Before the Taqba Dam impounded the Euphrates River in northern Syria in the 1970s, an archaeological site known as Abu Hureyra bore witness to the moment ancient nomadic people first settled down and started cultivating crops. A large mound marks the settlement, which now lies under Lake Assad.
But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food, and tools — an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth’s cultural and environmental history. Abu Hureyra, it turns out, has another story to tell.
Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures — far higher than what humans could achieve at the time — or that could be attributed to fire, lighting, or volcanism. James Kennett, a UC Santa Barbara emeritus professor of geology, said:
“To help with perspective, such high temperatures would completely melt an automobile in less than a minute.”
Such intensity, he added, could only have resulted from an extremely violent, high-energy, high-velocity phenomenon, something on the order of a cosmic impact. Based on materials collected before the site was flooded, Kennett and his colleagues contend Abu Hureyra is the first site to document the direct effects of a fragmented comet on a human settlement. These fragments are all part of the same comet that likely slammed into Earth and exploded in the atmosphere at the end of the Pleistocene epoch, according to Kennett.
An impact or an airburst must have occurred sufficiently close to send massive heat and molten glass over the entire early village. (Image: via UC)
This impact contributed to the extinction of most large animals, including mammoths, American horses, and camels; the disappearance of the North American Clovis culture; and to the abrupt onset of the end-glacial Younger Dryas cooling episode. The team’s findings are highlighted in a paper published in the Nature journal Scientific Reports. Kennett, who with his colleagues first reported evidence of such an event in the region in 2012, said:
“Our new discoveries represent much more powerful evidence for very high temperatures that could only be associated with a cosmic impact.”
Abu Hureyra lies at the easternmost sector of what is known as the Younger Dryas Boundary (YDB) strewnfield, which encompasses about 30 other sites in the Americas, Europe, and parts of the Middle East. These sites hold evidence of massive burning, including a widespread carbon-rich “black mat” layer that contains millions of nanodiamonds, high concentrations of platinum, and tiny metallic spherules formed at very high temperatures.
Location of Abu Hureyra (adapted from Moore et al. (a) Map of the Middle East, showing Abu Hureyra location (AH) in Syria. (b) Map of the Abu Hureyra tell, showing locations of excavation trenches labeled A-G near a back channel of Euphrates River that is now abandoned. Sediment samples from Trenches D, E, and G (blue rectangles) contain abundance peaks in YDB proxies, including spherules, nanodiamonds, meltglass, and platinum. (Image: via Scientific Reports (2020). DOI: 10.1038/s41598-020-60867-w)
The YDB impact hypothesis has gained more traction in recent years because of many new discoveries, including a very young impact crater beneath the Hiawatha Glacier of the Greenland ice sheet, and high-temperature meltglass and other similar evidence at an archaeological site in Pilauco, located in southern Chile. Kennett said:
“The Abu Hureyra village would have been abruptly destroyed.”
Unlike the evidence from Pilauco, which was limited to the human butchering of large animals up to but not younger than the YDB impact burn layer, Abu Hureyra shows direct evidence of the disaster in this early human settlement. An impact or an airburst must have occurred sufficiently close to send massive heat and molten glass over the entire early village.
James Kennett. (Image: via James Kennett)
The glass was analyzed for geochemical composition, shape, structure, formation temperature, magnetic characteristics, and water content. Results from the analysis showed that it formed at very high temperatures and included minerals rich in chromium, iron, nickel, sulfides, titanium, and even platinum — and iridium-rich melted iron — all of which formed in temperatures higher than 2200°C, Kennett said:
“The critical materials are extremely rare under normal temperatures, but are commonly found during impact events.”
According to the study, the meltglass was formed “from the nearly instantaneous melting and vaporization of regional biomass, soils, and floodplain deposits, followed by instantaneous cooling.” Additionally, because the materials found are consistent with those found in the YDB layers at the other sites across the world, it’s likely that they resulted from a fragmented comet, as opposed to impacts caused by individual comets or asteroids. Kennett said:
“A single major asteroid impact would not have caused such widely scattered materials like those discovered at Abu Hureyra. The largest cometary debris clusters are proposed to be capable of causing thousands of airbursts within a span of minutes across one entire hemisphere of Earth. The YDB hypothesis proposed this mechanism to account for the widely dispersed coeval materials across more than 14,000 kilometers of the Northern and Southern Hemispheres. Our Abu Hureyra discoveries strongly support a major impact event from such a fragmented comet.”
Provided by: Sonia Fernandez, University of California – Santa Barbara [Note: Materials may be edited for content and length.]
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