Astronomy, March 1998, p. 30: Collision With Earth: An Impact on the Weather
Frank Kyte, who discovered the impact of the Eltanin asteroid in 1981 when he was a graduate student, now believes that the planetoid may have been large enough to have devastated Earth's climate. Writing in the November 27, 1997, issue of Nature, Kyte and his 12 co-authors report that additional ocean-bottom sampling completed recently suggests that instead of being an estimated 0.5 kilometer in diameter, the asteroid was at least 1 km and possibly as large as 4 km across. That's big enough to have caused global "devastating megatsunamis," or 120-foot-tall tidal waves, after the object struck the Southern Ocean about 2.15 million years ago. "This was right before a significant cooling event, " said Kyte, a geochemist with UCLA's Institute of Geophysical and Planetary Physics. "Whether this impact was just a coincidence we can't say, but no one has looked." There are about 140 known terrestrial impacts of asteroids, but 60 percent of Earth is covered by oceans. Water impacts would leave little evidence behind other than pulverized pieces of the asteroid buried under more recent sediments, terrestrial evidence of ancient tsunamis, or other subtle clues . In the mid-1960s, the crew of the USNS Eltanin, an American research ship looking for evidence of ancient glacier activity, punched one of many 20-meter "piston cores" into the floor of the Southern Ocean about 1,400 km (900 miles) west of the southern tip of South America. The ocean bottom often is deeply covered with recent sediment but, fortunately, the ship passed above an area with little sediment when the fateful core sample was taken. The sample extended deep enough into the sea bottom to pierce a layer of asteroid debris. However, that core sample sat undisturbed on a shelf until Kyte examined it and discovered that it contained a region rich in iridium, a signature element of asteroids. "I just got lucky to find this one," said Kyte. "The labs of sedimentologists and paleontologists all over the world have processed sediments from deep-sea cores, and I wonder how many (asteroid) impacts are sitting on the back of people's shelves." Best wishes, Bernd ______________________________________________ Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
