User:Dmcdysan/sandbox/YDIH Draft

Proposed text for YDIH Summary
The Younger Dryas (YD) occurred approximately 12,900 to 11,700 years BP as determined from Greenland ice core analysis where at the onset temperatures decreased rapidly, stayed low for longer than a typical Dansgaard–Oeschger event cycle and then abruptly increased in high-latitude North America. and is a notable example of abrupt climate change. In 1989,a paper by Wallace S. Broecker and others became the accepted YD hypothesis that meltwater from Lake Agassiz shifting from drainage via the Mississippi river to the St. Lawrence drainage system that caused a shutdown of the thermohaline circulation in the North Atlantic. In 2006, Broecker reported that since no evidence had been found for the St. Lawrence flood scenario that instead the meltwater flood could have reached the North Atlantic via the McKenzie river.

A 1997 analysis suggested that to create continent-wide damage a 4 km  comet direct impact would be required, or tha the same damage could be caused by a smaller disintegrating comet airburst. A 2007 tpaper by Firestone and others speculated that a comet airburst over North America created a Younger Dryas boundary (YDB) layer comprised of, dubbed the Younger Dryas impact hypothesis (YDIH), that contributed to megafaunal extinctions, rapid cooling and rapid changes in human behavior at the end of the Clovis culture. Evidence was based upon a carbon rich black layer dating to approximately 12,900 years ago at more than fifty sites (that Vance Haynes later identified as black mats, carbonaceous silts or dark organic clays ) above which no evidence of megafauna nor Clovis culture was found.

In 2010, Broecker stated "The long-held scenario that the Younger Dryas was a one-time outlier triggered by a flood of water stored in proglacial Lake Agassiz has fallen from favor due to lack of a clear geomorphic signature at the correct time and place on the landscape," that evidence from Chinese stalagmites suggested that the YD is "an integral part of the deglacial sequence of events that produced the last termination on a global scale."

In 2011, Pinter and others published a requiem for YDIH. concluding that no YD impact signatures had been corroborated by independent tests and of the 12 original lines of evidence, 7 were non-reproducible.

Proposed text for a YDIH Overview section
Proponents have reported materials including nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, iridium, platinum, platinum/palladium ratios, charcoal, soot, and fullerenes enriched with helium-3 that they interpret as evidence for an impact event that marks the beginning the YDB. One of the most widely publicized discoveries (nanodiamonds in Greenland) has never been verified and is disputed.