Around 12,800 years ago, Earth collided with fragments of a disintegrating comet, triggering Younger Dryas climate change; this event created environmental conditions at Abu Hureyra, Syria, that favored the earliest known continuous cultivation of domestic-type grains and legumes, along with animal management, adding to the pre-existing practice of hunting-and-gathering. That’s the assertion made by scientists in one of four related papers, all appearing in the journal Science Open: Airbursts and Cratering Impacts.
The Paleolithic settlement at Abu Hureyra in what is now Syria may have been destroyed 12,800 years ago because of a comet. Image credit: Jennifer Rice, Comet Research Group.
Abu Hureyra is a mound settlement (commonly known as a tell) located in northern Syria along the Euphrates River.
The ancient site now lies beneath Lake Assad, created when the Tabqa Dam was completed in 1974.
In 1972 and 1973, before the settlement was flooded, archaeologists collected enough evidence of houses, food and tools to identify two sites — a Paleolithic settlement and evidence for an early agricultural society.
The settlement occupants left an abundant and continuous record of seeds, legumes and other foods.
“In this general region, there was a change from more humid conditions that were forested and with diverse sources of food for hunter-gatherers, to drier, cooler conditions when they could no longer subsist only as hunter-gatherers,” said Professor James Kennett, a researcher at the University of California, Santa Barbara.
“The villagers started to cultivate barley, wheat and legumes. This is what the evidence clearly shows.”
By studying these archaeological layers, Professor Kennett and colleagues were able to discern the types of plants that were being collected in the warmer, humid days before the climate changed and in the cooler, drier days after the onset of what we know now as the Younger Dryas cool period.
Before the impact, the inhabitants’ prehistoric diet involved wild legumes and wild-type grains, and small but significant amounts of wild fruits and berries.
In the layers corresponding to the time after cooling, fruits and berries disappeared and their diet shifted toward more domestic-type grains and lentils, as the people experimented with early cultivation methods.
By about 1,000 years later, all of the Neolithic ‘founder crops’ — emmer wheat, einkorn wheat, hulled barley, rye, peas, lentils, bitter vetch, chickpeas and flax — were being cultivated in what is now called the Fertile Crescent.
Drought-resistant plants, both edible and inedible, become more prominent in the record as well, reflecting a drier climate that followed the sudden impact winter at the onset of the Younger Dryas.
The evidence also indicates a significant drop in the area’s population, and changes in the settlement’s architecture to reflect a more agrarian lifestyle, including the initial penning of livestock and other markers of animal domestication.
To be clear, agriculture eventually arose in several places on Earth in the Neolithic, but it arose first in the Levant (present-day Syria, Jordan, Lebanon, Palestine, Israel and parts of Turkey) initiated by the severe climate conditions that followed the impact.
In the 12,800-year-old layers corresponding to the shift between hunting and gathering and agriculture, the record at Abu Hureyra shows evidence of massive burning.
The evidence includes a carbon-rich ‘black mat’ layer with high concentrations of platinum, nanodiamonds and tiny metallic spherules that could only have been formed under extremely high temperatures.
The airburst flattened trees and straw huts, splashing meltglass onto cereals and grains, as well as on the early buildings, tools and animal bones found in the mound — and most likely on people, too.
This event is not the only such evidence of a cosmic airburst on a human settlement.
The authors previously reported a smaller but similar event which destroyed the Biblical city at Tall el-Hammam in the Jordan Valley about 1650 BCE.
The black mat layer, nanodiamonds and melted minerals have also been found at about 50 other sites across North and South America and Europe, the collection of which has been called the Younger Dryas strewnfield.
According to the researchers, it’s evidence of a widespread simultaneous destructive event, consistent with a fragmented comet that slammed into the Earth’s atmosphere.
The explosions, fires and subsequent impact winter caused the extinction of most large animals, including the mammoths, saber-toothed cats, American horses, and American camels, as well as the collapse of the North American Clovis culture.
Because the impact appears to have produced an aerial explosion there is no evidence of craters in the ground.
“But a crater is not required. Many accepted impacts have no visible crater,” Professor Kennett said.
The scientists continue to compile evidence of relatively lower-pressure cosmic explosions — the kind that occur when the shockwave originates in the air and travels downward to the Earth’s surface.
“Shocked quartz is well known and is probably the most robust proxy for a cosmic impact,” Professor Kennett said.
“Only forces on par with cosmic-level explosions could have produced the microscopic deformations within quartz sand grains at the time of the impacts, and these deformations have been found in abundance in the minerals gathered from impact craters.”
This ‘crème de la crème’ of cosmic impact evidence has also been identified at Abu Hureyra and at other Younger Dryas Boundary sites, despite an absence of craters.
However, it has been argued that the kind of shock-fractured quartz found at the sites is not equivalent to that found in the large crater-forming sites, so the authors worked to link these deformations to lower-pressure cosmic events.
To do so, they turned to manmade explosions of the magnitude of cosmic airbursts: nuclear tests conducted at the Alamogordo Bombing Range in New Mexico in 1945 and in Kazakhstan, in 1949 and 1953.
Similar to cosmic airbursts, the nuclear explosions occurred above ground, sending shockwaves toward Earth.
“In the papers, we characterize what the morphologies are of these shock fractures in these lower-pressure events,” Professor Kennett said.
“And we did this because we wanted to compare it with what we have in the shock-fractured quartz in the Younger Dryas Boundary, to see if there was any comparison or similarities between what we see at the Trinity atomic test site and other atomic bomb explosions.”
Between the shocked quartz at the nuclear test sites and the quartz found at Abu Hureyra, the team found close associations in their characteristics, namely glass-filled shock fractures, indicative of temperatures greater than 2,000 degrees Celsius, above the melting point of quartz.
“For the first time, we propose that shock metamorphism in quartz grains exposed to an atomic detonation is essentially the same as during a low-altitude, lower-pressure cosmic airburst,” Professor Kennett said.
“However, the so-called ‘lower pressure’ is still very high — probably greater than 3 GPa.”
“The novel protocol we developed for identifying shock fractures in quartz grains will be useful in identifying previously unknown airbursts that are estimated to recur every few centuries to millennia.”
“Taken together, the evidence implies a novel causative link among extraterrestrial impacts, hemispheric environmental and climatic change, and transformative shifts in human societies and culture, including agricultural development.”
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Robert E. Hermes et al. 2023. Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts. Airbursts and Cratering Impacts 1 (1); doi: 10.14293/ACI.2023.0001
Andrew M.T. Moore et al. 2023. Abu Hureyra, Syria, Part 1: Shock-fractured quartz grains support 12,800-year-old cosmic airburst at the Younger Dryas onset. Airbursts and Cratering Impacts 1 (1); doi: 10.14293/ACI.2023.0003
Andrew M.T. Moore et al. 2023. Abu Hureyra, Syria, Part 2: Additional evidence supporting the catastrophic destruction of this prehistoric village by a cosmic airburst ~12,800 years ago. Airbursts and Cratering Impacts 1 (1); doi: 10.14293/ACI.2023.0002
Andrew M.T. Moore et al. 2023. Abu Hureyra, Syria, Part 3: Comet airbursts triggered major climate change 12,800 years ago that initiated the transition to agriculture. Airbursts and Cratering Impacts 1 (1); doi: 10.14293/ACI.2023.0004
