[meteorite-list] Meteorites from the bottom of the ocean - Part 2 of 2
From: David Weir <dgweir_at_meteoritecentral.com>
Date: Tue Sep 5 16:22:04 2006 Message-ID: <44FDDB80.8080904_at_earthlink.net> Here's a photo to go with the story: http://meteoritestudies.com/KTFOSSIL.JPG David bernd.pauli_at_paulinet.de wrote: > Sky & Telescope, March 1999, p. 22: Piece of a Killer Asteroid ? > > Like finding a stray bullet at a crime scene, a researcher believes he has uncovered > a long-sought chunk of the impactor thought to have snuffed out 70 percent of the > species of life on Earth 65 million years ago. Scientists found the "smoking gun" in > 1990: a 180-kilometer-wide circular structure centered beneath the town of Puerto > Chicxulub on the coast of Mexico's Yucat?n Peninsula. But no piece of the impactor > had surfaced. > Geochemist Frank T. Kyte (University of California, Los Angeles) has been studying > a core sample from the bottom of the Pacific Ocean containing dark clay marking the > boundary of the Cretaceous and Tertiary periods (the K-T boundary). As Kyte > describes in Nature for November 19, 1998, the clay layer included a 4-millimeter-wide > piece of lighter-colored clay. Upon splitting open the nugget, he discovered a fossil > meteorite. More detailed examination of this sedimentary pearl revealed that it contains > high concentrations of iron oxides, principally hematite. > While the mineralogy of the fossil meteorite has undoubtedly changed over time, Kyte > reports that the amounts of iron, chromium, and iridium are nevertheless close to the > ranges seen in carbonaceous chondrites, a common meteorite type. Yet the specimen > has one significant compositional oddity: it has 1,000 times more gold than chondritic > meteorites commonly have, a curiosity that Kyte finds puzzling. > Because the ocean-floor sediments at the K-T boundary accumulated over perhaps as > much as 500,000 years, there is no way to prove that this truly is a piece of the > K-T impactor. However, a meteoritic impact is most consistent with Kyte's analysis; > he largely discounts the possibilities that the material is interplanetary dust or > cometary debris. Moreover, he thinks it quite conceivable that a piece of the asteroid > that struck the Yucat?n Peninsula survived the blast and landed 9,000 kilometers away. Received on Tue 05 Sep 2006 04:18:08 PM PDT |
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