Scientists generally agree that a massive asteroid or comet killed the dinosaurs when it hit Earth 66 million years ago. Could a recent cosmic influence have had the opposite effect on humans, heralding the beginning of civilization?
The “overwhelming consensus of evidence” suggests that a comet did just that about 13,000 years ago, according to a new study published in Earth-Science Reviews. The study reviewed existing research on the Younger Dryas impact hypothesis, which argues in various forms that a comet was around 10,900 BC.
The idea is not exactly new. In his 1883 book Ragnarok: The Age of Fire and Gravel, Minnesota writer and congressman Ignatius L. Donnelly wrote how a giant comet hit Earth about 12,000 years ago and destroyed the mythical “lost continent” Atlantis. But the hypothesis first entered mainstream science with a 2007 study that suggested:
“… one or more large, low density [extraterrestrial] Objects exploded over northern North America, partially destabilizing and loosening the Laurentid Ice Sheet [Younger Dryas] Cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food restrictions) contributed to the megafaunal extinctions in the End Pleistocene and adaptive shifts among Paleo-Americans in North America.
In other words, prehistoric humans could have witnessed a catastrophic cosmic impact that caused widespread forest fires, global cooling, and the extinction of large animals, some of which may have hunted humans. It is still unclear whether the effects occurred. But in the centuries after the comet supposedly hit Earth, human cultures made far-reaching transitions away from hunter-gatherer societies to agricultural civilizations.
What Caused the Earth’s Recent Cooling?
One puzzle that is supposed to solve this hypothesis is the cause of the Younger Dryas, the short ice age that the earth experienced about 12,900 to 11,700 years ago. A “winter impact” could have been the culprit: It is a hypothetical scenario in which a cosmic impact causes global cooling, as the impact and the resulting groundfires would emit enough material into the atmosphere to make the sun’s radiation considerably to block.
This alleged comet left no crater; Proponents of the impact hypothesis argue that much of the comet is likely fragmented high in the atmosphere and could have hit a large ice sheet on the surface of the earth. But apart from the crater, the comet seemed to leave behind other evidence. One example is the Younger Dryas “black mats,” which are characteristic layers of soil (or “YD boundaries”) discovered in more than 100 locations on four continents.
A smoking gun?
It is unclear how the mats got their blackish color. One explanation is that it comes from charcoal that was produced during forest fires. It is clear, however, that the mats serve as a dividing line between the epochs on earth, mainly because only certain materials and fossils can be found above or below this layer. For example, no spearheads or other archaeological evidence of the prehistoric Paleo-American Clovis culture have been found over the black mats.
Location map with 53 YD border locations. Location map with 53 YD border locations.
“In general, many extinct megafaunal species are found under the black mat, but not within or above it, including horse, camel, mastodon, direwolf, American lion,” the researchers wrote.
The black mats also contain strange geochemical cues, the origins of which seem to fit the impact hypothesis, including:
Platinum group elements: Samples from ice in Greenland and border areas on several continents contain unusually high levels of platinum group elements (PGEs). The earth’s crust doesn’t contain many PGEs, but comets do. Volcanoes can also produce PGEs, but this process would leave chemical marks that cannot be found in the areas of the black matting. Taken together, this “strongly indicates a [extraterrestrial] Source, “write the researchers.
Microspheres: YD interfaces also contain large amounts of small particles called microspheres, which contain minerals that “melt at very high temperatures,” the researchers wrote. A cosmic impact can generate high temperatures, as can people, volcanoes and lightning. Given the lack of evidence suggesting a terrestrial source, combined with analysis suggesting the particles mixed with extraterrestrial material, the data suggests that an impact is the most likely source.
“The only reasonable explanation for its occurrence is a major cosmic impact event,” the researchers wrote. “They are found along with other high-temperature melts with a similar composition at three locations. The one in Abu Hureyra, Syria, can only be explained by a cosmic impact.”
Nanodiamonds: At least 22 black matt areas contain unusually high amounts of nanodiamonds, which are “extremely” seldom produced by natural terrestrial processes. “The widespread existence of all these nanodiamond shapes can only be reasonably explained by a cosmic influence,” the researchers write. Previous research has shown that the shock of a cosmic impact can create nanodiamonds.
There is no better explanation
Opponents of the impact hypothesis might suggest reasonable terrestrial explanations for some of the evidence. But proponents have synchronicity on their side: it’s hard to explain how these various anomalous geochemical signals all manifested themselves in a narrow window of time, represented stratigraphically by the black matting of the Younger Dryas.
This synchronicity is even more compelling when you consider that we have indisputable evidence that the earth became extinct 13,000 years ago and experienced a brief ice age. A 2008 study looked at the extinction component of the hypothesis and found, “Stratigraphically and chronologically, extinction appears to have been catastrophic, apparently too sudden and extensive for either human predation or climate change to be the primary cause.”
The researchers behind the current study wrote:
“No YD [boundary] It was also noted that the website apparently mismatched with a synchronous event, around 10,785 [BCE, plus or minus 50 years]. The only reasonable conclusion is that a major cosmic impact event occurred at this point. Its time is so close to the beginning of the YD cooling that a causal relationship is very likely. “
But even if a comet caused the Younger Dryas, it remains unclear how exactly it could have affected the future of human civilization.
“Such an event could plausibly lead to changes in human culture and megafauna extinction as suggested, but more detailed research is needed to investigate this,” the researchers wrote.