Researchers have been expanding on the Younger Dryas Impact hypothesis, which suggests that a fragmented comet collided with Earth’s atmosphere 12,800 years ago, causing significant climatic changes. UC Santa Barbara emeritus professor James Kennett and his colleagues have reported the presence of proxies associated with a cosmic airburst at various sites in the eastern United States. These proxies include platinum, microspherules, meltglass, and shock-fractured quartz, indicating the force and temperature involved in the event.
Different types of celestial impacts, ranging from everyday dust particles to catastrophic events like the Chicxulub impact that led to the extinction of dinosaurs, demonstrate the varying scales of impact events on Earth. The comet believed to have caused the Younger Dryas cooling episode was estimated to be 100 kilometers wide, much larger than the Tunguska object, and fragmented into thousands of pieces. The sediment layer associated with the airburst stretches across the northern hemisphere and contains high levels of rare materials associated with cosmic impacts, such as iridium, platinum, magnetic microspherules, meltglass, and nanodiamonds.
The presence of shocked quartz, a hard material deformed under great pressure, is a key piece of evidence for cosmic impact events. The researchers have observed that the fractures in the shocked quartz found in the impact layer associated with the Younger Dryas Boundary are irregular and do not follow the traditional parallel pattern seen in impact craters. These fractures show a web-like pattern of intersecting lines and surface and subsurface fissures, indicating lower pressures from explosions that occur above the ground, rather than impacts with the Earth’s surface.
The sediments associated with the impact layer also contain amorphous silica, melted glass, which is further evidence of the pressure and high temperatures generated by a low-altitude bolide airburst. Similar fractured quartz grains and melt glass have been found at present-day samples of above-ground explosions, such as at the Trinity atomic bomb test site in New Mexico. Together, these impact proxies support the theory of a fragmented comet causing widespread burning and abrupt climatic change that likely led to extinctions and the collapse of human cultures.
The researchers are striving to build a comprehensive case for the significance of the various types of shocked quartz found in the impact layer associated with the Younger Dryas Boundary, emphasizing their association with low-altitude airbursts likely caused by cometary impacts. These findings add to the growing body of evidence supporting the Younger Dryas Impact hypothesis and highlight the impact of cosmic events on Earth’s history, including mass extinctions and climate shifts.