The evidence pointing toward a major cometary impact that heralded the closure of the last ice age 13,000 years ago is steadily growing, with a new study from the University of Kansas offering more data that supports what is known as the Younger Dryas impact hypothesis.

"The hypothesis is that a large comet fragmented and the chunks impacted the Earth, causing this disaster," explains University of Kansas Emeritus Professor of Physics & Astronomy Adrian Melott. "A number of different chemical signatures–carbon dioxide, nitrate, ammonia and others–all seem to indicate that an astonishing 10 percent of the Earth’s land surface, or about 10 million square kilometers [3,9 million square miles], was consumed by fires."

20,000 years ago, the Last Glacial Maximum started to come to a close as the Earth’s temperature began to rise, as part of a longer cycle of glacial periods that began a little roughly 2.6 million years ago. But a sudden 2ºC-to-6ºC drop in temperature roughly 12,900 years ago saw the climate’s return to a brief, 1,200-year mini-ice age called the Younger Dryas.

The KU researchers studied core samples from both terrestrial sites and glaciers from over 170 sites around the world, adding fresh evidence that there was a continent-wide wildfire that occurred across North America, followed by a sudden flood that thickened the resulting ash and debris into an organic-rich "black mat" layer buried in the geological record.

The cometary impact that is hypothesized to have brought on the Younger Dryas is assumed to have exploded in an air burst over the Laurentide Ice Sheet, above the region of today’s Great Lakes region. Such an explosion would have melted a sizeable portion of the ice sheet, causing a massive flood that would extinguish the fires caused earlier by the explosion itself. The sudden influx of fresh water pouring into the North Atlantic Ocean would also interrupt the North Atlantic Current, disrupting the northern hemisphere’s climate, as is also evidenced in the geological record.

The onset of the Younger Dryas period also saw the extinction of most of the large mammal species in North America, and the decline of what is called the Clovis culture, a prehistoric Paleo-Indian culture. Melott’s team hypothesizes that the comet responsible for the impact was originally 62 miles in diameter, but that it was only fragments from this body that struck Earth’s atmosphere–the remainder of the comet is still present in our solar system. 

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