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A goodbye wave?

A goodbye wave?

If an extraterrestrial body hit Earth 65 million years ago and precipitated the extinction of the dinosaurs and perhaps half the other living species, chances are three to one it landed in the ocean, unleashing a whopper of a wave. Geologists have identified deposits in Texs that mayhave been left by such a wave.

Along the Brazos River there are meter-thick beds of coarse-grained sandstones and large chunks of clay that were deposited precisely at the Cretaceous-Tertiary boundary. Only wave rising 50 to 100 meters above the ocean surface could have created such a layer of uprooted material, report Joanne Bourgeois from the University of Washington and her colleagues in the July 29 SCIENCE. From the pattern of the sediments, the researchers have ruled out storms, mudslidesand other possible causes of the deposits. At the end of the Cretaceous, this area of Texas was 75 to 100 meters below the ocean surface.

Since there is almost incontrovertible evidence that one or several comets or meteorites crashed into Earth at the same geologic time as the wave hit Texas, the researchers say it is likely an extraterrestrial body created the tsunami deposits, either by landing in the water or by generating earthquakes or submarine landslides. All of these events can produce tsunamis. Volcanic eruptions -- another leading candidate for causing the mass extinctions -- also start tsunamis, but the researchers say there is no geologic evidence in Texas for an eruption at that time. The deposits do not explain the extinctions, but these types of deposits in other locations may help in pinpointing the location of ground zero for the impact.
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Title Annotation:tsunami from meteor impact may have caused mass extinction
Publication:Science News
Date:Jul 30, 1988
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