COMET CONTROVERSY: Ancient lake sediments reveal no evidence to support a controversial comet theory for an ice age extinction event, says paleoecologist Jacquelyn Gill of the University of Wisconsin-Madison.
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ALBUQUERQUE—After combing through layers of ancient lake sediments, paleoecologist Jacquelyn Gill of the University of Wisconsin–Madison says her team has found no evidence to support a controversial comet theory for an ice age extinction event.
"There's no physical trend to suggest that there was an impact event," Gill said Tuesday at the Ecological Society of America meeting held here this week. "If there was an impact event...it's not having the ecological effects [previously] suggested."
In 2007 Richard Firestone at the Lawrence Berkeley National Laboratory and colleagues published evidence suggesting that a comet exploding in the atmosphere 12,900 years ago near the Great Lakes set off massive fires in North America. These fires supposedly led to the rapid disappearance of the continent's Clovis culture as well as megafauna including mammoths, ground sloths and 33 other large mammal genera.
But skeptics point to the fact that no associated impact craters have been found, and evidence for continental forest fires and a rapid decline in human populations is sketchy. Besides, if such an episode had occurred, small mammals and birds somehow survived. (Another recent study has called into question the likelihood of comet impacts being responsible for more than one extinction event during Earth's history.)
Gill and her team decided to look for hints of the comet's impact not on land but in three lakes in Indiana and Ohio, where pollen and minerals have settled daily, creating an ecological record dating back millennia. She scoured core samples for evidence of ash, charcoal, magnetic grains, tiny silicate spheres, and elements such as titanium and chromium that could be associated with impact events. She did not look for rare earth minerals like iridium, which other researchers rely on as a signature of impacts.
The team failed to find a consistent signal that would indicate that a single catastrophe occurred around 12,900 years ago. At one lake, titanium actually decreased at the same time charcoal was increasing. "It's clearly not an impact event," Gill said.
Gill also questioned the view that animals died off right at the time of the proposed impact event.
Fungal spores called Sporormiella, associated with the dung of large mammals, actually begin to decline 14,600 years ago, soon after the end of the last ice age. The spores wink out of the record at one lake 13,600 years ago and only recover in the past few centuries with the rise in cattle grazing. At the same time, pollen from the plants that megafauna munched on—ash, ironwood and hop hornbeam—starts piling up, suggesting the plants' growth was no longer being kept in check by leaf-loving large mammals.
More recent megafauna fossils, dated between 13,600 and 12,900 years ago, were likely the last hangers-on as the Clovis people decimated species with their characteristic spears, Gill says.
But Firestone was not swayed by the new study, which he says "adds nothing to the argument." He says that he would not expect to find much evidence in lake sites because magnetic material would rust away, while the tiny spheres float and would not collect on the lake bottom. For him, the data still points toward an extraterrestrial impact. "As far as I'm concerned the debate is settled," he said.
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33 Comments
Add CommentWhen I hear of a scientist saying that the debate is settled, I no longer think of him as a scientist. This is especially true of things that happened thousands of years ago. The attitude is childish.
Reply | Report Abuse | Link to thisI agree Dano. I was formulating my comment as I finished reading the article. When I read that remark it annoyed me.
Reply | Report Abuse | Link to thisThat the researcher did not look for the elements typically found at an impact boundary brings into question the validity of her work but "the debate is settled" is like a burr under my saddle.
Has anyone considered the Deluge - about 13,000 years ago?
Reply | Report Abuse | Link to thisPoor research setup to yield the conclusion voiced. Poor ending comment that the science is all ready settled. Does two dumb conclusions equal anything of value?
Reply | Report Abuse | Link to thisThat the BIG game hunters had an effect on the BIG game numbers is rather obvious. As a hunter of a long line of hunters I don't need a collage education to figure that out.
Large animals do not withstand heavy predation that is why they evolve large size, to makeup for slow reproduction.
Kill half of a deer herd per year and you will have more deer.
Kill one elephant in a herd per year and soon there are no more elephants.
A true hunter will hunt down the last giant for the bragging rights. Just like intellectuals will will claim to have the definitive facts and the last say.
This is another example of a half baked attempt to derail other studies that actually did their homework. The fact that this "scientist" did not even check for the presence of iridium shows me that she is out to discredit the comet theory simply by hiding behind her title of "scientist", rather than actually doing the work necessary to be accountable in what her claims are. This type of half-baked research is the same kind of hocus-pocus that impedes real scientific progress, and causes delays in acceptance of theories that are eventually proven to be fact. The extraterrestrial object from which the iridium spike came did not need to leave a crater, it could have exploded in the atmosphere, and even if it did impact the ground, it may have hit the ice sheets, and thus the ice would have absorbed and dissipated the energy of the impact over a large area rather than making a clearly defined crater, and furthermore whether it impacted or exploded in the air, the retreat of the glaciers surely smoothed over any trace of such an impact. I find it hard to believe that small populations of humans could wipe out an entire gamut of large creatures in the blink of an eye. We modern humans are so conditioned to our current destructive abilities, that we forget that humanity lived in somewhat harmony with the rest of living things for the vast portion of our history, it is only in recent times that we have become populous enough to wreak havoc on the biosphere like we're doing right now. This reminds me of how no one wanted to accept the impact theory of the Dinosaurs' demise, until there was a smoking gun and they had to accept it, and even now there are people that still havent got the courage to accept the obvious - that the universe does not behave within the comfort zone of easy explanation by conservative or squeamish ideas.
Reply | Report Abuse | Link to thisHas anyone ever heard of Occam's razor? We're only talking just over 10,000 years ago, so I fail to see the need to invent some form of additional culprit beyond the usual suspects. No divine intervention and no need for extraterrestrial influences. Homo sapiens were present and they are a known cause for extinctions of any large animal they happen to come in contact with. Much more believable than a happenstance meteor strike that picked out which species to eliminate and which to keep. And much more believable than a mythical Deluge, wouldn't you say?
Reply | Report Abuse | Link to thisThe Deluge is not a myth.
Reply | Report Abuse | Link to thiswidespread Carolina Bay type craters from Clovis comet 12,900 BP? -- 0.7 M long NS crater with fractured red sandstone on SW rim, CR C 53A, 20 miles E of Las Vegas, NM: Rich Murray 2009.06.08
Reply | Report Abuse | Link to thishttp://rmforall.blogspot.com/2009_06_01_archive.htm
Monday, June 8, 2009
http://groups.yahoo.com/group/AstroDeep/27
As well as evidence for the probable time and cause of the extinction of Clovis culture in the Americas, many sites are also in Europe.
The connection with Carolina Bays confirms a continental disaster.
As a conscientious scientific amateur, I want to open up evidence and reason based dialogue re evidence I readily found for widespread fields of very similar craters in the Northern Hemisphere, starting with a specific, convenient, accessible crater near Las Vegas, New Mexico.
These kind of fields of round, oval, and irregular shallow craters, sometimes in durable bedrock, usually without connected drainage, with a fractal distribution of sizes, are simply too common to be volcanic in general -- take a look on Google Earth or Maps at the region about 40 miles from Amarillo to its southeast. With Google Maps set to Terrain, many of these 0.1 to 10 km features will show up a blue lakes, making it easy to find clusters. Where there are big craters, there are small ones.
Start from Las Vegas, NM and follow 104 east 20 miles to take the NE fork of CR CR53A -- in a mile, directly on the left, is the NS crater that I have walked directly, a mile long and 0.2 mile wide, showing the horizontal red sandstone beds on its rim, especially on the west, and a flat bottom. The rim is not raised. There are two parallel small ridges in the lower center, with a muddy cow wallow between. The south end of the crater is by a small road quarry about 200 feet wide and 16 feet deep of white mineral material, common in the region, completely distinct from the typical red sandstone bedrock.
The west rim shows progressive color changes and disruption as I walk along it by to and by the center, including 6 foot chunks tossed over in place, looking to my amateur eyes obviously scorched. Fragments up to 3 foot size abound in and around the crater.
I imagine that the explosion was on the surface, not buried as in typical iron or stone meteors. There is no sign of shocked or vaporized material, so it seems the impact was about 5 km/sec, from a low-impact angle for an mostly ice object falling out of a low orbital trajectory, with enough energy to create a superheated steam explosion, forming a shallow crater with white mineral deposits.
Extraterrestrial impacts are not "happenstance" nor are they less than 100% "believable". Modern society simply has not experienced an impact event, and since the periodicity of these occurrences is far longer in duration than the rise and fall of entire human civilizations, it is no wonder that their potential significance as a major player in the history of life on Earth is met with skepticism. We owe our existence to such events, and such events may well destroy us.
Reply | Report Abuse | Link to thisAs far as extraterrestrial impacts somehow "choosing which species to drive to extinction, look what happened with the Dinosaurs. All the huge creatures were wiped out. The only things that survived were tiny or able to hibernate, such as crocodilians, and moreover only the heartiest of creatures survived. As you know human beings are resilient and inventive and able to survive in circumstances through intelligence, than any other life form (not to say we are superbly adapted like sharks for example, only that we are adaptable). The difference in this circumstance is that all these large groups *suddenly* disappeared. Look at the number of buffalo on the great plains before the white man came to America. The indigenous peoples didn't wipe them out, there were millions of buffalo and the native peoples thrived off conscientious harvest of these animals but did not decimate them into extinction with over-hunting. The magnitude of greed in the current human civilization is far beyond anything these non-industrialized civilizations ever conceived of. And people then were no less intelligent than are people now, and people know how to manage wild game so as to leave their populations healthy to provide a continuous food source. And most importantly there were only the tiniest fraction of people alive than as compared to now. Yes human beings are destructive but neither the population sizes back then nor the wastefulness of current culture were present.
So in conclusion, there is nothing far-fetched about extraterrestrial impact theories pertaining to this extinction, nor are such denials grounds for embracing a weak and incomplete theory such as the theory presented in this article.
While I agree that an impact may have been responsible for the extinction of ice age megafauna in north America, I don't agree that an extinction event is necessary to explain the extinctions either.
Reply | Report Abuse | Link to thisThe "eco-friendliness" of native populations is an overrated new-age hippie fantasy. Or do we need another comet/meteor to explain the extinction of megafauna in Australia that occured soon after the aborigines crossed over from south-east asia?
As the scientist who led the study, I'd like to clear up a few misconceptions. We didn't look for elements like iridium because those elements are found at extremely trace levels in very tiny layers in other contexts (like the KT impact event). The lake sediment cores we work with are often ten-fourteen meters long in the region of this study - it would be beyond cost-prohibitive to sample the entire section for iridium (not only would such an endeavor likely not get funded, but would arguably be a mismanagement of taxpayer dollars!). Even after we identified the Younger Dryas interval, we still analyzed at least a meter of mud (or, more precisely, around 1000 years) around the boundary - which is still too wide a band.
Reply | Report Abuse | Link to thisHowever, we set out to look for preliminary evidence (such as the spherules, charcoal, magnetic grains, etc.) with the idea that we would then focus our study on an interval where we saw changes across a range of evidence that suggested an impact event. No such interval has been found at any of our sites, indicating no smaller segment of the cores to analyze further for ET-associated elements.
Contrary to Dr. Firestone's final quote, spherules (and other small materials, such as charcoal smaller than 125 micrometers, algae, pollen grains, etc.) do indeed settle out and are preserved in lake sediments. Ferromagnetic materials don't "rust," because lake bottoms are anoxic - otherwise, we wouldn't be able to reconstruct the past using pollen, which is destroyed by oxidation.
Lastly, whether or not the impact event actually took place, the paleoecological evidence from a range of sites do not support widespread continental fires or the megafaunal extinction. The suggestion that the debate is "settled" is extremely troubling, and not an accurate representation of the scientific community. Science works through a communal process of rigorous testing and retesting - this study isn't meant to be an attack on Firestone or his colleagues, but rather a participation in the process to better understand our world.
It's great fun to argue about "just-so" stories, but perhaps it would be more instructive to read the original publications on all sides of the issue before jumping in on one side or the other.
Reply | Report Abuse | Link to thisSteven C. Anderson
It's great fun to argue about "just-so stores" but it would be more informative to read the original publications before jumping in seriously
Reply | Report Abuse | Link to thisSteven C. Anderson
It's possible that, if there was a huge ice comet high-altitude explosion with production of very many high-velocity fragments of all sizes, over the ice cap of Canada, that huge amounts of water were suddenly released by ice melting.
Reply | Report Abuse | Link to thisThe website for the TV special "Last Extinction" includes a map of North America that shows the ice cover then, and also
many enormous inland lakes in the center of the west, including the ancestral Great Salt Lake.
When I survey the topography of North America with Google Maps and Earth, I see evidence for remarkable floods from central Colorado south along the western edge of the Rocky Mountains, and across Texas to the now underwater coastal slopes of the Gulf of Mexico.
Clovis sites and "Carolina Bay"-type craters are not found at low altitude sites that were targets for an immense, fast-moving, heavily debris filled and complex flood.
Can we have the locations for the lakes in Indiana and Ohio, to see if their region show any evidence of major erosion from a transient flood event?
Rich Murray rmforall@comcast.net 505-501-2298
Those who favor an impact event as the cause of the extinction of the North American megafauna are failing to look at the big picture. The disappearance of the North American megafauna was not a unique event. Over the last 50,000 years, the megafauna basically died out everywhere except for Africa and tropical Asia. The extinctions occurred at different times in different places. On all land masses that were not inhabited by humans prior to 50,000 years ago, the timing of the megafaunal extinctions is closely correlated with the first arrivals of humans (i.e., Australia first, then the Americas, and more recently Madagascar and New Zealand). It is clear that whatever caused the extinctions had little trouble spreading over the length and breadth of any land mass of any size, but at the same time this lethal influence had a hard time crossing large stretches of open water (e.g., woolly mammoths survived thousands of years longer on isolated islands like Wrangel off Siberia and St. Paul in the Pribilofs than anywhere else). The overall pattern makes perfect sense if humans hunted to extinction naive prey species that lacked the defensive behaviors requisite for evading them. It cannot be explained by impacting extraterrestrial bodies.
Reply | Report Abuse | Link to thishttp://www.pbs.org/wgbh/nova/clovis/
Reply | Report Abuse | Link to thishttp://www.pbs.org/wgbh/nova/clovis/preclovis.html
Interactive map of ice cover and pre-Clovis sites in North America
Before Clovis
When did humans first arrive in the Americas? For decades, the "Clovis-first" model of initial colonization held sway. It says that the first Americans were the Clovis people—named for an archeological site near Clovis, New Mexico—and that they walked across the Bering Land Bridge and spread into North America about 13,500 years ago. In recent years, however, researchers have unearthed many sites that appear to be pre-Clovis, some of them potentially doubling the time frame people have been in the Western Hemisphere. In this interactive map, explore 28 possible pre-Clovis sites found throughout North America.—Robson Bonnichsen and Robert Lassen
Robson Bonnichsen, who died in 2004, was a professor of anthropology and director of the Center for the Study of the First Americans at Texas A&M University. Robert Lassen is a former master's student at Texas A&M. This feature originally appeared on NOVA's America's Stone Age Explorers website.
Note: The map shows glaciers, lakes, and shorelines as of 12,900 years ago. Not shown is a famous pre-Clovis site in South America, Monte Verde in Chile, which is 14,500 years old and features many organic artifacts, stone tools, and house structures. This is an updated version of a map that originally appeared in "The Case for a Pre-Clovis People," by Robson Bonnichsen and Alan L. Schneider, American Archaeology, Winter 2001-2002. Special thanks also to Dennis Stanford, Smithsonian Institution.
http://www.pbs.org/wgbh/nova/clovis/prec-nf.html
Printable version of all of North America with 28 sites
When did humans first arrive in the Americas? For decades, the "Clovis-first" model of initial colonization held sway. It says that the first Americans were the Clovis people -- named for an archeological site near Clovis, New Mexico -- and that they walked across the Bering Land Bridge and spread into North America about 13,500 years ago. In recent years, however, researchers have unearthed many sites that appear to be pre-Clovis, some of them potentially doubling the time frame people have been in the Western Hemisphere. Below, explore 28 possible pre-Clovis sites found throughout North America. -- Robson Bonnichsen and Robert Lassen
Note the absence of sites south of 6 and west of 16 and 8, ie, west of the Rocky Mountains.
Likewise, fields of "Carolina Bay"-type craters lie east of the Rockies -- rare on the west.
What typically does not get mentioned in breathless press reports about possible pre-Clovis human campsites in the Americas is that there is a lot of negative evidence against them - namely, the absence of reliably dated human remains that are much older than the Clovis period. I think if someone were to make a plot the number of dated human remains in the Americas as a function of age, it would be illuminating.
Reply | Report Abuse | Link to thisIt's worth noting that the end-Cretaceous extinction event didn't just affect the megafauna - it also devastated N. American plants, invertebrates like warm-water corals and ammonoids, and planktonic species such as benthic forams. There were no comparable losses 13,000 years ago.
Reply | Report Abuse | Link to thisI didnt say the K-T extinction JUST affected the megafauna. I said ALL the megafauna were wiped out, and the only things that survived were small and or hearty. And an ASTEROID 6 miles across, made of metal and rock impacting the ground, is a different story than a low-density icy COMET that probably was an air-burst. So, I never compared the two events as if they were the same magnitude. So of course there were no comparable losses 13,000 years ago because the two events are nowhere near the same magnitude, nor did I ever say they were, I only said that sudden extinction events that affect large creatures have a strong possibility of being the cause of such events, especially when there is both IRIDIUM and HEXAGONAL DIAMONDS, both of which are indicators of extraterrestrial impacts, and both are present at the strata of sediment dating to 12,900 years ago.
Reply | Report Abuse | Link to thisIf the two events were nowhere near the same magnitude, just what WAS the magnitude of the putative impactor of 12.900 years ago? Has anyone estimated the size/mass of the object? And just to be clear - are you attributing the South American and northern Eurasian megafaunal extinctions to the same event?
Reply | Report Abuse | Link to thisExtensive work on the Carolina Bays over many decades indicate that they are eolian features, created in loess over tens of thousands of years. Many have been dated with radiocarbon and optically-stimulated luminescence dating as older than 40,000 years BP. Many contain well-preserved vertical stratigraphic layers, including pollen, which you just wouldn't get if they had been created from impacts.
Reply | Report Abuse | Link to thisTo respond to my own post... there is no answer to the question of whether or not the North Eurasian and South American megafaunal extinctions were caused by the same impact event as the North American megafaunal extinctions that does not create severe problems for the proposal of a Clovis-era impact event.
Reply | Report Abuse | Link to thisIf they were not caused by the same impact event, then you have two sets of megafaunal extinctions virtually identical to the North American extinctions that happened at roughly the same time, due to completely independent causes - a coincidence that is untenable. If they were caused by the same impact event, then you have to explain how the small, isolated (and thus extremely vulnerable) island populations of woolly mammoths (as well as the megafauna of the Antilles and other islands) survived in the midst of all this devastation. You also have to claim that the strong indications that the megafaunal extinctions were not synchronous across all 3 continents are erroneous.
Regarding the suggestion that preindustrial humans always managed their game carefully and thus would never have hunted their prey into extinction, counterexamples are available. Such a situation may have existed with the plains Indians and the bison, but that outcome was the result of a long period of coexistence in which each species adjusted to the other. The same relationship need not have prevailed when hunters first arrived on a virgin land mass and encountered prey that had never seen humans before and had no innate or learned fear of them (and was thus easily taken). It is well-documented that there was large-scale butchering of moas by the early Maori of New Zealand that involved a great deal of wastage of the less choice cuts of meat. This was shortly before the moas went extinct. In common with other species, human populations have the capacity to expand rapidly to fully exploit the food supply available to them, and this is likely what happened during the Clovis era.
Reply | Report Abuse | Link to thisThe claim that the North American megafaunal extinctions were caused by a relatively small impact (relative to the K-T event) invites another criticism of the comet proposal. Small impacts are much more common than large impacts. For example, the estimated frequencies of impacts by bodies of diameters of 5 km, 1 km, and 50 m are roughly once per 10 million years, 500,000 years, and 1000 years, respectively. If a relatively small impact could cause the megafaunal extinctions of the Clovis period, there should be numerous examples of similar megafaunal extinctions throughout Earth's geologic history. But there aren't. Prior to 50,000 years ago, there is no evidence for any extinctions that were remotely comparable in terms of severity, selectivity for megafauna, and geographic limitation at any time in the Cenozoic era; there are also no similar examples known from earlier periods. The megafaunal extinctions of the last 50,000 years appear to have no antecedents. That novelty can be most easily explained by the recent appearance of a novel agent of extinction: advanced human hunters.
Reply | Report Abuse | Link to thisWhile there is no reason an impact of some sort couldn't have occurred in the Clovis time frame, the evidence as a whole indicates that any such impact could not have been the primary cause of the megafaunal extinctions.
Nicely stated, Professor Mike, a cogent rebuttal. It is astonishing that so many "scientists" do not know what a theorey is and this lack of understanding only drives greater public ignorance.
Reply | Report Abuse | Link to thisHere, in Michigan, we just finished an exhaustive study of a lake sediments in Duck Lake. There is no conclusive evidence, going back over 15,000 years, that the extinction event of 9/11/2001 ever happened.
Reply | Report Abuse | Link to thisThis evidence is conclusive. The case is closed. 9/11 never happened!
We *can* prove it.
http://georgehoward.net/Vance%20Haynes%27%20Black%20Mat.htm
Reply | Report Abuse | Link to thishttp://georgehoward.net/Haynes%20(2008)_PNAS_YD.pdf 6 p free full text
CV Haynes, Jr. PNAS 2008.05.06 105(18) 6520–5
"Abstract: Of the 97 geoarchaeological sites of this study that bridge the Pleistocene-Holocene transition (last deglaciation), approximately two thirds have a black organic-rich layer or ‘‘black mat’’ in the form of mollic paleosols, aquolls, diatomites, or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the Younger Dryas cooling episode 10,900 B.P. to 9,800 B.P. (radiocarbon years). This layer or mat covers the Clovis-age landscape or surface on which the last remnants of the terminal Pleistocene megafauna are recorded. Stratigraphically and chronologically the extinction appears to have been catastrophic, seemingly too sudden and extensive for either human predation or climate change to have been the primary cause. This sudden Rancholabrean termination at 10,900 +- 50 BP appears to have coincided with the sudden climatic switch from Allerod warming to Younger Dryas cooling. Recent evidence for extraterrestrial impact, although not yet compelling, needs further testing because a remarkable major perturbation occurred at 10,900 BP that needs to be explained" [ corrected RC dates = 12,900 BP ]
"Fig. 1. Map of the United States showing 57 locations listed in SI Table 2 where one or more sites with black mats of Younger Dryas age occur (filled circles).
Open circles are 27 localities with Pleistocene-Holocene transitional sediments but no black mats (SI Table 3)."
[ 2 are in Oklahoma, 1 Ohio, 1 New York -- with no other Folsom sites in the huge area around the Great Lakes -- few east of Houston longitude -- which confirms Jacqueline Gill's results of no impact evidence in 4 lakes in Minnesota, Indiana, and Ohio, as well as Murray's observation of no Clovis sites in the Rio Grande Rift and from El Paso to the Gulf of Mexico -- higher altitudes avoid huge floods. ]
http://picasaweb.google.com/Swampmerchant/LIDARElevationImagesOfBays#5293889901367112994
image #1 of 34 LIDAR jpg color images of Carolina Bay elevation terrain data 2009.01.21
http://picasaweb.google.com/Swampmerchant/LIDARElevationImagesOfBays#5277819822906998290
image # 2 gives clear elevation color code and length scale: many Carolina Bays are about 0.05 - 1.3 miles long
http://picasaweb.google.com/Swampmerchant/CarolinaBaysJanuary182005#
165 fine aerial color photos of Carolina Bays 2005.01.18
Do lake sediment records show evidence of a Younger Dryas impact event or its potential ecological effects? Jacquelyn L. Gill et al: abstract of talk 2009.08.03
Reply | Report Abuse | Link to thisEcological Knowledge and Society (ESA) 94th Annual Meeting 2009 Albuquerque Convention Center, Albuquerque, NM
http://eco.confex.com/eco/2009/techprogram/P20277.HTM
Monday, August 3, 2009 - 2:50 PM
COS 13-5: Do lake sediment records show evidence of a Younger Dryas impact event or its potential ecological effects?
Jacquelyn L. Gill 1,
Jeremiah P. Marsicek 1,
J. P. Donnelly 2,
Bruce Simonson 3,
and Jack W. Williams 1.
(1) University of Wisconsin-Madison,
(2) Woods Hole Oceanographic Institution,
(3) Oberlin College
Background/Question/Methods
We test the hypothesis of a North American impact event at ~12.9 cal. yrs. BP (Firestone et al. 2007) with lake sediment records.
The impact, hypothesized to have occurred on or over the Laurentide Ice Sheet (LIS) near the Great Lakes, may have contributed to the megafaunal extinction, collapse of the Clovis culture, and destabilization of the LIS resulting in Younger Dryas (YD) cooling.
Firestone reported data from ten North American sites, but only one was Midwestern and none were lakes, historically robust sources of data used for paleoenvironmental reconstructions.
We collected sediment cores from Appleman
and Spicer Lakes, IN,
Silver Lake, OH,
and Kirchner Marsh, MN,
with radiocarbon-dated records spanning the YD.
Our sites are ideally situated to record regional environmental responses to a nearby impact.
Sediments were analyzed for changes in stratigraphy, charcoal, pollen (including Sporormiella, a dung fungus proxy for megafaunal abundance),
loss-on-ignition (LOI),
magnetic susceptibility,
carbon microspherules,
and elemental composition determined from x-ray fluorescence spectrometry (XRF).
An impact event should be associated with
elevated charcoal,
microspherules,
magnetics,
and concentrations of ET-associated elements,
and a decline in Sporormiella.
Results/Conclusions
Results from LOI, magnetics, microspherules, charcoal and XRF do not show the signatures predicted for a YD event.
Vegetation reconstructions are still in progress as of the time of this abstract, but at Appleman, the Sporormiella decline precedes the YD.
We are continuing analyses to determine whether this apparent discrepancy between the predictions of the YD impact hypothesis and the lack of evidence in lake sediments persist across sites.
maps showing regions of North America with few Clovis sites and points -- possible hint of surface erosion from sudden flood from 12,900 BP ice comet event: Gill: Murray 2009.08.08
Reply | Report Abuse | Link to thishttp://www.pnas.org/content/104/40/15625.full.pdf+html free full text
http://www.pnas.org/content/104/40/15625.full
Spatial gradients in Clovis-age radiocarbon dates across North America suggest rapid colonization from the north
Marcus J. Hamilton *,a and
Briggs Buchanan b,c
* Department of Anthropology, University of New Mexico, Albuquerque, NM 87131; and
Department of Anthropology, University of British Columbia, Vancouver, BC, Canada V6T 1Z1
Edited by Linda S. Cordell, University of Colorado, Boulder, CO, and approved August 20, 2007 (received for review May 6, 2007)
a To whom correspondence should be addressed. E-mail: marcusj@unm.edu
Author contributions: M.J.H. and B.B. designed research, performed research, analyzed data, and wrote the paper.
c Present address: Department of Archaeology, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
Abstract
.....
We find clear spatial gradients in the distribution of these dates across North America, which indicate a rapid wave of advance originating from the north.
We show that the high velocity of this wave can be accounted for by a combination of demographic processes, habitat preferences, and mobility biases across complex landscapes.
Our results suggest that the Clovis-age archaeological record represents a rapid demic colonization event originating from the north.
http://www.pnas.org/content/104/40/15625/F1.expansion.html
Fig. 1. Map showing the location of Early Paleoindian sites mentioned in text.
Numbers correspond to those found in Table 1.
http://www.pnas.org/content/104/40/15625/T1.expansion.html
Spatial gradients in Clovis-age radiocarbon dates across North America suggest rapid colonization from the north
Table 1. Radiocarbon and calibrated dates used in Fig. 1
Number, Site, Date 14C yr B.P., Error (±1 σ), *Calibrated date B.P., Ref(s).
http://books.google.com/
The early settlement of North America, By Gary Haynes [ page 50 ]
Paleo Crossing Clovis site in northeastern Ohio
Marion County in Ohio
http://www.andaman.org/BOOK/chapter54/text-Clovis/text-Clovis.htm#sitelist
54. Possible Relatives in the Americas Clovis People (New Mexico, USA) and Minnesota Woman (Minnesota, USA), by George Weber
Clovis geography and the ice-free corridor
A map of North America showing large regions with low densit
http://www.andaman.org/BOOK/chapter54/text-Clovis/text-Clovis.htm#sitelist
Reply | Report Abuse | Link to this54. Possible Relatives in the Americas Clovis People (New Mexico, USA) and Minnesota Woman (Minnesota, USA), by George Weber
Clovis geography and the ice-free corridor
A map of North America showing large regions with low density of numbers of Clovis points --
includes Colorado, New Mexico, West Texas, and Oklahoma, Arkansas, Mississippi.
Coming late to the party...reading through this discussion has been most interesting. I read the book by Firestone et al, "The Cycle of Cosmic Catastrophes" (Bear & Company, 2006) a while back. It presents what seems to be incontrovertible evidence for SOMETHING happening that was astronomical in nature; a comet was not the only option. Everyone who wishes to criticize Firestone should read that book first.
Reply | Report Abuse | Link to thisI agree that his remark about the "issue being settled" was unfortunate, but the combination of different kinds of data presented in his book appears conclusive for something astronomical taking place: C14 reversal anomalies centered around the Great Lakes; iron "pepper" only on the upper surface of Clovis chert flakes; the directional orientation of the iron speck impact pits in the chert (fitting the axis of the Carolina Bays, a consistent axis not easily fit with the aeolian idea); pit depth decreasing with distance from the Great Lakes; pit angle from vertical increasing with distance from the Great Lakes; reddening of the chert flakes, consistent with exposure to neutron radiation; and elevated levels of radioactive uranium, plutonium and thorium. Elevated K40 was also found, said to be a classic signature of a supernova. The three latter indicators seem more consistent with the debris shell of a supernova impacting Earth, rather than a comet explosion like Tunguska.
The megafauna survived 26 successive ice ages, then, on every continent and island, died out a few thousand years after fully modern humans arrived. 40,000 years ago in Australia. 25,000 years ago in East Asia. 13,000 years ago in the Americas. Humans wipe out species. Big, slow moving species are easily tracked and seen, and provide a big package of meat for the least effort. Looking at comets is looking for excuses for primitive humans doing what humans do best. Killing.
Reply | Report Abuse | Link to thisIs it possible the megafauna died off as a consequence of viral or bacterial infections caught from the first encroaches of man at that time? The megafauna would have had little or no resistance to new pathogens. Small mammals and birds would have been vulnerable as well but perhaps their faster reproductive rates allowed them to weather the immunological storm and survive the onslaught.
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