New scientific research provides additional evidence supporting the hypothesis that a fragmented comet exploded in Earth's atmosphere approximately 12,800 to 13,000 years ago. This proposed event is theorized to have contributed to the abrupt climatic cooling known as the Younger Dryas period, the extinction of North American megafauna, and the decline of the Clovis culture.
The Younger Dryas Impact Hypothesis
The Younger Dryas impact hypothesis posits that an extraterrestrial impact event, specifically atmospheric explosions of fragmented comets, initiated significant environmental changes. This event is proposed to have generated widespread heat and shockwaves, triggering extensive wildfires. These fires would have released smoke, soot, and dust into the atmosphere, potentially leading to reduced sunlight and an "impact winter." Additionally, rapid melting of ice sheets may have contributed to regional cooling. These combined effects are suggested to have disrupted ecosystems, contributing to the disappearance of large Ice Age mammals such as mammoths and mastodons, and affecting human populations, including the Clovis culture in North America.
New Evidence: Shocked Quartz Discovery
Researchers, led by James Kennett, Emeritus Professor of Earth Science at UC Santa Barbara, identified shocked quartz at three Clovis archaeological sites: Murray Springs (Arizona), Blackwater Draw (New Mexico), and Arlington Canyon (California's Channel Islands). Shocked quartz consists of sand grains exhibiting physical alterations consistent with exposure to extreme heat and pressure.
Microscopic analysis of these grains revealed distinct fractures and melted silica or veins, indicating conditions exceeding those typically associated with volcanic activity or anthropogenic fires. This finding, detailed in a study published in PLOS One, is considered notable given the absence of a large impact crater corresponding to this event.
The Airburst Mechanism
The lack of an identified large impact crater suggests an airburst mechanism, where a comet or its fragments detonated in the mid-atmosphere without directly impacting the Earth's surface. This mechanism is comparable to the 1908 Tunguska event in Siberia, though potentially on a larger scale.
To investigate this, the research team employed hydrocode modeling to simulate low-altitude explosions. These simulations generated shock patterns in quartz grains that align with the characteristics observed in the samples from the study sites.
Context: The Younger Dryas Period and Associated Changes
The proposed impact event coincides with the beginning of the Younger Dryas period, an interval lasting approximately 1,000 years, which represented an abrupt return to glacial-like conditions, interrupting a broader post-Last Glacial Period warming trend. The extinction of North American Ice Age megafauna and the cessation of Clovis tool use also align with the onset of this period.
Previous Supporting Indicators
Over the past two decades, various lines of evidence have been accumulated in support of the Younger Dryas impact hypothesis. These include:
- Black Mat Layer: A widespread, dark, carbon-rich sedimentary layer found in geological records across North America and Europe, indicative of extensive burning. This layer is contemporaneous with the onset of the Younger Dryas.
- Impact Proxies: Elevated concentrations of rare elements, such as platinum and iridium, which are associated with extraterrestrial objects.
- High-Temperature Materials: The presence of nanodiamonds, metallic spherules, and meltglass or melted silicate materials, consistent with formation under extreme heat and pressure.
Conclusion of Findings
The discovery of shocked quartz, alongside previously identified indicators such as the "black mat" layer, nanodiamonds, and impact spherules within the same sedimentary layer, provides additional data for the Younger Dryas impact hypothesis. This accumulating evidence supports a cosmic impact as a factor in the megafaunal extinctions and the decline of the Clovis culture at the beginning of the Younger Dryas.