there appears to be a rather large non-monotonicity in the 14C calibration curve within 12700 - 12400 Cal Y BP. How does one correct for that?

http://www.radiocarbon.org/IntCal04%20files/intcal04.14c

[Andre]

This pollen diagram of the Meerfelder maar (Lucke and Brauer 2004) (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6R-4CWBMMN-2&_user=10&_coverDate=08%2F19%2F2004&_alid=847659050&_rdoc=2&_fmt=high&_orig=search&_cdi=5821&_sort=d&_docanchor=&view=c&_ct=4&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=086e0cbd375d033a4a0dbadeb513a5be) clearly exposes the dating discrepancy

http://img515.imageshack.us/img515/2065/meerfelderjs6.gif

At the bottom is the Laacher See tephra, giving the date horizon of 12,900 years, then they count 200 annual layers (varves) to the Allerod - Younger Dryas Boundary.

About the non-linearity of the carbon dating calibration data, what you see is what you get. During the carbon dating platforms there is simply a large to very large error. But at the steeper gradient periods, the error margin actually decreases as happens exactly at the period of interest, 13000-12700 cal BP But with varve counting or dendrochronology the carbon dating scale becomes irrelevant

[Evo]

The article by Kennett et al doesn't directly claim an extraterrestrial cause for the YD, but neither does it make any mention of possible ambiguity in the dating of the YD onset. It unreservedly asserts that the YD began at 12.9KY BP and it cleverly lets the reader make the connection.Their paper was refused by both Science and Nature.

While there might have been meteors, there doesn't appear to be archeological evidence that supports their claims that it wiped out the mammoths or Clovis.

[Gokul43201]

The article by Kennett et al doesn't directly claim an extraterrestrial cause for the YD, but neither does it make any mention of possible ambiguity in the dating of the YD onset. It unreservedly asserts that the YD began at 12.9KY BP and it cleverly lets the reader make the connection.Their paper was refused by both Science and Nature.What paper are you talking about?

Kennett D.J, et al 2009 Nanodiamonds in the Younger Dryas Boundary Sediment Layer, Science 2 January 2009: Vol. 323. no. 5910, p. 94

Brevia(bold tags added by me)

[Evo]

What paper are you talking about?

(bold tags added by me)Ooops, I thought we were discussing the PNAS paper.

But the paper by Kennett you are referring to is still making the same claims of megafaunal extinction and an abrupt end to clovis culture.

[Andre]

However whatever happens with publications is basically irrelevant, it's all about data, records, interpretations, hypotheses, models and evidence.

The original publication Firestone et al 2007 may have been rejected by Science and Nature. But it's not changing facts and fictions.

Firestone et al 2007 Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021

[Andre]

I see that I forgot to elaborate on another element against the impact hypothesis causing the Younger Dryas, the deuterium excess analysis (http://www.science.uottawa.ca/~eih/ch2/ch2.htm) from Greenland Isotopes, Jouzel et al 2007 (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6R-4CWBMMN-2&_user=10&_coverDate=08%2F19%2F2004&_alid=847659050&_rdoc=2&_fmt=high&_orig=search&_cdi=5821&_sort=d&_docanchor=&view=c&_ct=4&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=086e0cbd375d033a4a0dbadeb513a5be). also here (www.iceandclimate.nbi.ku.dk/publications/papers/pdfs/242.pdf)

It may be noticed that the negative correlation between deuterium excess during the Dansgaard Oeschger events and the Younger Dryas are virtually the same. Note also that Jouzel et al relate the isotope data solely, one dimensionally to temperature variation without a clear conclusion. Note also that the hydrological textbook states:

Vapour generated under low humidity conditions has a high deuterium excess.

Apparantly there is a second dimension to deuterium excess, humidity. Reason for revisiting the science behind the isotopes in ice cores?

[Xnn]

Yes; the problem of deuterium-excess from Greenland ice cores is much more complex than for Antarctica.

Further progress should result from the use of isotopic ocean atmosphere
General Circulation Models to account for the complexity of topographic changes, source conditions and atmospheric circulation. They have, however, up to now, shown a very poor representation of the predicted characteristics of deuterium-excess in precipitation and clearly require additional work.

Nonetheless, these models are our best hope to account for sources of complexity,
such as the shifts of source locations. In addition, they can be used to investigate some of the implicit but important assumptions embedded in the simple models. With significant improvements, isotopic GCMs would be ideal tools to examine the properties of stable isotopes, including excess, in regions such as Greenland.

[Andre]

Yes; the problem of deuterium-excess from Greenland ice cores is much more complex than for Antarctica.

Do tell about it.

And perhaps the greenland problem could disappear if somebody brought the two dimensions in, temperature AND humidity

Further progress should result from the use of isotopic ocean atmosphere
General Circulation Models to account for the complexity of topographic changes, source conditions and atmospheric circulation. They have, however, up to now, shown a very poor representation of the predicted characteristics of deuterium-excess in precipitation and clearly require additional work.

Nonetheless, these models are our best hope to account for sources of complexity,
such as the shifts of source locations. In addition, they can be used to investigate some of the implicit but important assumptions embedded in the simple models. With significant improvements, isotopic GCMs would be ideal tools to examine the properties of stable isotopes, including excess, in regions such as Greenland.

If you don't have the basics right, models go nowhere.

[Xnn]

It's all part of the continual improvement process!

Make a model, check it out against observations and then make it better.

One always has to keep an open mind that there will be room for improvement.
It's a good reason to write grants and keep unemployment down!

Check out the following for a discussion:

http://pubs.giss.nasa.gov/docs/2006/2006_Hansen_etal_1.pdf

[Andre]

It's all part of the continual improvement process!

Make a model, check it out against observations and then make it better.

One always has to keep an open mind that there will be room for improvement.
It's a good reason to write grants and keep unemployment down!

Check out the following for a discussion:

http://pubs.giss.nasa.gov/docs/2006/2006_Hansen_etal_1.pdf

Not really. when you're off on the wrong trail, the only improvement is going back to where you lost track and that's rather ..erm.. counter intuitive. See also Kuhn's structure of scientific revolution (http://www.des.emory.edu/mfp/Kuhn.html)

[Mammo]

Firestone et al 2007 Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021

I had an inspirational thought recently regarding the above event. Is it not a possibility that a comet ocean impact could be responsible for the observed evidence? I imagined that the ocean could act like a solid due to the extreme impulse of the impact and therefore the ejecta would be forced skyward just like a terrestrial event. It would explain the lack of any cratering and also the increase in seawater in the Greenland ice cores. The cooling phase could be attributed to a direct disruption of the thermohaline circulation, rather than the suggested influx of meltwater into the Gulf Stream (which is complete speculation).

[JusDennis]

R.B. Firestone et al. Also described a 109Megaton above ground explosion with a fireball around 107 Deg. C. that set fire to the continent, and reduced it's ecosystem to ashes. But they could only guess at the location.

Here's a good candidate for you:
http://theholocenecomet.spaces.live.com/

What do you think?

[Andre]

I think that an event like that would have left a lot of physical evidence that could be traced back. Actually I know that a research after that by Nilequeen is in it's final stage.

Don't hold your breath

[JusDennis]

My problem is that the explanations I get from the geologists I've talked to about it just don't fit what I see. or as my Grandpa would say; "that dog don't hunt!" The thing is' I've seen all of those features before. But on a much smaller scale.

Thanks to the army I know what the ground looks like after a really big explosion. after thirty years my ears have never quit ringing. As for the epicenter; If you go to a large structural steel shop where they have high energy plasma cutting equipment all you need to do is tweak the controls untill the cutter head explodes. Imagine a fircracker, but at 105 oC. you'll get a two inch mark in the surface of the steel just like the one you see in the pictures.

It may, or may not, relate to the YD event, but I know blast damage when I see it.

[Gokul43201]

Your source does not meet the requirements spelled out in our guidelines. Please provide links to original sources and publications. Also, appeals to authority (~ I know an explosion when I see one) are wasted here.

[Gokul43201]

Ooops, I thought we were discussing the PNAS paper.

But the paper by Kennett you are referring to is still making the same claims of megafaunal extinction and an abrupt end to clovis culture.Missed this post before.

No, the Kennett article does not make this claim.

PS: That the Firestone paper was rejected by Science and Nature before being accepted by PNAS tells you nothing about the quality of the paper or specifically about the validity of certain conclusions. Most scientists will give an arm and a leg to publish in PNAS (it has a higher impact factor than even PRL, which many physicists will give an arm and a few toes to publish in). I think we should stick to discussion of the content of the papers rather than try to score points by asserting that they were rejected by X or Y journal.

[JusDennis]

Sorry I didn't intend to hijack this thread. But I've been studying these two papers for weeks.

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling
http://tsun.sscc.ru/hiwg/Activity/Firestone+25_2007.pdf

and:

Younger Dryas ‘‘black mats’’ and the Rancholabrean termination in North America
http://www.georgehoward.net/Haynes%20(2008)_PNAS_YD.pdf

[JusDennis]

I am admittedly over my head here but this thing seems to be beyond anything old school geology can describe. Or even acknowledge as possible.

It is my hope that someone here might take a look at it while geology waits in the hall.

http://theholocenecomet.spaces.live.com/

[matthyaouw]

Hello again. I believe we spoke on sciforums.com

In that discussion, I asked you if we see any evidence of thermal alteration of the rocks in that area and I never got an answer.
On your site you say:
The theory is that, if a fireball were higher than the atmosphere, convection would have no room to form a mushroom cloud. And the heat, having no where else to go, would stay and spread out at ground level and be absorbed into the surface. Causing partial thermal metamorphism in the surface materials or sediments

You don't state whether or not we actually see this. Do you have any evidence for this?

[JusDennis]

If you had read the thing and the refernces included you may have noticed that I called the epicenter of the blast structure a plasma burn. There is a certain high temp. implication in that word don't you think? And in fact the only reason the site is worthy of any note at all is because it looks like the stuff you see in a war zone. But covering a third of the continent.

I'm afraid if you need me to spell it out any clearer I am at a loss for words.

[matthyaouw]

Yes, you do call it a plasma burn and I did notice this. I also noticed you fail to do two things. The first is you fail give a definition of 'plasma burn'. A quick google search tells me that it is a problem with flatscreen TVs, but I have a feeling this isn't what you're talking about. The second is you fail to provide any evidence of any burning or heating going on there. If I have missed this, do point me towards the specific line or paragraph on your site or your references that show evidence of recent thermal alteration of the rocks in the area you describe.

[JusDennis]

In the steel industry a high energy plasma cutting machine called a burn table makes a very distintive mark in the steel. Called a plasma burn, or a burn caused by high energy plasma. Very different from a simple oxygen breathing fuel burning fire.

Here's a link to describe the equipment.

http://www.kaliburn.net/products/proline2260/downloads/ProLine-2260-Plasma-Cutter-Family-Brochure.pdf

I've stated that it is a blast zone. If you see no evidence of a high energy explosion thank you for telling me that.

[matthyaouw]

Thanks for the clarification there. Nah, I don't really see any evidence for an explosion, but I watch with interest if you have any to add :smile:

[JusDennis]

Look I am a layman. nothing more.

If I found a dinosaur bone I'd tell a paleontologist about it. If he wanted me to give a long explanation of why I think it's dinosaur bone. I'd walk away and tell someone else.

As for how I can know what the ground looks like after a large explosion. Or the effects of a powerful surface compression shock wave, I'm afraid the only diploma I've got are couple of scars, an honorable discharge from the US Army, and ears that are still ringing after thirty years.

[GENIERE]

...I'm afraid the only diploma I've got are couple of scars, an honorable discharge from the US Army...

More than good enough for me.

The arc formation is a remnant scar of plate tectonics, the making and breaking of ancient super continents and the birth of the Atlantic Ocean. The arc is a southern fragment of the juncture of what is called the Ouachita (Wichita) Salient and the Tennessee Salient. The junction is a noticeable (salient) deformation of terrain due to these large parts of the Earth’s crust colliding.

(information from William A. Thomas - Uv Kentucky)

[JusDennis]

Every other arc shaped landform on earth that is the product of such a continental collision; The Hymalayas, island arks like the Aleutians, the roots go all the way down through the basement bedrock beneath.

But on a map available from the USGS, and Titled Preliminary Precambrian Basement Structure Map of Continental United States http://pubs.usgs.gov/of/2005/1029/downloads/plate1.pdf There is no hint of them at all in the geologic and aeromagnetic data. The Appalachians are there, and every other ancient continental collision. But not the arks. They exist only in the surface material.

Perhaps you would be so kind as to explain how this can be?

[matthyaouw]

Can I ask you what exactly you expect to see by examining the precambrian basement? What do you expect the map should look like for this to be a feature of tectonic origin?

Looking at the map, I see the southern end of a long major thrust fault. Thrust faults cause uplift. This still suggests tectonic origin to me.

[JusDennis]

I don't buy it.

I expect those features to be evident in the precambrian basement structure like everywhere else on earth a continental collision has occured.

Whenever I hear the words "Most geologists agree that those rings are the result of an ancient tectonic collision." it gives me pause. That's pure dogma, right up there with "Most scholars and scribes agree that the earth is a flat plate, carried on the back of a turtle at the center of the universe"

I'm sorry but "most______agree" is not good science. No matter how old and firmly held the opinion might be.

Show me the data.

[matthyaouw]

I will ask again. exactly what do you expect to see? What do you think evidence for uplift would look like? If you don't know what you're looking for, chances are you won't see it.


It is rather hypocritical of you do demand evidence when you yourself can provide none.
Unless you can, your speculation is wholely useless.

[JusDennis]

Thank you for your opinion. In fact I see no evidence of any uplift whatsoever. I do, however, see compelling visual evidence of massive surface compression shock waves. That, judging by their dimensions, are from a surface explosion which would have been large enough to devastate most of the continent. And to kill and incinerate everything for hundreds of miles. The "Black Mat" at the YD boundary layer is the biomass of half a continent reduced to ashes. Furthermore, note the location, and direction that most of the heat would have flowed down-range from the site; It would have melted thousands of square miles of the Laurentide ice sheet in seconds. The sudden inflow of fresh water into the North Atlantic would have shut down the thermal haline cycle like turning a switch.

The evidence is virtually conclusive that just such an explosion did indeed happen somewhere over North America at the beginning of the Younger Dryas cooling. To say that it did so without trace is much more of a stretch than pointing to the obvious epicenter of a giant blast zone and saying it happened right there.

I have stated my qualitifacations for recognizing a blast zone. I haven't heard anything from you on that account. What do you know of the ground effects of powerful explosions? Did you learn it in a classroom? Or on a battlefield?

You, my good man are starting to sound a bit strident. Like the Wizard of Oz. Frantically trying to cover while shouting into the microphone "Pay no attention to the old man behind the curtain." And since you clearly have no idea what a blast zone looks like your opinion in this matter is wholely useless.

[Evo]

I suggest that you read this paper.

Just as close scrutiny of the Holocene impacts belies an extraterrestrial source, an impact on the southeastern Laurentide ice sheet at 12.9 ka proposed at the 2007 American Geophysical Union Joint Assembly (Firestone et al., 2007a, 2007b) engenders similar doubts. This purported impact is cited as a trigger for the Younger Dryas climate event, extinction of Pleistocene mega-fauna, demise of the Clovis culture, the dawn of agriculture, and other events (Firestone et al., 2007a, 2007b). Evidence of the 12.9-ka impact includes magnetic grains, microspherules, iridium, glass-like carbon, carbonaceous deposits draped over mammoth bones, fullerenes enriched in 3He (Becker et al., 2007), and micron-scale “nanodiamonds” (Firestone et al., 2007c). We suggest that the data are not consistent with the 4–5-km-diameter impactor that has been proposed, but rather with the constant and certainly noncatastrophic rain of sand-sized micrometeorites into Earth's atmosphere.

The 12.9-ka impact story has struggled to bring its disparate evidence under a single umbrella. The impact story originated in Firestone and Topping (2001) and the Firestone et al. (2006) book, both of which contain observations and claims so wild that other work by these authors invites careful scrutiny. The nature of the 12.9-ka event changes radically with each iteration, from a supernova-generated “cosmic ray jet” (Firestone et al., 2006) to a massive atmospheric airburst (Firestone et al., 2007a, 2007b) to “multiple ET airbursts along with surface impacts” (Firestone et al., 2007c). Airbursts are a convenient explanation, given the lack of an impact crater, tektites, shocked quartz, or high-pressure minerals. Airburst events are associated with small impactors, perhaps <160 m diameter (e.g., Chapman and Morrison, 1994). Furthermore, the 12.9-ka event is identified as an oblique strike with “high-speed projectile material” (Firestone et al., 2007a) creating the elliptical “Carolina Bays” of the southeastern United States. Yet, of all impacts in the solar system, only a handful represent strikes capable of generating visibly elliptical forms (Pierazzo and Melosh, 2000). No meteorite material has ever previously been recovered from the Carolina Bays. Firestone and colleagues return to an impact origin for the Bays, ignoring a half-century of mainstream research focused on geomorphic mechanisms and age control documenting formation over extended time (Grant et al., 1998; Ivester et al., 2007). Similar elliptical depressions in Argentina, once claimed as an oblique impact swarm, were recently debunked and are now recognized as eolian (Bland et al., 2002).

http://www.gsajournals.org/perlserv/?request=get-document&doi=10.1130%2FGSAT01801GW.1&ct=1

I have merged the two threads.

[JusDennis]

Ok, I read the mans paper. I don't agree.

Time will tell

[Evo]

Here is another paper that disputes the extraterrestrial impact theory.

Abstract - Paleoindian demography and the extraterrestrial
impact hypothesis

Briggs Buchanan*, Mark Collard, and Kevan Edinborough

Recently it has been suggested that one or more large extraterrestrial
(ET) objects struck northern North America 12,900 100
calendar years before present (calBP) [Firestone RB, et al. (2007)
Proc Natl Acad Sci USA 104: 16016–16021]. This impact is claimed to
have triggered the Younger Dryas major cooling event and resulted
in the extinction of the North American megafauna. The
impact is also claimed to have caused major cultural changes and
population decline among the Paleoindians. Here, we report a
study in which 1,500 radiocarbon dates from archaeological sites
in Canada and the United States were used to test the hypothesis
that the ET resulted in population decline among the Paleoindians.
Following recent studies [e.g., Gamble C, Davies W, Pettitt P,
Hazelwood L, Richards M (2005) Camb Archaeol J 15:193–223), the
summed probability distribution of the calibrated dates was used
to identify probable changes in human population size between
15,000 and 9,000 calBP. Subsequently, potential biases were evaluated
by modeling and spatial analysis of the dated occupations.
The results of the analyses were not consistent with the predictions
of extraterrestrial impact hypothesis. No evidence of a population
decline among the Paleoindians at 12,900 100 calBP was found.
Thus, minimally, the study suggests the extraterrestrial impact
hypothesis should be amended.

http://www.hecc.ubc.ca/pdf/PaleoDem_PNAS2008.pdf

[JusDennis]

Ok

Buchanon et al. disagrees with Firestone et al.

I am not qualified to be the arbiter in that debate. I'm an old ex GI who still knows his place in the firing line. I ‘m not sure how it fits into all of the different scientists pet theories, or research. I think, after all of the fur stops flying, it will turn out that they are all absolutely correct. But each holding a different part of the elephant.

[matthyaouw]

Thank you for your opinion. In fact I see no evidence of any uplift whatsoever.

I have to wonder where (if anywhere) you have looked and if you indeed know what evidence for uplift would look like. On page 2 of this paper (http://www.gly.fsu.edu/~holm/Tull%20and%20Holm.pdf) you will see that there are a series of thrust faults around the area you describe. Take note.


I do, however, see compelling visual evidence of massive surface compression shock waves.

I am still waiting for you to present it, but I have a feeling my wait will be indefinate.

To say that it did so without trace is much more of a stretch than pointing to the obvious epicenter of a giant blast zone and saying it happened right there.

I am not saying there was not an impact. I am not saying there is not an impact site somewhere in the US. I am saying there is no evidence for one wher you claim.


I have stated my qualitifacations for recognizing a blast zone. I haven't heard anything from you on that account. What do you know of the ground effects of powerful explosions? Did you learn it in a classroom? Or on a battlefield?

Classroom, of course. And in the course of my learning I would bet that I learned a hell of a lot more than you about how rock responds to heat, pressure and ET impacts on such large scales.

You, my good man are starting to sound a bit strident. Like the Wizard of Oz. Frantically trying to cover while shouting into the microphone "Pay no attention to the old man behind the curtain." And since you clearly have no idea what a blast zone looks like your opinion in this matter is wholely useless.

And you are starting to sound like every other nutjob that ever brought their own pet theory along to an internet forum. By your own admission you have no evidence beyond what you have gathered from a cursory glance at google earth, yet you are convinced to the point of certainty that you are right and seem to be ready to defend your position to the death. You clearly have no evidence to support your position or refute anyone elses therefore your opinion in the matter is useless.


Seriously, if what you say is true, you will find evidence for it if you look in the right places. Never mind trying to tell everyone else they are wrong. Their being wrong would not automatically make you right. What you need to fucus on is supporting your positon. Go away and find out how rock would respond to the heat and pressure you describe, or what telltale signatures an ET impactor may leave. Then go and look for these things. Come back if you find them. You have already stated your case, and until you have something to add in support of this, the discussion will not progress any further.

[Mk]

Evo, I do not quite understand your logic or what you mean by, "the Firestone paper has been thoroughly debunked." How? Do you mean the hypothesis of an extraterrestrial impact impacting the Clovis culture itself, or also the supporting original research published in the paper?

[Evo]

Evo, I do not quite understand your logic or what you mean by, "the Firestone paper has been thoroughly debunked." How? Do you mean the hypothesis of an extraterrestrial impact impacting the Clovis culture itself, or also the supporting original research published in the paper?There are several papers. One was sent to me by the author himself, I will need to check if I can post it. He is an authority on Clovis and has shown why what they propose did not happen, the archeological evidence isn't there.

Here is a good paper.

http://www.gsajournals.org/perlserv/?request=get-document&doi=10.1130%2FGSAT01801GW.1

[Andre]

As far as I can see it, there may or may not have been an extraterrestrial event but it can be considered refuted that this hypothetical event had any significant impact on climatological changes and extinctions of species.

[Mammo]

As far as I can see it, there may or may not have been an extraterrestrial event but it can be considered refuted that this hypothetical event had any significant impact on climatological changes and extinctions of species.
How do you come to that conclusion? A micrometeorite bombardment which persisted long enough to leave a blanket deposited layer, which is still magnetic enough to deflect a compass (I saw it on TV), must have been a spectacular event. It seems reasonable to assume that it is possible that the event did cause climate change. Here is a paper which discusses this type of subject: Violette 2005 report (http://www.etheric.com/Downloads/solar.pdf#search='Mt.%20Erebus%20AND%20fluorine').

[Andre]

How do you come to that conclusion?

Please reread the thread then. Essentially all isotope indications of the start of the Younger Dryas (YD) match the isotope indications of the 20+ Dansgaard-Oeschger (D-O) events in the last ~70 Ka. So the YD can be seen as just another end of a D-O event, which was bound to happen regardless of any extra terrestrial event.

Second, there is no indication of the predicted wild fire spike at 12,900 y BP. (Marlon et al 2009 Wildfire responses to abrupt climate change in North America, PNAS doi10.1073pnas.0808212106 early edition)