Nanodiamantes descobertos na camada de gelo da Groelândia: evidência de um impacto cósmico?

sexta-feira, setembro 17, 2010

Nanodiamonds Discovered in Greenland Ice Sheet, Contribute to Evidence for Cosmic Impact

ScienceDaily (Sep. 15, 2010) — Nanosize diamonds have been discovered in the Greenland ice sheet, according to a study reported by scientists in a recent online publication of the Journal of Glaciology. The finding adds credence to the controversial hypothesis that fragments of a comet struck across North America and Europe approximately 12,900 years ago.

Scanning transmission electron microscope image of nanodiamonds from the Greenland ice sheet. (Credit: James C. Weaver, UCSB)

"There is a layer in the ice with a great abundance of diamonds," said co-author James Kennett, professor emeritus in the Department of Earth Science at UC Santa Barbara. "Most exciting to us is that this is the first such discrete layer of diamonds ever found in glacial ice anywhere on Earth, including the huge polar ice sheets and the alpine glaciers. The diamonds are so tiny that they can only be observed with special, highly magnifying microscopes. They number in the trillions."

This discovery supports earlier published evidence for a cosmic impact event about 12,900 years ago, Kennett explained. He said that the available evidence in the Greenland ice is consistent with this layer being at or close to this age, although further study is needed.

Researchers from the University of Maine led the expedition to Greenland in 2008. Co-authors on the study, besides Kennett and the team from Maine, include scientists from many universities and research entities. James Kennett's son, Douglas J. Kennett, of the University of Oregon, is one of the 21 scientists who contributed to the report.

Read more here/Leia mais aqui: Science Daily


Journal of Glaciology, Vol. 56, No. 199, 2010

Discovery of a nanodiamond-rich layer in the Greenland ice sheet

Andrei V. KURBATOV,1 Paul A. MAYEWSKI,1 Jorgen P. STEFFENSEN,2 Allen WEST,3
Douglas J. KENNETT,4 James P. KENNETT,5 Ted E. BUNCH,6 Mike HANDLEY,1
Douglas S. INTRONE,1 Shane S. QUE HEE,7 Christopher MERCER,8 Marilee SELLERS,9
Feng SHEN,10 Sharon B. SNEED,1 James C.WEAVER,11 James H. WITTKE,6
Thomas W. STAFFORD, Jr,12 John J. DONOVAN,13 Sujing XIE,13 Joshua J. RAZINK,14
Adrienne STICH,15 Charles R. KINZIE,15 Wendy S. WOLBACH15

1Climate Change Institute, University of Maine, 303 Bryand Global Sciences Center, Orono, Maine 04469-5790, USA


2Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen,
3GeoScience Consulting, Dewey, Arizona 86327, USA
4Department of Anthropology, University of Oregon, Eugene, Oregon 97403-1272, USA
5Department of Earth Science, University of California, Santa Barbara, California 93106-5131, USA
6Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011-4099, USA
7Department of Environmental Health Sciences/Center for Occupational and Environmental Health, University of California,
Los Angeles, California 90095-1772, USA
8National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
9Imaging and Histology Core Facility, Northern Arizona University, Flagstaff, Arizona 86011, USA
10FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, Oregon 97124-5793, USA
11Department of Physics, University of California, Santa Barbara, California 93106-5131, USA
12Stafford Research Laboratories, Inc., 200 Acadia Avenue, Lafayette, Colorado 80026-1845, USA
13CAMCOR High Resolution and MicroAnalytical Facilities, University of Oregon, Eugene, Oregon 97403-1272, USA
14Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1272, USA
15Department of Chemistry, DePaul University, Chicago, Illinois 60614, USA

ABSTRACT. We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5 106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 0.1 ka. However, more investigation is needed to confirm this association.




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