Debris from a comet may have leveled an ancient village in Syria during several such explosions around the world, according to new findings. Abu Hureyra was a mound settlement in northern Syria around 13,000 years ago. The site was quickly excavated in 1972 and 1973, before the Euphrates River was dammed, flooding the site under Assad Lake.
But hurried excavations revealed charcoal-rich surfaces containing glass spheres shaped from melting soil, melted iron and sulfur-rich samples, and nanodiamonds. Such materials are all indicators of extremely high temperatures, such as those generated by a piece of rock exploding in the air.
The team led by Andrew Moore, an archeologist at the Rochester Institute of Technology in New York, who led the emergency excavation of the site in the 1970s, recently re-evaluated some of the excavated material in far more detail. The researchers then established experimental methods to reproduce the materials they found in the village.
“These provided new insights into how the meltglass was formed and how plant and other materials became incorporated in it,” said Moore. The melting of minerals found in the soil requires temperatures above 3.630 degrees Fahrenheit (2,000 degrees Celsius), “hot enough to cause quartz grains to boil,” Moore added. This suggests something cataclysmic.
“It is impossible to explain these melted minerals on meltglass by any natural process other than a cosmic impact event,” Moore said.
A deadly explosion
The first settlers of Abu Hureyra were hunter-gatherers who were living off the territory. The terrible drought has led people to start cultivating grains that they had originally obtained from the wild, turning them into the first known farmers, according to previous research.
Then, about 13,000 years ago, something really bad seems to have happened, leaving a carbon layer with dramatic fires. But for much of the last decade, scientists who have been inspecting the remains of the village have been discussing what has happened, unable to determine whether the carbon developed during an airburst or during more mundane fires among the thatched huts.
So Moore decided to re-examine the glass in far more detail. His analysis of the glass composition matched the 2012 finding that the airburst had destroyed Abu Hureyra, suggesting that the bucolic lifestyle of the villagers ended unexpectedly when one or more pieces of a passing comet exploded in the nearby air.
“People who were in or near the village of Abu Hureyra at the time the airburst exploded would have seen an immense flash in the sky, equivalent to a nuclear explosion,” Moore said. “A few seconds later, they would have been incinerated by the blast emanating from the airburst. The heat wave destroyed the village and everything in it, leaving a layer of burned material across the surface.”
Observers several tens of kilometers from the site would have seen the flash heard the explosion, and felt the heatwave, but probably survived the explosion. Moore and his colleagues heated glass segments in a laboratory furnace until they had fully melted, which occurred at 2,400 F (1,300 C), setting a lower temperature limit for which the spheroids had initially been exposed. But it took higher temperatures for the quartz and other particles to melt on the exterior.
Researchers also compared Abu Hureyra material with glass melted at other prehistoric sites on Earth and found several correlations. The abundance of melt-glass dating to about the same timeframe suggests to researchers that thousands of fragments of debris shed from a comet crashed into Earth’s atmosphere 12,800 years ago, affecting more than 40 sites across North America and Europe.
The new findings of Moore’s team match the 2007 hypothesis that Earth experienced several multi-continental airbursts. Since an individual comet or asteroid that is large enough to cause such widespread damage is doubtful, researchers believe the disparate impacts could have been caused by cometary debris.
“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 authors wrote. “An encounter with such a million-km-wide debris cluster would be thousands of times more probable than a collision with a 100-km-wide comet or a 10-km-wide asteroid.”