Geochemistry

Tracing Tektites to Their Craters

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Science  06 Oct 2000:
Vol. 290, Issue 5489, pp. 15
DOI: 10.1126/science.290.5489.15a

Impacts on Earth that create craters with diameters larger than about 3 kilometers may eject melt droplets from the surface. These droplets do not escape Earth's gravity and are distributed globally as glasses (tektites) or glasses with microcrystals (krystites). Strewn fields or thin layers of tektites have been identified, and the challenge is to associate these glassy concentrations with a particular impact. Once these are connected, models can be developed to understand the size and composition of the bolide, as well as the impact's effect on the surface and atmosphere.

Whitehead et al. analyzed the major element and Sr and Nd isotopic characteristics of one microtektite layer and two microkrystite layers from deep sea drilling cores from the Atlantic, Pacific, and Indian Oceans. The 35.5-million-year-old microtektite layer has chemical characteristics which correlate with the Chesapeake impact structure on the east coast of North America, as previously suggested. The two, slightly older, lower microkrystite layers show a chemical correlation with the Popigai impact structure in Siberia. These geochemical markers can now be used to model the physical process of these impact events. — LR

Earth Planet. Sci. Lett.181, 473 (2000).

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