Proxy Evidence for an Increase in Human Populations at a site in South Carolina Circa 12,838 Years BP

The Younger Dryas Impact Hypothesis, or YDIH for short, is a crank theory that has been thoroughly debunked.  The YDIH proposes a comet impact on a glacier in the Northern Hemisphere 12,900 years ago sparked continent wide fires, caused a sudden drastic climate reversal, and resulted in the extinction of Pleistocene megafauna.  The Younger Dryas was a climate stage that lasted for about 1500 years; and it was a sudden return to cold, arid Ice Age conditions, following thousands of years of warmer, wetter climate.  It’s named for a flower that flourished in Europe during this climate phase.

Dryas octopetalus likes open, cold, landscapes.

The YDIH is fatally flawed.  There is no known impact crater, dating to the proposed time of impact.  The Hiawatha Crater recently discovered in Greenland has been proposed as the possible impact crater, but the lack of a young ejecta blanket suggests it is millions rather than thousands of years old.  Its ejecta blanket has eroded away–a process that would take a very long time.  There is no evidence of continent wide fires.  Instead, the sites first noted by YDIH proponents to have evidence of the fires dated to many different ages both before and after 12,900 years BP, and the fires were most likely caused by lightning or humans.  Many of the other claimed impact indicators date to different ages.  Megafauna extinctions and extirpations also occurred at various ages–not all at 12,900 years BP.  Some of the so-called impact indicators are not necessarily diagnostic of an impact but can have terrestrial origins.  Other scientists looking for impact markers have not been able to replicate the results of the original YDIH studies.

The Younger Dryas was caused by well understood cyclical climate variations known as Heinrich Events.  12,900 years ago, an ice dam in Canada broke, leading to an enormous influx of cold fresh water into the North Atlantic.  This shut down thermohaline circulation, causing temperatures in the Northern Hemisphere to plunge.  This is the explanation for the Younger Dryas I accept.  Nevertheless, the ridiculous YDIH just will not die.  A paper advocating this bizarre almost pseudo-scientific belief was published as recently as October of this year.  Though I reject the YDIH, this paper had interesting data that I interpret differently from the authors.

Scientists who published this paper took a 1 meter core of sediment from White Pond in South Carolina. White Pond is a ~32,000 year old Carolina Bay.  Carolina Bays are bodies of water formed by wind and water erosion during dry climate phases of Ice Ages, and they are found throughout the Carolinas and Georgia.  The scientists dated the sediment layer by layer and looked for charcoal and sporomiella.  The abundance of charcoal indicates fire in the environment, and sporormiella is a fungus that grows on megafauna feces and is used as proxy evidence for the abundance of large mammal populations.  The scientists found charcoal amounts peaked at 12,838 years ago, indicating lots of fire on the landscape.  Megafauna populations declined to a low point 12,752 years ago.  The authors of this study think the fire was caused by the comet impact, and the resulting changes in the environment led to the local extirpation of the megafauna.

Location of White Pond where this study took place.  Image from the below reference.

My interpretation is different.  I think the fires were set by humans to improve habitat for megafauna. (Indians set fire to southeastern landscapes until Europeans removed them from the region.)  Then it took 86 years for humans to wipe out megafauna at this locality.  Nomadic hunters possibly moved away after eliminating most of the big game, allowing megafauna populations to rebound until 10,399 years BP when they disappear again from the region, this time permanently.

Graph from the below referenced paper.  Note how megafauna populations rebounded until 10,399 years ago–2500 years after the proposed comet impact.  This suggests the proposed comet impact could not have been a factor in their extinctions.

The authors of this study note there is an unconformity in the core dating to the Younger Dryas.  Normally, during wet climate cycles sediment builds up as vegetation dies and turns into soil.  But during dry phases when vegetation is sparse, exposed soil erodes and is blown away by wind, and there is little to no sedimentation.  If this is the case, there should be a gap rather than a continuous line in the graph.  I’m not sure how this impacts the conveyed data.  However, the data is interesting to me because I think it shows when humans arrived at this locality in significant numbers, and how long it took them to extirpate the megafauna.

Reference:

Moore. C; et. al.

“Sediment Core from White Pond, South Carolina contains a Platinum Anomaly, Pyrogenic Carbon Peak, and Coprophilous Decline at 12.8 Ka”

Scientific Reports October 2019

https://www.nature.com/articles/s41598-019-51552-8

 

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