Prehistoric Cosmic Airburst Preceded the Advent of Agriculture In the Levanthttps://phys.org/news/2023-10-prehistoric-cosmic-airburst-advent-agriculture.html
Agriculture in Syria started with a bang 12,800 years ago as a fragmented comet slammed into the Earth's atmosphere. The explosion and subsequent environmental changes forced hunter-gatherers in the prehistoric settlement of Abu Hureyra to adopt agricultural practices to boost their chances for survival. That's the assertion made by an international group of scientists in one of four related research papers, all appearing in the journal
Science Open: Airbursts and Cratering Impacts. The papers are the latest results in the investigation of the Younger Dryas Impact Hypothesis, the idea that an anomalous cooling of the Earth almost 13 millennia ago was the result of a cosmic impact.
"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 Earth scientist James Kennett, a professor emeritus of UC Santa Barbara . The settlement at Abu Hureyra is famous among archaeologists for its evidence of the earliest known transition from foraging to farming. "The villagers started to cultivate barley, wheat and legumes," he noted. "This is what the evidence clearly shows."
... 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 winter at the onset of the Younger Dryas.
And what an impact it must have been. https://phys.org/news/2020-03-evidence-cosmic-impact-destruction-world.htmlIn 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—higher than any that could have been produced by man's technology at the time.
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.
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.
![](https://news.ucsb.edu/sites/default/files/images/2019/cosmic-impact-uc-santa-barbara.jpg)
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," Kennett said. "Many accepted impacts have no visible crater." 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," he continued. 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 (YDB) sites, despite an absence of craters.
... Between the shocked quartz at the nuclear test sites and the quartz found at Abu Hureyra, the scientists 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," Kennett said. However, the so-called "lower pressure" is still very high—probably greater than 3 GPa or about 400,000 pounds per square inch, equivalent to about five 737 airplanes stacked on a small coin.
Andrew M.T. Moore, James P. Kennett and Malcolm A. LeCompte et al.
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 (2023)
https://www.scienceopen.com/hosted-document?doi=10.14293/ACI.2023.0003Andrew M.T. Moore, James P. Kennett and William M. Napier et al.
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 (2023)
https://www.scienceopen.com/hosted-document?doi=10.14293/ACI.2023.0002Andrew M.T. Moore, James P. Kennett and William M. Napier et al.
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. (2023)
https://www.scienceopen.com/hosted-document?doi=10.14293/ACI.2023.0004Robert E. Hermes, Hans-Rudolf Wenk and James P. Kennett et al.
Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts. Airbursts and Cratering Impacts (2023)
https://www.scienceopen.com/hosted-document?doi=10.14293/ACI.2023.0001----------------------------------------------------------------------
https://www.scienceopen.com/hosted-document?doi=10.14293/ACI.2023.0004... A large comet, >100 km in diameter, the progenitor of the Kreutz sungrazing comets, entered the planetary system from the Centaur region during the late Pleistocene/early Holocene and fragmented, as confirmed by its still-visible debris [86]. It is currently disintegrating in a high-inclination, retrograde orbit. Another is now seen as a cometary debris field known as the Taurid Complex, composed of Comet Encke, an array of meteor streams, and ~90 asteroids with diameters of 1.5 to 5 km in similar orbits [83]. The measured light curves of 34 of the associated asteroids [87] and the mass and spread of the Complex, when the derivative zodiacal dust and its possible loss rate are estimated, indicate that the Complex represents the remains of a ~100-km-wide progenitor comet whose disintegration and dispersion has continued for at least the last ~20,000 years [88–91]. These data confirm and strengthen an early proposal by Whipple that Comet Encke is the progenitor of much of the meteoroid population in the inner solar system [92].
Comet Encke, a relatively small comet (~5 km) with a short orbital period (3.3 years), is in an orbit whose perihelion, q = 0.34 au, is closer to the Sun than the orbit of Mercury and whose aphelion, Q = 4.1 au, is just short of Jupiter’s sphere of influence (1 au is roughly the distance between the center of the Earth and the Sun). We determined the past evolution of Comet Encke by backtracking from its AD 2007 orbital characteristics given in the Minor Planet Center, using the Mercury orbital integration package [93] and considering gravitational perturbations produced by all the planets. This analysis revealed five “double jeopardy” high-risk episodes during the past 14,000 years, separated by intervals of ~2500 years when the modeled orbit intersected that of the Earth while passing north to south through the Earth’s orbital plane. This intersection was followed a few centuries later by another intersection during its orbit south to north (Figure 3A). The orbital inclination oscillates between about 3° and 21° from Earth’s orbital plane (i.e., the plane of the ecliptic) (Figure 3B) with the low inclinations occurring when the orbit of comet and Earth intersect.
Comet destruction proceeds largely through random splittings, with sublimation as a minor process [94]. The disintegration history of short-period comets is varied but may be modeled statistically either by frequent splitting events with a slight mass loss per event or by fewer events with larger mass losses [82]. Simulations of the progenitor comet’s disintegration over the past 14,000 years have been carried out in accordance with these models, with the fragments dispersing at velocities of 2 to 10 m/s, producing debris trails whose fragments spread along the orbital track [94]. A comet in an Encke-like orbit may undergo substantial fragmentation every few orbits, and many hundreds of fragment clusters may be produced, yielding an expectation that Earth would have intersected a few of them over the lifetime of the comet. In addition, the 2:7 orbital resonance with Jupiter’s orbit produces long-lived concentrations of Taurid dust swarms [95, 96].
Modeling of Taurid disintegration leads to an estimation that during the last 20,000 years, Earth possibly experienced several “meteor hurricanes” with kinetic energies between 3,000-40,000 megatons (Mt) and durations of a few hours to a few days [94]. The bolides colliding with Earth are a mixture of ice, dust, boulders, and larger bodies. Observations show that the comet fragments often have dimensions of tens to hundreds of meters [97], and the encounters can be hemispheric to global in scope. One of many scenarios assumes that if the incident energy is in the form of 1-3-Mt bolides, the mean distance of any point on an exposed hemisphere from such an airburst event is in the range of 50-300 km. Thus, adequate energy was available at Abu Hureyra to transform terrestrial sediments into meltglass, ignite local fires, and destroy the village, whether by a radiation pulse from the bolide or the subsequent blast wave [98, 99].
The probability of Earth passing through a trail of fragments is highest at low orbital inclinations, varying roughly as the inverse sine of the inclination. The episode at ~12,800 years yields a combination of an orbital intersection coupled with low orbital inclination when the orbits of Earth and the modeled orbit of Comet Encke were almost coplanar (Figure 3B). Between ~12,800 and 12,200 years ago (before AD 2007), the orbit of the modeled Comet Encke was at a shallow inclination (3–6°). Given that a debris trail dense enough to produce the YDB airburst proxies may be 1000 to 10,000 Earth radii in length, Earth may have passed through such a debris trail multiple times, approximately once per century near 12,800 cal BP [94]. This episode is shown in high resolution in Figure 3C. The intersection of the orbits of Earth and the comet coincides closely with the YD boundary.
There is a near overlap between the intersection dates of the progenitor comet with Earth that produced the YDB airburst proxies. However, when extrapolating back in time, there are a few decades of uncertainty about the current orbital elements of Comet Encke and the non-gravitational forces produced by material ejected from the comet [100]. Within that range, the YDB occurs within the highest risk interval of encountering the comet fragments. For more details, see Appendix, Text S1.