Guest “No, this does not confirm the YDIH,” by David Middleton.

Vast patches of glassy rock in Chilean desert likely created by ancient exploding comet
Heat from a comet exploding just above the ground fused the sandy soil into patches of glass stretching 75 kilometers, a study led by Brown University researchers found.

PROVIDENCE, R.I. [Brown University] — Around 12,000 years ago, something scorched a vast swath of the Atacama Desert in Chile with heat so intense that it turned the sandy soil into widespread slabs of silicate glass. Now, a research team studying the distribution and composition of those glasses has come to a conclusion about what caused the inferno.

In a study published in the journal Geology, researchers show that samples of the desert glass contain tiny fragments with minerals often found in rocks of extraterrestrial origin. Those minerals closely match the composition of material returned to Earth by NASA’s Stardust mission, which sampled the particles from a comet called Wild 2. The team concludes that those mineral assemblages are likely the remains of an extraterrestrial object — most likely a comet with a composition similar to Wild 2 — that streamed down after the explosion that melted the sandy surface below.

“This is the first time we have clear evidence of glasses on Earth that were created by the thermal radiation and winds from a fireball exploding just above the surface,” said Pete Schultz, a professor emeritus in Brown University’s Department of Earth, Environmental and Planetary Sciences. “To have such a dramatic effect on such a large area, this was a truly massive explosion. Lots of us have seen bolide fireballs streaking across the sky, but those are tiny blips compared to this.”

[…]

The analysis found minerals called zircons that had thermally decomposed to form baddeleyite. That mineral transition typically happens in temperatures in excess of 3,000 degrees Fahrenheit — far hotter than what could be generated by grass fires, Schultz says.

The analysis also turned up assemblages of exotic minerals only found in meteorites and other extraterrestrial rocks, the researchers say. Specific minerals like cubanite, troilite and calcium-aluminum-rich inclusions matched mineral signatures from comet samples retrieved from NASA’s Stardust mission.

“Those minerals are what tell us that this object has all the markings of a comet,” said Scott Harris, a planetary geologist at the Fernbank Science Center and study co-author. “To have the same mineralogy we saw in the Stardust samples entrained in these glasses is really powerful evidence that what we’re seeing is the result of a cometary airburst.”

More work needs to be done to establish the exact ages of the glass, which would determine exactly when the event took place, Schultz says. But the tentative dating puts the impact right around time that large mammals disappeared from the region.

“It’s too soon to say if there was a causal connection or not, but what we can say is that this event did happen around the same time as when we think the megafauna disappeared, which is intriguing,” Schultz said. “There’s also a chance that this was actually witnessed by early inhabitants, who had just arrived in the region. It would have been quite a show.”

Schultz and his team hope that further research may help to constrain the timing and shed light on the size of the impactor. For now, Schultz hopes this study may help researchers identify similar blast sites elsewhere and reveal the potential risk posed by such events.

[…]

Brown University

Here’s the abstract of the paper…


RESEARCH ARTICLE| NOVEMBER 02, 2021
Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile
Peter H. Schultz; R. Scott Harris; Sebastián Perroud; Nicolas Blanco; Andrew J. Tomlinson
Geology (2021)

Twisted and folded silicate glasses (up to 50 cm across) concentrated in certain areas across the Atacama Desert near Pica (northern Chile) indicate nearly simultaneous (seconds to minutes) intense airbursts close to Earth’s surface near the end of the Pleistocene. The evidence includes mineral decompositions that require ultrahigh temperatures, dynamic modes of emplacement for the glasses, and entrained meteoritic dust. Thousands of identical meteoritic grains trapped in these glasses show compositions and assemblages that resemble those found exclusively in comets and CI group primitive chondrites. Combined with the broad distribution of the glasses, the Pica glasses provide the first clear evidence for a cometary body (or bodies) exploding at a low altitude. This occurred soon after the arrival of proto-Archaic hunter-gatherers and around the time of rapid climate change in the Southern Hemisphere.

Schultz et al., 2021

The full text of the paper is available and well-worth reading. The mineralogical similarity to material collected from the tail of Comet Wild-2 by the Stardust mission is quite compelling.

“Analysis of the samples revealed a mineralogy consistent with a cometary origin.”

While these mineral associations are common in meteorites…

Cubanite
January 5, 2014

Chemical Formula: CuFe2S3
Locality: Barracanao, Cuba.
Name Origin: Named after its locality.

Cubanite is a yellow mineral of copper, iron, and sulfur, CuFe2S3.Cubanite was first described in 1843 for an occurrence in the Mayarí-Baracoa Belt, Oriente Province, Cuba.Cubanite occurs in high temperature hydrothermal deposits with pyrrhotite and pentlandite as intergrowths with chalcopyrite. It results from exsolution from chalcopyrite at temperatures below 200 to 210 °C. It has also been reported from carbonaceous chondrite meteorites.

Geology Page

Troilite

[…]

Occurrence: In serpentine (Del Norte Co., California, USA); with Fe–Cu–Ni sulfides in a layered ultramafic intrusive (Sally Malay deposit, Australia); and as nodules in meteorites.

Association: Pyrrhotite, pentlandite, mackinawite, cubanite, valleriite, chalcopyrite, pyrite (Wannaway deposit, Australia); daubr´eelite, chromite, sphalerite, graphite, various phosphates and silicates (meteorites).

Distribution: From the Alta mine, Del Norte Co., California, USA. In the Wannaway Fe–Ni–Cu deposit, and at the Sally Malay Cu–Ni deposit, 120 km north of Halls Creek, Western Australia. In the Panzhihua-Xichang district, Sichuan Province, China. From Disco Island and the Il´ımaussaq intrusion, southern Greenland. At Nordfjellmark, Norway. In many meteorites and some lunar rocks.

[…]

Handbook of Mineralogy

Pyrrhotite

[…]

Occurrence: Mainly in mafic igneous rocks, typically as magmatic segregations; also in pegmatites, and in high-temperature hydrothermal and replacement veins, and in sedimentary and metamorphic rocks; in iron meteorites.

Association: Pyrite, marcasite, chalcopyrite, pentlandite, many other sulfides, magnetite, calcite, dolomite.

[…]

Handbook of Mineralogy

The abundance of “calcium-aluminum–rich inclusions (CAIs) is “exceedingly rare” chondrites (CI meteorites); however CAI’s were identified in Stardust samples from Comet Wild-2.

Every sample examined thus far (70 thin sections) also contained thousands of exotic mineral grains and rock fragments (10 to 100 mineral grains and rock fragments per section) atypical of the local sediments. The observed minerals included euhedral Ni-troilite, buchwaldite (Fig. S10C), and Si-bearing chlorapatite that coat smooth vesicle walls (Figs. 4A and 4B); calcium-aluminum–rich inclusions (CAIs) (Figs. 4C and 4D); refractory Ca-Al-Ti–rich grains containing perovskite and corundum (Fig. 4E); and aqueously altered assemblages of Mg-rich silicates with troilite (for example, the serpentinite clast in Fig. 4F). The Ni-troilite (0.5–2 wt% Ni) is intergrown with Ni-free pyrrhotite and rimmed by cubanite (CuFe2S3) with submicron inclusions of pentlandite (Fig. 4B).

[…]

Although CAIs are exceedingly rare in CI meteorites, CAI materials have also been found in Stardust samples (Brownlee et al., 2012).

[…]

Schutz et al., 2021

The authors’ best estimate of the timing of the airburst was between 11,500 and 12,300 calendar years ago, with 12,300 being the maximum age (95% confidence). This would seem post-date the acute decline in South American megafaunal genera from 12,900 to 12,200 calendar years ago (Prates & Perez, 2021).

References

Prates, L., Perez, S.I. Late Pleistocene South American megafaunal extinctions associated with rise of Fishtail points and human population. Nat Commun 12, 2175 (2021). https://doi.org/10.1038/s41467-021-22506-4

Schultz, Peter H., R. Scott Harris, Sebastián Perroud, Nicolas Blanco, Andrew J. Tomlinson. “Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert”. Chile. Geology 2021; doi: https://doi.org/10.1130/G49426.1

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2021 November 4