Some 12,800 years ago, when the climate was warming very fast and temperatures had almost reached present day levels... they suddenly plumetted again in a matter of months and remained at Ice Age levels for more than a thousand years before warming again. That period is known as the Younger Dryas.
 |
| The Younger Dryas is the last cold gorge by the left |
There used to be several explanations but since some time ago, the meteorite impact theory has been gaining weight. This evidence would seem to consolidate it.
It was already quite consolidated as a theory because, while some had questioned the earliest evidence, further data had been collected from around the world that reinforced the model by about the same time.
The new evidence comes in form of melted glass (siliceous scoria like objects, SLOs) mineral inclusions from Pennsylvania (USA), which appears to require such an impact to have been produced. This kind of product requires temperatures similar to those of a nuclear explosion.
 |
| The glass-like grains at two different imaging resolutions |
These remains have been found so far in North and South America, Europe and West Asia, suggesting several impacts from an already fragmented meteorite. It is unclear if there could be more such findings elsewhere on Earth.
One of the places directly affected by the impact was the site of Abu Hureyra, at the Mid-Upper Euphrates (Syria), where a layer of ashes followed by an archaeological hiatus mark the boundary between an Epipaleolithic and the more important Neolithic settlement.
The impact and the subsequent sudden cooling probably was a major influence in the extinction of some subarctic megafauna in North America and Northern Eurasia such as the mammoths.
Source: Science Daily.
Thanks for posting this. I'm looking forward to reading this.
ReplyDelete"The impact and the subsequent sudden cooling probably was a major influence in the extinction of some subarctic megafauna in North America and Northern Eurasia such as the mammoths".
ReplyDeleteProbably unlikely to be the explanation. The climate during the Younger Dryas was nowhere near as cold as it had been during the actual ice ages, which the mammoth had had no trouble surviving.
Here is an article I read yesterday that says that very notion of "the explanation" (just one) is wrong, that there were many convergent causes.
DeleteHere's a nice related paper on mega fauna extinctions:
ReplyDeletehttp://cteg.berkeley.edu/~nielsen/wordpress/wp-content/uploads/2011/11/Nielsen-R.et-al.-Nature.-2011.pdf
Thanks for the link. From the paper:
ReplyDelete"Intriguingly, however, we find no distinguishing characteristics in the rate or pattern of decline in those species that went extinct compared with those that have survived".
Surely it is obvious that the species that went extinct were the slow breeders. The authors even alude to that fact:
"The success of reindeer may be explained by high fecundity ..."
That would surely explain why the slow reproducing Mammoth and woolly rhinosceros went extict early in the piece while the more fecund horse survived for longer.
"notion of 'the explanation' (just one) is wrong, that there were many convergent causes".
Very true. But the presence of humans was the decisive factor. Without their presence the species would have recovered with the return of suitable conditions. I note that the article mentions Australia. To me it seems strange that all are prepared to accept human-induced extinctions in the Pacific and in Australia but most are very keen to absolve humans from any role in European or american extinctions. Why the distinction?
Slow fecundity, very large size, human predation . . . probably all contributed.
ReplyDeleteI noticed this morning in the blogroll sidebar on this blog a link to this excellent June 12th announcement on mammoth extinction:
http://www.heritagedaily.com/2012/06/woolly-mammoth-extinction-has-lessons-for-modern-climate-change/
Again, no one cause, but the authors argue that Holocene warming diminished the mammoth grassland, its food source and territory.
Another good link thanks Marnie. On ehighlighted quote sums it up, I think:
ReplyDelete"'It’s not just the climate change that killed them off,' MacDonald said. 'It’s the habitat change and human pressure. Hunting expanded at the same time that the habitat became less amenable.'"
In fact climate change alone would not have killed them off. And the 'habitat change' was probably caused at least in part by the lowered number of mammoths. In Africa elephants keep the forest open and increase the area of grassland. If it weren't for elephants much of African would not be the mosaic of vegetation we see today.
"If it weren't for elephants much of African would not be the mosaic of vegetation we see today."
ReplyDeleteProbably giraffes and other undulates contribute as well. Most people don't know that many grassland sequester almost as much carbon as forests, because of the very deep root systems of native grasses . . . another climate feedback system.
Some of you may be interested in this latest discovery from Australia regarding diptrotodon:
ReplyDeletehttp://nz.news.yahoo.com/a/-/world/14007627/australians-find-huge-mega-wombat-graveyard/
Quote:
"Diprotodon, the largest marsupial ever to roam the earth, weighing up to 2.8 tonnes, lived between two million and 50,000 years ago and died out around the time indigenous tribes first appeared".
Coincidence?
You cannot extrapolate what happened in Australia to the rest of the World: the ecosystem of Australia was always too fragile for what I have watched in several documentaries. Similar things did not happen in Eurasia nor Africa in fact. Some species and ecosystems are more fragile, while others are sturdier.
Delete"You cannot extrapolate what happened in Australia to the rest of the World"
ReplyDeletePerhaps not. But you cannot argue that humans could not have caused megafauna extinction 12,000 years ago through northern Eurasian and America when they were quite capable of causing megafauna extinction 50,000 years ago in Australia.
"the ecosystem of Australia was always too fragile for what I have watched in several documentaries".
You have consistently argued that it was the fragile ecosystem in northern Eurasia that caused megafauna extinction there. How about a little consistency instead of your usual approach. Besides which quite a large region of Australia is not particularly fragile. It is quite moist tropical and temperate forest land, especially the east coast, southwest coast and the tropics.
12,000 years ago is not the time of arrival of our ancestors to Eurasia.
Delete"You have consistently argued that it was the fragile ecosystem in northern Eurasia that caused megafauna extinction there".
I have not consistently argued anything. I have not put forward any theories on the matter but mostly just dismissed your one sided idealist theories by which we must always blame Homo sapiens and only Homo sapiens of all the extinctions on Earth, regardless that extinctions also happened before our evolution as species or even genus and regardless of the role that natural climate change and other elements like the every day better supported Clovis meteorite impact may have played.
You are one sided and quite extremist on this matter and I sincerely prefer to keep a much more prudent attitude and evaluate each case on its own data.
"12,000 years ago is not the time of arrival of our ancestors to Eurasia".
ReplyDeleteIrrelevant. That is the time that megafauna became extinct in Northern Eurasia and also the time humans were able to venture far to the north. presumably the northern regions humans had been unable to reach provided a refuge for megafauna before that time.
"I have not consistently argued anything".
You have very consistently searched for any other cause apart from humans.
"You are one sided and quite extremist on this matter and I sincerely prefer to keep a much more prudent attitude and evaluate each case on its own data".
On the contrary you appear to have been desperate to excuse humans from having any influence on megafauna extinction whatsoever, as shown by:
"regardless of the role that natural climate change and other elements like the every day better supported Clovis meteorite impact may have played".
Almost certainly each has played a very minor role in megafauna extinctions, although I agree habitat change is usually the main cause of extinction. Even pre-human extinctions, such as dinosaur etc., were most likely caused by changing environmental conditions through the evolution of new species rather than simple 'climate change' or the arrival of any meteotite.
Northern Eurasia as in Altai or Central Russia? If so you have it wrong by some 30,000 years.
Delete"presumably the northern regions humans had been unable to reach provided a refuge for megafauna before that time".
That's polar bears, not mammoths or bisons, never mind tropical megafauna like elephants, buffaloes, etc. H. Sapiens co-existed with Eurasian megafauna in essentially all its range for many many millennia. However most extinctions happened only at the end of this co-existance, with the end of the Ice Age (and/or the Younger Dryas) or later in the Neolithic/Industrial land grab.
"You have very consistently searched for any other cause apart from humans".
Because there are other causes. It's you who insist in a single cause for all extinction processes equally - against the facts.
"On the contrary you appear to have been desperate to excuse humans"...
I do not emotionally care about this (I know humans are destroying Earth as we speak but the techno-economic reality is very different: elephants were hyper-common in South Africa before the Dutch - so it was not humans in general: it was and is the European-Industrial genocidal mentality: let's make room for the cattle, let's keep burning coal and oil).
Otherwise I'm just stating the obvious: the evidence does not support your simplistic model. Certainly not in Eurasia nor in Africa.
"... although I agree habitat change is usually the main cause of extinction".
Then why do you insist on arguing?
"... rather than simple 'climate change' or the arrival of any meteotite".
Climate change IS habitat change. Meteorites, I understand, can also cause climate/habitat change.
???
"That's polar bears, not mammoths or bisons"
ReplyDeleteMore stupidity on your part. Mammoths survived on Wrangel Island until some 4-6000 years ago. That island lies fairly well north. Presumably we can date human arrival on the island to around that time. In fact mammoth extinction was not simultaneous across its whole range. The extinction basically occurred from south to north. That is not what we would expect if climate change or a meteorite was to blame.
"tropical megafauna like elephants, buffaloes, etc. H. Sapiens co-existed with Eurasian megafauna in essentially all its range for many many millennia".
Tropical survival of megafauna suggests efficient hunting and habitat destruction by humans did not reach such regions until quite recently.
"I do not emotionally care about this (I know humans are destroying Earth as we speak but the techno-economic reality is very different"
The Australian Aborigines' 'techno-economic reality' was litle different to that of Paleolithic humans.
"so it was not humans in general: it was and is the European-Industrial genocidal mentality"
It is far from confined to 'the European-Industrial genocidal mentality'. Pacific islanders, including Maori in New Zealand, were very effective at eliminating species, independent of climate change or meteorite collisions.
"Climate change IS habitat change. Meteorites, I understand, can also cause climate/habitat change".
Climate change simply moves ecological zones north or south or alters altitudinal distribution, depending on cooling or warming. Meteors usually have little more than a local effect so unless a particular species has avery limited distribution it can recolonise from regions not affected. Habitat change is more complex and is not confined just to vegetation change. It is usually caused by the evolution or, these days, by the introduction off a new species.
"More stupidity on your part".
DeleteAs I'm so stupid, I'd recommend you not to show up again. You probably deserve much better (sarcasm meant).
Go to Hell!
'As I'm so stupid, I'd recommend you not to show up again. You probably deserve much better (sarcasm meant)".
ReplyDeleteI understand your attitude. After all the survival of mammoth on Wrangel makes nonsense of this whole post and all your comments here.
It has nothing to do with mammoths in Wrangel, it has to do with your attitude of insults.
DeleteI put up with your insults so why can't you put up with mine?
ReplyDeleteI do not think I have "insulted" you any time recently. Anyhow, I'm much more likely to say "fuck off" (for instance) than insults, using swear words is not necessarily insults but attitude.
DeleteYou come up with repeated personal attacks in a row, just because you don't like that I say that human presence alone is not enough reason for megafauna to go extinct. I happen to be right so I am "stupid" and "an idiot".
Therefore: fuck off, please.
"I do not think I have 'insulted' you any time recently".
ReplyDeleteSeveral times during comments at this post alone. And I've noticed that whenever anyone at all makes a suggestion that you are not prepared to consider you immediately reply with an insult. Without exception. So I will now fuck off.