Word: sediments
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Dates: during 1980-1989
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Beyond the human density, the capital has a shaky geological base that makes it especially susceptible to earthquakes. Mexico City is built on the soft, moist sediment of an ancient lake bed; when jolted, says Caltech Earthquake Expert George W. Housner, it reacts "like a bowl of jelly." The city has, in fact, been sinking into its soft base at up to 10 in. annually. The drop has been uneven, creating a tilt in some foundations, thus placing those buildings at greater peril than others when the earth begins to rumble...
...silver tray nestled in sediment. Bottles of vintage Bordeaux wine scattered on the ocean floor. A gaping hole where once a giant smokestack had stood. The ship's bridge, damaged by a falling boom. These and other poignant images of disaster, all in Picasso blue, were distributed in Washington last week at a news conference held by Marine Geologist Robert Ballard, leader of the expedition that early this month located and photographed the sunken liner Titanic. They were only a few of the 12,000 photos shot at the bottom of the Atlantic by the unmanned submersibles Argo and Angus...
Alvarez, his curiosity aroused, shipped samples of the sediment back to the U.S. and showed them to his father Luis, a Nobel-prizewinning physicist also at the University of California, who had the clay analyzed. To everybody's surprise, it turned out to be 30 times as rich in iridium as normal rocks. The Berkeley team knew of only a few places where such high concentrations of the rare element might occur: in the earth's core, perhaps 2,000 miles belowground; in extraterrestrial objects like asteroids (or their fragments, meteors) and comets; or in the cosmic dust drifting...
...chiseled, Alvarez was struck by a configuration of sediment layers, which resembled a sandwich in stone. The bottom or older layer consisted of Cretaceous limestone, which was full of tiny fossils. On top was a second slice of limestone, from the Tertiary period, almost devoid of these fossils. Like other samples of rock from that era, it showed that the creatures alive during the late Cretaceous period had, by geological time scales, suddenly disappeared. In between the limestone layers was a dull red layer of clay about half an inch thick, first discovered by an Italian paleontologist around...
...rapidly accumulating. Other geologists uncovered similar iridium deposits just above Cretaceous rock beneath the floor of the Atlantic Ocean and under the Raton basin in northeastern New Mexico. Additional analysis showed that the samples contained ratios of gold and platinum nearly identical to those found in meteorites. Furthermore, other sediment layers containing abnormally high amounts of iridium were discovered under both the Caribbean Sea and the Gulf of Mexico; these layers were deposited around the time of a smaller mass extinction that occurred more than 30 million years ago, at the end of the Eocene epoch. In addition...