In the Sør Rondane Mountains of Antarctica, atop Walnumfjellet, scientific investigators have uncovered spherules originating from meteorites.
The disintegration of a substantial celestial body in the primary asteroid belt. Image credit: NASA / JPL-Caltech.
The lead author, Dr. Matthias Van Ginneken of the University of Kent’s School of Physical Sciences, and his associates commented, “The vestiges of terrestrial high-velocity impacts are predominantly evident as impact craters, typically circular depressions formed by asteroids of sufficient size and/or density to reach the Earth’s surface without undergoing significant atmospheric disintegration.”
They further elaborated, “The genesis of impact craters is intrinsically linked to the development of distinctive shock-metamorphic indicators, the formation of high-pressure mineral phases within the impacted strata, discernible geochemical discrepancies, and the forceful expulsion of target and projectile material at elevated velocities.”
“The process of identifying hypervelocity impacts within the geological archive is generally facilitated by the presence of one or more of these characteristic signatures,” the researchers stated.
“However, impactors ranging from several tens to 150 meters in diameter are completely fragmented and vaporized during atmospheric entry, leading to a low-altitude airburst. This phenomenon bears resemblance to the Tunguska and Chelyabinsk incidents that occurred over Russia in 1908 and 2013, respectively.”
“Observations, supported by direct visual testimonies and indirect data from infrasound, seismic activity, video surveillance, and computational modeling of medium-sized airbursts, indicate that these impacts contribute a significant proportion of the extraterrestrial matter deposited on Earth. Events akin to Tunguska are estimated to occur between once every 100 and 10,000 years, a frequency vastly greater than that of large crater-forming impacts.”
“Nevertheless, corroborating evidence of these events is exceedingly rare in the geological record, primarily due to the inherent challenges in pinpointing and characterizing potential remnants.”
“Consequently, the discovery of evidence pertaining to these low-altitude meteoritic occurrences remains paramount for advancing our comprehension of Earth’s impact chronology and for accurately assessing the potential hazards posed by asteroid collisions.”
Electron microscopy images showing backscattered particles from the apex of Walnumfjellet, located in the Sør Rondane Mountains, Antarctica; these particles are the result of an asteroid impact approximately 430,000 years ago. Scale bars – 100 μm. Image attribution: Van Ginneken et al., doi: 10.1126/sciadv.abc1008.
Seventeen extraterrestrial condensation spherules recovered by the research team from the summit of Walnumfjellet provide evidence of an extraordinary impact event. This event involved a high-velocity jet of molten and vaporized meteoritic material, generated by the atmospheric entry of an asteroid at least 100 meters in diameter, reaching the Earth’s surface.
This specific type of impact, stemming from a single asteroid, is categorized as an intermediate event, falling between the scale of an airburst and a full crater-forming impact.
The extraterrestrial origin of the collected particles is substantiated by their chondritic bulk major and trace element geochemistry, as well as their elevated nickel content.
Furthermore, their distinctive oxygen isotopic compositions suggest an interaction with oxygen derived from the Antarctic ice sheet during their formation within the impact plume.
Dr. Van Ginneken proposed, “To comprehensively document Earth’s asteroid impact record, we advocate that future investigations should extend to identifying comparable events on diverse geological substrates, such as terrestrial bedrock or shallow marine environments, given that the Antarctic ice sheet presently covers only 9% of the planet’s landmass.”
“Our findings may also prove beneficial for the detection of such events in deep-sea sediment cores and, should the plume’s expansion reach continental areas, within terrestrial sedimentary sequences.”
“While touchdown events occurring over Antarctica may not pose a threat to human endeavors, a similar occurrence above a densely populated region would inevitably lead to catastrophic consequences, including millions of fatalities and widespread destruction extending hundreds of kilometers.”
The research findings of the team have been formally published in the journal Science Advances.
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M. Van Ginneken et al. 2021. A significant meteoritic event over Antarctica approximately 430 thousand years ago, as inferred from chondritic spherules originating from the Sør Rondane Mountains. Science Advances 7 (14): eabc1008; doi: 10.1126/sciadv.abc1008
