Geology

Glass at a Crash Site

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Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1843
DOI: 10.1126/science.314.5807.1843a

Hundreds of thousands of years ago, Stone Age peoples inhabited the Dakhleh Oasis, in central western Egypt, when the ancient landscape included lakes. The area has attracted substantial archaeological and geological investigation, and one unresolved mystery has been the origin of unusual darkly colored glass, termed “Dakhleh glass,” found at the site. Osinski et al. have probed the glass using x-ray fluorescence techniques, isotopic analysis, and electron microscopy. Its chemical composition (in particular, an anomalously high proportion of CaO and Al2O3) differs from that of all known volcanic glasses, and there is no evidence of volcanism in the region. The authors argue that the glass was probably created through a meteorite impact occurring 100,000 to 200,000 years ago. The energy of the impact would have fused the local carbonate and sandstone rocks into glass. The imprints of plant stems and leaves from that time were also uncovered in the glass, but no signs of shock metamorphosis were evident. Because an impact crater has not yet been located, the authors note the possibility of an aerial burst; in either case, such an event would have devastated the local population. — JB

Earth Planet. Sci. Lett. 10.1016/j.epsl.2006.10.039 (2006).

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