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| The revealing micro-spherules |
After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight.
Malcom A. LeCompte et al. Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis. PNAS 2012. Pay per view (for 6 months/depending on world region) ··> LINK [doi]
Abstract
Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesized North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155–18158] collected and analyzed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.
Most interesting in this research is that it was done directly at an archaeological layer of the Clovis clulture, what makes the chronology very solid.
Also the authors claim that some of the negative reports did not follow the protocol to detect the spherules and that is why they missed them, stirring controversy.
Partial source: Science Daily.
See also for background (this blog and its predecessor in reverse chronological order):
- More evidence in support of the Younger Dryas impact theory (2012)
- Clovis impact theory: scam? (2011)
- Clovis impact theory rejected (2010)
- Clovis impact theory finds new support (2010)
- More evidence for Clovis age meteorite impact (2009)
"After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight.After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight".
ReplyDeleteAs far as I'm aware there has been no debate as to whether or not a meteorite hit at that time. The debate is over how great an effect it had on the fauna and flora of North America, and how widespread that effect was. The extinction at the time was very selective and so is unlikely to have been the product of a meteor impact, although I grant it may have reduced population size. However it should not have affected the recovery of the flora and fauna in the slightest. Something else held that recovery up.
That may be your debate or greatest concern but the actual debate was about the impact happening or not at all. See the "see also" section for background: some researcher failed to find any micro-spherules and caused the initial theory to be doubted, with some heated debate after it. Nowadays however it seems consolidated.
DeleteThe study certainly firms up this data point, in terms of the cause of the Younger Dryas and in terms of its relative temporal relationship to the Clovis culture.
ReplyDeleteIt suggests that something very different was going on in the pre-YD migration into the Americas of the earliest indigenous Americans and the modestly later Clovis expansion. Perhaps the initial human population of North America was exclusively via a Pacific coast route and the passage across Canada was accessable for large scale migration that opened the door to a subsequent east to west expansion of the Clovis people only after YD.
It also suggests that the process at work in American megafauna extinctions may have been fundamentally different in North America where inter-related YD and Clovis expansion processes culminated in the rapid slaughter on North American mammals from the megafauna extinctions in South America (especially east of the Andes), where it may have been incident to the expansion of the human range into the area that may have been more gradual.
I did not think it would come up but it was also briefly mentioned in this blog that Clovis culture may well have ended for reasons other than the impact.
DeleteIn any case, Clovis pre-dates the impact, no gate was opened for them by the meteorite. Instead the meteorite, or rather the subsequent rapid climatic changes (in America as in Eurasia and elsewhere) are surely an important part explaining the extinction of megafauna in that period.
"Instead the meteorite, or rather the subsequent rapid climatic changes (in America as in Eurasia and elsewhere) are surely an important part explaining the extinction of megafauna in that period".
ReplyDeleteNo, a completely inadequate explanation for the extinction.
In Europe at least the first warming caused expansion of forest, what harmed the steppe beasts, like the mammoth, while the sudden freezing in a matter of months of the YD must have totally dislocated the survival mechanisms of most species, humans included. If that's not a extinction factor, then what is it?
DeleteNotice that I'm never saying it was the only factor but an important one.
"In Europe at least the first warming caused expansion of forest"
ReplyDeleteWe've been through the most likely reason for that, so I don't want to waste my time.
I just found this, via 'The archeology News Network' link at the side:
ReplyDeletehttp://archaeologynewsnetwork.blogspot.co.nz/2012/11/hunting-or-climate-change-megafauna.html#.UKW0FmcmWuI
Quote:
"This does not mean that archaeological evidence of killing (or absence of such evidence) is useless in testing the overkill hypothesis. Surovell and Grund show it can be useful, by comparing the archaeological records of Australia, North America and New Zealand. All three places lost their megafaunas when people arrived, but this happened a very long time ago in Australia, and very recently (700 years ago) in New Zealand. North America is intermediate, with human arrival and extinction from 14,000 to 13,000 years ago.
"Applying the same logic to all three cases, we predict that if overkill caused megafaunal extinction in each place the archaeological evidence of killing should be abundant in New Zealand, rare in North America, and vanishingly rare in Australia. That is exactly what we find.
"There is so much evidence showing New Zealand’s moa were heavily hunted that nobody doubts overkill was the main cause of their extinction. In North America, there are undoubted kill sites for mammoths, mastodons and a few other species, but this evidence is far thinner than in New Zealand. Australian archaeology is yet to reveal any convincing evidence for megafauna-killing.
"So, far from disproving overkill, the archaeological evidence from Australia is actually consistent with the overkill hypothesis".
A lack of evidence is to be expected so that is evidence? What kind of logic is that? One that was dismissed (by (Grayson et al Journal of World Prehistory, Vol. 16, No. 4, December 2002) when something remarkedly similar was previously suggested (by Martin et al 1973,1984):
Delete"Martin’s only response to this situation has been to argue
that it all happened so fast that there was no time for the results to have been
preserved (e.g., Martin, 1973, 1984), that the wonder is not that there are so
few kill sites but that there are any at all, and that “much evidence of killing
or processing of the extinct fauna is not predicted” by his position (Martin,
1984, p. 397). This is an argument whose scientific logic has always eluded
us (Grayson, 1984b; Meltzer, 1993b). It does, however, make a great deal of
sense once it is accepted that Martin’s argument is meant to appeal not to
scientific reason but instead to faith, more akin to religion than to biology
(Grayson, 2001; Grayson and Meltzer, in press). His suggestion that overkill
happened so fast that no evidence of it is either expected or required follows
inexorably from that stance." http://faculty.washington.edu/grayson/jwp02.pdf
"It does, however, make a great deal of
ReplyDeletesense once it is accepted that Martin’s argument is meant to appeal not to
scientific reason but instead to faith, more akin to religion than to biology"
It may be a religion but unlike other religions it is based on fact. Humans, like all other species, alter the habitat whenever they manage to reach a region previously unexploited by their species. It would be absolutely incredible if the first inhabitants in Australia and America did not alter the environment in some way, perhaps extremely. Besides which I believe that extinction-deniers are the ones with a religious problem. They have some idealised view of prehistoric man as living totally in harmony with the environment. Balderdash. They usually exploited it ruthlessly until the resources began to run out, the same as everybody else.
"A lack of evidence is to be expected so that is evidence? What kind of logic is that?"
You're ignoring the thrust of the article. Quote:
"Surovell and Grund show it can be useful, by comparing the archaeological records of Australia, North America and New Zealand. All three places lost their megafaunas when people arrived, but this happened a very long time ago in Australia, and very recently (700 years ago) in New Zealand. North America is intermediate, with human arrival and extinction from 14,000 to 13,000 years ago".
So you are claiming that although megafauna species extinction occurred in each region soon after humans arrived this is purely coincidence? Now, I'm sure that almost everyone would disagree with that view in the case of new Zealand, where we find much evidence in support of overkill. As the authors ay:
"There is so much evidence showing New Zealand’s moa were heavily hunted that nobody doubts overkill was the main cause of their extinction".
And to say that no evidence of megafauna hunting has been found in America is to greatly overstate the true position. Again from the article:
"In North America, there are undoubted kill sites for mammoths, mastodons and a few other species, but this evidence is far thinner than in New Zealand. Australian archaeology is yet to reveal any convincing evidence for megafauna-killing".
To repeat a couple of comments I quoted:
"So, far from disproving overkill, the archaeological evidence from Australia is actually consistent with the overkill hypothesis".
"Applying the same logic to all three cases, we predict that if overkill caused megafaunal extinction in each place the archaeological evidence of killing should be abundant in New Zealand, rare in North America, and vanishingly rare in Australia. That is exactly what we find".
"They have some idealised view of prehistoric man as living totally in harmony with the environment. Balderdash. They usually exploited it ruthlessly until the resources began to run out, the same as everybody else".
DeleteYou claim that based on what? Because as far as I know of every single forager community, they tend to take only what they need and be reasonably aware of the ecology implicit in their economy. Said, that, in fragile ecosystems even such a minimal impact can be harmful but then they were co-factors and not the only factor.
Every time I've read of tribal communities behaving ruthlessly against the ecosystem, they were part-time farmers. Still, anthropological studies show that with the same general economical system, two different tribes can behave very differently based on cultural elements of each.
Whatever the case your attempt to generalize what you infer that happened in Australia to all continental reginons (but Africa and Tropical Asia quite curiously) or what may have happened in small islands to huge continents is what looks to me a fanatic endeavor, Terry. More so when you never seem to consider any other co-adjutant extinction factor, nor exceptions nor incomparable timelines... just that at some point some species went extinct and you choose to blame Homo sapiens for that, even if they had arrived to the area many thousand years earlier and other factors like hyper-fast climate change was at play when the extinction happened.
You just have decided that Humankind is to blame always and exclusively for every extinction... unless, like dinosaurs (and many others) does not fit in the time frame... or unless, like most tropical megafauna, did not go extinct at all.
Try criticizing your own biases before you accuse others, please.
"All three places lost their megafaunas when people arrived"...
Not true in America. Megafauna (with some notable exceptions, let's not forget) went extinct long after human arrival, some five or six millennia later and with no obvious signature of decline that we know of. It went extinct coincident with the Young Dryas, whose onset we know was radically fast (in a matter of months Ireland went from a climate like today's Ireland to a climate like today's Greenland) and was seemingly associated to a meteorite impact, which incidentally fell on North America (where most of that lost megafauna was).
"In North America, there are undoubted kill sites for mammoths"...
In Europe too, associated to H. heidelbergensis or Neanderthal. But mammoth survived them. Maybe we should blame mammoths for the demise of Neanderthals? Lions kill elephants preferentially in some parks of Zimbabwe but elephants do not go extinct for that alone.
...
...
Delete"Applying the same logic to all three cases, we predict that if overkill caused megafaunal extinction in each place the archaeological evidence of killing should be abundant in New Zealand, rare in North America, and vanishingly rare in Australia. That is exactly what we find".
It sounds fallacious, sorry. Of course that they knew the results of their "prediction" beforehand but I see no reason why we should not find an "overkill record" in Australia if there was one actually.
Why should we find an "overkill record" in Europe much older than the colonization of Australia by H. sapiens if mammoths survived and your fetish authors' prediction should be that there should be none? Archaeology is not that way; let's be serious and compare apples with apples, like the Jersey and Atapuerca kill sites vs the total absence of any kills sites in Australia.
Said that our kin surely altered the ecological balance somehow, maybe by introducing dogs or just by surviving themselves but it's also true that Australia is in many aspects more like an island than a true continent: with too many animals in "dodo mode", just waiting for a tiny push to reach extinction. But it does not look like they were in massacre rampage mode at all, rather that, as they do now, they have some care not to abuse their resources. After all the hunting grounds of a tribe or clan are like their "farm", so to say, and they care about it as much or more as any modern proprietary.
"You claim that based on what? Because as far as I know of every single forager community, they tend to take only what they need and be reasonably aware of the ecology implicit in their economy".
ReplyDeleteThey do so only once it become absolutely necessary for them to do so, otherwise they would starve. Evidence? The extinction of any number of species during the early human occupation of any land mass.
"Whatever the case your attempt to generalize what you infer that happened in Australia to all continental reginons (but Africa and Tropical Asia quite curiously)"
There was actually a run of extinctions in Africa, but spread over a considerable time scale. I have been unable to find any reliable information on South Asian extinctions although Sivatherium seems a likely candidate.
http://en.wikipedia.org/wiki/Sivatherium
And you may find the following link relevant although it deals primarily with Holocene extinctions. Sorry, it's a 'google' link. Hope you can reach it:
http://www.google.co.nz/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&sqi=2&ved=0CEUQFjAD&url=http%3A%2F%2F192.38.112.111%2Fpdf-reprints%2FTurvey_PToTRSBS_2011.pdf&ei=RWXGUJXYGIWziQf6tYCIBQ&usg=AFQjCNHkn-fyey7yzBpuz_-talGtkjvJ_w
"More so when you never seem to consider any other co-adjutant extinction factor, nor exceptions nor incomparable timelines... just that at some point some species went extinct and you choose to blame Homo sapiens for that"
Here's what the paper claims:
"The staggered timing of Late Pleistocene mammal extinctions and their close temporal association with first human colonization of different continental regions is increasingly well understood for North America and Australia, and direct or indirect human involvement with these events is now widely accepted by most palaeontologists".
So I'm far from being alone.
"or unless, like most tropical megafauna, did not go extinct at all".
But is now rapidly approaching extinction. The above paper explains why that is so.
"Not true in America. Megafauna (with some notable exceptions, let's not forget) went extinct long after human arrival, some five or six millennia later and with no obvious signature of decline that we know of".
Not according to this 2009 paper:
http://www.pnas.org/content/106/49/20641.full
Quote:
"The surge in extinction rates between 12,000 and 10,000 radiocarbon years B.P. is particularly significant in that this time period encompasses the earliest secure evidence of human foragers in North America (24, 25), the Younger Dryas cold interval (26), and a possible extraterrestrial impact (15, 16). Thus, the chronology is consistent with anthropogenic, environmental, and extraterrestrial extinction mechanisms. The chronological synchroneity of these events means that we cannot readily identify a single mechanism responsible for the sudden surge in extinction rates. That the massive terminal Pleistocene losses are the direct result of the fortuitous intersection of these events also remains possible"
So the authors are non-committal concerning the cause, but do say:
"The evidence for a catastrophic terminal Pleistocene extinction requires that we attribute to the extinction cause a number of properties, most notably speed and breadth (19). Thus, explanations for the extinctions must be able to account for the disappearance of up to 35 genera, characterized by varied feeding habits and habitat preferences, in a geologic instant".
Note: 'varied feeding habits and habitat preferences'. Both climate change and asteroid impact are likely to be far more specific as to the type of species they take out.
More on the subject:
ReplyDeletehttp://news.mongabay.com/2006/0505-extinction.html
"New research suggests that prehistoric horses in Alaska may have been hunted into extinction by man, rather than doomed by climate change as previously thought. The study is published this week in Proceedings of the National Academy of Sciences (PNAS).... While no one is yet certain what caused the demise of these mammals — which included such wild beasts as giant sloths, mammoths, sabertooth cats, and oversized horses and rhinos— one of the leading theories argues that habitat fragmentation, caused by global climate change, split species into small populations, making them more vulnerable to extinction by human hunters. Models suggest that by merely killing off 2 percent of the mammoth population every year, the entire species would be doomed to eventual extinction some three or four centuries down the road. These natural (climate change) and unnatural (human) influences working in concert may have condemned to extinction some of the most magnificent creatures ever seen by man".
http://thelede.blogs.nytimes.com/2007/01/25/researchers-say-prehistoric-extinctions-in-australia-were-mans-work-not-natures/
"Among the most important conclusions is that the rainfall in the Nullarbor Plain when the animals were alive was not significantly different from the rainfall today, leading to the conclusion that it is unlikely that climate change alone explains the extinction of so many species. Professor Richard Roberts, a geochemist at the University of Wollongong who dated the bones, said that by comparing the dates of the remains with evidence of rainfall at the time, the scientists established that different species had managed to survive relatively major changes in the climate. …Their conclusions deal a blow to the longstanding argument that the extinction of Australia’s giant native fauna … was caused by natural changes in the environment and not humans".
http://phys.org/news/2012-05-prehistoric-cold-case-links-humans.html
"Analysis carried out at the Australian Nuclear Science and Technology Organisation (ANSTO) on the skeletal remains of extinct megafauna is providing substantial proof that for about 2,000 years they infact shared the island with early humans before suddenly disappearing some time before the last ice age. The findings challenge for the first real time history's version of events and by now placing our ancestors in Tasmania at the same time as large prehistoric animals, like the Protemnodon anak (a giant wallaby), raises the chances we were involved in their extinction...Popular belief has centred on three likely scenarios for the mass extinction of the megafauna in the region: environmental causes related to climate change, which was considered the key cause of their extinction. Hyper-disease and human hunting have been a distant second in the debate. Geological work on sea level change suggests humans could not have crossed Bass Strait until around 43,000 years ago when the island was temporarily connected by a land bridge to Australia. The vanishing of megafauna was thought to have occurred thousands of years preceding human arrival, clearing them from any involvement. That is, of course, until now ... "
But wait. There's more:
ReplyDeletehttp://en.wikipedia.org/wiki/Quaternary_extinction_event
"Evidence supporting the prehistoric overkill hypothesis includes the persistence of certain island megafauna for several millennia past the disappearance of their continental cousins. Ground sloths survived on the Antilles long after North and South American ground sloths were extinct. The later disappearance of the island species correlates with the later colonization of these islands by humans. Similarly, woolly mammoths died out on remote Wrangel Island 7000 years after their mainland extinction. Steller's sea cows also persisted off the isolated and uninhabited Commander Islands for thousands of years after they vanished from continental shores of the north Pacific".
"The Old World tropics have been relatively spared by Pleistocene extinctions. Africa and Asia are the only regions that have megamammals weighing over 1000 kg today. However, during the early, middle and late Pleistocene some large animal forms disappeared from these regions without being replaced by comparable successor species".
"Large animals,which disappeared in Africa or Asia during the Early and Middle and Late Pleistocene:
Giraffes, including Sivatherium.
A species of wolf (Xenocyon lycaonoides)
A few species of warthog such as Metridiochoerus
Chalicotheres
Deinotherium, Anancus and Mammuthus subplanifrons, relatives of the elephant
Hippopotamus gorgops (a giant hippopotamus)
False saber-toothed cats like Dinofelis
Saber-toothed cats like Megantereon and Homotherium
Giant tapir Megatapirus
Giant ape Gigantopithecus
Giant hyena Pachycrocuta
Large animals, which disappeared in parts of Africa and Asia during the Late Pleistocene:
Giant Long-horned Buffalo (Pelorovis)
Giant hartebeest Megalotragus
Elephas recki (a species of elephant)
Loxodonta adaurora (a species of African elephant)"
In America it seems all we see is an alleged coincidence of chronology, which would be more than suspicious, if it were not that there is no such coincidence because people arrived to America some 5000 years earlier (at least) than the Clovis model claimed.
ReplyDeletewhere is the 16 Ka North American extinction event? Nowhere!
That's an extremely week response.
ReplyDelete"where is the 16 Ka North American extinction event? Nowhere!"
Even the most ardent overkill supporter would not claim instant extinction. Try to be a little bit sensible.
"In America it seems all we see is an alleged coincidence of chronology"
And that's all we see with both the asteroid and climate change hypotheses.
"It went extinct coincident with the Young Dryas, whose onset we know was radically fast".
Just a few months ago you were claiming it was the climate warming and expansion of forest that led to the megafauna extinctions in Europe. Here you're claiming it was climate cooling the led to the extinction. Seems you're prepared to support any theory as long as it doesn't involve humans in any way. More laughs for me.
The overkill hypothesis was outlined when "Clovis First" was dogma (until a few years ago, mind you) and there was not yet evidence of the Younger Dryas meteorite (also very recent news) and the YD episode was not understood as one of almost "instant freezing", as we know now it was.
DeleteSo the most ardent overkill supporters actually used to claim almost "instant extinction". Now they cannot anymore, of course.
"Just a few months ago you were claiming it was the climate warming and expansion of forest that led to the megafauna extinctions in Europe. Here you're claiming it was climate cooling the led to the extinction".
They happened in rapid succession so they can be both one after the other. One removed the pastures (replacing them by forests), the other caused near-instant freeze of everything, killing or putting in near-extinction situation to species that had already been weakened by the previous process. Nature adapts but it needs time and the swings around the YD episode were too fast, notably the sudden freeze.
Whatever the case, how do you imagine that ancient Homo sapiens killed every single horse in North America (and left not a single evidence of kills for this animal specifically). Wouldn't horses just leave behind our supposedly genocidal relatives with ease?
I can't imagine our kin hunting horses to extinction prior to horse domestication itself.
"how do you imagine that ancient Homo sapiens killed every single horse in North America (and left not a single evidence of kills for this animal specifically)".
DeleteWe know from extinction events in the last few hundred years that it is by no means necessary to kill every last individual to cause a species to become extinct. Overhunting breaks up a species' distribution, and the small isolated populations die out. Inbreeding is a huge problem for efforts today to save species threatened with extinction. If it were not for human assistance many birds now hanging on in New Zealand, for example, would already be extinct.