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Old 1st August 2015, 01:57 PM   #41
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Filling in the bits...

Quote:
A cataclysmic event of a certain age
July 27, 2015
http://phys.org/news/2015-07-cataclysmic-event-age.html
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Old 1st August 2015, 02:12 PM   #42
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Originally Posted by BenBurch View Post
We urgently need to develop a minor planet/comet interception and steering capability.
Bah! We have survived Nibiru approaching many times.

Lord forgive me, and be with the pygmies there in New Guinea.
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Old 1st August 2015, 08:36 PM   #43
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Quote:
Originally Posted by BenBurch View Post
We urgently need to develop a minor planet/comet interception and steering capability.
rather extreme climate engineering there Ben
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Old 2nd August 2015, 08:06 AM   #44
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Looks like an interesting hypothesis.
My understanding of the current position is that the warming that melted the Lawrentide ice sheet caused huge lakes of cold fresh water, which eventually burst through the ice dams containing them. The water that then flowed out, mainly through the St. Lawrence seaway, was sufficient to cause the Gulf Stream to position itself much further south.
That would logically happen were a huge amount to be released catastrophically. If the impact hypothesis is true, then I suppose we are looking at a more gradual release for the melted glacial water. However, the scablands in Washington state do show that catastrophic release did happen, albeit that it drained into the Pacific in that case.
It could be that both things happened, but only one mechanism was responsible, or that the combination of the two exacerbated the effect.
Will have to keep my eyes on this.
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Old 2nd August 2015, 09:20 AM   #45
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Catastrophic releases happened in the Northwest of the USA. I forget the lake's name, but I've done some work on formations that were carved out by the outflow, so have seen the results myself. And the sediment.

The Great Lakes weren't carved out by catastrophic outflow, but rather by very fast-moving water under the ice. You can tell by the glacial grooves exposed throughout the Great Lakes region--only water under some sort of confining pressure can produced those sorts of formations. Catastrophic dam failures do not flow uphill.

As for comet impacts, I highly doubt it. I've seen the black mats, in a few places (including an ancient river bed in the Central Valley, which was beyond cool) but that's not sufficient evidence. The thing is, once people accepted the Alvarez Hypothesis, they started looking to impacts for ALL major changes in Earth's history. That's why you get the occasional "mass extinctions have a periodicity" nonsense (with five datapoints we can't be confident of any periodicity, and when you look at origination rates it's pretty clear that they weren't all the same so looking for a single cause is simply irrational). We don't know why the extensive black mats formed, but without a great deal more evidence than anyone has presented thus far I simply cannot accept the impact hypothesis.

I also don't think mammoths would be killed by rapid climate change. They survived OIS 11. If they could survive that, the early Holocene held no terrors. The thing is, humans disrupted ecosystems prior to entering them in some cases--ecosystems are connected, and things done in one ecosystem can affect others. Humans are very good at removing top predators, which has very bad effects on prey (see deer in Ohio and Pennsylvania, or the otter/urchin/kelp system). Plus, there is a limit to the precision that we can reach in geology. The Holocene and Late Pleistocene are best in terms of precision, but still, FADs and LADs are not originations or extinctions. It's a complex issue, to be sure, but I'm dubious.
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Old 2nd August 2015, 11:07 AM   #46
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As always, a place to start for a summary is Google https://en.wikipedia.org/wiki/Younge...act_hypothesis and at least one point is pertinent: apparently the disappearance of the megafauna was not globally synchronous. The delayed extinction on places like Wrangel Island seems more consistent with the hunting hypothesis, assuming some places were not discovered and exploited until later. The survival of the grizzly is another oddity.

So, it certainly seems like an idea worth considering, but it's likely to be a while before the dust settles.
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Old 2nd August 2015, 11:24 AM   #47
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Originally Posted by macdoc View Post
Mass and kinetic energy do not change under that scenario - only impact crater and there is some evidence that an airburst energy release may be more devastating than a crater event.

Remember all that energy will still go into the atmosphere .
Of course, this just means you're not thinking big enough. Just breaking a body into pieces does not really improve our position. As the saying goes, "Whether the rock hits the pitcher, or the pitcher hits the rock, the pitcher is in trouble."

If we get there soon enough and use a big enough bomb, we can produce a debris field which is much larger than the earth, and we miss a significant fraction of it. For instance, if we create a nominally spherical shell of debris with a diameter 10 times earth, we "only" get hit by about 0.5% of the total mass of the body. Not only that, but it comes in 2 separate encounters, so there is some time for energy to dissipate.

Not saying that's a good outcome, but it's not the worst of the alternatives.
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Old 2nd August 2015, 11:30 AM   #48
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oh for FFS....c'mon Dinwar....you'd argue black was white if it served your pet theories...

This is VERY robust science....you have what??....opinion???

Quote:
At the end of the Pleistocene period, approximately 12,800 years ago—give or take a few centuries—a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.

New research by UC Santa Barbara geologist James Kennett and an international group of investigators has narrowed the date to a 100-year range, sometime between 12,835 and 12,735 years ago. The team's findings appear today in the Proceedings of the National Academy of Sciences.

The researchers used Bayesian statistical analyses of 354 dates taken from 30 sites on more than four continents. By using Bayesian analysis, the researchers were able to calculate more robust age models through multiple, progressive statistical iterations that consider all related age data.

"This range overlaps with that of a platinum peak recorded in the Greenland ice sheet and of the onset of the Younger Dryas climate episode in six independent key records," explained Kennett, professor emeritus in UCSB's Department of Earth Science. "This suggests a causal connection between the impact event and the Younger Dryas cooling."

In a previous paper, Kennett and colleagues conclusively identified a thin layer called the Younger Dryas Boundary (YDB) that contains a rich assemblage of high-temperature spherules, melt-glass and nanodiamonds, the production of which can be explained only by cosmic impact. However, in order for the major impact theory to be possible, the YDB layer would have to be the same age globally, which is what this latest paper reports.

"We tested this to determine if the dates for the layer in all of these sites are in the same window and statistically whether they come from the same event," Kennett said. "Our analysis shows with 95 percent probability that the dates are consistent with a single cosmic impact event."


All together, the locations cover a huge range of distribution, reaching from northern Syria to California and from Venezuela to Canada. Two California sites are on the Channel Islands off Santa Barbara.
However, Kennett and his team didn't rely solely on their own data, which mostly used radiocarbon dating to determine date ranges for each site. They also examined six instances of independently derived age data that used other dating methods, in most cases counting annual layers in ice and lake sediments.

Two core studies taken from the Greenland ice sheet revealed an anomalous platinum layer, a marker for the YDB.

A study of tree rings in Germany also showed evidence of the YDB, as did freshwater and marine varves, the annual laminations that occur in bodies of water.

Even stalagmites in China displayed signs of abrupt climate change around the time of the Younger Dryas cooling event.

"The important takeaway is that these proxy records suggest a causal connection between the YDB cosmic impact event and the Younger Dryas cooling event," Kennett said. "In other words, the impact event triggered this abrupt cooling.

"The chronology is very important because there's been a long history of trying to figure out what caused this anomalous and enigmatic cooling," he added. "We suggest that this paper goes a long way to answering that question and hope that this study will inspire others to use Bayesian statistical analysis in similar kinds of studies because it's such a powerful tool."
http://phys.org/news/2015-07-cataclysmic-event-age.html

So you ignored the obvious massive and relatively abrupt climate change the Younger Dryas inflicted on North American mega-fauna and dwell on anthro....
Indeed humans may have had some impact.....Occam's razor sez it's minor one at best ....wuz a cosmic impact wut dunnit.

Move on.
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Old 2nd August 2015, 01:20 PM   #49
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Originally Posted by macdoc View Post
oh for FFS....c'mon Dinwar....you'd argue black was white if it served your pet theories...
Move on.
I have to agree with Dinwar here. This isn't some pet theory of his. The issue is fiercely contested all around. True your source lands squarely on one side of the issue, but there are many papers out there just as confident going the other direction. And a fair number claiming varying degrees of both.

No one knows for sure if the primary driver was a human caused trophic cascade which changed the environment enough to cause the extinctions, or if the environmental changes first caused populations to drop low enough that relatively light human pressure was enough to cause the final extinctions. Or maybe both to some degree or another. But either way, it is not some pet theory that Dinwar pulled out of a hat. And there is absolutely NOT a consensus yet. That is obvious.

ETA PS One thing I certainly agree with, I think it is very highly unlikely it was all climate.... caused by a comet strike. Humans played their part in the megafauna extinctions. How large a part? Hard to say for sure.
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Old 2nd August 2015, 02:16 PM   #50
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Just how many humans do you think there were in North America 13,000 years ago....???
I'm not talking about SIberia - this is limited to North America and the Younger Dryas period....and humans weren't here very long compared to SIberia and Eurasia where the human presence was measured in millenia.

You think humans would tackle terribly dangerous megafauna when there were and still are millions upon millions, of elk, caribou, moose and deer not to mention fish and other food sources.

Humans might have nudged things along, there is no way there sufficient numbers present to have any appreciable impact during that period. C'mon man, use your common sense.

Remember - this is North America, not Eurasia.

The impact time is measured within a 100 years and the oldest Clovis is not that far off that date nor is the earliest trace of humans.

This is a good overview of the prevailing contentions in 2009
and one pundits view of human intervention

Quote:
Could what scholars agree must have been a relatively modest initial population of hunters have emptied an entire continent of its megafauna virtually overnight, geologically speaking? (In fact, it's three continents: South America and, to a lesser extent, Northern Eurasia also lost many large species at the end of the Ice Age.) For his part, Ross MacPhee (overill) finds it hard to swallow. "I just don't think it's plausible, especially if we're also talking about collapses for megafauna that didn't actually go extinct." Certain populations of surviving big beasts, including bison in North America and musk oxen in Asia, are known to have fallen precipitously at the end of the Ice Age. "It gets a little bit beyond probability in my view that people could have been so active as to hunt every animal of any body size, in every context, in every possible environment, over three continents."
ya think !!!!!

http://www.pbs.org/wgbh/nova/evoluti...ig-beasts.html

6 years on - the impact is confirmed and more is known about the Younger Dryas and THAT combination certainly has the scale to precipitate the mega-fauna extinction.

This reminds me of the Chicxulub controversy.....took a while for that to be established.
T- Rex and Crater in of Doom is a tongue in cheek title for a tour de force journey through that discovery by the scientists that made it.
Evidence is still accumulating on how the impact played out including new linking between volcanic outbreaks and the asteroid hit.

Quote:
Did dinosaur-killing asteroid trigger largest lava flows on Earth?

By Robert Sanders | APRIL 30, 2015

The asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe that may have contributed to the devastation, according to a team of UC Berkeley geophysicists.
http://news.berkeley.edu/2015/04/30/...lows-on-earth/

Humans may be pernicious ....but bear in mind this is the full extent of humans now.!!!!



http://www.huffingtonpost.com/2014/0...n_5255076.html

just how much impact do you think a scatter of primitive H Sapiens had on the vast biome in North and South America???
IF there was no other hypothesis, human causation might be considered - right now the impact and climate change as a primary cause has far far more weight and evidence to it.....and the evidence continues to grow.
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Old 2nd August 2015, 02:34 PM   #51
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Originally Posted by WhatRoughBeast View Post
As always, a place to start for a summary is Google https://en.wikipedia.org/wiki/Younge...act_hypothesis and at least one point is pertinent: apparently the disappearance of the megafauna was not globally synchronous. The delayed extinction on places like Wrangel Island seems more consistent with the hunting hypothesis, assuming some places were not discovered and exploited until later. The survival of the grizzly is another oddity.

So, it certainly seems like an idea worth considering, but it's likely to be a while before the dust settles.
The lack of synchronicity is obvious--it hasn't happened in Africa yet. (No sarcasm here--there is a causal connection.)
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Old 2nd August 2015, 02:42 PM   #52
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Originally Posted by macdoc View Post
oh for FFS....c'mon Dinwar....you'd argue black was white if it served your pet theories...

This is VERY robust science....you have what??....opinion???



http://phys.org/news/2015-07-cataclysmic-event-age.html

So you ignored the obvious massive and relatively abrupt climate change the Younger Dryas inflicted on North American mega-fauna and dwell on anthro....
Indeed humans may have had some impact.....Occam's razor sez it's minor one at best ....wuz a cosmic impact wut dunnit.

Move on.
I have six years' experience studying the Desert Southwest, and in particular the Quaternary megafauna, plus extensive conversations with my boss, with 40+ years' experience. Oh, and I studied the K/Pg event in grad school, including the ecological effects.

I am not ignoring the climate change. I am merely pointing out the paucity of evidence for a bolide impact. Show me the creator. Show me the rare earth elements. Show me the synchronicity. Show me how an impact can reduce the number of predators in a way that parallels the invasion of humans into the environment. Show me something other than climate change. Show me the shift in marine fauna. Do those things that were done to prove the Alvarez Hypothesis. YOU proposed the hypothesis, YOU defend it. It is perfectly within my rights as a paleontologist to state that in my professional opinion you have not met that burden, and to point out a potential reason for this premature acceptance of a relatively unevidenced hypothesis.

The honest thing to say is that we just do not know. We have a few ideas, some better than others. An impact is one; overkill is one; there are others but I honestly can't think of them right now (I had a report touching on this due this morning at 6 am, so I had to be up working early).
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Old 2nd August 2015, 02:47 PM   #53
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Originally Posted by macdoc View Post

Humans might have nudged things along, there is no way there sufficient numbers present to have any appreciable impact during that period. C'mon man, use your common sense.
I think you are missing the "cascade" part of trophic cascade. It can be like tossing a snowball at the side of a mountain, and causing an avalanche!

Originally Posted by macdoc View Post
IF there was no other hypothesis, human causation might be considered - right now the impact and climate change as a primary cause has far far more weight and evidence to it.....and the evidence continues to grow.
The evidence for the impact part is sketchy at best. Climate certainly changed, due to a comet? hard to say. Equally possible it was at least partly driven by a human caused cascade. No need to invent a comet impact we can't even find.

The reason many people hypothesize a comet impact is they previously didn't understand how that rapid a climate change could be caused by a cascade. Proving the climate change happened in a 100 year window doesn't exclude the trophic cascade at all. 100 years is easily enough time. Look how fast the dust bowl happened!
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Old 2nd August 2015, 02:55 PM   #54
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No need to invent human causes, either. Weather is volatile in ice ages. Either way, the survival of the megafauna through multiple interglacial so demonstrates that such an explanation is not, by itself, sufficient. It may contribute, but cannot be the sole cause.
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Old 2nd August 2015, 02:57 PM   #55
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We, human caused climate change, that is. No solid mechanism for such a thing has been established in the Pleistocene/early Holocene. To use that as an explanation demands we first establish that it in fact did happen (so, same problem with the impact hypothesis).
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Old 2nd August 2015, 03:03 PM   #56
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Originally Posted by Dinwar View Post
To use that as an explanation demands we first establish that it in fact did happen (so, same problem with the impact hypothesis).
I actually agree when you word it that way. There isn't enough evidence to be sure. It is POSSIBLE, but where is the evidence? Most the evidence I have seen has more than one possible explanation. That makes it kind of circular. Until we find evidence that only works in one model, but not the other........

Like if we had a crater, or a 3 month window instead of a 100 year window. That would make all the evidence squarely on the side of impact and the fact humans just arrived a coincidence.
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Old 2nd August 2015, 04:19 PM   #57
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A good example is this: There is evidence to show that humans arrive very close to the megafauna collapse, and that climate change occurred much later than the collapse[1]. This evidence comes in the form of spores of the fungus Sporormiella, pollen, and microscopic pieces of charcoal.

Using the much more abundant charcoal, pollen, and fungal spore information allows better temporal resolution than the vertebrate fossil record and provides a means of estimating human occupation, climate, megafauna abundance. It shows at least the sequence of events much better. They are as follows......Humans arrive with significant numbers but little impact immediately. A bit of time passes. Then there is a simultaneous sudden collapse of large herbivore populations and development of clovis points. Soon after the collapse, a huge amount of charcoal, much later comes the climate shift. Lastly the remnant populations of many megafauna species finally go extinct after lingering a while at very low levels.

That's the evidence. The hypothesis is that there was a pre-clovis colonization of North America at least 400-500 years or more both before the megafauna collapse and the advent of clovis technology. Then the clovis culture shows up and the megafauna population collapses but doesn't go extinct. However, the collapse both triggers and is caused by a trophic cascade and the evidence for that is the charcoal that immediately follows. IE a loss of herbivores or a change in their behaviour causes an excess of vegetation which is susceptible to natural fire and collapsing herbivore numbers means humans start using fire to hunt at increased rates. Between the two there is a huge pressure on the remaining reduced herbivore herds, both hunting pressure, and loss of habitat due to widespread fire. Finally comes climate change later which causes the bulk of the final extinctions and the end to the clovis culture.

That's one view, there are at least 3-4 others I know of, including yours Mac. I suppose we could have had a 100 year period of unusually heavy meteor impacts used to explain that charcoal, and several smaller impacts wouldn't necessarily leave big craters that last till today, but it seems to me that man's use of fire in hunting explains it as least as well if not better. The important thing to note though is this: The herbivore numbers collapsed BEFORE the black charcoal layer. So that means something collapsed the herbivore numbers before either manmade wildfire or comet impact. Admittedly it is somewhat circular though, to say that a trophic cascade is both the cause and the result. Think of it like ripples in a pond, as the cascade spreads the impact increases, that impact creating even more ripples which create new impacts, and on and on...... That kind of impact certainly can last 100 years and is more believable to me than the comet impact.

To make your hypothesis as strong as the human caused trophic cascade hypothesis, you need to explain this Sporormiella fungus evidence. So far you haven't.
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Old 2nd August 2015, 06:31 PM   #58
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The problem with palynological data is dating it. You have to be very careful to avoid circularity. That said, it gives you very good temporal and special resolution. A lot of this sort of data comes from Neotoma middens. They also look pretty cool. Just....don't eat it. Amberat is not fit for human consumption.

The other thing to look into is Jay Quade's work on springs in the Mojave. The criticisms do not hold up when you see the outcrops.
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Old 2nd August 2015, 06:40 PM   #59
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There were (estimated) millions of bison running around NA when the Spanish arrived. If we killed off all the megafauna round-about the Clovis period the bison would have gone with them.
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Old 2nd August 2015, 06:58 PM   #60
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Originally Posted by Gawdzilla Sama View Post
There were (estimated) millions of bison running around NA when the Spanish arrived. If we killed off all the megafauna round-about the Clovis period the bison would have gone with them.
I have also read papers arguing that the microverts didn't do so hot, either. The extinction is far more complex than many realize.

Plus, there is the fact that the extinction isn't over yet. There is a temporal component to this that simply isn't present in the K/Pg mass extinction. Impacts big enough to do ecological damage at that scale tend to have rather immediate and large-scale effects. And it is VERY telling that the place where humans evolved is the place that best serves as a Pleistocene refuge. The reason, as my boss pointed out to me, is co-evolution. The critters that taste good knew to avoid the funny hairless apes before the apes could do serious damage to the ecology. Which suggests that human predation is a major component of the event.

Does this explain the black mats? No, at least not directly. It may indirectly. Does it need to? That part is less clear.
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Old 2nd August 2015, 07:03 PM   #61
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I agree that lots of speculation on the extinctions is just that. I also admit to not being up to date on this.
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Old 3rd August 2015, 01:16 PM   #62
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Another factor that needs to be considered: e Holocene stripping event (yeah....I did not come up with the name; scientists often have the minds of twelve year olds). I have seen the results in a few field sites. Basically, in the early Holocene (I think; been a while, so my recollection of the time may be off) a lot of sediment was stripped off valleys in the Desert Southwest. In the Pahrump Valley you can see a row of dunes where this sediment was caught up by springs. Since then, the sediment has been slowly migrating back into the valleys. An impact cannot explain this, nor can human activity directly explain it. A combination may well be able to do so, but thus far no one is sure.

Which is my point: there is a lot of data to consider, much of which is apparently contradictory, most of which is not currently explained, and we aren't even sure what is and isn't relevant. It is premature to declare ANY explanation in my opinion. More research is pretty clearly necessary.
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Old 4th August 2015, 03:29 AM   #63
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Originally Posted by WhatRoughBeast View Post
Of course, this just means you're not thinking big enough. Just breaking a body into pieces does not really improve our position.
A fragmented object hitting the atmosphere imparts as much energy and momentum as a solid one but is far less likely to cause localised surface impacts as the pieces are more likely to burn-up from atmospheric friction and be deflected over a wide area. Thus there will be less material thrown into the atmosphere.
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Old 4th August 2015, 10:00 AM   #64
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Nit pick ...the same mass will end in the atmosphere - the "burn up" does not elminate the mass...and the remainder will still kick up debris tho not as much.

You are trading excavated debris for comet debris...but it might fall out quicker than a deep impact like the Dino killer.

You still have to account for the kinetic energy of the bolide entering the atmosphere and or/impacting the surface. Thinking is wide spread wild fires also creating a climate hit.
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Old 4th August 2015, 10:14 AM   #65
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Originally Posted by macdoc View Post
Nit pick ...the same mass will end in the atmosphere - the "burn up" does not elminate the mass...and the remainder will still kick up debris tho not as much.

You are trading excavated debris for comet debris...but it might fall out quicker than a deep impact like the Dino killer.

You still have to account for the kinetic energy of the bolide entering the atmosphere and or/impacting the surface. Thinking is wide spread wild fires also creating a climate hit.
Chixilub was particularly bad as Ground Zero--lots of bad stuff was thrown up when it was vaporized. Other areas wouldn't be as bad. Still Ragnarok levels of bad, but not AS bad.

Plus, while there would be the same energy, I do not believe it would have the same effects. Ecosystems are astonishingly robust in some ways. If you spray the Earth with the celestial equivalent of rock salt it won't have the same effect as the same mass hitting in one place at one time. The physics aren't the issue; the ecology is.
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Old 4th August 2015, 11:11 AM   #66
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The YD doesn’t fit the profile for impact induced climate change.

First of all it was too long. The Toba eruption 70K years ago was far larger than any possible impact 12K years ago and its impact only lasted about a decade while the YD lasted hundreds of years. Second and most importantly Dust, smoke, etc from an impact would be a global effect and the cooling would also be global. The YD was confined to the Northern Hemisphere, this is characteristic of changing heat distribution patterns caused by ocean currents re-organizing.
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Old 4th August 2015, 11:26 AM   #67
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If it kicks the climate regime into a different phase for North America as volcanos did for the LIA then you do not need ongoing aerosols to keep it cooler for a long while.

I don't think anyone is claiming a world wide effect, rather an effect local to North America and its biome with some spill over to Northern Eurasia.

If you apply Occam's razor, it's far more likely that an impact started the decline than a handful of humans.
And the impact and the LIA are now within 100 years of each other.
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Old 4th August 2015, 01:24 PM   #68
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Originally Posted by macdoc View Post
If it kicks the climate regime into a different phase for North America as volcanos did for the LIA then you do not need ongoing aerosols to keep it cooler for a long while.

I don't think anyone is claiming a world wide effect, rather an effect local to North America and its biome with some spill over to Northern Eurasia.

If you apply Occam's razor, it's far more likely that an impact started the decline than a handful of humans.
And the impact and the LIA are now within 100 years of each other.
You still haven't explained the Sporormiella fungus evidence.

Just to be clear what that evidence shows: The Sporormiella fungus is a fungus specific to large ruminant herbivore dung. The spores of that fungus dropped radically BEFORE the controversial black charcoal layer. So even if the black layer was caused by a bolide impact and not wildfires from some other cause, it can't explain the catastrophic collapse of large herbivore numbers. We can argue about the exact dates all you want, but the sequence is both critical and the evidence robust. Man came to North America first, then the herbivore numbers dropped after a period of time, and then finally the mysterious black layer formed after another period of time. No way whatever caused the black layers caused the drop in herbivore numbers, because those numbers were already down before whatever caused that layer.

There is some wiggle room to fit in an impact hypothesis as adding to other causes, but it can't be simplified into an "Occam's razor" solution as you keep insisting. It is a complex problem that defies simplification like that. An impact couldn't possibly have killed the huge megafauna herds, they were already mostly gone! That's even if it happened at all.


Which is BTW pretty common in Nature. Understanding biology is nearly always a complexity task, not something you can easily reduce into simplified "Occam's razor" type solutions. Sometimes you can. If the bolide impact was large enough you could. But that is not the case here at all.
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Old 4th August 2015, 05:58 PM   #69
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Originally Posted by lomiller
First of all it was too long.
The K/Pg impact is thought to have kicked up dust that reduced incidental radiation for 1k years.

The real problem is we don't HAVE a good profile for impact-caused mass extinctions. We have precisely one to work with, so saying we have a profile is very drastically over-stating things. We have a fairly good idea of what happened at the K/Pg boundary (Gerta Keller's nonsense not withstanding), but again, Chixilub was a particularly bad place for something to strike. It vaporized a lot of sulphates and carbonates, causing even more ecological mayhem than would otherwise have occurred. I've no doubt that a mass die-off style mass extinction would have occurred regardless, but it certainly complicates things.

Quote:
Second and most importantly Dust, smoke, etc from an impact would be a global effect and the cooling would also be global.
The thing is, one of the few things we can say for certain about impact-caused mass extinctions is that while they are a global scale event, the effects would be mitigated or exacerbated by regional and local conditions. Antarctica wasn't as heavily affected as, say, North America, and all the reefs that weathered the transition that we know of (one in Austria, one in Spain, and one in Italy, last I heard) are in Tethys, almost certainly due to local conditions hardening the reefs against the nutrient overload that killed off the rest.

With the equitorial current in operation, I can see the northern and southern hemispheres reacting differently to a global forcing mechanism.

Note that I don't believe an impact is the cause; the best evidence thus far presented is ambiguous, necessary evidence to conclude it was an impact has not been found, and contradictory evidence is present. I'm just saying that your objections aren't necessarily valid. Impacts of this scale are complex things, and ecosystems are pretty much the definition of complex systems; the interaction between the two is extremely difficult to figure out. Some of the best minds of two generations of scientists have been working on it and we still aren't sure.

Originally Posted by Red Baron Farms
Just to be clear what that evidence shows: The Sporormiella fungus is a fungus specific to large ruminant herbivore dung. The spores of that fungus dropped radically BEFORE the controversial black charcoal layer.
I would have to see the sampling methods before I accepted this. No slight on you or the folks doing the sampling--it's just that there are a whole universe of issues involved in making such a statement, and we have to rule out all of them. It's trivial to demonstrate the impact differing sampling methodologies can have on this sort of thing. Got a pretty good lecture on this when we did some microfossil sample collections on a project site two years ago (damn....it HAS been that long....my first kid was born during that job....). Look up the Signor-Lipps Effect to see just one of them, and how complicated THAT can be. And that's a relatively easy one to address.

Originally Posted by macdoc
If you apply Occam's razor, it's far more likely that an impact started the decline than a handful of humans.
No. Emphatically and categorically NO. I consider anyone who says such nonsense to thereby abandon ALL credibility in these discussions.

You probably don't realize this, but it is drilled into paleontologists' heads during our training that this sort of thinking is not only intellectually slovenly (seriously, your conclusions FAR outstrip your data, which by itself is sufficient reason to dismiss them), but they are DANGEROUS. Once humans have an answer, we stop looking for alternative hypotheses--whether or not the answer is correct. Paleontology has not infrequently been held back for GENERATIONS due to such errors. It is not just wrong to commit them in these discussions; for anyone with even a hint of knowledge about the history of this field it is negligent.

I get that you don't have such a history, and I'm not saying you're negligent (though I AM saying you are demonstrating a lack of knowledge on these issues that renders your opinion irrelevant). I'm merely trying to emphasize the magnitude of the error your are committing here. It may seem reasonable to you, but history has shown--quite brutally--that what you are doing holds back knowledge in paleontology.

Simply put, Occam's Razor has little place in historical sciences. Either the data support a conclusion, they don't, or we don't know--and it is CRITICALLY, by which I mean the science CANNOT survive without it, that we acknowledge the limits of our knowledge.

Show me the data equivalent to those found during the verification of the Alvarez Hypothesis and we can discuss impacts. Otherwise, we can't. It's that simple. Using Occam's Razor to ignore this is using it to cut our own throats.
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Old 4th August 2015, 08:19 PM   #70
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Originally Posted by Dinwar View Post

I would have to see the sampling methods before I accepted this. No slight on you or the folks doing the sampling--it's just that there are a whole universe of issues involved in making such a statement, and we have to rule out all of them. It's trivial to demonstrate the impact differing sampling methodologies can have on this sort of thing. Got a pretty good lecture on this when we did some microfossil sample collections on a project site two years ago (damn....it HAS been that long....my first kid was born during that job....). Look up the Signor-Lipps Effect to see just one of them, and how complicated THAT can be. And that's a relatively easy one to address.
I'd be happy for you to look at it and give an opinion. I posted the paper above as a reference.#57 Look at it and tell me what you think. I also read a review of it that was more in layman's terms I could understand, I'll try to google that again too, if you want.
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Old 5th August 2015, 03:23 AM   #71
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Cultists do love a big story for which there is little concrete evidence, because they get to paint their pet story over it (ignoring the weakness of evidence available), and then declare that as the only possible explanation.

Dinwar, good luck, you are taking on people who are highly motivated to wear blinkers and absolutely no amount of rational reasoning or critical thinking will make them take those blinkers off.
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Old 5th August 2015, 03:55 AM   #72
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I do not have access to Science. I'm also dubious about any grandiose claim made in paleontology that's published in that journal--not because it's a bad journal, but because there isn't room for a full discussion. Paleo data tends to be extremely dry and bulky, not the kind of thing amenable to high-impact journals.

The abstract doesn't give much hope, either. It reads more like a literature review than a rigorous sampling effort. "Tracing the three players through time" isn't exactly the kind of thing that one can do while analyzing properly sampled sediment for microfossils. Microfossil picking is time- and labor-intensive (not to mention coffee-intensive). Post-picking analysis certainly can track multiple things through time, but no one talks that way.

Originally Posted by CoolSceptic
Dinwar, good luck, you are taking on people who are highly motivated to wear blinkers and absolutely no amount of rational reasoning or critical thinking will make them take those blinkers off.
Thanks. My goal isn't to convince anyone--I know better than that--but rather to point out how a real paleontologist approaches these issues.
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Old 5th August 2015, 04:13 AM   #73
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Originally Posted by CoolSceptic View Post
you are taking on people who are highly motivated to wear blinkers and absolutely no amount of rational reasoning or critical thinking will make them take those blinkers off.
Sounds like every creationist, conspiracy theorist, woo slinger and climate change denier I ever argued with.
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Old 5th August 2015, 07:41 AM   #74
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The best I can find is a popular-press article on Australian mud cores. Not a bad option, but without knowing a lot more about the depositional basin I can't comment on the validity of 100-year incriments for sampling. Plus, Gondwana continents are not necessarily going to have the same things going on as North America. I also find the idea of basing grand-scale ecological naratives off of two mud cores to be rather dubious at best. It's certainly an interesting hypothesis, and not intrinsically invalid (ie, it doesn't contradict any known facts), but far more testing is necessary before we can accept the grand story built off this rather scant (even by paleontology standards) dataset.
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Old 5th August 2015, 07:45 AM   #75
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Originally Posted by macdoc View Post
Nit pick ...the same mass will end in the atmosphere - the "burn up" does not elminate the mass...and the remainder will still kick up debris tho not as much.

You are trading excavated debris for comet debris...but it might fall out quicker than a deep impact like the Dino killer.

You still have to account for the kinetic energy of the bolide entering the atmosphere and or/impacting the surface. Thinking is wide spread wild fires also creating a climate hit.
Yes as I said the mass, momentum and energy will be the same. However, as I also said, they'll be far more dispersed and there will be less ejecta due to the fewer, less penetrating impacts on the surface.
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Old 5th August 2015, 07:51 AM   #76
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Originally Posted by catsmate View Post
Yes as I said the mass, momentum and energy will be the same. However, as I also said, they'll be far more dispersed and there will be less ejecta due to the fewer, less penetrating impacts on the surface.
I thought of a good analogy last night: If you throw a handful of gravel into a pond every hour, eventually you will impart the same amount of energy as throwing a stick of dynomite into the pond. However, I think it's pretty obvious that the results will be very different. Fish may avoid the new gravel bar you've built; with the TNT, in contrast, there will be significantly fewer fish once the dust settles!

Ecology isn't physics. There are numerous feedback loops that cause ecology to be fairly robust (and, like all chaotic systems, fragile in certain ways). Hitting an ecosystem with a bunch of small rocks is not going to have the same effect as hitting it with one big rock, even if we assume that all the pieces hit the ecosystem in question (a bad assumption, as most pieces would end up in the ocean).
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Old 5th August 2015, 01:23 PM   #77
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Originally Posted by Dinwar View Post
The best I can find is a popular-press article on Australian mud cores. Not a bad option, but without knowing a lot more about the depositional basin I can't comment on the validity of 100-year incriments for sampling. Plus, Gondwana continents are not necessarily going to have the same things going on as North America. I also find the idea of basing grand-scale ecological naratives off of two mud cores to be rather dubious at best. It's certainly an interesting hypothesis, and not intrinsically invalid (ie, it doesn't contradict any known facts), but far more testing is necessary before we can accept the grand story built off this rather scant (even by paleontology standards) dataset.
I found this from Dartmouth.
Quote:
Their analysis revealed that first the megafauna population collapsed, indicated by a 10-fold decrease in Sporormiella spores. Soon after this, charcoal abundances jumped 10-fold. According to Robinson, Burney and Burney, human hunting of megafauna would have led to an overabundance of fuel for both human and natural fires. Only around 1,000 years later did pollen data show the last major cooling in the Pleistocene. The last megafauna bones in the fossil record appear during this last cooling period, indicating that a combination of anthropogenic effects and climate may have led to the extinction of the megafauna, but only after humans had drastically reduced the megafauna population numbers. Similar patterns of extinctions indicated by fungal spores and charcoal in Madagascar, where extinctions occurred in the last 2,000 years without climate change, show that climate change may not even be necessary to provide a “knock out punch” [1]
Madagascar
Quote:
at the site with best stratigraphic resolution the spore declines sharply by ≈1,720 yr B.P. (radiocarbon years ago). Within a few centuries there is a concomitant rise in microscopic charcoal that probably represents human transformation of the local environment. Reduced megaherbivore biomass in wooded savannas may have resulted in increased plant biomass and more severe fires. Some now-extinct taxa persisted locally for a millennium or more after the inferred megafaunal decline.
Australia
Quote:
They found that Sporormiella spores, which grow predominantly in the dung of large herbivores, virtually disappeared around 41,000 years ago.
...
The results were also compared with previous pollen and charcoal studies. These showed a transition from mixed rainforest species to grasses and leathery leaved, dry tolerant sclerophyll vegetation, and an increase in fire activity beginning at least 100 years after the animal extinctions - indicating they were the result of the extinction and not its cause.

The researchers argue that newly arrived humans hunted the animals to extinction, with the reduced grazing pressure causing an increase in the fuel load and fire intensity.
Since it is the temporal pattern we are looking for and the Australian and Madagascar pattern also fits, yet all 3 happened at completely different times and different local conditions, (but each following soon after man's immigration) it would seem to me that makes the human caused extinction hypothesis a front runner. It's the only hypothesis that fits all three. It also is far less likely to be an artifact of the Signor–Lipps effect.

First humans arrive, then the megafauna collapses, then fire, then extinction of the greatly reduced populations due to habitat loss, hunting, and/or climate. It's the temporal pattern that makes the hypothesis strong. And honestly we have some historical evidence that can also back it up to some degree. When the bison where extirpated almost entirely from their former range in relatively recent history, there were HUGE grass fires in increasing frequency and intensity. Some areas are still having them at a rate 30 times more than before. We would probably be seeing much more though if we didn't actively suppress them or convert the land to agriculture.
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Old 5th August 2015, 01:40 PM   #78
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Quote:
It's the only hypothesis that fits all three.
That assumes all three have the same explanation, an argument for which no evidence is provided.

Quote:
It also is far less likely to be an artifact of the Signor–Lipps effect.
Let's see the math.

I also dislike the pollen spore data. For a few reasons, not the least of which is that there are both desert and arctic species growing in Ohio (I've seen them, on a geology field trip). Ask yourself why Joshua trees are where they are in the Mojave sometime. There is a lag time between environmental shifts and botanical responses. How big? Dunno, it varies. But the fact that they don't address this does nothing to support their case.

Quote:
First humans arrive, then the megafauna collapses, then fire, then extinction of the greatly reduced populations due to habitat loss, hunting, and/or climate. It's the temporal pattern that makes the hypothesis strong.
The problem is, you're basing this off of a few bore holes and a handful of fossils--and I've yet to see ANYTHING that indicates proper sampling techniques were used (where are the discussions of sedimentation rate? where are the statistical analyses? how much sediment did they process? how did they process it?). It's not a robust enough dataset to justify such a complex story--and once you've got the story, you're trapped. Humans like an answer, and will take ANY answer, so once you've got a story you stop looking.

Here's the question for you: What would prove you wrong? What evidence would you look for, right now, that would disprove your story? Don't give me nonsense like "If you could prove the spore data wrong"; given what you believe is known, what data would disprove your hypothesis?
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Old 5th August 2015, 02:06 PM   #79
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Originally Posted by Dinwar View Post
Here's the question for you: What would prove you wrong? What evidence would you look for, right now, that would disprove your story? Don't give me nonsense like "If you could prove the spore data wrong"; given what you believe is known, what data would disprove your hypothesis?
The easiest way to disprove the hypothesis is to show another reason for the radical reduction in Sporormiella spores. ie Disprove the inference that reduced Sporormiella spores indicates reduced megafauna herbivore numbers. OR Prove the spores were there, but somehow were "washed away" from the record by some means. OR Prove some disturbance caused the pattern, and not actually a temporal pattern but rather a pattern caused by some other mechanics, like filtration, erosion, and/or soil biological activity. For example earthworms/dung beetles/small arthropods might favor dung over charcoal and pull the spores down below the surface, so the layers wouldn't strictly follow the temporal pattern they were laid down, they would become inverted. Things like that would either disprove it, and/or at least call into question if the evidence actually means what we think it means. Or maybe prove man used so much dung for their camp fires, that is the real reason for the reduction of Sporormiella spores and increase in charcoal. That the actual megafauna numbers were still large when the Sporormiella spore counts dropped. Or find a novel virus/bacteria man somehow brought with him that attacks Sporormiella fungus and dropped its population even though the dung (and the herbivore that produced it) was still present. Or if the evidence was obtained from sediments in a body of water, prove the spores and microscopic charcoal sink at significantly enough different rates through the water column that it gives a misleading result. Something along those lines.

That's why I specifically asked Mac to explain the Sporormiella spores evidence. If there is a legitimate alternative reason for a reduction in spore prior to the other evidence, that would give at least some credence to the bolide impact hypothesis he seems to favor. Still would need more evidence, but at least it couldn't be dismissed. You simply can't have an impact cause the dramatic reduction in numbers if the numbers dropped before the impact even happened. It's impossible. So that hypothesis MUST show some other explanation for the Sporormiella spores evidence.
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Old 5th August 2015, 04:37 PM   #80
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Originally Posted by Pixel42 View Post
Sounds like every creationist, conspiracy theorist, woo slinger and climate change denier I ever argued with.
Right - anyone who denies climate changes clearly knows nothing about the geological history of the earth.
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