Micrometeorite Impacts in Beringian Mammoth Tusks and a Bison Skull
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.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Nuclear Science Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 1023384
- Report Number(s):
- LBNL-4681E; TRN: US1105034
- Journal Information:
- Journal of Siberian Federal University. Engineering&Technologies, Vol. 3, Issue 1; Related Information: Journal Publication Date: February, 2010
- Country of Publication:
- United States
- Language:
- English
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ABLATION
ACTIVATION ANALYSIS
ANIMALS
ARCHAEOLOGICAL SPECIMENS
ELECTROMAGNETIC PULSES
ELECTRON MICROPROBE ANALYSIS
FLUORESCENCE
FOSSILS
GENETICS
IMAGES
IRON
LASERS
MASS SPECTROSCOPY
METEORITES
NICKEL
PLASMA
SKULL
SULFIDES
TITANIUM
global climate changes
megafauna
micrometeorites
multiple impacts
Siberian bison skull
Pleistocene Alaskan mammoth tusks
plasma mass spectrometry analyses
X-ray fluorescence analyses
electron microprobe analyses
gamma-ray activation analysis
scanning electron microscope images