[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.

[marco_polo]

Originally Posted by 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...0403141109.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....

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'

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.

[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/n...ootprints.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.

[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...1127140706.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...1119141029.htm

[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...1130112421.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.

[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...1208132734.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."

[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/ar...s-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?

[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...1214151946.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.

[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...0914143626.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.