Evidence of Younger Dryas impacts? A cold snap at the end of the last Ice Age

[lpetrich]

The  Younger Dryas impact hypothesis states that some impact or impacts caused a cold period called the Younger Dryas, a cold period that interrupted the Earth's warming from the last Ice Age. It lasted from around 12,900 BP to around 11,700 BP (BP = "Before Present", with "present" being 1950 CE).

It has caused a lot of controversy, with the detractors of this hypothesis finding the purported evidence less-than-convincing and finding a lack of evidence of what they expect to be present.

I recently came across these recent papers:
Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 1. Ice Cores and Glaciers
Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 2. Lake, Marine, and Terrestrial Sediments

The Younger Dryas boundary (YDB) cosmic-impact hypothesis is based on considerable evidence that Earth collided with fragments of a disintegrating ≥100-km-diameter comet, the remnants of which persist within the inner solar system ∼12,800 y later. Evidence suggests that the YDB cosmic impact triggered an “impact winter” and the subsequent Younger Dryas (YD) climate episode, biomass burning, late Pleistocene megafaunal extinctions, and human cultural shifts and population declines. The cosmic impact deposited anomalously high concentrations of platinum over much of the Northern Hemisphere, as recorded at 26 YDB sites at the YD onset, including the Greenland Ice Sheet Project 2 ice core, in which platinum deposition spans ∼21 y (∼12,836–12,815 cal BP). The YD onset also exhibits increased dust concentrations, synchronous with the onset of a remarkably high peak in ammonium, a biomass-burning aerosol. In four ice-core sequences from Greenland, Antarctica, and Russia, similar anomalous peaks in other combustion aerosols occur, including nitrate, oxalate, acetate, and formate, reflecting one of the largest biomass-burning episodes in more than 120,000 y. In support of widespread wildfires, the perturbations in CO2 records from Taylor Glacier, Antarctica, suggest that biomass burning at the YD onset may have consumed ∼10 million km2, or ∼9% of Earth’s terrestrial biomass. The ice record is consistent with YDB impact theory that extensive impact-related biomass burning triggered the abrupt onset of an impact winter, which led, through climatic feedbacks, to the anomalous YD climate episode.

Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes.

So something or other caused huge wildfires at about that time, and those fires produced a lot of smoke that blocked off sunlight and caused a small Ice Age.

It would be difficult for a single impact to cause all those wildfires, but multiple impacts might. If they are separate events, then that would be asking too much of coincidence, so they would have to be related. They can indeed be related by being fragments of the same disintegrating comet, fragments that did not move very far from each other before they hit the Earth.

 

[Jobar]

There are some good YouTube videos on this.

[YOUTUBE]https://www.youtube.com/watch?v=icqRjF04w_E[/YOUTUBE]

[YOUTUBE]https://www.youtube.com/watch?v=Aw5chtNWzo8[/YOUTUBE]

I always found it highly unlikely that newly arrived paleolithic hunters, without even bows and arrows, could have managed to exterminate mammoths, sabertooth tigers, giant sloths, and the entire megafauna of North America. The impact hypothesis seems far more believable.

The recent LIDAR images of the Carolina bays along the east coast are damned frightening! A bad day, indeed...

 

[bilby]

There are some good YouTube videos on this.

[YOUTUBE]https://www.youtube.com/watch?v=icqRjF04w_E[/YOUTUBE]

[YOUTUBE]https://www.youtube.com/watch?v=Aw5chtNWzo8[/YOUTUBE]

I always found it highly unlikely that newly arrived paleolithic hunters, without even bows and arrows, could have managed to exterminate mammoths, sabertooth tigers, giant sloths, and the entire megafauna of North America. The impact hypothesis seems far more believable.

The recent LIDAR images of the Carolina bays along the east coast are damned frightening! A bad day, indeed...

It seems rather coincidental that the Australiasian megafauna went extinct shortly after the arrival of humans on this continent; And that the American ones also went extinct shortly after the arrival of humans on that continent; But that the extinctions and the arrival of humans were unrelated.

I don't think there's any good reason to believe that cosmic impact(s) were the cause of the Australasian extinctions. Of course, two data points don't make for much of a trend, so I guess it could be one cause in America, and another in Australasia. Detective Colombo would be slightly suspicious, and would probably want to ask just one more question though...

 

[Treedbear]

...
I don't think there's any good reason to believe that cosmic impact(s) were the cause of the Australasian extinctions. ... Detective Colombo would be slightly suspicious, and would probably want to ask just one more question though...

Carolina Bays in Australia?

Google Earth 34° 15′ 34.49″S, 117° 42′ 08.49″E

 

[bilby]

...
I don't think there's any good reason to believe that cosmic impact(s) were the cause of the Australasian extinctions. ... Detective Colombo would be slightly suspicious, and would probably want to ask just one more question though...

Carolina Bays in Australia?

Google Earth 34° 15′ 34.49″S, 117° 42′ 08.49″E

A bunch of craters of unknown age and origin really don't constitute 'good reason to believe that cosmic impacts were the cause' of any other event. Australia has been hit by lots of cosmic debris; absent a clear coincidence of timing, any particular impact crater is meaningless. And those are not even known to be impact craters at all.

 

[Treedbear]

...
I don't think there's any good reason to believe that cosmic impact(s) were the cause of the Australasian extinctions. ... Detective Colombo would be slightly suspicious, and would probably want to ask just one more question though...

Carolina Bays in Australia?

Google Earth 34° 15′ 34.49″S, 117° 42′ 08.49″E

A bunch of craters of unknown age and origin really don't constitute 'good reason to believe that cosmic impacts were the cause' of any other event. Australia has been hit by lots of cosmic debris; absent a clear coincidence of timing, any particular impact crater is meaningless. And those are not even known to be impact craters at all.

I'm sure Lt Columbo would agree. I'm sorry I took up so much of your time.

 

[repoman]

So, the burning of such a large amount of biomass is not in dispute, just the initial cause?

 

[lpetrich]

So, the burning of such a large amount of biomass is not in dispute, just the initial cause?

That's pretty much it.