Guest “geology lesson” by David Middleton
Fire from the Sky
Researchers find evidence of a cosmic impact that caused destruction of one of the world’s earliest human settlements
By Sonia Fernandez
Friday, March 6, 2020Before the Taqba Dam impounded the Euphrates River in northern Syria in the 1970s, an archaeological site named Abu Hureyra bore witness to the moment ancient nomadic people first settled down and started cultivating crops. A large mound marks the settlement, which now lies under Lake Assad.
But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food and tools — an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth’s cultural and environmental history.
Abu Hureyra, it turns out, has another story to tell. Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures — far higher than what humans could achieve at the time — or that could be attributed to fire, lighting or volcanism.
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Abu Hureyra lies at the easternmost sector of what is known as the Younger Dryas Boundary (YDB) strewnfield, which encompasses about 30 other sites in the Americas, Europe and parts of the Middle East. These sites hold evidence of massive burning, including a widespread carbon-rich “black mat” layer that contains millions of nanodiamonds, high concentrations of platinum and tiny metallic spherules formed at very high temperatures. The YDB impact hypothesis has gained more traction in recent years because of many new discoveries, including a very young impact crater beneath the Hiawatha Glacier of the Greenland ice sheet, and high-temperature meltglass and other similar evidence at an archaeological site in Pilauco, located in southern Chile.
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The biggest problem with Younger Dryas impact crater hunters is their insistence on describing everything as evidence for their pet hypothesis. This is the most egregious example I have seen so far:
The YDB impact hypothesis has gained more traction in recent years because of many new discoveries, including a very young impact crater beneath the Hiawatha Glacier of the Greenland ice sheet…
The Younger Dryas fits right into a well-established warming and cooling cycle exhibited throughout the Northern Hemisphere during the final Pleistocene glacial stage. Approximately every 1,500 years, Northern Hemisphere, occasionally global, temperatures sharply rose (Dansgaard-Oeschger events) and then rapidly cooled back to full glacial stage levels. The cold episodes are called glacial stadials and the warm episodes are called glacial interstadials. The final pair was the Bølling–Allerød glacial interstadial and Younger Dryas glacial stadial. The Bølling–Allerød interstadial was particularly warm, as warm as the Little Ice Age in Central Greenland. Setting aside the fact that the Younger Dryas stadial doesn’t really require a unique explanation, some of the evidence for a significant Younger Dryas impact event is actually quite compelling. The platinum anomalies (Petaev et al., 2013 and Moore et al., 2017) comprise the first (and just about only) relatively unambiguous pieces of evidence for a significant bollide event(s) at, or near the transition from the Late Pleistocene Bølling–Allerød interstadial to the Younger Dryas stadial (AKA the Younger Dryas Boundary (YDB)). The GISP 2 anomaly (Petaev et al., 2013) is most compelling.
The most recent paper by the intrepid crater hunters alleges YDB impact evidence from an archaeological site at Abu Hureyra, Syria. For anyone interested, the full text is available. The paper cites Petaev et al., 2013, regarding a YDB platinum anomaly in the GISP2 ice core, as supporting evidence, which it isn’t. The paper also mentions the Hiawatha crater in Greenland. While it doesn’t specifically link it to the YDB, the UCSB press release does. The subject of this post is limited to the reasons why the GISP2 platinum anomaly and Hiawatha crater do not support any version of the YDB impact hypothesis.
GISP2 YDB Platinum Anomaly
In this paper, the term “airburst/impact” refers to a collision of a cosmic body with the Earth’s atmosphere, after which numerous smaller fragments may strike the ground forming transient surface craters. These studies propose that such an impact event triggered a cascade of secondary effects, including a brief impact winter and severe Younger Dryas (YD) climate change (span: ~12,800–11,500 cal BP)1,13,14, along with possible contributions to the megafaunal extinctions and human population declines23. Moore and Kennett24 concluded that impact-triggered climate change caused the prehistoric villagers at Abu Hureyra to transition from hunting/gathering to cultivation, indicative of earliest agriculture, one of the most significant cultural transformations in human history.
Petaev et al., 2013 comes just about as close as you can get, short of finding a crater, to unambiguous evidence of a significant YDB impact event. Unfortunately, it contradicts one of the favored hypotheses: The bolide triggered widespread fires, triggering a sort of nuclear winter, sinking Earth into the Younger Dryas cooling period.
Until the question about the nature of Pt-rich material and the means of its delivery to the ice is resolved, an extraterrestrial source of Pt appears likely. For example, the Pt anomaly could be explained by multiple impacts of an iron meteorite like Sikhote-Alin or Grant (21, 26); the former is a large crater-forming meteorite shower. Assuming a global anomaly, the 62.5-cm-thick ice layer with the average Pt concentration of 30 parts per trillion (ppt) (Fig. 1) would require an iron meteorite like Sikhote-Alin of ∼0.8 km in diameter to account for the Pt budget at the YDB. Because complete disintegration of such a large iron meteorite during its atmospheric passage seems unlikely, the event is expected to form a crater of a few kilometers in diameter. No such crater at YDB has been found so far.
The main conclusion of our study is the detection of an unusual event during the Bølling-Allerød–YD transition period that resulted in deposition of a large amount of Pt to the Greenland ice. The Pt anomaly precedes the ammonium and nitrate spike in the GISP2 ice core (2) by ∼30 y and, thus, this event is unlikely to have triggered the biomass burning and destruction thought to be responsible for ammonium increase in the atmosphere and the Greenland ice (11). Although the data do not allow an unambiguous identification of the Pt source, they clearly rule out a chondritic origin of Pt. One of the plausible sources of the Pt spike is a metal impactor with an unusual composition derived from a highly fractionated portion of a proto-planetary core.
The YDB platinum anomaly is not consistent with a cometary or chondritic airburst. The platinum anomaly is consistent with a Pt-rich, Al-poor, Ir-poor iron meteorite, which would have left a significant crater. Furthermore, Pt anomalies have not been found in any other Greenland ice cores, nor has any ejecta material been observed in any Greenland ice cores.
So, where’s the YDB crater?
Hiawatha Crater
What he brought home clinched the case for a grand discovery. Hidden beneath Hiawatha is a 31-kilometer-wide impact crater, big enough to swallow Washington, D.C., Kjær and 21 co-authors report today in a paper in Science Advances. The crater was left when an iron asteroid 1.5 kilometers across slammed into Earth, possibly within the past 100,000 years.
Though not as cataclysmic as the dinosaur-killing Chicxulub impact, which carved out a 200-kilometer-wide crater in Mexico about 66 million years ago, the Hiawatha impactor, too, may have left an imprint on the planet’s history. The timing is still up for debate, but some researchers on the discovery team believe the asteroid struck at a crucial moment: roughly 13,000 years ago, just as the world was thawing from the last ice age. That would mean it crashed into Earth when mammoths and other megafauna were in decline and people were spreading across North America.
The impact would have been a spectacle for anyone within 500 kilometers. A white fireball four times larger and three times brighter than the sun would have streaked across the sky. If the object struck an ice sheet, it would have tunneled through to the bedrock, vaporizing water and stone alike in a flash. The resulting explosion packed the energy of 700 1-megaton nuclear bombs, and even an observer hundreds of kilometers away would have experienced a buffeting shock wave, a monstrous thunder-clap, and hurricane-force winds. Later, rock debris might have rained down on North America and Europe, and the released steam, a greenhouse gas, could have locally warmed Greenland, melting even more ice.
The news of the impact discovery has reawakened an old debate among scientists who study ancient climate. A massive impact on the ice sheet would have sent meltwater pouring into the Atlantic Ocean—potentially disrupting the conveyor belt of ocean currents and causing temperatures to plunge, especially in the Northern Hemisphere. “What would it mean for species or life at the time? It’s a huge open question,” says Jennifer Marlon, a paleoclimatologist at Yale University.
A decade ago, a small group of scientists proposed a similar scenario. They were trying to explain a cooling event, more than 1000 years long, called the Younger Dryas, which began 12,800 years ago, as the last ice age was ending. Their controversial solution was to invoke an extraterrestrial agent: the impact of one or more comets. The researchers proposed that besides changing the plumbing of the North Atlantic, the impact also ignited wildfires across two continents that led to the extinction of large mammals and the disappearance of the mammoth-hunting Clovis people of North America. The research group marshaled suggestive but inconclusive evidence, and few other scientists were convinced. But the idea caught the public’s imagination despite an obvious limitation: No one could find an impact crater.
Proponents of a Younger Dryas impact now feel vindicated. “I’d unequivocally predict that this crater is the same age as the Younger Dryas,” says James Kennett, a marine geologist at the University of California, Santa Barbara, one of the idea’s original boosters.
There is little doubt that this is an impact crater, a fairly big one. There is also little doubt that it is, geologically speaking, fairly young, almost certainly less than 2 million years old. There’s just one problem with it having occurred at the onset of the Younger Dryas: There is no evidence that the ice sheets were affected.
The full text of Kjær et al., 2018 is also available. The paper is well-worth reading. While it does not assert that the impact occurred at the YDB, it notes that the radar imagery below the Holocene is “either poorly expressed or absent stratigraphic layering”. We can see in Figure S5, from the Supplemental Material, that the Younger Dryas reflector is not present in at the location of the nearest ice core, Camp Century, and that the Pleistocene ice is poorly imaged. A similar pattern is observed at the most distant ice core, DYE-3.
Radar imaging of the Younger Dryas and Pleistocene is poor at both outboard (Camp Century & DYE-3) core locations. These are also where the most ice has been lost since the end of the Pleistocene.
A massive impact 13-14 ka would have left a very clear mark in the Late Pleistocene-Early Holocene ice record, however there is no indication of a disruptive event in any of the ice cores, not even the nearby (~130 miles) Camp Century…
Radiostratigraphy (MacGregor et al, 2015) indicate there there is a continuous ice column from 11.7 ka down to 29 ka very close to Hiawatha crater, and the edge of the full Holocene to Last Glacial Maximum column is no different anywhere else along the northern edge of the Greenland Ice Sheet.
The closest Greenland ice core to Hiawatha, Camp Century, encountered a full section through the Last Glacial Maximum, including the Younger Dryas. It exhibits a nearly perfect correlation to the most distant, Dye 3.
Furthermore, the area near Hiawatha crater was covered by ice up until at least 10,000 years ago (Dyke, 2004). There is no indication that this portion of the Greenland coastline was uncovered any earlier than about 10,000 years ago. The Hiawatha impact most likely occurred, prior to the onset of the final Pleistocene glacial stage, possibly during the Eemian interglactial stage, more likely in an earlier warm interglacial stage.
So, while it is young, geologically speaking, the Hiawatha impact predated the Younger Dryas, most likely before the Last Glacial Maximum.
Proponents of the YDB impact theory would be better served by sticking to the less ambiguous evidence. The fact that they insist on hammering every “square peg into a round hole” undercuts their cause… Which is another problem, science shouldn’t have causes.
References
Kjær, Kurt, Larsen, Nicolaj, Binder, Tobias, Bjørk, Anders, Eisen, Olaf, Fahnestock, Mark & Funder, Svend & Garde, Adam & Haack, Henning & Helm, Veit, Houmark-Nielsen, Michael, Kjeldsen, Kristian, Khan, Shfaqat, Machguth, Horst, Mcdonald, Iain, Morlighem, Mathieu, Mouginot, Jeremie’ Paden, J., Waight, Tod & MacGregor, Joseph. (2018). “A large impact crater beneath Hiawatha Glacier in northwest Greenland”. Science Advances. 4. eaar8173. 10.1126/sciadv.aar8173.
MacGregor, J. A., Fahnestock, M. A., Catania, G. A., Paden, J. D., Prasad Gogineni, S., Young, S. K., Rybarski, S. C., Mabrey, A. N., Wagman, B. M. and Morlighem, M. ( 2015), “Radiostratigraphy and age structure of the Greenland Ice Sheet”. J. Geophys. Res. Earth Surf., 120: 212– 241. doi: 10.1002/2014JF003215.
Moore, A.M.T., Kennett, J.P., Napier, W.M. et al. Evidence of Cosmic Impact at Abu Hureyra, Syria at the Younger Dryas Onset (~12.8 ka): High-temperature melting at >2200 °C. Sci Rep 10, 4185 (2020). https://ift.tt/2QW4mJY
Moore, C., West, A., LeCompte, M. et al. Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences. Sci Rep 7, 44031 (2017). https://ift.tt/39nvdEZ
Petaev, Michail I., Shichun Huang, Stein B. Jacobsen, Alan Zindler. “Large Pt anomaly at the onset of the Younger Dryas”.
Proceedings of the National Academy of Sciences Aug 2013, 110 (32) 12917-12920; DOI: 10.1073/pnas.1303924110
Day 13 of America Held Hostage by ChiCom-19
Since Harris County (Houston) is now locked down like Dallas, pretty well the entire company is working from home. Because oil companies are deemed “critical infrastructure”, we can go to the office if necessary, we just have to get a letter from the company, just in case the “authorities” stop us and want to see our permission slips… Is this next?
In the meantime…
| Dallas County | CHICOM-19 | |
| Population | Cases | Deaths |
| 2,637,772 | 367 | 7 |
| % of population with | 0.0139% | 0.00027% |
| % without | 99.9861% | 99.9997% |
| % without rounded | 100.0% | 100.000% |
The county is ramping up drive-through testing. It’s still mostly limited to people with symptoms, medical professionals, first responders and Parkland Hospital (the county hospital) patients and employees. About 10% are testing positive. I’m still working on a “when a coronavirus gets its lime” meme.
Featured Image
via Watts Up With That?
March 28, 2020 at 08:18PM
Iowa Climate Science Education 