The Younger Dryas Impact Hypothesis is back again

[lpetrich]

 Younger Dryas impact hypothesis - it's back again: Geologic evidence supports theory that major cosmic impact event occurred approximately 12,800 years ago noting Sedimentary record from Patagonia, southern Chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka | Scientific Reports The abstract:

The Younger Dryas (YD) impact hypothesis posits that fragments of a large, disintegrating asteroid/comet struck North America, South America, Europe, and western Asia ~12,800 years ago. Multiple airbursts/impacts produced the YD boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across ~50 million km² of Earth’s surface. This proposed event triggered extensive biomass burning, brief impact winter, YD climate change, and contributed to extinctions of late Pleistocene megafauna. In the most extensive investigation south of the equator, we report on a ~12,800-year-old sequence at Pilauco, Chile (~40°S), that exhibits peak YD boundary concentrations of platinum, gold, high-temperature iron- and chromium-rich spherules, and native iron particles rarely found in nature. A major peak in charcoal abundance marks an intense biomass-burning episode, synchronous with dramatic changes in vegetation, including a high-disturbance regime, seasonality in precipitation, and warmer conditions. This is anti-phased with northern-hemispheric cooling at the YD onset, whose rapidity suggests atmospheric linkage. The sudden disappearance of megafaunal remains and dung fungi in the YDB layer at Pilauco correlates with megafaunal extinctions across the Americas. The Pilauco record appears consistent with YDB impact evidence found at sites on four continents.

From the Wikipedia article:

The evidence given by proponents of an impact event includes "black mats" of organic-rich soil that have been found at some 50 Clovis sites across the continent. Proponents have reported materials (nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, iridium, platinum, charcoal, soot, and fullerenes enriched in helium-3), which they interpret to be potential evidence of an impact event, at the very bottom of black mats of organic material that marks the beginning of the Younger Dryas,[10][11] and it is claimed these cannot be explained by volcanic, anthropogenic, or other natural processes.[3]

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A 100-fold spike in the concentration of platinum has also been found in Greenland ice cores, dated to 12,890 BP with 5-year accuracy.[15] A much weaker Pt anomaly was subsequently reported with approximate age dating at 11 continental Younger Dryas sites.[16]

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It is conjectured that this impact event brought about the extinction of many species of North American Pleistocene megafauna. These animals included camels, mammoths, the giant short-faced bear, and numerous other species that the proponents suggest died out at this time.[20] The proposed markers for the impact event are claimed to appear at the end of the Clovis culture.[21]

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Some of the original proponents published a re-evaluation in June 2013 of spherules from 18 sites worldwide which they interpret to support their hypothesis.[11] Further analysis of Younger Dryas boundary sediments at 9 sites, released in June 2016, found no evidence of an extraterrestrial impact at the YDB.[29] In December 2016, an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the YDB.[30] Radiocarbon dating, microscopy of paleobotanical samples, and analytical pyrolysis of fluvial sediments "[found] no evidence in Arlington Canyon for an extraterrestrial impact or catastrophic impact-induced fire."[31] Exposed fluvial sequences in Arlington Canyon on Santa Rosa Island "features centrally in the controversial hypothesis of an extra-terrestrial impact at the onset of the Younger Dryas."[31]

In 2018 two new papers were published dealing with a "Extraordinary Biomass-Burning Episode" associated with the Younger Dryas Impact.[32][33]

along with this most recent result.

 

[lpetrich]

Comets, Diamonds, & Mammoths - Comet Research Group about the hypothesis that some asteroid or comet impact caused the  Younger Dryas[wiki] cold snap. Around 12,800 years ago, something interrupted the Earth's warming after the [wiki]Last Glacial Maximum some 26,500 years ago. The Earth's average surface temperature dropped by some 10 C for some 1200 years, bringing Ice-Age conditions back again. It was the most unusual cooling event in the last 2 million years -- most of the Pleistocene with its ice ages.

There was a mass extinction of megafauna - large animals - around then, like furry elephants (mammoth, mastodon) and sabertoothed felines.

Humanity was also affected, with the manufacture of Clovis spear points stopping, and with humanity's population dropping by 30% to 60%.

Announcing the 2016 CRG Coloring Contest - Comet Research Group - this blog entry features a depiction an incoming asteroid and a mammoth, must like the asteroid-and-dinosaur cartoons that we often see.

 

[lpetrich]

1. Comet Impact Overview
2. Craters & Comets
3. Diamonds & Viruses
4. Melted Spherules
5. Melted Rocks & Glass
6. Impact-related Wildfires
7. Black Mat Layer
8. Extinctions
9. Climate Change

Instead of a single object, they propose a swarm of comet fragments, like Comet Shoemaker-Levy-9, which crashed into Jupiter in 1994.

About 13,500 years ago, before the Younger Dryas Boundary (YDB) impact, most of Canada and some of the northern United States were covered by a huge continental glacier. Big lakes formed on its southern edge, including Glacial Lake Agassiz, larger than any present-day freshwater lake.

The YDB impact was in that big ice sheet, and it broke up the ice tha was keeping those lakes in place. They emptied into the northern oceans in a huge flood, and being freshwater, their water stayed on top of the "normal" seawater. This shut down the Gulf Stream current, making Europe and North America much colder. Ocean circulation returned to normal only after about 1,100 years.

 

[repoman]

I think there may be another reason for fires.

At the ending of an ice age (technically the beginning of an interglacial period) The forests that were on the edge of the glaciers may have warmed up quite a bit and then the fires took off. Also think of how long it had been since there were large spread fires. That is a lot of material to burn, dead branch kindling on the forest floor. Seems like an analogy to what is happening now in the arctic.

Also, what about permafrost that was finally melting very quickly releasing lots of methane. If a fire got near that then kaboom. Would even lightning set off a methane fire?

If there were lots of fires for this reason and also comet impacts, maybe the comets did not really increase the amount of fires.