Word: sedimentation
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Dates: during 1990-1999
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ACTIVATED-CARBON FILTRATION. These systems are the most popular and the most effective in reducing so-called aesthetic contaminants like chlorine and sediment. Filters made of carbon in solid block form, as opposed to granules, are also highly effective in reducing lead. Systems range from inexpensive pour-through carafes to filters that are mounted on faucets, on countertops or under the sink. Cost...
...mechanism, speculates Knoll, could have been erosion from steep mountain slopes. Over time, he notes, tons of sediment and rock that poured into the sea could have buried algal remains that fell to the sea floor. In addition, he says, rifting continents very likely changed the geometry of ocean basins so that water could not circulate as vigorously as before. The organic carbon that fell to the sea floor, then, would have stayed there, never cycling back to the ocean surface and into the atmosphere. As levels of atmospheric carbon dioxide dropped, the earth would have cooled. Sure enough, says...
...drive north of Nairobi along the shores of Lake Turkana in the East African Rift Valley. An 1,800-mile-long gash in the surface of the earth, the Rift has yielded many important clues to early human history, because of its unique geology. Layers of sediment preserved animal specimens, while the volcanic eruptions that periodically shook the valley produced ash and lava whose radioactive elements make the fossils easy to date. Probably the most famous inhabitant of the valley was the diminutive creature known as Lucy (Australopithecus afarensis), whose fossil skeleton was discovered in 1974 and who lived more...
...bombs, gouging out a crater the size of Rhode Island and throwing so much pulverized real estate into the stratosphere that the sun is blocked for months and Earth goes into a worldwide deep freeze. If the comet hits an ocean, a pall of dust rises from underwarter sediment, and a tidal wave several thousand feet high races across the sea and hundreds of miles inland...
...Here's a fresh concern: lead spewed into the skies above Europe by ancient silver smelters as far back as 2,600 years ago. The toxic by-product has been discovered in lake sediment in Sweden; the lead traces could still cause poisoning...