At the end of the Ice Age some 13,000 years ago, the northern hemisphere seemed to be hotting up as glaciers were retreating and grasslands spreading. But then something happened: there was a sharp drop in temperatures and a return to glacial conditions for another thousand years.
This sudden cooling event is known as the Younger Dryas, and the causes behind aren’t fully understood. Now a new study is claiming to have found further evidence for the argument that the onset of this cold period occurred after Earth was bombarded with comets that set off vast wildfires.
“The hypothesis is that a large comet fragmented and the chunks impacted the Earth, causing this disaster,” said Professor Adrian Melott, who co-authored the study published in The Journal of Geology. “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, was consumed by fires.”
As these fires whooshed across the landscape, the smoke and ash they created were swept up into the atmosphere, blocking out the Sun, altering ocean currents, killing wildlife and plants, and cooling the planet once more.
There has long been a fair amount of skepticism about the Younger Dryas impact hypothesis, to put it lightly. The hypothesis first emerged in 2007, and maintains that around 12,800 years ago there was some form of comet impact on Earth that triggered the Younger Dryas.
There have been various discoveries that have been suggested as proof of the validity of the hypothesis. One includes tiny, glassy “spherules” that were discovered in Pennsylvania a few years back, which it is argued were formed by the impact. Another suggests that the traces of platinum found on the Greenland icecap is a result of the impact event.
Only last year, ancient carvings uncovered on a stone temple in Turkey that dates to 13,000 years old were interpreted as representing what may have been the impact. Discovered at Gobeekli Tepe in the south of the country, the researchers argue that the images show the fragmenting comet and that the pillar they were etched on may “have served as a memorial to this devastating event”.
This latest study used data collected from 170 different sites around the world to see if they could find evidence of the massive fires that they say would have raged. They are claiming that the evidence does indeed show that there were huge wildfires, bigger in fact than the ones after the Cretaceous impact event that did away with the dinosaurs.
They argue that this would help explain the shifts and extinctions seen in animals at the end of the Pleistocene, as well as human cultural changes seen at the time.