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No. 104: Mar-Apr 1996

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"Where the East Antarctic icesheet meets the Transantarctic Mountains, old, deep glacial ice is tilted upward and exposed. Within this visible cross section of the icesheet, layers of dark volcanic tephra serve as stratigraphic markers and datable age horizons. Systematic sampling of these layers at a well-known meteorite collection site (the Allan Hills Main Icefield) has revealed a band consisting of unusually dark and rounded particles, many of which are spheroidal. This debris layer (BIT-58) extends parallel to the stratigraphy of the ice established from the tephra bands, and thus apparently marks a single depositional event. Several kilograms of ice from two sites along this band were subsequently collected and melted, yielding a few grams of sediment for further study."

Microscopic examination and microprobe analysis led to the following conclusions:

"Although direct evidence of an extraterrestrial origin for this debris layer (such as the presence of cosmogenic 10 Be and 26Al) has not yet been obtained, the available data strongly suggest that this sediment originated as meteoritic spallation debris. This debris is distinct from other Antarctic 'cosmic dust' collections by virtue of its uniform, recognizable, ordinary chondrite composition and the consistent relation shown between grain size and texture. The BIT-58 layer probably originated from a single transient event, the passage and/or impact of a single large meteorite over the East Antarctic icesheet."

(Harvey, R.P. et al; "A Meteoritic Event Layer in Antarctic Ice," Meteoritics, 30:517, 1995)

Comment. The Petrozavodsk Phenomenon under ASTRONOMY might well have left a layer like this. The 1908 Tunguska Event (Siberian Meteor) undoubtedly did. (SF#102)

From Science Frontiers #104, MAR-APR 1996. � 1996-2000 William R. Corliss