Christopher R. Moore, University of South Carolina
What kicked off the Earth’s rapid cooling 12,800 years ago?
In the space of just a couple of years, average temperatures abruptly dropped, resulting in temperatures as much as 14 degrees Fahrenheit cooler in some regions of the Northern Hemisphere. If a drop like that happened today, it would mean the average temperature of Miami Beach would quickly change to that of current Montreal, Canada. Layers of ice in Greenland show that this cool period in the Northern Hemisphere lasted about 1,400 years.
This climate event, called the Younger Dryas by scientists, marked the beginning of a decline in ice-age megafauna, such as mammoth and mastodon, eventually leading to extinction of more than 35 genera of animals across North America. Although disputed, some research suggests that Younger Dryas environmental changes led to a population decline among the Native Americans known for their distinctive Clovis spear points.
Conventional geologic wisdom blames the Younger Dryas on the failure of glacial ice dams holding back huge lakes in central North America and the sudden, massive blast of freshwater they released into the north Atlantic. This freshwater influx shut down ocean circulation and ended up cooling the climate.
Some geologists, however, subscribe to what is called the impact hypothesis: the idea that a fragmented comet or asteroid collided with the Earth 12,800 years ago and caused this abrupt climate event. Along with disrupting the glacial ice-sheet and shutting down ocean currents, this hypothesis holds that the extraterrestrial impact also triggered an “impact winter” by setting off massive wildfires that blocked sunlight with their smoke.
The evidence is mounting that the cause of the Younger Dryas’ cooling climate came from outer space. My own recent fieldwork at a South Carolina lake that has been around for at least 20,000 years adds to the growing pile of evidence.
What would an Earth impact leave behind?
Around the globe, scientists analyzing ocean, lake, terrestrial and ice core records have identified large peaks in particles associated with burning, such as charcoal and soot, right at the time the Younger Dryas kicked in. These would be natural results of the cataclysmic wildfires you would expect to see in the wake of Earth taking an extraterrestrial hit. As much as 10% of global forests and grasslands may have burned at this time.
Looking for more clues, researchers have pored through the widely distributed Younger Dryas Boundary stratigraphic layer. That’s a distinctive layer of sediments laid down over a given period of time by processes like large floods or movement of sediment by wind or water. If you imagine the surface of the Earth as like a cake, the Younger Dryas Boundary is the layer that was frosted onto its surface 12,800 years ago, subsequently covered by other layers over the millennia.
In the last few years, scientists have found a variety of exotic impact-related materials in the Younger Dryas Boundary layer all over the globe.
These include high-temperature iron and silica-rich tiny magnetic spheres, nanodiamonds, soot, high-temperature melt-glass, and elevated concentrations of nickel, osmium, iridium and platinum.
While many studies have provided evidence supporting the Younger Dryas impact, others have failed to replicate evidence. Some have suggested that materials such as microspherules and nanodiamonds can be formed by other processes and do not require the impact of a comet or asteroid.
A view of 12,800 years ago from White Pond
In the southeastern United States, there are no ice cores to turn to in the quest for ancient climate data. Instead, geologists and archaeologists like me can look to natural lakes. They accumulate sediments over time, preserving layer by layer a record of past climate and environmental conditions.
White Pond is one such natural lake, situated in southern Kershaw County, South Carolina. It covers nearly 26 hectares and is generally shallow, less than 2 meters even at its deepest portions. Within the lake itself, peat and organic-rich mud and silt deposits upwards of 6-meters thick have accumulated at least since the peak of the last ice age more than 20,000 years ago.
So in 2016, my colleagues and I extracted sediment from the bottom of White Pond. Using 4-meter-long tubes, we were able to preserve the order and integrity of the many sediment layers that have accumulated over the eons.
Based on preserved seeds and wood charcoal that we radiocarbon dated, my team determined there was about a 10-centimeter thick layer that dated to the Younger Dryas Boundary, from between 12,835 and 12,735 years ago. That is where we concentrated our hunt for evidence of an extraterrestrial impact.
We were particularly looking for platinum. This dense metal is present in the Earth’s crust only at very low concentrations but is common in comets and asteroids. Previous research had identified a large “platinum anomaly” – widespread elevated levels of platinum, consistent with a global extraterrestrial impact source in Younger Dryas layers from Greenland ice cores as well as across North and South America.
Most recently, the Younger Dryas platinum anomaly has been found in South Africa. This discovery significantly extends the geographic range of the anomaly and adds support to the idea that the Younger Dryas impact was indeed a global event.
Volcanic eruptions are another possible source of platinum, but Younger Dryas Boundary sites with elevated platinum do not have other markers of large-scale volcanism.
More evidence of an extraterrestrial impact
In the White Pond samples, we did indeed find high levels of platinum. The sediments also had an unusual ratio of platinum to palladium.
Both of these rare earth elements occur naturally in very small quantities. The fact that there was so much more platinum than palladium suggests that the extra platinum came from an outside source, such as atmospheric fallout in the aftermath of an extraterrestrial impact.
My team also found a large increase in soot, indicative of large-scale regional wildfires. Additionally, the amount of fungal spores that are usually associated with the dung of large herbivores decreased in this layer compared to previous time periods, suggesting a sudden decline in ice-age megafauna in the region at this time.
While my colleagues and I can show that the platinum and soot anomalies and fungal spore decline all happened at the same time, we cannot prove a cause.
The data from White Pond are, however, consistent with the growing body of evidence that a comet or asteroid collision caused continent-scale environmental calamity 12,800 years ago, via vast burning and a brief impact winter. The climate change associated with the Younger Dryas, megafaunal extinctions and temporary declines or shifts in early Clovis hunter-gatherer populations in North America at this time may have their origins in space.
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Christopher R. Moore, Archaeologist and Special Projects Director at the Savannah River Archaeological Research Program and South Carolina Institute of Archaeology and Anthropology, University of South Carolina
This article is republished from The Conversation under a Creative Commons license. Read the original article.
HT/Jerry HH
Now where have I heard this before? Velikovsky anyone?
I wonder why catastrophic explanations have such a strong appeal to people and are so popular. Even if global catastrophes do exist, they are extremely rare so it is a lot safer to bet on the explanation being somewhere else.
A common theme is that you have to take an event and make it look unique even if it has been happening many times. For that it helps if the event is the most recent one of its kind as then we have more information, and better resolution to make it look unique.
Cooling periods like the one that took place at the onset of the Younger Dryas are very common. There were probably a couple of dozens in the last 100,000 years. What makes this one special is that it is the most recent one. We have more and better proxies for it. We can claim uniqueness because the deglaciation had already started. We can analyze charcoal evidence for it and say the world was set ablaze without anybody demanding to see what happened during previous cooling periods of the same kind. We can claim a meteorite was responsible without having to explain what was responsible for all the rest of the similar cooling periods. It is a unique event because we have defined it as such so a unique explanation can be made responsible.
Now you see this is the same tactic used with the present warming period. It is made unique because it is the one we have better information (even satellites) and a much higher spatial and temporal resolution. then we can ignore all other similar warming periods during the Holocene and claim that this one is unique and demands a unique explanation. Then we can claim that CO2 is responsible without having to explain what was responsible for all the rest of the similar warming periods.
Lyell took Cuvier to the bushes for a serious beating, but the catastrophists refuse to yield. There is only one thing I don’t understand. How is it possible that people that strongly criticize the CO2 catastrophism then go out and subscribe to meteorite catastrophism to explain the YD. It is the same thing folks. I guess it has to do with the strong appeal that catastrophic explanations have to people. Perhaps it comes from not understanding probability properly. Over the entire geological record global catastrophes have indeed taken place, but when looking at a particular recent event the chances are abysmally low. Same principle as the lottery tickets. Somebody is going to win, but your chances are awful.
IMO the last cold snap owing to the same cause as the YD was the 8.2 Ka Event:
https://en.wikipedia.org/wiki/8.2_kiloyear_event
Subsequent coolings have been less pronounced and probably produced by Bond Cycles alone, there being not much more collapsible ice sheet left in the NH, the Greenland IS only waxing and waning slightly in the past 8000 years.
Catastrophism becomes uniformitarianism if you wait long enough.
Javier : ” I wonder why catastrophic explanations have such a strong appeal to people and are so popular ” ?
Why don’t you turn the amateur psychology spotlight on to yourself as they seem to appeal to you [ why else are you lingering here ? ] as alternative hypotheses for the Younger Dryas : ” Abrupt cooling results in an increase in the ice load over certain parts of the crust ,leading to an increase in volcanic activity ” .You even mentioned a multi causal catastrophic hypothesis after deriding ” hypothesis driven science” .. This is the second instance of you contradicting yourself .
Maybe it was the 250 species of animal that disappeared at the YD? That seems kinda special too.
George A. Howard says :
“Maybe it was the 250 species of animal that disappeared at the YD? That seems kinda special too.”
————————–
And no it was not a small population of stone age hunters. With rock spear tips made by banging rocks on other rocks. That killed every one of millions of large to giant mammals, some of whom were 2-3 times as heavy as their modern cousins. Some of whom were apex predators with very nasty sharp teeth and claws.
The predators died off after humans wiped out their megafaunal prey species.
Humans were responsible for the extinctions, just as in Australia, Eurasia, Madagascar, Hawaii, New Zealand and many oceanic islands. The Pleistocene megafauna had survived prior deglaciation cycles. Only when human hunters pursued them did they die out.
In Africa, more of the megafauna survived because they were used to humans, with whom they coevolved, so weren’t naive.
Size matters! Closing the case in favor of the human (to include Neanderthal and Denisovan) overkill hypothesis. Not that any further evidence should be necessary, given the history of extinctions during the past 125,000 years on every continent and island invaded by humans.
Body size downgrading of mammals over the late Quaternary
https://science.sciencemag.org/content/360/6386/310
Stone Age hunters of 15,000 years ago were deadly. They had atlatls, to attack from a distance. Probably bows as well. They had fire, to stampede big game over cliffs or into traps. They had dogs. They had cooperative tactics honed for millennia on the Eurasian steppe and tundra.
They went for the biggest mountains of meat, hide and sinew first, the mammoths. K!ll the cows and the slowly reproducing monsters are history, as would have happened with American bison had one former hunter not rescued them from doom.
Then came the ancient bison, camels, ground sloths, horses, etc. All driven to extinction in North America by humans hunting there naive, vulnerable beasts.
John
Interestingly, when Native Americans killed large numbers of bison, they tended to take primarily tongues and livers, and just enough hides and muscle for their immediate needs. Thus, they wasted a lot of potential food. That means they could have gotten by with smaller animals to meet their needs. It may be that stampeding bison over ‘jumps’ was easier than stampeding deer or antelope. Thus, the ‘dumber’ animals were preferred game. Strangely, the bison persisted in large numbers while the Pleistocene megafauna disappeared!
Clyde,
The much bigger Pleistocene bison species were wiped out. The wood and plains bison which survived were smaller.
John
I’m aware of the size difference. My point is, if the smaller plains bison provided them with an embarrassment of riches that they couldn’t efficiently use, why would they focus on even larger animals?
During the American megafaunal extinction event around 12,700 years ago, 90 genera of mammals weighing over 44 kilograms became extinct. But all the evidence shows that an alleged impact couldn’t have been responsible.
If an ET impact were the cause, then why did Caribbean island megafauna survive, close to the supposed impact, while those large species far away in Patagonia disappeared?
The timing of extinctions coincides with human entry into the doomed animals’ habitats.
First setence of second paragraph after this heading
“What would an Earth impact leave behind?”
“Looking for more clues, researchers have pored through the widely distributed Younger Dryas Boundary stratigraphic layer.”
Typo? Should it read researchers have bored…”
No impact proxies have been found anywhere.
Every supposed such proxy isn’t.
Do you believe Dr. Ted Bunch is unqualified to identify an impact proxy when he sees one? He is a lead author on dozens of YDIH papers. He was an ally of Gene Shumaker in the early in the early 60’s and has maintained a peer-reviewed publishing record of proxy study since that time. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C34&q=t.e+bunch&btnG=
He and his comrades have claimed to find impact proxies, but in every case, the supposed material has been shown not to result from such a cosmic collision.
The gang’s “work” has been repeatedly debunked and rebunked.
Tillman : ” No impact proxies have been found anywhere ” ….This research paper was published in March of this year : ” Evidence of Cosmic Impact at Abu Hureyra Syria at the Younger Dryas Onset [ 12.8ka] : High Temperature Melting at 2200C ” Nature Communications March 2020 ….Where and in what journal were the researchers findings recently debunked ? This particular paper nature.com/articles/s41598-020-60867-w
A pack of lies. Even if there were a Pt signature, it confirms nothing.
Please learn how real science works.
What if the asteroid hit a one mile thick glacier in the North American hemisphere? I do not think that an impact crater would be found, and this would be consistent with a sudden release of water into the Atlantic (no AMOC) and the release of sunlight blocking particles from the asteroid and forest fires. Perhaps a volcano or two decided to do a Mount Pinatubo around the same time.
Hey John Tillman, that’s really authoritative sounding. Except Pete Schultz of NASA, and Ted Bunch retired NASA, are co-authors of the YDIH and have confirmed the proxies as entirely in line with the KT boundary science, which is the standard. Oh, and Andronikov, of Arizona’s Lunar and Planetary lab, confirmed them independently, as have many others. Certainly you have failed to read LeCompte 2012: https://www.pnas.org/content/109/44/E2960.abstract
Read it very carefully now, so you won’t embarrass yourself in the future making baseless declaratory statements on the internet. https://cosmictusk.com/younger-dryas-impact-hypothesis-bibliography-and-paper-archive/
Please don’t embarass yourself by citing anything from Cosmic Tusk.
Do I really need to post again the many papers by real scientists humiliating the YDIH gang’s drivel?
Cosmic Tusk is only a publisher Mr Tillman …..Like WUWT .. Best not embarrass yourself any further
Cosmic Tusk exists to publish antiscientific garbage.
Clearly you did not read the paper savaging LeCompte.
https://www.pnas.org/content/110/18/E1651
Every feeble attempt by the Gang to spew their garbage is always immediately shot down by real scientists.
Answer the question John Tillman
I already did. You’re just afraid to read the truth, since you can’t handle it.
Tillman : ” No impact proxies have been found anywhere ” ….This research paper was published in March of this year : ” Evidence of Cosmic Impact at Abu Hureyra Syria at the Younger Dryas Onset [ 12.8ka] : High Temperature Melting at 2200C ” Nature Communications March 2020 ….Where and in what journal were the researchers findings recently debunked ? This particular paper nature.com/articles/s41598-020-60867-w
As I’ve already pointed out, the paper doesn’t support the debunked :hypothesis”. All it does is show another site with a signature of the Eifel Hot Spot eruption. The supposed glass and tektite “ejecta” aren’t.
So the paper you keep citing doesn’t support this crackpot “hypothesis”.
Its obvious who the lying troll is John . The paper does support the YDIH in the conclusion
Anyone can read it for themselves . I see Javier has disappeared ..Where is the relevant recent publication in a reputable science journal rebutting the March 2020 Nature Communications Abu Hureyra YDIH paper ? ….There was no abundant volcanic tephra in the soil analyses pointing to any Eifel Hot Spot eruption according to their research …So where is the 2020 citation for this “debunking” paper ? You mentioned iridium as a meteorite signature [ an impact proxy ] which exists in elevated concentrations in that region of Syria . You unwittingly validated a hypothesis you denounced as ” crackpot” . You and Javier were trounced in this debate but of course you never intended debating here in good faith …
No debate. Just the facts.
YDIH zealots have nothing. You never had anything. Your gibberish was promptly shown false in 2008, and it has only gotten worse since then.
Where is the published scientific research rebutting the facts outlined in the March 2020 Nature Communications paper Mr Tillman ?
John Tillman, trolls like you are embarrassment to science. Clearly interested and capable of understanding, you nonetheless misrepresent and defame people you disagree with. You are simply gross style, with no substance. The 70+ scientists on the YDIH paper are indeed “real scientists” You may disagree them, but that does not demote their status as real. Here’s is one example from many: Dr. Andrew M. T. Moore. Moore led the recent paper, Evidence of Cosmic Impact at Abu Hureyra Syria at the Younger Dryas Onset, kindly cited above by Stu. (The paper is #141 on my bibliography at the Cosmic Tusk: https://cosmictusk.com/younger-dryas-impact-hypothesis-bibliography-and-paper-archive/) Moore is the immediate past President of the Archaeological Institute of America. AIA has over 200,000 members, was found in 1879, and is chartered by Congress. Moore led the dig of Abu Hureyra in the 70’s. He’s a real scientist, John. His qualifications to write this paper exceed those of anyone who would question it. Anyone is welcome to question it, including you, but please do not misinform casual readers here by defaming these researchers as unqualified, and not “real.” Just crawl back in your hole and do some reading, and if you can’t read, listen: https://sevenages.org/podcasts/seven-ages-audio-journal-episode-36-impact-at-abu-hureyra/
I have done the reading which you need to do. Adherents of the YDIH cult are the embarrassments to science.
Real scientists who do real work have repeatedly shown in detail that every single lame argument spewed by these shameless liars is bogus. Yet they keep polluting journals with their mendacious garbage.
Why? Because it beats working.
It is evident on this thread who the liars and embarrassments are ..Who are these ” real scientists ” that have supposedly “debunked” the authors of the March 2020 Nature Communications paper cited by myself and George ? I think the a past president of the Archaeological Institute of America is much more familiar with hard, respectable work than you
Stuart,
I don’t know about you, but George is the Crackpot in Chief, who has made an ill-gotten career out of peddling utter garbage to the poorly educated masses.
Stuart,
Clearly you have not bothered to educate yourself. Please read the innumerable papers from 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 and 2020 showing what an antiscientific farce is the YDIH.
The proponents of this nonsense are even less scientific than climate alarmists, whom I describe in the same terms.
To be a real scientist, you have to practice the scientific method. It doesn’t matter how many times you pay a journal to publish your hased and rehashed drivel.
George,
Far better than trolls speaking the truth are crackpots in chief such as yourself, here as a tourist to spread your insane garbage, for which low information viewers have rewarded you richly.
You should be ashamed.
Although OTOH, you’ve done well for yourself as a sociology grad snookering the gullible folk into buying your total, complete and utter garbage “books”.
Let us invoke that an asteroid hit a one mile thick glacier in Northern American hemisphere and left no impact crater at ground surface. This would not only release massive quantities of ash, but also vast quantities of liquid water that then overcame the natural ice dams holding back the huge water volumes in the Great Lakes area. This would account for massive influxes of fresh water into the Atlantic, shutting down the AMOC, but also causing global cooling from asteroid material and resulting forest fires.
Massive influxes of fresh, cold water happen during deglaciations as a matter of course, without ET intervention. Just as armadas of icebergs launch into the North Atlantic during glaciations.
The main problem with this WAG is that there is no reason to imagine such a highly improbable scenario in the first place, the odds against which are about 2000:1.
The scheme’s shills suppose that the YD is different from the hundreds of other such cold snaps because of extinctions which appear to have happened during it. But extinctions occcurred before and after it, and always in association with humans.
Real scientists are convinced to the highest degree of probability that no impact caused extinctions during the YD because the pattern thereof doesn’t support this baseless conjecture. As I keep asking, but no proponent of this unfounded assertion can answer, is why didn’t megafauna on Caribbbean islands die out during the YD, when related species much farther away, to include in South America, did?
The answer is simple. Because the cold snap didn’t k!ll them off any more than did the prior such excursions in the last glacial termination. Human hunters did, invading continents with naive giant beasts.
Same as happened in Eurasia, Australia, Madagascar and oceanic islands when modern people with advanced technology and tools arrived.
Is Andrew Moore a real scientist, John Tillman?
He wont respond directly to that question George …..Nor to any request for scientific research publications supposedly “debunking” the Nature Communications paper we cited . Still waiting John Tillman
George and Stuart,
Of course I respond.
No, he’s not a real scientist, because he doesn’t practice the scientific method.
Looking for platinum signatures isn’t science, if the goal is to support an antiscientific, baseless, religious assertion.
John Tillman I have no idea who George is ..Of course archaeologists are versed in empirical scientific methodologies ..You however are now debasing this discussion with puerile insults because you have nothing when questioned …Platinum is not the only once trace element ….You admitted iridium is a cosmic impact signature and it was discovered in elevated concentrations at the Abu Hureyra site in Syria along with cobalt ,chromium FE silicides and 2200C melt-glass
George Howard, the famous Crackpot in Chief, comments right before you.
The supposed iridium signature is just as bogus as every other supposed support for this blatantly false assertion.
Please see my links and quotations below.
You’ve been taken in by professional liars.
I’m amazed at how many people immediately go with the “impact” premise.
When it could just as easily have been the result of 1 to dozens of “extraterrestrial” objects of various sizes bursting / arcing / flashing across the upper to lower atmosphere over a variety of time lapses and distances.
=8-|
No, it can’t be that. All the evidence shows that it wasn’t.
For all your YDIH fanboys, here’s the truth (previously posted):
Geologists, paleoclimatologists, oceanographers and atmospheric scientists do have a very good grasp of what caused the YD and the alternating stadials and interstadials during glaciations and deglaciations (terminations). Cold, fresh water released into the oceans by armadas of icebergs (Heinrich events) or by meltwater from the ice sheets.
The YDIH and other gods on machines “explanations” are not only wrong, having been repeatedly shown false in detail, but totally unnecessary. They’re time-wasting exercises akin to looking for evidence of phlogiston after the isolation of oxygen or for the humors theory of disease after the discovery of germs.
The only problem with the meltwater hypothesis before 2005 was ascertaining by which route the flood entered the ocean. It had been shown by 1989 that the usual drainage of the Laurentide Ice Sheet (LIS) via the Mississippi didn’t flow during the YD. Broecker (please forgive him for being the “Father of Global Warming”) in that year suggested the St. Lawrence, which seemed a natural given Niagara’s date of c. 12,000 BP. But analysis of its channels and sediments didn’t really show any clear sign of such an ice-dammed outwash flood. And in any case, proglacial meltwater Lake Agassiz was SW of the LIS. An arm of it could have hooked around the southern face of the retreating LIS, but the lay of the land was against this possibility.
And there the situation stood until 2005, when Tarasov and Peltier proposed that the meltwater discharge was not into the Gulf of Mexico or North Atlantic, but into the Arctic Ocean, via the MacKenzie River drainage.
https://www.atmosp.physics.utoronto.ca/~peltier/pubs_recent/Lev%20Tarasov%20and%20W.R.%20Peltier,%20Arctic%20Freshwater%20Forcing%20of%20the%20Younger-Dryas%20Cold%20Reversal,%20Nature,%20435,%20662-665,%202005.pdf
The last deglaciation was abruptly interrupted by a millennialscale reversal to glacial conditions, the Younger Dryas cold event. This cold interval has been connected to a decrease in the rate of North Atlantic Deep Water formation and to a resulting weakening of the meridional overturning circulation owing to surface water freshening. In contrast, an earlier input of fresh water (meltwater pulse 1a), whose origin is disputed, apparently did not lead to a reduction of the meridional overturning circulation. Here we analyse an ensemble of simulations of the drainage chronology of the North American ice sheet in order to identify
the geographical release points of freshwater forcing during deglaciation. According to the simulations with our calibrated glacial systems model, the North American ice sheet contributed about half the fresh water of meltwater pulse 1a. During the onset of the Younger Dryas, we find that the largest combined meltwater/iceberg discharge was directed into the Arctic Ocean. Given that the only drainage outlet from the Arctic Ocean was via the Fram Strait into the Greenland–Iceland–Norwegian seas, where North Atlantic Deep Water is formed today, we hypothesize that it was this Arctic freshwater flux that triggered the Younger Dryas
cold reversal.
Perhaps their paper didn’t get the respect it deserved because the North Atlantic paradigm ruled so strongly. The chain of lakes from Manitoba across the NW Territories, marking the retreating LIS edge stared everyone in the face, but like geographers since AD 1500 looking at South America and Africa before Wegener, had eyes but couldn’t see.
In any case, two years later Firestone and unindicted coauthors perpetrated their ET impact hypothesis, if the wild conjecture may be so designated. It was promptly shown false, and has been repeatedly since then, but its easy career-making potential meant that it took on a zombie-like existence, with a voodooist cult following. It lurches along, from one new lame excuse to another.
Even loopier “hypotheses” have been floated, in this debased age when just about anything but reality gets published readily. Broecker’s former coauthor Kennett even deserted to the Dark Side of the farce.
But a few real scientists over the years have investigated the MacKenzie River hypothesis, and repeatedly confirmed it. Both observations and simulations of drainage and the effect on the Atlantic meridional overturning circulation (AMOC, the zonally-integrated component of Atlantic surface and deep currents). and atmospheric circulation supported it.
After this 2018 paper, the case is effectively closed, as it long ago should have been, had the scientific method ruled. Science is never settled, of course, but no present alternative hypothesis can compete with this ice-rafted deluge of valid evidence. The iceebergs and meltwater deliver cold, fresh water to where it will have the most effect, and the flow lasts hundreds of years, solving the issues of duration and amplitude of YD cooling.
https://www.nature.com/articles/s41561-018-0169-6?proof=trueMay.
A period of cooling about 13,000 years ago interrupted about 2,000 years of deglacial warming. Known as the Younger Dryas (YD), the event is thought to have resulted from a slowdown of the Atlantic meridional overturning circulation in response to a sudden flood of Laurentide Ice Sheet meltwater that reached the Nordic Seas. Oxygen isotope evidence for a local source of meltwater to the open western North Atlantic from the Gulf of St Lawrence has been lacking. Here we report that the eastern Beaufort Sea contains the long-sought signal of 18O-depleted water. Beginning at ~12.94 ± 0.15 thousand years ago, oxygen isotopes in the planktonic foraminifera from two sediment cores as well as sediment and seismic data indicate a flood of meltwater, ice and sediment to the Arctic via the Mackenzie River that lasted about 700 years. The minimum in the oxygen isotope ratios lasted ~130 years. We suggest that the floodwater travelled north along the Canadian Archipelago and then through the Fram Strait to the Nordic Seas, where freshening and freezing near sites of deep-water formation would have suppressed convection and caused the YD cooling by reducing the meridional overturning.
The scientific method still survives in a few refugia.
Comparing the last termination with the previous six going back to the Mid-Pleistocene Transition (the switch from ~40,000-year glacial cycles to those averaging ~100,000 years) is instructive, but beyond the scope of a comment. The four before Termination VII occurred during the transition, ie ~700 Ka to 1.2 Ma. Suffice it to say, that stadials (coolings) caused by meltwater and iceberg armadas are evident in all of them, although not all have coolings as pronounced and long-lasting as the YD. Those that do reflect similar Milankovitch cycle alignments, hence summer solar insolation regimes. Those which don’t experienced higher insolation.
The duration of the Younger Dryas glaciation may best be explained by a multi -causal hypothesis
Whatever hypothetical other contributing factors might be proposed, the fact remains that flow of ice sheet meltwater via the MacKenzie drainage for 700 years from the start of the YD affected the AMOC.
The paper on Texas cave sediments cited by David Middleton shows yet again that there is no evidence whatsoever supporting a catastrophic impact, and all the evidence in the world against it.
Volcanic origin for Younger Dryas geochemical anomalies ca. 12,900 cal B.P.
https://advances.sciencemag.org/content/6/31/eaax8587
Each of these four possible triggers for the YD event is complex, and there is not a clear consensus as to which mechanism or combination of these events initiated the YD cold period. Of these explanations, the impact hypothesis has received the most attention, but problems plague this hypothesis. The fundamental issue is delineating if the markers used to support the hypothesis extracted from the YD layers at various sites are really impact markers (1, 11). The grains interpreted as carbon spherules and “elongates” and “glass-like carbon” have been instead identified as fungal sclerotia common in Northern Hemisphere forest litter and soils (12). In addition, the micrograins interpreted as hexagonal nanodiamonds from YD sites of Murray Springs (AZ) and Arlington Canyon on Santa Rosa Island (CA) are instead assessed as graphene/graphene aggregates (13). These disagreements are compounded by a lack of valid age control at many of the YD boundary (YDB) layer sites. It is now thought that only 3 of the 29 sites dated to the onset of YD event were within the prerequisite time period. Furthermore, there are problems in that the reproducibility of observations at the YD level has been questioned for the presence of magnetic grains, spherules, and Ir enrichments. Surovell et al. (14) failed to duplicate the magnetic grain or microspherule peaks associated with the YD basal boundary. Thus, there is a lack of consensus on how to interpret the impact markers.
Highly elevated concentrations of Ir together with enrichments of other highly siderophile elements (HSEs) (Os, Ir, Ru, Pt, Pd, and Re) in nearly chondritic ratios are considered indicators of a meteoritic contribution delivered when an extraterrestrial (ET) object affects the Earth or airbursts over it (15). These HSE enrichments may be from an external source because the Earth’s crust has 1 (18), such that small amounts of ET material added to continental crust will shift the 187Os/188Os ratios of the hybridized material to lower values.
The cause of the elevated HSE concentrations and the Os isotopic ratios in YD layer sediments remains equivocal and has been used to both support and negate the YD impact hypothesis. For example, Petaev et al. (19) found a Pt enrichment accompanied with an extremely high Pt/Ir but Al-poor signature in the Greenland Ice Sheet Project 2 ice core at the Bølling-Allerød/YD transition period, which they interpreted to be consistent with an ET impactor. Also, the elevated Pt abundance anomalies of 100 to 65,600 parts per trillion (ppt) at the onset of the YD in sites from North America is purportedly consistent with the Greenland ice core Pt data (20). Moore et al. (9) found Pt and Pd/Pt anomalies in the YD basal layer in South Carolina. These data are used to support a model of wide-ranged atmospheric input of platinum-rich dust during the YD, potentially related to a bolide impact or airburst. In contrast, the 187Os/188Os ratios obtained on YD basal boundary layers from widely dispersed locales in North America and Europe have largely been similar to those for continental crust or seawater with no evidence of unradiogenic 187Os/188Os ratios from ET or mantle sources, both having 187Os/188Os ratios of 0.11 to 0.13 (21, 22). This is exceptional because <1% of ET material from an impactor mixed into continental crust would shift the resultant hybridized material away from terrestrial crustal 187Os/188Os values toward the less radiogenic values of 187Os/188Os chondrites (17). Only one site has been identified with an unradiogenic Os signature, with an 187Os/188Os ratio of 0.4 for the YD basal boundary layer at Melrose, PA (22). This signature is attributed to surface films on glass spherules with highly elevated Os concentrations and unradiogenic 187Os/188Os ratios of 0.113 to 0.121 that may have been caused by mobilization of Os within a bolide fireball and possibly terrestrial in origin and ejected as molten material following impact (22). An important question remains: Why are low 187Os/188Os ratios found only at one site and not more widely dispersed if it is derived from impact or air burst of a bolide?
The above studies show that there is no clear consensus on the interpretation of HSE concentrations and 187Os/188Os compositions of YD basal boundary sediments (21, 22). A better understanding of their systematics is crucial for determining the role, if any, of a bolide event for the YD cooling and to refine conclusive evidence in the rock record for bolide impacts. To further examine this issue, we measured HSE abundances and 187Os/188Os isotope ratios in samples from Hall’s Cave, TX, including those from the YDB. Hall’s Cave formed in the Segovia Formation of the lower Cretaceous Edwards Group and contains sediments dating from 20,000 years before the present (B.P.) to present (23). The cave has a consistent depositional environment with minimal reworking or disturbance over this time period (23). The stratigraphy is well dated based on 162 accelerator mass spectrometry (AMS) 14C dates from vertebrate fossils, snails, charcoal, and sediment chemical fractions (23, 24). The YD basal boundary layer at Hall’s Cave also contains purported ET proxies including nanodiamonds, aciniform soot, and magnetic spherules (25). Here, we present Os isotopes and HSE abundances from the YD basal boundary strata in addition to layers above and below that horizon. Our measurements span ~4000 years of sediment deposition at Hall’s Cave. The HSE chondrite-normalized patterns combined with 187Os/188Os at different levels within this section at Hall’s Cave including the YD basal boundary layer show a repeating record of Os concentration enrichment. Multiple occurrences above and below the anticipated YD basal boundary layer bring into question the single impact theory for the YD climate event. Instead, we propose that the five layers containing HSE enrichments and Os isotopic signatures represent volcanic aerosols and cryptotephra contributed from distant volcanic eruptions over the ~4000 years.
Mr. Tillman for the umpteenth time , if the iridium ,chromium cobalt and meltglass cosmic impact signatures identified at the Abu Hureyra site in Syria and reported in the March 2020 Nature Communications paper are ” bogus” where is the RECENT rebuttal research published in a reputable scientific journal ? …Answer the question and specify the publication ..Your Gish Gallop tactics [ above ] streaming slabs of irrelevant information are not working and you want others to believe the authors of that research paper are ” professional liars” ….Thats absurd and defamatory …..You have ,moreover, contradicted yourself – departing from emphatically stating the YD was caused by volcanism to ” Each of these four possible triggers for the YD event and there is not a clear consensus as to which mechanism or combination of these events initiated the YD cold period ” .Your turgid text above .even acknowledges : ” may have been caused by mobilization of Os with a bolide fireball and possibly terrestrial in origin and ejected as molten material following impact ” ..
.Made up your mind yet or did you intend to blow the smoke and tilt the mirrors on this thread from the outset ?