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Thread: Mega-crater discovered in Greenland, 12,000 years old?

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    Exclamation Mega-crater discovered in Greenland, 12,000 years old?

    Article has several superb color illustrations, must see.


    https://phys.org/news/2018-11-huge-c...-northern.html

    Huge crater discovered in Greenland from impact that rocked Northern Hemisphere
    November 14, 2018, University of Kansas

    A survey of ice in Greenland has uncovered evidence suggesting a kilometer-wide iron asteroid slammed into that island, perhaps as recently as 12,000 years ago during the end of the Pleistocene. The resulting 19-mile-wide impact crater has remained hidden under a half-mile-thick ice sheet until now. It recently was exposed by an ultra-wideband chirp radar system developed at the Center for the Remote Sensing of Ice Sheets (CReSIS) headquartered at the University of Kansas.

    The impact crater beneath the Hiawatha Glacier in remote northwest Greenland is detailed in a new paper in Science Advances published today.

    It was identified with data collected between 1997 and 2014 by KU for NASA's Program for Arctic Regional Climate Assessment and Operation IceBridge, and supplemented with more data collected in May 2016 using the Multichannel Coherent Radar Depth Sounder (MCoRDS) developed at KU.

    QUOTE: The iron meteorite penetrated seven kilometers into the Earth’s crust, creating a crater that was initially 20 kilometers wide and collapsed within minutes into the final 31 kilometer crater we see today.

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    Quote Originally Posted by Roger E. Moore View Post
    Article has several superb color illustrations, must see.


    https://phys.org/news/2018-11-huge-c...-northern.html

    Huge crater discovered in Greenland from impact that rocked Northern Hemisphere
    November 14, 2018, University of Kansas

    A survey of ice in Greenland has uncovered evidence suggesting a kilometer-wide iron asteroid slammed into that island, perhaps as recently as 12,000 years ago during the end of the Pleistocene. The resulting 19-mile-wide impact crater has remained hidden under a half-mile-thick ice sheet until now. It recently was exposed by an ultra-wideband chirp radar system developed at the Center for the Remote Sensing of Ice Sheets (CReSIS) headquartered at the University of Kansas.

    The impact crater beneath the Hiawatha Glacier in remote northwest Greenland is detailed in a new paper in Science Advances published today.

    It was identified with data collected between 1997 and 2014 by KU for NASA's Program for Arctic Regional Climate Assessment and Operation IceBridge, and supplemented with more data collected in May 2016 using the Multichannel Coherent Radar Depth Sounder (MCoRDS) developed at KU.

    QUOTE: The iron meteorite penetrated seven kilometers into the Earth’s crust, creating a crater that was initially 20 kilometers wide and collapsed within minutes into the final 31 kilometer crater we see today.
    Great report, thanks for flagging it, i am wondering how many major impacts happened during the end of the ice age and the Younger Dryas.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    Great report, thanks for flagging it, i am wondering how many major impacts happened during the end of the ice age and the Younger Dryas.
    Younger Dryas impact.... now, that's odd you should mention that. I was looking into that a year or two ago. There's a lot of smoke looking for a gun in the literature.

    ==========

    http://www.pnas.org/content/104/41/16016

    Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

    Firestone, R. B. et al.
    Proceedings of the National Academy of Sciences, vol. 104, issue 41, pp. 16016-16021
    Publication Date: 10/2007

    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. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

    ========

    http://www.pnas.org/content/106/31/12623

    Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

    Kennett, Douglas J.; et al.
    Proceedings of the National Academy of Sciences, Volume 106, Issue 31, 2009, pp.12623-12628
    Publication Date: 08/2009

    The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (<named-content content-type="genus-species">Mammuthus exilis</named-content>) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at ≈12,900 ± 100 cal BP.

    ========

    http://adsabs.harvard.edu/abs/2013PNAS..110E2088W

    Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago

    Wittke, James H., et al.
    Proceedings of the National Academy of Sciences, Volume 110, Issue 23, 2013, pp.E2088-E2097
    Publication Date: 06/2013

    Airbursts/impacts by a fragmented comet or asteroid have been proposed at the Younger Dryas onset (12.80 ± 0.15 ka) based on identification of an assemblage of impact-related proxies, including microspherules, nanodiamonds, and iridium. Distributed across four continents at the Younger Dryas boundary (YDB), spherule peaks have been independently confirmed in eight studies, but unconfirmed in two others, resulting in continued dispute about their occurrence, distribution, and origin. To further address this dispute and better identify YDB spherules, we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry, morphologies, origins, and processes of formation. We investigated 18 sites across North America, Europe, and the Middle East, performing nearly 700 analyses on spherules using energy dispersive X-ray spectroscopy for geochemical analyses and scanning electron microscopy for surface microstructural characterization. Twelve locations rank among the world's premier end-Pleistocene archaeological sites, where the YDB marks a hiatus in human occupation or major changes in site use. Our results are consistent with melting of sediments to temperatures >2,200 °C by the thermal radiation and air shocks produced by passage of an extraterrestrial object through the atmosphere; they are inconsistent with volcanic, cosmic, anthropogenic, lightning, or authigenic sources. We also produced spherules from wood in the laboratory at >1,730 °C, indicating that impact-related incineration of biomass may have contributed to spherule production. At 12.8 ka, an estimated 10 million tonnes of spherules were distributed across ∼50 million square kilometers, similar to well-known impact strewnfields and consistent with a major cosmic impact event.

    ========

    http://adsabs.harvard.edu/abs/2017AGUFMEP11B1563S

    Testing the Younger Dryas impact hypothesis with platinum-group elements (PGE), Re, and Os isotopes in sediments from Hall's Cave and Freidken Archaeological site, Texas

    Sun, N.; Brandon, A. D.; Forman, S. L.
    American Geophysical Union, Fall Meeting 2017, abstract #EP11B-1563
    Publication Date: 12/2017

    The Younger Dryas impact hypothesis suggests that extraterrestrial (ET) object(s) hit and exploded over North America 12,900 years ago and triggered the onset of Younger Dryas (YD) cooling and widespread megafaunal extinctions and the demise of the Clovis archeological culture. Supporting signatures such as concentrated carbon spherules and enlogaes, magnetic grains and spherules, nanodiamonds, and Ir-enrichment have been reported, but over time their lack of reproducibility of results at different locations have brought into question the impact hypothesis. Among the impact signatures investigated by previous studies, only few researchers included Re and platinum group element (PGE: Os, Ir, Ru, Rh, Pt, and Pd) characteristic concentrations, and 187Os/188Os ratios for ET mixing in terrestrial materials. Less than 1% of ET materials can provide enriched PGE concentrations, such that PGE are a sensitive tool to identify ET input in terrestrial materials. Because of the large difference between chondritic and continental crust 187Os/188Os ratios, 0.127 and >1.4, respectively, the 187Os/188Os ratios are also highly sensitive indicators of an extraterrestrial component in terrestrial and marine sediments. In this study, we examine sediments associated with the YD from two reported sites in North America, Hall's Cave and the Freidken Archaeological site in Central Texas, using the PGE and Re geochemical approach to test the evidence of the extraterrestrial projectiles during Younger Dryas period. Our current data show at Hall's Cave the PGE concentrations and patterns do not confirm the presence of an elevated meteoritic contribution. However, the 187Os/188Os depth profile shows a sudden 187Os/188Os decrease from 2.28 2.45 to 1.64 at the YD boundary layer, consistent with an increase in material derived from ET projectiles with chondritic 187Os/188Os ratios contaminating the Earth surface at the time of the YD extinction. Additional samples from the YD boundary at the Freidken site will also be presented in order to determine if a change in the 187Os/188Os signature occurs here as well. The combination of data across the YD boundary in both locales allows for a better evaluation of the possible causes for the YD extinction.

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    Whoa, the Greenland connection was already suspected!


    http://www.pnas.org/content/110/32/12917

    Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas

    Petaev, Michail I.; Huang, Shichun; Jacobsen, Stein B.; Zindler, Alan
    Proceedings of the National Academy of Sciences, Volume 110, Issue 32, 2013, pp.12917-12920
    Publication Date: 08/2013

    One explanation of the abrupt cooling episode known as the Younger Dryas (YD) is a cosmic impact or airburst at the YD boundary (YDB) that triggered cooling and resulted in other calamities, including the disappearance of the Clovis culture and the extinction of many large mammal species. We tested the YDB impact hypothesis by analyzing ice samples from the Greenland Ice Sheet Project 2 (GISP2) ice core across the Bølling-Allerød/YD boundary for major and trace elements. We found a large Pt anomaly at the YDB, not accompanied by a prominent Ir anomaly, with the Pt/Ir ratios at the Pt peak exceeding those in known terrestrial and extraterrestrial materials. Whereas the highly fractionated Pt/Ir ratio rules out mantle or chondritic sources of the Pt anomaly, it does not allow positive identification of the source. Circumstantial evidence such as very high, superchondritic Pt/Al ratios associated with the Pt anomaly and its timing, different from other major events recorded on the GISP2 ice core such as well-understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction, hints for an extraterrestrial source of Pt. Such a source could have been a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis.

    =========

    http://www.pnas.org/content/109/28/E1903

    PNAS Plus: Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago

    Bunch, Ted E., et al.
    Proceedings of the National Academy of Sciences, Volume 109, Issue 28, 2012, pp.E1903-E1912
    Publication Date: 07/2012

    It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe3Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO2 glass, or lechatelierite, with flow textures (or schlieren) that form at > 2,200 °C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.

    ==========

    Not everyone agrees, however.

    http://www.pnas.org/content/110/45/E4170

    Younger Dryas impact model confuses comet facts, defies airburst physics

    Boslough, Mark; Harris, Alan W.; Chapman, Clark; Morrison, David
    Proceedings of the National Academy of Sciences, Volume 110, Issue 45, 2013, pp.E4170-E4170
    Publication Date: 11/2013

    In PNAS, Wittke et al. (1) present evidence that they indicate supports major airbursts and/or impacts at the beginning of the Younger Dryas, as proposed by Firestone et al. (2). One of the major criticisms of the hypothesis has been the lack of any physics-based model for the hypothesized event (3). Wittke et al. (1) attempt to remedy this flaw by including a section entitled “Preliminary Impact Model.” Their model diverges significantly from the original but still provides no physics-based argument and demonstrates a misunderstanding of comets, as well as the physics of airbursts.

    Wittke et al. (1) state “The impactor most likely broke apart in solar orbit before encountering Earth, as do most comets, including Comet Shoemaker–Levy 9.” However, Shoemaker–Levy 9 broke up while in orbit about Jupiter, and the tidal fragmentation process leading to impact on Jupiter does not apply to comets in solar orbit or for approaches to terrestrial planets (4). A spontaneous breakup in heliocentric space, such as one recent example (5), would have to be exquisitely timed for an expanding cloud of fragments to strike the Earth. Near-Earth comets have average lifetimes of at least a century before breaking up. Within months after disintegration the comet fragments would be dispersed over an area much greater than that spanned by the Earth, precluding many nearly simultaneous impacts. Thus, dispersed impacts of multiple fragments would be at least 1,000 times less frequent (probable) than the impact of a single nucleus. [continues on a bit]

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    My take: smoking gun has been FOUND.

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    Go here: http://adswww.harvard.edu/ (SAO/NASA search engine for research papers), input "Younger" and "Dryas", then things like "airburst" "Greenland" "nanodiamonds" "impact" etc. From around 2007 onward you start to get a lot of stuff. Some think woolly mammoths and the human Clovis culture were destroyed by an airburst. This was one of the biggest astronomical, paleontological, and anthropological combined mysteries in modern times! WOO-HOO

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    Good thread, Roger. Thank you!

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    I have a list of great astronomy mysteries I was researching, getting nowhere with most, then a few of them got solved within the last 2 years. Might post about them separately.

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    Quote Originally Posted by Roger E. Moore View Post
    Go here: http://adswww.harvard.edu/ (SAO/NASA search engine for research papers), input "Younger" and "Dryas", then things like "airburst" "Greenland" "nanodiamonds" "impact" etc. From around 2007 onward you start to get a lot of stuff. Some think woolly mammoths and the human Clovis culture were destroyed by an airburst. This was one of the biggest astronomical, paleontological, and anthropological combined mysteries in modern times! WOO-HOO
    Yes thanks for a great compendium, it is indeed a hint that we will have to reconsider the pre YD state of human diaspora. It was such a recent pinch point, more recent than people reaching and then becoming isolated, in Australia. The sea level rise at that pinch point, recorded as it was in aborigine oral history, must have destroyed so much evidence of littoral societies.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Let's not jump the gun here:
    "the impact may have happened during the Pleistocene Epoch, between 2.6 million and 11,700 thousand years ago."
    That date has a Lot of slop in it.

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    A large impact crater beneath Hiawatha Glacier in northwest Greenland
    The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.
    ...
    The sum of these tentative age constraints suggests that the Hiawatha impact crater formed during the Pleistocene, as this age is most consistent with inferences from presently available data. An impact before the Pleistocene cannot clearly explain the combination of the relative freshness of the crater’s morphology and the ice sheet’s apparently ongoing equilibration with the presence of the crater. We emphasize that even this broad age estimate remains uncertain and that further investigation of the age of the Hiawatha impact crater is necessary. Regardless of its exact age, based on the size of the Hiawatha impact crater, this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally (35).

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    Someone is going to have to dig a trench down across parts of the crater, and date the stones relative to known outcrops elsewhere.
    It could be years before we have a tight date.

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    Quote Originally Posted by Roger E. Moore View Post
    Article has several superb color illustrations, must see.


    https://phys.org/news/2018-11-huge-c...-northern.html

    Huge crater discovered in Greenland from impact that rocked Northern Hemisphere
    November 14, 2018, University of Kansas

    A survey of ice in Greenland has uncovered evidence suggesting a kilometer-wide iron asteroid slammed into that island, perhaps as recently as 12,000 years ago during the end of the Pleistocene. The resulting 19-mile-wide impact crater has remained hidden under a half-mile-thick ice sheet until now. It recently was exposed by an ultra-wideband chirp radar system developed at the Center for the Remote Sensing of Ice Sheets (CReSIS) headquartered at the University of Kansas.

    The impact crater beneath the Hiawatha Glacier in remote northwest Greenland is detailed in a new paper in Science Advances published today.

    It was identified with data collected between 1997 and 2014 by KU for NASA's Program for Arctic Regional Climate Assessment and Operation IceBridge, and supplemented with more data collected in May 2016 using the Multichannel Coherent Radar Depth Sounder (MCoRDS) developed at KU.

    QUOTE: The iron meteorite penetrated seven kilometers into the Earth’s crust, creating a crater that was initially 20 kilometers wide and collapsed within minutes into the final 31 kilometer crater we see today.
    I've been hoping for years that indisputable proof of just such an event would be found and become mainstream. I started my journey many years ago with a simple question: What happened to our Past? For a species that had been around for 100+ thousand years (keeps getting longer...last I heard was in the 200+ thousand years) we sure didn't seem to have much of a history going back even a small % age of that time. Why? I asked. With the advent of the internet my search for answers, "my hobby" , became more fruitful, though I found many interesting "clues" and ideas long before then from many different sources. A lot of it was highly speculative and some just outright "crazy! I have 10's, probably hundreds of links in various folders on my computers now relating to the subject..... Here is just one that I found many years ago …..

    http://www.pibburns.com/catastro/clubenap.htm


    Consider Stonehenge.....consider the innumerable other "stonehenges'" being found all over the Earth. Is there a reason for them other than what the mainstream thought? I think they were constructed so that cyclical asteroid showers and comets could be anticipated and prepared for as they "rained" destruction on the planet. Remember, 78% of the planets surface is ocean, no craters just tsunamis. Additionally much of the terrestrial surface was, and is, covered with glaciers, jungles and deserts. Again difficult terrain to find craters in. More and more underground cities/shelters are being found all over the planet as well. One in Turkey is estimated to be able to accomodate 20-30,000 persons for an extended period of time. I find these subjects highly interesting in the search for our past.

    Interesting link to many translated ancient manuscripts....

    https://www.bibliotecapleyades.net/e...anuscripts.htm
    Last edited by Grant Hatch; 2018-Nov-29 at 05:59 PM.

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    Quote Originally Posted by Grant Hatch View Post
    Consider Stonehenge.....consider the innumerable other "stonehenges'" being found all over the Earth. Is there a reason for them other than what the mainstream thought? I think they were constructed so that cyclical asteroid showers and comets could be anticipated and prepared for as they "rained" destruction on the planet. Remember, 78% of the planets surface is ocean, no craters just tsunamis. Additionally much of the terrestrial surface was, and is, covered with glaciers, jungles and deserts. Again difficult terrain to find craters in. More and more underground cities/shelters are being found all over the planet as well. One in Turkey is estimated to be able to accomodate 20-30,000 persons for an extended period of time. I find these subjects highly interesting in the search for our past.
    Grant Hatch

    Do not advocate your non-mainstream ideas outside of ATM. And no, this one crater and publications about it do not make the rest of your idea mainstream.
    At night the stars put on a show for free (Carole King)

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    JEEEZ...squelch...OK.

    No, no I have to add this....
    The underground cities/shelters/areas created by man being found worldwide are mainstream and undisputed. Why they exist and their age is not yet well understood. Stonehenge is mainstream as are the many other similar constructs being found world wide. Their purpose is not well understood by the mainstream though their are many theories. The Younger Dryas event which led to the extinction of many species of the larger mammals as well as Clovis Man in North America approx. 12,000 years ago is not yet well understood by the mainstream though once again there are many competing theories. I, and many others are simply trying to make sense of the data. Do you feel that there ARE Mainstream conclusions for these events and constructs? If so i'll move to the ATM ....
    Last edited by Grant Hatch; 2018-Nov-30 at 01:37 AM.

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    Quote Originally Posted by Grant Hatch View Post
    I started my journey many years ago with a simple question: What happened to our Past? For a species that had been around for 100+ thousand years (keeps getting longer...last I heard was in the 200+ thousand years) we sure didn't seem to have much of a history going back even a small % age of that time. Why? I asked.
    This part might be an interesting topic for the Science and Technology section, though I think the most plausible answer is that nobody had the tools to record events until the last several thousand years. Much of history comes down to things that were written down or tied to things that were written down. I'd be quite surprised if small hunter gatherer groups would have the time and resources to develop a sophisticated language, further develop some form of writing, have time to maintain the skill if they did, and keep a cadre of scribes to record events on materials that would survive until the present day.


    With the advent of the internet my search for answers, "my hobby" , became more fruitful, though I found many interesting "clues" and ideas long before then from many different sources.
    And there's a communication method that didn't even exist when I was young. Anyway, I hope you checked to see what professional archaeologists say about these things.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." — Abraham Lincoln

    I say there is an invisible elf in my backyard. How do you prove that I am wrong?

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    Quote Originally Posted by Grant Hatch View Post
    I've been hoping for years that indisputable proof of just such an event would be found and become mainstream. I started my journey many years ago with a simple question: What happened to our Past?
    The simple answer is that we have not been producing large scale, enduring evidence of our past until maybe the last 10,000 years. Stone tools date back over a million years. The number of tools generated by a small population of semi-nomadic Homo sapiens over the last ~315,000 years spread over the world leads to a low density of tools. In addition there are rare sites such as cave paintings.
    Then along comes civilization, writing, etc. People start building and recording in stone. Pottery begins. Cities generate and retain higher densities of evidence. We start using metals.

    There will be old underground dwellings if only because that is an easy way to get a home. Likewise for cities such as Derinkuyu underground city. Why they exist is no mystery. They were built for most of the same reasons as any city. Ages nay be not known precisely but this is true of many archeological sites.

    It was the Clovis culture that vanished and is attributed to the Younger Dryas. There is a small chance that they may have caused Younger Drya by hunting larger fauna to extinction. Either way, a change in tool usage need not mean the extinction of people.
    Last edited by Reality Check; 2018-Nov-30 at 03:44 AM.

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    Quote Originally Posted by Reality Check View Post
    Either way, a change in tool usage need not mean the extinction of people.
    -Typed on an IBM System/360.
    Or more likely, not.

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    Another giant astrobleme detected under the ice in Greenland.

    https://phys.org/news/2019-02-nasa-i...nland-ice.html

    NASA finds possible second impact crater under Greenland ice
    February 11, 2019 by Maria-José Viñas, NASA's Goddard Space Flight Center

    A NASA glaciologist has discovered a possible second impact crater buried under more than a mile of ice in northwest Greenland. This follows the finding, announced in November 2018, of a 19-mile-wide crater beneath Hiawatha Glacier—the first meteorite impact crater ever discovered under Earth's ice sheets. Though the newly found impact sites in northwest Greenland are only 114 miles apart, at present they do not appear to have formed at the same time. If the second crater, which has a width of over 22 miles, is ultimately confirmed as the result of a meteorite impact, it will be the 22nd largest impact crater found on Earth.

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    https://www.nature.com/articles/s41598-018-38089-y

    New paper that adds fuel to the Younger Dryas Impact Theory: crater found in South America.

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