Agriculture started with a huge bang 12,800 years ago – when a fragmented comet slammed into the Earth’s atmosphere, according to a new study.
The explosion and subsequent environmental changes forced hunter-gatherers in the prehistoric settlement of Abu Hureyra, in present-day Syria, to adopt agricultural practices to boost their chances of survival, say scientists.
An international research team presented their findings in four related papers, published in the journal Science Open: Airbursts and Cratering Impacts.
The team was investigating the Younger Dryas Impact Hypothesis – the idea that a cooling of the Earth almost 13,000 years ago was the result of a cosmic impact.
Professor James Kennett, of the University of California, Santa Barbara, said: “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.”
The settlement at Abu Hureyra is known among archaeologists for evidence of the earliest known transition from foraging to farming.
Kennett said: “The villagers started to cultivate barley, wheat and legumes. This is what the evidence clearly shows.”
Abu Hureyra and its rich archaeological record today lie under Lake Assad, a reservoir created by the construction of the Taqba Dam on the Euphrates River in the 1970s.
But before the flood, archaeologists managed to extract lots of material to study.
Kennett said: “The village occupants left an abundant and continuous record of seeds, legumes and other foods.”
By studying the layers of remains, the scientists 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 researchers found, 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 of winter at the onset of the Younger Dryas.
The research team said 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.
Kennett says agriculture eventually arose in several places on Earth in the Neolithic Era, 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, nano-diamonds and tiny metallic spherules that could only have been formed under extremely high temperatures – higher than any that could have been produced by human technology at the time.
The researchers say that the airburst flattened trees and straw huts, splashing melted glass 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.
The research team previously reported a smaller but similar event that destroyed the biblical city at Tall el-Hammam in the Jordan Valley about 1600 BC.
The black mat layer, nano-diamonds and melted minerals have also been found at around 50 other sites across North and South America and Europe, the collection of which has been called the Younger Dryas strewnfield.
The researchers say it’s evidence of a “widespread” simultaneous destructive event, consistent with a fragmented comet slamming into Earth’s atmosphere.
They believe the resulting explosions, fires and subsequent impact of winter caused the extinction of most large animals, including mammoths, saber-toothed cats, American horses, and American camels, as well as the collapse of the North American Clovis culture.
Kennett says that because the impact appears to have produced an aerial explosion there is no evidence of craters in the ground.
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.
Kennett said: “Shocked quartz is well known and is probably the most robust proxy for a cosmic impact.
“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.”
He said the “crème de la crème” of cosmic impact evidence has also been identified at Abu Hureyra and at other Younger Dryas Boundary (YDB) sites, despite an absence of craters.
The research team found “close associations” in the characteristics of quartz found at Abu Hureyra and shocked quartz at nuclear test sites – namely glass-filled shock fractures, indicative of temperatures greater than 2,000 degrees Celsius, above the melting point of quartz.
Kennett added: “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.”
He said the evidence presented in the papers “implies a novel causative link among extraterrestrial impacts, hemispheric environmental and climatic change, and transformative shifts in human societies and culture, including agricultural development.”
Produced in association with SWNS Talker
