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Old 6th February 2018, 01:33 AM   #121
jonesdave116
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Here is the 2011 paper which summarises multiple objections to their previous claims of a YD impact scenario:

The Younger Dryas impact hypothesis: A requiem
Pinter, N. et al.
http://www2.nau.edu/ScottAnderson/docs/135.pdf

It's pretty scathing. From the final paragraph:

Quote:
This paper has systematically reviewed evidence presented as signatures of a YD impact event, and this review has been framed as a “requiem,” suggesting the end of the YD impact hypothesis. It is fair then to ask whether we are indeed seeing the end of this hypothesis. As for some proponents, the answer is certainly ‘no’— several have stated that they will continue their quest until the hypothesis is confirmed. Some insight is gained by adding a historical perspective here. Scientific hypotheses are constantly being proposed, tested, confirmed, or cleanly rejected, but a small minority of these stray from this time-proven path. Many scientists are unaware of the surprising number of hypotheses that have gone badly astray, often after widespread initial interest and support (Langmuir and Hall, 1989; Gratzer, 2000; Park, 2000). Characteristics of these wayward hypotheses include claims that are spectacular, data that are subjective or at the limit of precise measurement, and criticisms met with ad hoc excuses and/or shifts in the original claims (after Langmuir and Hall, 1989). We suggest that much can be gained by stepping back and looking at the broader lessons for the earth sciences, impact science, archeology, and other affected fields.
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Old 14th November 2018, 05:17 PM   #122
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Fancy that

Quote:
Impact crater 19 miles wide found beneath Greenland glacier
Crater appears to be result of mile-wide iron meteorite just 12,000 years ago


A huge impact crater has been discovered under a half-mile-thick Greenland ice sheet.

The enormous bowl-shaped dent appears to be the result of a mile-wide iron meteorite slamming into the island at a speed of 12 miles per second as recently as 12,000 years ago.

The impact of the 10bn-tonne space rock would have unleashed 47m times the energy of the Little Boy nuclear bomb dropped on Hiroshima in 1945. It would have melted vast amounts of ice, sending freshwater rushing into the oceans, and blasted rocky debris high into the atmosphere.
more

https://www.theguardian.com/science/...enland-glacier
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Old 14th November 2018, 06:34 PM   #123
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AWC, Astronomical Weather Change anybody?
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Old 14th November 2018, 10:10 PM   #124
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Originally Posted by macdoc View Post
From the actual paper

http://advances.sciencemag.org/content/4/11/eaar8173
Quote:

The age of the crater is presently unknown, but an impact sometime during the Pleistocene is consistent with presently available geological and geophysical data.
IOW "maybe sometime in the last 3 million years but we don't really know".
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Old 15th November 2018, 04:18 PM   #125
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Pleistocene ended 11,700 years ago ....strange that.

Quote:
While the overall appearance of the Hiawatha impact crater is relatively fresh, its morphological deviations from a typical complex crater are likely due to a combination of glaciofluvial and subglacial erosion of the rim and central uplift, sediment deposition within the crater, and post-impact rim collapse. This crater is the only known terrestrial crater of this size that retains aspects of its original surface topographic expression. The age of the crater is presently unknown, but an impact sometime during the Pleistocene is consistent with presently available geological and geophysical data.
we'll wait...the smoking gun is found...just need the date now.

Quote:
Regardless of its exact age, based on the size of the Hiawatha impact crater, this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally (35).
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Old 16th November 2018, 09:54 AM   #126
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Originally Posted by macdoc View Post


we'll wait...the smoking gun is found...just need the date now.
Don’t you think you should have a dead body before you go looking for a smoking gun? There is nothing unique about the period 11.7KYA. Yes, there is unusual cooling, but there are many similar cooling events in the last 1m years. If only one was caused by an impact, how do you explain all the others. If you all the others can be explained by meltwater pulses that occur on melting ice sheets, what makes the most recent one any different?
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Old 16th November 2018, 10:32 AM   #127
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It's hardly the only evidence ....what was lacking was the gun...the traces are widespread

Quote:
The South Carolina researchers found an abundance of platinum in soil layers that coincided with the "Younger-Dryas," a climatic period of extreme cooling that began around 12,800 ago and lasted about 1,400 years. While the brief return to ice-age conditions during the Younger-Dryas has been well-documented by scientists, the reasons for it and the demise of the Clovis people and animals have remained unclear.
"Platinum is very rare in the Earth's crust, but it is common in asteroids and comets," says Christopher Moore, the study's lead author. He calls the presence of platinum found in the soil layers at 11 archaeological sites in California, Arizona, New Mexico, Ohio, Virginia, North Carolina and South Carolina an anomaly.
"The presence of elevated platinum in archaeological sites is a confirmation of data previously reported for the Younger-Dryas onset several years ago in a Greenland ice-core. The authors for that study concluded that the most likely source of such platinum enrichment was from the impact of an extraterrestrial object," Moore says


Read more at: https://phys.org/news/2017-03-discov...eople.html#jCp
Quote:
carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it.
http://www.pnas.org/content/104/41/16016


http://www.pnas.org/content/early/2013/07/17/1303924110

and the nano-diamonds

Quote:
Diamond clues to beasts' demise

By Molly Bentley
Science reporter
http://news.bbc.co.uk/2/hi/science/nature/7808171.stm

Now none of that proves the Younger Dryas hypothesis for climate change wiping out Clovis and mega fauna - it does however provide a weapon.

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Old 16th November 2018, 11:39 AM   #128
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Originally Posted by lomiller View Post
Don’t you think you should have a dead body before you go looking for a smoking gun? There is nothing unique about the period 11.7KYA. Yes, there is unusual cooling, but there are many similar cooling events in the last 1m years. If only one was caused by an impact, how do you explain all the others. If you all the others can be explained by meltwater pulses that occur on melting ice sheets, what makes the most recent one any different?
a) you need to edit your last sentence.

b) Maybe all those other cooling periods were initiated by other Dirty Winters ? Some I know off off the top of my head: Crater in New Mexico, The Yucatan basin /Gulf of Mexico (biggest?) , Tanguska, many HUGE volcanoes: Krakatoa, Mt St Helens, mt Pinatubo,......... And with statistically 70% underwater ? Or even what percent under Antarctic ice?
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Old 16th November 2018, 01:16 PM   #129
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Quote:
. Yes, there is unusual cooling, but there are many similar cooling events in the last 1m years
such as ??

And the Younger Dryas is not similar to any historical volcanic episode - that's completely irrelevant.

Quote:
Analyses of stable isotopes from Greenland ice cores provide estimates for the start and end of the Younger Dryas. The analysis of Greenland Summit ice cores, as part of the Greenland Ice Sheet Project-2 (GISP-2) and Greenland Icecore Project (GRIP), estimated that the Younger Dryas started about 12,800 ice (calendar) years BP. Depending on the specific ice core analysis consulted, the Younger Dryas is estimated to have lasted 1,150–1,300 years.[2][3] Measurements of oxygen isotopes from the GISP2 ice core suggest the ending of the Younger Dryas took place over just 40 to 50 years in three discrete steps, each lasting five years.
https://en.wikipedia.org/wiki/Younger_Dryas

What ever triggered it coming at terminus of a ice age makes the assessement harder and it could be a combination of factors and there are other events similar in other glaciated world exits.
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Old 16th November 2018, 01:58 PM   #130
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Originally Posted by casebro View Post

b) Maybe all those other cooling periods were initiated by other Dirty Winters ? Some I know off off the top of my head: Crater in New Mexico, The Yucatan basin /Gulf of Mexico (biggest?) , Tanguska, many HUGE volcanoes: Krakatoa, Mt St Helens, mt Pinatubo,......... And with statistically 70% underwater ? Or even what percent under Antarctic ice?
Eruptions etc that block sunlight don’t fit the climate fingerprint of these events, because this would create simultaneous cooling in both the northern and southern hemispheres. These events, including the one 12K years ago seem confined to the Northern Hemisphere.

This asymmetric behavior of the 2 hemispheres fits well with theory that a meltwater pulse into the artic can move the gulf steam south causing Greenland and western Europe to cool rapidly. The only thing missing from the meltwater pulse theory was locating the pulse itself as it would have left considerable evidence.

This was resolved a few years ago when it was identified that there was rapid draining of glacial lake Agassiz draining into the artic though the McKenzie river just prior to the start of the Younger Dryas cooling.
https://www.researchgate.net/publica..._Younger_Dryas
https://www.livescience.com/31810-big-freeze-flood.html
https://www.giss.nasa.gov/research/briefs/gornitz_10/
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Old 20th November 2018, 12:37 PM   #131
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So you are talking about the thermohaline circulation stopping or slowing dramatically.

Good coverage here
https://geol155.academic.wlu.edu/the...as-glaciation/

And there is no reason to think it could not be a combination of events.

Here's cover on the impact theory

Quote:
Abstract
We report abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earth's typical surficial processes but common to cosmic impacts. N-diamond concentrations range from ≈10 to 3700 parts per billion by weight, comparable to amounts found in known impact layers. These diamonds provide strong evidence for Earth's collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.
http://science.sciencemag.org/content/323/5910/94

Now they have the crater ....and a big one

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Old 21st November 2018, 01:13 PM   #132
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Originally Posted by macdoc View Post

Here's cover on the impact theory



http://science.sciencemag.org/content/323/5910/94

Now they have the crater ....and a big one
Sorry, Mac, but the paper you linked was seriously criticised in the paper I linked at the top of the page. And they have 'a' crater. The chances of it being dated as coincidental with the YD are vanishingly small. The age is loosely constrained as Pleistocene. So 12 000 - 3 Ma.
Let's not claim things that are dubious at best.
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Old 21st November 2018, 06:51 PM   #133
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Originally Posted by jonesdave116 View Post
Sorry, Mac, but the paper you linked was seriously criticised in the paper I linked at the top of the page. And they have 'a' crater. The chances of it being dated as coincidental with the YD are vanishingly small. The age is loosely constrained as Pleistocene. So 12 000 - 3 Ma.
Let's not claim things that are dubious at best.
As much as I disagree with Mac about the rest of his conclusions, I tend to begrudgingly agree with him here. One of the major flaws with his hypothesis was always the lack of a candidate crater. Now he has a crater, so we wait until the timeline can be dated better, but this could actually be the smoking gun that was missing all this time. We can't use this argument of no crater any longer, until we prove this happened in a different era.
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Old 21st November 2018, 07:22 PM   #134
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Originally Posted by macdoc View Post
Here's cover on the impact theory
http://science.sciencemag.org/content/323/5910/94
However the next year there is: No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event (2010). With papers on both sides since then.
Younger Dryas impact hypothesis explains that the nanodiamond evidence is not clear.
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Old 21st November 2018, 07:38 PM   #135
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NONE of it is clear as yet but the missing elephant in the room for impact has been found lazing around Greenland.
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Old 21st November 2018, 08:17 PM   #136
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Originally Posted by macdoc View Post
NONE of it is clear as yet but the missing elephant in the room for impact has been found lazing around Greenland.
Wishful thinking, macdoc. Read the paper
Quote:
The age of the crater is presently unknown, but an impact sometime during the Pleistocene is consistent with presently available geological and geophysical data.
The undated crater is not an elephant or smoking gun.
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Old 22nd November 2018, 05:45 AM   #137
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Originally Posted by macdoc View Post
NONE of it is clear as yet but the missing elephant in the room for impact has been found lazing around Greenland.
And the Greenland impact site is pretty much equidistant from the alleged nano-diamond finds in North America as it is from much of Europe. Is there any impact evidence from Europe around the YD time?
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Old 22nd November 2018, 09:02 AM   #138
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Originally Posted by macdoc View Post
And there is no reason to think it could not be a combination of events.
If something can occur repeatedly without an asteroid strike, what does the asteroid strike add in terms of explanatory power? If the asteroid strike isn’t needed, Occam’s razor tells us not to include it.
Originally Posted by macdoc View Post
Now they have the crater ....and a big one
There is a crater dated to sometime in the last 3 million years.
Originally Posted by macdoc View Post
Dated. Most claims, including those related to nano-diamonds and fires have been subsequently refuted.
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Old 22nd November 2018, 09:07 AM   #139
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Originally Posted by Red Baron Farms View Post
One of the major flaws with his hypothesis was always the lack of a candidate crater.
The major flaw was always that the theory didn’t match the climate signature. A really big impact would have thrown enough dust in the air to cause cooling globally, but the paleo-climate data suggests that on the Northern Hemisphere cooled.



Originally Posted by Red Baron Farms View Post
Now he has a crater,
But not a crater that has been show to fit any of the data.
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Old 22nd November 2018, 09:09 AM   #140
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Originally Posted by macdoc View Post
A mile wide? No impact of that size would've gone unnoticed.
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Old 22nd November 2018, 09:24 AM   #141
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Originally Posted by lomiller View Post
The major flaw was always that the theory didn’t match the climate signature. A really big impact would have thrown enough dust in the air to cause cooling globally, but the paleo-climate data suggests that only the Northern Hemisphere cooled. (FTFY)




But not a crater that has been shown to fit any of the data.
I actually agree with you. This hasn't actually changed my mind yet. But it at least opens the possibility. I think in the end it will probably be shown to be a crater from some other era, and that the multiple large fauna extinctions really are attributed to Human impact (both hunting and human cause changes in climate resulting from the trophic cascades triggered) And maybe even a much smaller meteor strike possible if it hit an ice sheet and flooded the conveyor with fresh water.

But I can't really say that my view is any where even close to consensus either. We really do have quite a lot of uncertainty about the Younger dryas.
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Old 22nd November 2018, 11:54 AM   #142
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One thing that just occurred to me is this - if there was a large impact at the YD time, then wouldn't this have a considerable signature in the dust levels in Greenland ice core data?

I'm not really seeing anything that makes me sit up and say 'wow';

Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records
Walker, M. et al.
https://onlinelibrary.wiley.com/doi/....1002/jqs.1227
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Old 22nd November 2018, 01:13 PM   #143
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Quote:
All of the cores contain a thick (55–80 cm), grey clay layer that represents the Younger Dryas event. The clay ends abruptly at the Pleistocene–Holocene boundary with a switch from grey clay to dark-brown gyttja occurring within 5cm, and loss-on- ignition values (organic carbon) rapidly increasing over that increment from <5% to >30%; the Pleistocene–Holocene boundary is therefore visually and lithologically striking
From the paper
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Old 22nd November 2018, 02:01 PM   #144
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Originally Posted by Reality Check View Post
However the next year there is: No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event (2010). With papers on both sides since then.
Younger Dryas impact hypothesis explains that the nanodiamond evidence is not clear.
And more recently;

Comprehensive analysis of nanodiamond evidence reported to support the Younger Dryas Impact Hypothesis
Daulton, T.L. et al. (2017)
https://researchportal.port.ac.uk/po...Hypothesis.pdf

Personally, having read a lot of the criticism of the methods and interpretations of the people pushing this YD impact scenario, my view is that they probably don't really have any evidence. It appears to be misinterpretation, followed by confirmation bias.
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Old 22nd November 2018, 02:38 PM   #145
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Nice graphics ...
https://www.cbc.ca/radio/quirks/nov-...-ice-1.4906871

The nano-diamonds are far less critical now than dating the crater.
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Old 22nd November 2018, 02:48 PM   #146
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Originally Posted by macdoc View Post
Nice graphics ...
https://www.cbc.ca/radio/quirks/nov-...-ice-1.4906871

The nano-diamonds are far less critical now than dating the crater.
If the 'evidence' for an impact is actually non-existent. and the result of poor science, then I suspect that the dating is not going to help, unless it comes out bang on the YD time frame. Which, IMHO, is very bloody unlikely. However, we shall see, I imagine.
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Old 22nd November 2018, 03:53 PM   #147
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Originally Posted by macdoc View Post
From the paper
Not quite what jonesdave116 was pointing out, macdoc.
The Younger Dryas happened. A "thick (55–80 cm), grey clay layer" in the cores represents that event. The question is are there any indications of a Greenland impact in the cores, especially just before or at the bottom of that layer?

Look at Figure 1 in that paper and note where Camp Century is. This is the Hiawatha Glacier with the crater site is marked on a Greenland map. The sites are not far apart. Is the existence of cores dating back 100,000 years at Camp Century evidence that no impact happened? Or are the sites far enough apart for the impact not to destroy the ice sheet at Camp Century. In that case where is the ejecta from the impact in the cores? Would the impact have caused enough melting to cause a discontinuity in the ice core record?

There are another 5 sites spread across Greenland. I would expect that impact ejecta would appear in these ice cores

Last edited by Reality Check; 22nd November 2018 at 04:01 PM.
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Old 23rd November 2018, 12:46 PM   #148
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Yet the paper indicates the impact did not precede the glacier formation
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Old 23rd November 2018, 03:20 PM   #149
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Originally Posted by macdoc View Post
Yet the paper indicates the impact did not precede the glacier formation
That is their best estimate, but there are a lot of ifs, buts and maybes in the date estimation. Not the fault of the authors. Their best guess is Pleistocene, so from 2.6 Ma to ~ 12 Ka.
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Old 25th November 2018, 01:17 PM   #150
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Originally Posted by macdoc View Post
Yet the paper indicates the impact did not precede the glacier formation
The paper places constraints on the age of the crater to be within the Pleistocene:
  • "We can confidently assume that the structure is younger than the 1.985 to 1.740 Ga old Paleoproterozoic bedrock that outcrops in the immediately adjacent foreland".
  • Assume that the crater has been covered with ice all of its lifetime and erosion adds another constraint ( ~50 Myr with current erosion estimates making the crater "younger").
  • Two channels predate the crater and predate the Pleistocene inception of the Greenland Ice Sheet (~2.6 Ma ago).
  • "Previous modeling of hydrothermal systems within martian subaerial impact craters suggests that such systems have a life span of ~100 ka for a 30-km-wide crater"
  • "Last, Hiawatha Glacier’s radiostratigraphy is highly anomalous compared to the rest of the Greenland Ice Sheet". Perturbation of the ice formation from unknown sources. Suggestion of the retreat of Humboldt Glacier around 9 to 8 ka ago but no evidence that would have affected the Hiawatha Glacier.
That leads to
Quote:
The sum of these tentative age constraints suggests that the Hiawatha impact crater formed during the Pleistocene, as this age is most consistent with inferences from presently available data. An impact before the Pleistocene cannot clearly explain the combination of the relative freshness of the crater’s morphology and the ice sheet’s apparently ongoing equilibration with the presence of the crater. We emphasize that even this broad age estimate remains uncertain and that further investigation of the age of the Hiawatha impact crater is necessary. Regardless of its exact age, based on the size of the Hiawatha impact crater, this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally (35).
If we take the constraints as absolute then the crater may be ~100,000 years old (age of the hydrothermal system). Or even formed just before the retreat of Humboldt Glacier after the Younger Dryas. But we actually have an undated crater.

Last edited by Reality Check; 25th November 2018 at 01:23 PM.
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Old 25th November 2018, 06:38 PM   #151
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Then it would be in the ice cores.

We have a crater with constrained dates and little erosion. Since at least one of the team in on the discovery thinks there is a good chance of a Younger Dryas connection ...I figure they've got a good handle it.

Will wait and see.
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Old 25th November 2018, 07:37 PM   #152
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Originally Posted by macdoc View Post
Then it would be in the ice cores.

We have a crater with constrained dates and little erosion. Since at least one of the team in on the discovery thinks there is a good chance of a Younger Dryas connection ...I figure they've got a good handle it.

Will wait and see.
That is the point you missed before, macdoc. We have Greenland ice cores older than the Younger Dryas. If there was an impact that caused the Younger Dryas then there should evidence in those ice cores. That is especially true for the Camp Century site close to the impact site.

We have a crater that is "constrained" to have formed about 2,588,000 to 11,700 years ago. Even that "little erosion" gives a ~50 Myr constraint. It is modern erosion rates that make the crater vaguely younger.

Search the paper for "Younger Dryas" and find only 2 mentions in the "Radiostratigraphy of Hiawatha Glacier" section. The upper unit (two thirds of the ice column) is identified in Greenland ice cores as a sequence from 11.7 to 0 thousand years (ka) ago. The second unit below that doe not conform to known units. The third unit looks like basal ice.

Read the news report (Impact crater 19 miles wide found beneath Greenland glacier) and see no mention of Younger Dryas. No researcher on the team is reported there as thinking here is a connection with the Younger Dryas.

One news report has a personal opinion from Kjær: “We do not discuss it in the paper, but I think it is a possibility,” Kjær adds. “This may generate a lot of discussion, and we need to find out. We won’t know until we have a proper date.”
But then there is another news report: "Leery of the earlier controversy, Kjær won't endorse that scenario. "I'm not putting myself in front of that bandwagon," he says. But in drafts of the paper, he admits, the team explicitly called out a possible connection between the Hiawatha impact and the Younger Dryas."

This leads to Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas (2013). That shows that people expect an impact to have measurable effects in Greenland ices cores. The downside is that this is not a Ir anomaly as expected from a meteor indicating "a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis". The author is saying that there was evidence for an impact that was not that needed for the impact hypothesis.

Last edited by Reality Check; 25th November 2018 at 07:57 PM.
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