Younger Dryas also known as Dryas III was a mini Ice Age that lasted from around 10,700 BC until around 9600 BC. It is named after a flower that flourished during this relatively short period. In Ireland the period is known as the Nahanagan Stadial and in Britain as the Loch Lomond Stadial. For about thirteen hundred years the glaciers had been slowly retreating until within a short time-span temperatures dropped and they began to advance again. The cause of this cooling is not absolutely clear. One view is that a sudden release into the North Atlantic of vast quantities of fresh water that had been contained by huge ice dams is assumed to have closed down the Gulf Stream, resulting in a twelve hundred year lowering of global temperatures. There is evidence that the change only took one or two decades. The same threat is said to exist today with the possibility of the melting of the Greenland ice cap.
The most recent theory, by Firestone, West and Warwick-Smith, links the onset of the Younger Dryas with the explosion of a comet over North America that led to the extinction of many species, the collapse of the Clovis culture(a)(b) as well as the creation of the Carolina Bays.
A 2014 paper(g) entitled Nanodiamond-Rich Layer Across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP by Charles R. Kinzie et al., has developed further the idea of this event being associated with the Younger Dryas. In a similar vein is an article(h) from Megan Gannon.
A recent application of archaeoastronomy by Martin Sweatman and Dimitrios Tsikritsis led them to conclude that the carved symbols at Göbekli Tepe recorded an encounter involving the explosion or impact of part of Encke’s Comet around 13,000 years ago, which triggered the Younger Dryas Event that provided the impetus for the Neolithic Revolution. Sweatman later expanded their work in his book Prehistory Decoded  and in an article on the Ancient Origins website(m).
Kevin A. & Patrick J. Casey maintain that a globally catastrophic event occurred 13,000 years ago(l). The kernel of their theory is that originally the Earth had two moons that at some later point collided, producing our current Moon, while the remnant of the second one eventually exploded over North America kick-starting what we refer to as the cooler Younger Dryas period. They are adamant that it was not a comet or asteroid that caused the devastation, and so clash with the work of Richard Firestone and his colleagues.
In 2015 a paper constraining the impact date to within 100 years using Bayesian statistical analyses, now proposed as 12,835 -12,735 years ago(j).
Coincidentally, Professor Emilio Spedicato independently arrived at the conclusion that it was a cometary impact in the North Atlantic that was responsible for the Younger Dryas. Subsequently, when temperatures rose again it resulted in the flooding of vast areas of low-lying landmasses that in Spedicato’s opinion, included Atlantis, which he locates in Hispaniola.
Conflicting evidence regarding the possibility of the Younger Dryas being caused by such an impact is impartially outlined on the internet(c).
December 2014 saw Graham Hancock raising the issue of a cometary cause for the Younger Dryas and its possible association with ancient Egypt(f).
The November 2013 issue of the BBC Focus magazine (p.30) had a brief article on the impact theory, noting that the northern hemisphere saw a drop of as much as 15°C around 11,000BC. In the absence of a suitable impact crater there is still much scientific scepticism(d).
However in early 2017, further possible evidence of an impact at the start of the Younger Dryas was offered by a team led by Christopher Moore of the University of South Carolina, when they identified a distinct layer of platinum in the soil that coincided with the start of YD. Commenting on this anomaly Moore noted that “Platinum is very rare in the Earth’s crust, but it is common in asteroids and comets.”(i)
In early 2018, two papers were published online(k), reinforcing the YD impact theory and adding evidence that the event resulted in a conflagration that “may have consumed – 10 million km2, or – 9% of Earth’s terrestrial biomass”.*Related to this is a paper by Andrew Collins that draws attention to the ‘Usselo horizon’, a charcoal-rich layer of between 1 and 8 inches, found on all continents, indicating widespread fires, now dated to 12,900 years ago(n).*
Ice cores from Greenland indicate a further cooling period circa 6200 BC that may be related to the abandonment of many Neolithic settlements during this period. Other periods of abrupt climate change have been identified from 3800 BC to 3500 BC and 2800 BC to 2000 BC.
The fact that Plato’s apparent date for the demise of Atlantis, circa 9600 BC, roughly corresponds with the current, best estimate for the date of the Younger Dryas is interesting but unfortunately not conclusive proof of any direct connection. In the absence of any supportive archaeological evidence, a linkage between Atlantis and the Younger Dryas will have to remain a matter of faith rather than fact. Interesting but inconclusive.
Recent discoveries in northern Sudan of dozens of skeletons, the majority of whom were apparently killed by flint-tipped arrows, have led to the suggestion(e) they were the result of food shortages resulting from the Younger Dryas that in turn led to warfare over diminished food availability.
(c) http://blogs.nicholas.duke.edu/thegreengrok/climatedebate/ (offline Dec. 2016) See: https://web.archive.org/web/20130310032309/http://blogs.nicholas.duke.edu/thegreengrok/climatedebate/