Advertisement
We've partnered up with Nixers.com to offer a space where you can talk directly to Peter from Nixers.com and get an exclusive Boards.ie discount code for a free job listing. If you are recruiting or know anyone else who is please check out the forum here.
If you have a new account but can't post, please email Niamh on [email protected] for help to verify your email address. Thanks :)

California's Channel Islands Hold Evidence Of Clovis-age Comets

  • 21-07-2009 8:33am
    #1
    Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    In a paper appearing online ahead of regular publication in the Proceedings of the National Academy of Sciences, University of Oregon archaeologist Douglas J. Kennett and colleagues from nine institutions and three private research companies report the presence of shock-synthesized hexagonal diamonds in 12,900-year-old sediments on the Northern Channel Islands off the southern California coast.

    Thius lends support to the theory that held that climate change possibly triggered by a series of small and widely dispersed comet strikes across North America was to blame for these mass extinctions of large mammals at the end of the ice age, and not overhunting by the Clovis people.
    "The type of diamond we have found -- Lonsdaleite -- is a shock-synthesized mineral defined by its hexagonal crystalline structure. It forms under very high temperatures and pressures consistent with a cosmic impact,"

    http://www.sciencedaily.com/releases/2009/07/090720190719.htm


Comments

  • Registered Users Posts: 30,747 ✭✭✭✭ Galvasean


    Good read. I always taught the 'Clovis kill' theory lacked evidence and seemed a bit unlikely.


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Galvasean wrote: »
    Good read. I always taught the 'Clovis kill' theory lacked evidence and seemed a bit unlikely.

    Yeah I would have to agree, it does not seem likely that massive continent + smallish human population does not a mass extinction make.

    I have seen the argument before that because the American Megafauna had not evolved hand in hand with Humans they would not have been as wary of them as their African cousins.

    One problem I have with this argument is Sabre Tooth Tigers, I am having severe trouble imagining them meekly approaching the early american settlers looking for a belly rub :D


  • Registered Users Posts: 30,747 ✭✭✭✭ Galvasean


    One good idea was related to the 'megabear'. As a prominant scavenger he would raise up on his back legs to appear bigger and intimidate rivals. Unfortunately this would make him vunerable to having spears thrown at him. Although no evidence of human and 'megabear' interaction has been found yet so it's just an interesting idea at best for now.


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    And the inevitable counter assault :)
    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.

    http://www.scientificamerican.com/article.cfm?id=comet-doubts


  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 58,884 Mod ✭✭✭✭ Wibbs


    The other problem I have with the human driven extinction is that IMH clovis wasn't ground zero for humans in the americas. It's a fiercely defended position though and quite a few academics have been blasted for even suggesting there was a human presence in the Americas before the clovis culture.

    I'll make a bet now that good evidence will be found that humans were there before. Well here's one http://www.sciencedaily.com/releases/2008/04/080403141109.htm There's a chilean site that is pretty strong for a date of 13000 yrs ago. So they would have likely come down from the north all the way to the tip of south america. Chances are that didn't take 100 years or anything like it, so there must exist northerly sites earlier. They don't even have to have come from asia either. The clovis tools show far more similarities to european tools than asian. Though as kennewick man showed that's a political hot potato.

    I suspect even earlier finds are out there. There's a contested site in carolina that carbon 14 dating suggests a figure of 50,000 years ago. There's another again in south america that returns a carbon date of 21000 years ago. If humans got to somewhere like Australia 50/60,000 years ago, I find it really hard to swallow that the Americas was 40,000 odd years later. If flores man is a definite dwarf relict erectus, then that strongly suggests homo erectus had some sea navigation capability. its at least possible that erectus made it to the americas too. They were around for over a million years and got everywhere else(except australia). Hell we're nearly 200,000 years old as a species and as student backpackers show we can't bloody sit still for long.... :D

    It does look like humans arriving in australia killed off the megafauna though. Or at least helped it on it's way. The climate changed too, but even there humans have been partially blamed. Hunting practices using fire clearance. Around the time of the earliest human evidence large areas show burning. May be a coincidence though.

    I suspect the more we find out about Homo and our ancient travels some pretty amazing stuff is going to come up. I reckon we've barely scratched the surface.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Advertisement
  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Wibbs wrote: »
    The other problem I have with the human driven extinction is that IMH clovis wasn't ground zero for humans in the americas. It's a fiercely defended position though and quite a few academics have been blasted for even suggesting there was a human presence in the Americas before the clovis culture.

    I'll make a bet now that good evidence will be found that humans were there before. Well here's one http://www.sciencedaily.com/releases/2008/04/080403141109.htm There's a chilean site that is pretty strong for a date of 13000 yrs ago. So they would have likely come down from the north all the way to the tip of south america. Chances are that didn't take 100 years or anything like it, so there must exist northerly sites earlier. They don't even have to have come from asia either. The clovis tools show far more similarities to european tools than asian. Though as kennewick man showed that's a political hot potato.

    I suspect even earlier finds are out there. There's a contested site in carolina that carbon 14 dating suggests a figure of 50,000 years ago. There's another again in south america that returns a carbon date of 21000 years ago. If humans got to somewhere like Australia 50/60,000 years ago, I find it really hard to swallow that the Americas was 40,000 odd years later. If flores man is a definite dwarf relict erectus, then that strongly suggests homo erectus had some sea navigation capability. its at least possible that erectus made it to the americas too. They were around for over a million years and got everywhere else(except australia). Hell we're nearly 200,000 years old as a species and as student backpackers show we can't bloody sit still for long.... :D

    It does look like humans arriving in australia killed off the megafauna though. Or at least helped it on it's way. The climate changed too, but even there humans have been partially blamed. Hunting practices using fire clearance. Around the time of the earliest human evidence large areas show burning. May be a coincidence though.

    I suspect the more we find out about Homo and our ancient travels some pretty amazing stuff is going to come up. I reckon we've barely scratched the surface.

    Practically all genetic studies suggest an earlier date of migration, I have seen figures of up to 30,000 years mentioned in some studies. A recent one, suggests isolation of the eventual population in Beringia beginning roughly 23,000 years ago followed by a rapid expansion between 18 and 15,000 years ago along the West Coast of the Americas.

    http://www.familytreedna.com/pdf/Fagundes-et-al.pdf


  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 58,884 Mod ✭✭✭✭ Wibbs


    That sounds more like it datewise. Good link. I have some issues with DNA evidence though, in particular so called genetic clocks. It's a fashionable science and as such IMHO is relied on too much. There are cases where the DNA stuff doesn't quite match the palaeontology too. The out of africa theory for a start, where stone tool technology is ahead of the genetic clock by a long mark. You can see other issues in cases like Mungo man in Australia. His line left no descendants so it's very possible there were earlier moderns in the New world that left no genetic legacy to measure against.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Wibbs wrote: »
    That sounds more like it datewise. Good link. I have some issues with DNA evidence though, in particular so called genetic clocks. It's a fashionable science and as such IMHO is relied on too much. There are cases where the DNA stuff doesn't quite match the palaeontology too. The out of africa theory for a start, where stone tool technology is ahead of the genetic clock by a long mark. You can see other issues in cases like Mungo man in Australia. His line left no descendants so it's very possible there were earlier moderns in the New world that left no genetic legacy to measure against.

    It is a good point in that it only tells the story of the those who survived, but this is sometimes noted by researchers to be fair. Strictly speaking such DNA studies are a purely statistical tool, so while you can never prove anything in their own right they can give strong support / evidence against a particular theory.

    I am not sure what you are refering to about the stone tools? Any links would be appreciated, I enjoy this sort of stuff. :)


  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 58,884 Mod ✭✭✭✭ Wibbs


    As do I :) Our evolution is a subject that has fascinated me since I was a young un. When I was a kid the progression was very linear and then it became more bushy and complex. Then DNA was thrown into the mix and it seemed to get both bushy and linear all at the same time.

    First off I'll lay my cards on the table by saying I don't put much stock in the current out of Africa theory. I think it became fashionable on the back of another fashionable diagnostic tool(genetics) and has become almost gospel, an article of faith with little creedence given to any even slightly opposing theory. That in my humble is a bad place for science, though a common enough situation as the past has taught us. Don't get me started on string theory or some of the current cosmology... :D At least with science if a new theory does come along it can with evidence usurp the old and the "fashionable".

    What I do believe happened was that there were many out of africas and our modern humans in the various places in the world encountered earlier out of africa cousins and exchanged genes. Much more than is currently accepted.

    Ok lets look at some of the genetic evidence. Lets look at what marco_polo mentioned about the story of who survived. OK I'm of european stock. Lets say I marry an african lassie and we have two sons. One of them marries a japanese woman and the other marries a south american woman from the high andes. If we look at their kids mitichondrian DNA it'll show that they're either Japanese or Andean indian. No trace of African or European. If you look at their Y chromosome DNA they'll look like Europeans. In both cases No trace of African DNA at all, yet they would share the genetic heritage of the oldest people on the planet. That's just over 3 generations, yet we're supposed to believe that over 100's of 1000's generations we're not missing out some huge chunks of what is going on? I dont buy it.

    The second problem is that even if you take the genetic clocks as a good indicator, there are some issues there too. Among the various human groups on the planet today there are specific genes that are older than this supposed single migration 100,000 odd years ago. There are markers exclusive to Asians and Europeans and Africans that are older than 120,000 years. Older than 200,000 years. That makes no sense if it's a purely out of africa migration 100,000 yrs ago.

    Red hair in europeans is a good example. It's only found in europeans and those of european ancestry(this extends to the middle east, I'm using "european" as a population with common genetics rather than geopolitical stuff). It's not found in Africans, yet according to the out of africa theory where we would be exclusively african genetically, they should have it even as a recessive gene, or europeans evolved it very rapidly(which is possible I grant you). Now the current theory is that Neandertals had red hair http://www.sciencedaily.com/releases/2007/10/071025143311.htm but they're saying even in this article that the gene involved is somehow different and it was arrived at by separate evolution. Again trying to fit the square peg into the round hole of out of Africa theory. I would be inclined to use occams razor and suggest that if the population of modern humans with the gene overlaps exactly the ancient range of Neandertals, then that's where it's more likely to have come from. Ditto with white skin and other european traits. Plus the dna sequenced from the Neandertals is naturally miniscule and only represents a teeny tiny sample, who is to say that they got lucky and they're the rosetta stone of what Neandertal genes were? It would be like the example above of the grandkids not showing african genetic heritage, yet clearly they would have. The evidence like the fossil evidence is way too sparse to make judgements.

    Look at the common idea of the "caveman" the Neandertal. The most famous of our ancestors. You often can hear people call others Neandertal as a pejorative term, yet if you called someone an australopithecine you would rightfully locked up:D The notion is of a dim witted hunched and shambling non human. That idea mostly came from the first fossil of the type. A 40 odd year old elderly broken boned individual. It's not what they were like at all. A strong resourceful upright human who survived countless ice ages and upheavals. A magnificent creature that we should be proud to call a relative, distant or not as the case may be. Our understanding of erectus is even more limited and open to interpretation. In eastern europe just three skulls of the type show such diverse morphology that they are hard to pin down as a type. Evidence is very sparse. The field is so wide open to theory and wild conjecture that to ascribe anything like a given in our ancestors evolution and how that relates to all us modern humans is very ephemeral and should be treated as such. Any hard and fast rule has to be mostly BS unless we got very lucky out of the gate.

    The bones show yet more problems with a purely out of africa migration. EG Modern Asian populations have a slightly different tooth profile in both the incisors and the molars. A profile found in erectus in Asia. Neither is seen in erectus or moderns elsewhere. Eye socket shape is another one. Jawbone angles, patellas, etc. Differences that are used by forensic pathologists today to ascertain population affiliations in modern humans. Many of these can be used to ascertain population affiliations in earlier hominids. Now some may well be locally adaptive, but its hard to explain all IMHO.

    OK It's late and I'm knackered so I'll leave the ramblings at that. Cries of "thank god/dawkins" will not be taken well :D

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Registered Users Posts: 687 Zadkiel


    There was a programme recently on TV about the Chinese believing they evolved along a seperate line from the rest of the early humans and at a later date. I can't find any links to it at the moment but does anyone else recall seeing it? I think this has since been disproven but its quite a while since I watched.


  • Advertisement
  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 58,884 Mod ✭✭✭✭ Wibbs


    Yea I've heard that one before alright. They believe they came from homo erectus, not the recent sapiens from africa. Pure multiregionalists. I wouldn't agree with that either, but I can see why they would come to that conclusion as far as the evidence of some local continuity in the bones.

    There are a few other strange ones too. Australia is a good example. The earliest Australians have less archaic features in the bones than later populations. That makes no obvious sense. Unless as one explanation there were two waves of expansion. The first took a faster route through asia to get to australia and didnt have time mix with resident erectus in asia. The second wave to come in came from closer by in asia where they had lived with populations of archaic humans for 1000s of years and that group brought the archaic features with them. The only other option I can see is that it was local adaptation that happened to mimic archaic features, which is possible but sounds a bit of a stretch. The earliest known australian Mungo man, has mtDNA is of an extinct form, which may further support the notion of multiple migrations.

    I dont have an issue with the ability of archaic hominids and more modern hominids interbreeding. This seems to be a sticking point for the out of africa proponents. Many of them suggest that say a modern and a Neandertal wouldn't be able to produce fertile young because of the time and separation involved. Let's look at wolves and coyotes. They have been separate species for over a million years, yet they can produce fertile hybrids. As can domestic dogs with coyotes. Indeed a population like the indian wolf or ethiopian wolf would produce fertile hybrids with the american coyote and they're very separate. I don't see a problem with hominids separated by less time being able to do so.

    As I say I think our ancestry is very complex and easy answers like simple out of africa or mulitregionalism are way off IMHO. Its going to be a lot more complex than that I reckon.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Registered Users Posts: 687 Zadkiel


    http://www.palenews.net/2009/09/underwater-expedition-delivers-key.html

    "In one of the more dramatic moments of an underwater archaeological survey co-led by Mercyhurst College archaeologist James Adovasio along Florida's Gulf Coast this summer, Andy Hemmings stood on an inundated river's edge where man hasn't set foot in more than 13,000 years. Donning full scuba gear, Hemmings stood in 130 feet of water on a peninsula at the intersection of two ancient rivers nearly 100 miles offshore from Tampa. The last time humans could have stood in that spot, mammoth and mastodon roamed the terrain.
    "The successful tracking of the St. Marks-Aucilla River and the Suwannee River, between 50 and 150 kilometers respectively, represents what we believe to be the most extensive delineation of submerged prehistoric river systems ever done anywhere in the world," Adovasio said.
    Another pivotal find is the identification of chert at three dive sites along the river systems; chert is a superior quality fine-grained stone used by prehistoric peoples to make tools.
    "There is no doubt," Adovasio said, "that we have found the haystacks and are one step closer to uncovering the archaeological needles;" in effect, narrowing the search for evidence of early Americans in the now submerged Inner Continental Shelf in the Gulf of Mexico off the Florida coast.
    Hemmings, one of the leading Paleoindian underwater archaeologists in North America, agreed. "My feeling is, given a little time to probe the sediments with a dredge, we will quickly find human artifacts."
    The signature expedition of the National Oceanic and Atmospheric Administration (NOAA) Office of Ocean Exploration and Research began in the summer of 2008 when a distinguished group of scientists led by Mercyhurst's Adovasio and Hemmings identified and mapped buried river channels that could potentially help document the late Pleistocene landscape. This year's mission, undertaken July 23 to Aug. 5, further traced the river systems along whose beaches prehistoric people may have populated and identified raw materials that they may have used in tool making. "

    They will be going back next year to dive deeper ( 165ft) so hopefully they'll find something give solid dates.


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Wibbs wrote: »
    That sounds more like it datewise. Good link. I have some issues with DNA evidence though, in particular so called genetic clocks. It's a fashionable science and as such IMHO is relied on too much. There are cases where the DNA stuff doesn't quite match the palaeontology too. The out of africa theory for a start, where stone tool technology is ahead of the genetic clock by a long mark. You can see other issues in cases like Mungo man in Australia. His line left no descendants so it's very possible there were earlier moderns in the New world that left no genetic legacy to measure against.

    Bit of a bump here but I came across this article in Sci-Am that provides some support for your reservations about genetic clocks. From the scientists that gave you evolution in a test tube. They have been busy analysing the DNA sequences changes between each generation of their Ecoli evolution experiment. It is interesting how the mutation rate jumped signifigantly after 26,000 generations.
    http://www.scientificamerican.com/blog/post.cfm?id=evolution-details-revealed-through-2009-10-18

    Early changes in the bacteria appeared to be largely adaptive, helping them be more successful in their environment. "The genome was evolving along at a surprisingly constant rate, even as the adaptation of the bacteria slowed down," he noted. "But then suddenly the mutation rate jumped way up, and a new dynamic relationship was established."

    By generation 20,000, for example, the group found that some 45 genetic mutations had occurred, but 6,000 generations later a genetic mutation in the metabolism arose and sparked a rapid increase in the number of mutations so that by generation 40,000, some 653 mutations had occurred. Unlike the earlier changes, many of these later mutations appeared to be more random and neutral.

    The long-awaited findings show that calculating rates and types of evolutionary change may be even more difficult to do without a rich data set. "The fluid and complex coupling observed between the rates of genomic evolution and adaptation even in this simplistic system cautions against categorical interpretations about rates of genomic evolution in nature without specific knowledge of molecular and population-genetic processes," the paper authors wrote.

    Such detailed pictures of mutation rates have been made possible since the advent of rapid genome sequencing. "It's extra nice now to be able to show precisely how selection has changed the genomes of these bacteria, step by step over tens of thousands of generations," Lenski said.


  • Registered Users Posts: 30,747 ✭✭✭✭ Galvasean


    One theory as to why the North American megabeasts (such as the legendary sabertooth cat Smilodon) were wiped out suggested that a large meteorite impact may have been responsible. However, recent analysis suggests that the evidence for this theory was misinterpretated, with the debris of numerous tiny (non life threatening) meteorite impacts being mistaken for one larger devastating one.

    Full article here.

    adapted-smilidon.jpg


  • Registered Users Posts: 25,560 ✭✭✭✭ Kess73


    Meh that is not factual at all.

    Wolverine killed Sabretooth, everybody knows that.

    Chopped his head clean off with the Muramasa Blade, the one weapon that prevents his healing factor from working.




    WolverineVsSabretooth.jpg


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Wibbs wrote: »
    The other problem I have with the human driven extinction is that IMH clovis wasn't ground zero for humans in the americas. It's a fiercely defended position though and quite a few academics have been blasted for even suggesting there was a human presence in the Americas before the clovis culture.

    I'll make a bet now that good evidence will be found that humans were there before. Well here's one http://www.sciencedaily.com/releases/2008/04/080403141109.htm There's a chilean site that is pretty strong for a date of 13000 yrs ago. So they would have likely come down from the north all the way to the tip of south america. Chances are that didn't take 100 years or anything like it, so there must exist northerly sites earlier. They don't even have to have come from asia either. The clovis tools show far more similarities to european tools than asian. Though as kennewick man showed that's a political hot potato.

    I suspect even earlier finds are out there. There's a contested site in carolina that carbon 14 dating suggests a figure of 50,000 years ago. There's another again in south america that returns a carbon date of 21000 years ago. If humans got to somewhere like Australia 50/60,000 years ago, I find it really hard to swallow that the Americas was 40,000 odd years later. If flores man is a definite dwarf relict erectus, then that strongly suggests homo erectus had some sea navigation capability. its at least possible that erectus made it to the americas too. They were around for over a million years and got everywhere else(except australia). Hell we're nearly 200,000 years old as a species and as student backpackers show we can't bloody sit still for long.... :D

    It does look like humans arriving in australia killed off the megafauna though. Or at least helped it on it's way. The climate changed too, but even there humans have been partially blamed. Hunting practices using fire clearance. Around the time of the earliest human evidence large areas show burning. May be a coincidence though.

    I suspect the more we find out about Homo and our ancient travels some pretty amazing stuff is going to come up. I reckon we've barely scratched the surface.

    This is turning into a very good week for Wibbs and the phrase 'I told you so' :D

    Archaeologists have discovered the earliest human artifact found thus far in the Americas.

    Oldest American artefact unearthed

    Archaeologists claim to have found the oldest known artefact in the Americas, a scraper-like tool in an Oregon cave that dates back 14,230 years.

    The tool shows that people were living in North America well before the widespread Clovis culture of 12,900 to 12,400 years ago, says archaeologist Dennis Jenkins of the University of Oregon in Eugene.

    Studies of sediment and radiocarbon dating showed the bone's age. Jenkins presented the finding late last month in a lecture at the University of Oregon.


  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 58,884 Mod ✭✭✭✭ Wibbs


    Great!:) Now hopefully some other previously contentious sites will be looked at anew, now the clovis point cherry has been well and truly popped. I'd be looking at ones that have suggested figure in the 30,000 40,000 BCE range.

    http://news.nationalgeographic.com/news/2005/12/1201_051201_footprints.html An interesting site. Personally I don't credit the 1.3 MYA date. For a number of reasons. I do think it possible that later erectus may have gotten there, but not that far back. The 40,000 yr old works for me though as far as moderns go. Later immigrations may be hiding or confusing the earlier ones. The earlier ones may have even gone extinct. It would be interesting to look at secondary clues. Is there any evidence of changes in the flora and fauna around that time in the americas. Foods we may have imported that show up then, or extinctions or reductions of certain animal species(particularly mega fauna).

    There seems to have been a worldwide expansion of sapiens bracketing the 50,000 years ago timeframe. This would make sense at least for me. It's also coincidentally (or not IMHO), the timeframe for the worldwide explosion in culture and of us living much longer than before and a few interesting climate shifts and animal extinctions. It may go hand in hand with an increased wanderlust in our species.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    It would appear that the timeframe for the mass extinction was quite short and took place between 13.8 and 11.4 years ago. It doesn't lend support to any one particular theory but it doeis evidence against those theories that propose a slower gradual decline to extinction.

    http://www.sciencedaily.com/releases/2009/11/091127140706.htm

    However, new findings from Faith indicate that the extinction is best characterized as a sudden event that took place between 13.8 and 11.4 thousand years ago. Faith's findings support the idea that this mass extinction was due to human overkill, comet impact or other rapid events rather than a slow attrition.

    "The massive extinction coincides precisely with human arrival on the continent, abrupt climate change, and a possible extraterrestrial impact event" said Faith. "It remains possible that any one of these or all, contributed to the sudden extinctions. We now have a better understanding of when the extinctions took place and the next step is to figure out why."

    Another article using sediment cores that suggest the decline took place over the course of about 1000 years at least at one particular location. To the geography professor who conducted the study calls this a gradual decline, but I think that to a palaeontologist that would be more or less an instant in gelogical time.


    http://www.sciencedaily.com/releases/2009/11/091119141029.htm


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    A study of sediment cores has suggest that the onset of the Younger Dryas Ice age may have happened much more quickly than previously thought, and that changes cause but the halting of the oceanic currents could have had an effect on the climate within a few short months.
    http://www.sciencedaily.com/releases/2009/11/091130112421.htm

    Patterson and his colleagues have created the highest resolution record of the 'Big Freeze' event to date, from a mud core taken from an ancient lake, Lough Monreach, in Ireland. Using a scalpel layers were sliced from the core, just 0.5mm thick, representing a time period of one to three months.

    Carbon isotopes in each slice reveal how productive the lake was, while oxygen isotopes give a picture of temperature and rainfall. At the start of the 'Big Freeze' their new record shows that temperatures plummeted and lake productivity stopped over the course of just a few years. "It would be like taking Ireland today and moving it up to Svalbard, creating icy conditions in a very short period of time," says Patterson, who presented the findings at the European Science Foundation BOREAS conference on humans in the Arctic, in Rovaniemi, Finland.


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    The impact strike hypothesis has taken another blow as scientists led by researchers at the University of Hawaii at Manoa were unable to replicate the findings of the orignal study from about two years ago reporting high iridium concentrations in sediments, but seperate additional line of inquiry also failed to support the theory.

    http://www.sciencedaily.com/releases/2009/12/091208132734.htm

    A team led by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this theory, to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas.

    Their results will be published in the December 7th early online edition of the Proceedings of the National Academy of Sciences.

    The idea that an impact event may have been the instigator for this cooling period was appealing because of several alleged impact markers, especially the high iridium concentrations that the previous team reported. However, it is difficult for proponents of this theory to explain why no impact crater of this age is known. "There is a black mat layer across North America which is correlated to the Younger Dryas climatic shift seen in Greenland ice cores dated at 13,000 years ago by radio carbon," explains Paquay. "Initially I thought this type of layer could be associated with an impact event because concentration in the proxies of widespread wildfires are sky high. That plus very high levels of iridium (which is one indicator used to indicate extraterrestrial impact events). So the theory was conceptually appealing, but because of the missing impact site, the idea of one or multiple airburst arose."

    To corroborate the theory, Paquay and his colleagues decided to take a three-pronged approach. The first was to replicate the original researchers data, the second step was to look for other tracers, specifically osmium isotopes, of extraterrestrial matter in those rocks, and the third step was to look for these concentrations in other settings. "Because there are so many aspects to the impact theory, we decided to just focus on geochemical evidence that was associated with it, like the concentration of iridium and other platinum group elements, and the osmium isotopes," says Paquay. "We also decided to look in very high resolution sediment cores across North America, and yet we could find nothing in our data to support their theory."


  • Advertisement
  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    Interesting article in SciAm as three different recent studies (two of which I highlighted a few posts back), give three different dates for the dissapperance of American Megafauna.
    http://www.scientificamerican.com/article.cfm?id=lost-giants-did-mammoths.

    Lost Giants: Did Mammoths Vanish Before, During and After Humans Arrived?

    ....

    To pin down when the megafauna vanished, paleoecologist Jacquelyn Gill of the University of Wisconsin–Madison and her colleagues analyzed fossil dung, pollen and charcoal from ancient lake sediments in Indiana. The dung of large herbivores harbors a fungus known as Sporomiella , and its amounts in the dung gives an estimate of how many mammoths and other megafauna were alive at different points in history. Pollen indicates vegetation levels, and charcoal signals how many fires burned; the extent of flora and wildfires is related to the presence of herbivores, the researchers say in the November 20 Science. Without megaherbivores to keep them in check, broad-leaved tree species such as black ash, elm and ironwood claimed the landscape; soon after, buildups of woody debris sparked a dramatic increase in wildfires. Putting these data together, Gill and her team conclude that the giant animals disappeared 14,800 to 13,700 years ago —up to 1,300 years before Clovis.

    A different study, however, suggests that this mass extinction happened during Clovis. Zooarchaeologist J. Tyler Faith of George Washington University and archaeologist Todd Surovell of the University of Wyoming carbon-dated prehistoric North American mammal bones from 31 different genera (groups of species). They found that all of them seemed to meet their end simultaneously between 13,800 to 11,400 years ago, findings they detailed online November 23 in the Proceedings of the National Academy of Sciences USA.

    But if ancient DNA recovered from permafrost is any sign, megafauna survived in the New World millennia after humanity arrived. As the permafrost in central Alaska cracked during springtime thaws, water that held DNA from life in the region leaked in, only to freeze again during the winter. As such, these genes can serve as markers of “ghost ranges” — remnant populations not preserved as fossil bones.

    ..............

    Johnson suggests the fungus research is superb evidence for when the decline began, but it is not as good at confirming exactly when the extinction was completed, especially over larger areas where sparse populations might have persisted. The DNA finds, on the other hand, can detect late survivors, he says, “maybe very close to the actual time that the last individuals were alive, at least in Alaska.” The bones analyzed from the period roughly in between show that the extinction process afflicted many species simultaneously. Those fossils came from the contiguous U.S., which back then was separated from Alaska by the massive Laurentide and Cordilleran ice sheets and so, Faith notes, could explain why the pattern of extinction differed up there.

    And is it me, or are the comments sections of Scientific American and New Scientist becoming more like YouTube with every passing day?


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    To complete the set here is the science daily report on the DNA studies. Some clever work IMO, involving DNA sampling from permafrost cores. And 10,500 years is the upper range of the estimate.
    http://www.sciencedaily.com/releases/2009/12/091214151946.htm

    In order to prospect for genetic fossils, the team collected soil cores from undisturbed Alaskan permafrost. Wind-blown Stevens Village, situated on the bank of the Yukon River, fit the bill perfectly. Here, sediments were sealed in permafrost soon after deposition. Two independent methods (radiocarbon and optically stimulated luminescence) were used to date plant remains and individual mineral grains found in the same layers as the DNA.

    "With these two techniques, we can be confident that the deposits from which the DNA was recovered haven't been contaminated since these lost giants last passed this way," said Roberts, director of the Centre for Archaeological Science at the University of Wollongong. "It's a genetic graveyard, frozen in time."

    Cores collected at Stevens Village offer a clear picture of the local Alaskan fauna at the end of the last ice age. The oldest sediments, dated to about 11,000 years ago, contain remnant DNA of Arctic hare, bison, and moose; all three animals were also found in higher, more recent layers, as would be expected. But one core, deposited between 7,600 and 10,500 years ago, confirmed the presence of both mammoth and horse DNA. To make certain that the integrity of this sample had not been compromised by geologic processes (for example, that ancient DNA had not blown into the surface soils), the team did extensive surface sampling in the vicinity of Stevens Village. No DNA evidence of mammoth, horse, or other extinct species was found in modern samples, a result that supports previous studies which have shown that DNA degrades rapidly when exposed to sunlight and various chemical reactions.


  • Moderators, Science, Health & Environment Moderators Posts: 10,073 marco_polo


    A little more evidence in support of the comet theory, from the same team as in the OP. Nanodiamonds dating from the Younger Dryas boundary aproximately 12,900 years ago, have been discovered in the Greenland ice sheets.
    http://www.sciencedaily.com/releases/2010/09/100914143626.htm

    "There is a layer in the ice with a great abundance of diamonds," said co-author James Kennett, professor emeritus in the Department of Earth Science at UC Santa Barbara. "Most exciting to us is that this is the first such discrete layer of diamonds ever found in glacial ice anywhere on Earth, including the huge polar ice sheets and the alpine glaciers. The diamonds are so tiny that they can only be observed with special, highly magnifying microscopes. They number in the trillions."

    This discovery supports earlier published evidence for a cosmic impact event about 12,900 years ago, Kennett explained. He said that the available evidence in the Greenland ice is consistent with this layer being at or close to this age, although further study is needed.

    .....................................


    A high proportion of the nanosize diamonds in the Greenland ice sheet exhibit hexagonal mineral structure, and these are only known to occur on Earth in association with known cosmic impact events, said Kennett. This layer of diamonds corresponds with the sedimentary layer known as the Younger Dryas Boundary, dating to 12,900 years ago.


Advertisement