We have discovered what appear to be micrometeorites imbedded in seven late Pleistocene Alaskan mammoth tusks and a Siberian bison skull. The micrometeorites apparently shattered on impact leaving 2 to 5 mm hemispherical debris patterns surrounded by carbonized rings. Multiple impacts are observed on only one side of the tusks and skull consistent with the micrometeorites having come from a single direction. The impact sites are strongly magnetic indicating significant iron content. We analyzed several imbedded micrometeorite fragments from both tusks and skull with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and X-ray fluorescence (XRF). These analyses confirm the …
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Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (United States)
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We have discovered what appear to be micrometeorites imbedded in seven late Pleistocene Alaskan mammoth tusks and a Siberian bison skull. The micrometeorites apparently shattered on impact leaving 2 to 5 mm hemispherical debris patterns surrounded by carbonized rings. Multiple impacts are observed on only one side of the tusks and skull consistent with the micrometeorites having come from a single direction. The impact sites are strongly magnetic indicating significant iron content. We analyzed several imbedded micrometeorite fragments from both tusks and skull with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and X-ray fluorescence (XRF). These analyses confirm the high iron content and indicate compositions highly enriched in nickel and depleted in titanium, unlike any natural terrestrial sources. In addition, electron microprobe (EMP) analyses of a Fe-Ni sulfide grain (tusk 2) show it contains between 3 and 20 weight percent Ni. Prompt gamma-ray activation analysis (PGAA) of a particle extracted from the bison skull indicates ~;;0.4 mg of iron, in agreement with a micrometeorite ~;;1 mm in diameter. In addition, scanning electron microscope (SEM) images and XRF analyses of the skull show possible entry channels containing Fe-rich material. The majority of tusks (5/7) have a calibrated weighted mean 14C age of 32.9 +- 1.8 ka BP, which coincides with the onset of significant declines<36 ka ago in Beringian bison, horse, brown bear, and mammoth populations, as well as in mammoth genetic diversity. It appears likely that the impacts and population declines are related events, although their precise nature remains to be determined.
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Hagstrum, Jonathon T.; Firestone, Richard B; West, Allen; Stefanka, Zsolt & Revay, Zsolt.Micrometeorite Impacts in Beringian Mammoth Tusks and a Bison Skull,
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February 3, 2010;
Berkeley, California.
(https://digital.library.unt.edu/ark:/67531/metadc835563/:
accessed July 16, 2024),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
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