Word: sediment
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Trudged. Trudging, a moving upstream in a steep riverbed; the sediment becoming softer and deeper, the further one goes. This is her motion, now, walking; her motion in life always, these days. Invisible fetters are wrapped around her limbs; her arms and legs; flimsy but horribly restricting. To move at all is a victory. To appear to move 'normally', miraculous. She sees the same gentle restraining threads on everyone; scarf-like chains on every person near her; even threaded to their roving eyes. She sees them and smiles, feeling tired. Her walk slows. There are moaning pains in her toes...
Writing in Science, Emiliani reports that the earth has undergone at least eight periods of extreme cold and seven of torrid heat in the past 400,000 years. His conclusion is based on cores of ocean sediment from the Caribbean. Composed of the remains of tiny sea animals, the layered sediment provides a record of climatic changes. When the oceans warm up, there is a decrease in the ratio of the isotope oxygen-18 to ordinary oxygen in the shells of the little creatures; when temperatures go down, the concentration of oxygen-18 goes up. Moreover, the proportions are preserved...
...dating technique was conceived by Chemist Jeffrey Bada of the Scripps Institution of Oceanography while he was trying to date some fossil-laden sediment from the ocean floor. The standard method for determining the age of fossils is the so-called carbon 14 clock, which is based on the ratio of ordinary carbon atoms to atoms of the radioactive isotope carbon 14 found in the specimen. The carbon 14 atoms decay at a known rate and are not replenished after the creature dies; thus the proportion of ordinary carbon to carbon 14 slowly increases. But the carbon clock only works...
...Australia's bush country. Last September, while exploring a rock-rimmed stream in eastern Victoria, he discovered, preserved in the rock, several small imprints of an ancient four-legged creature with webbed five-toed hind feet and possibly three-toed front feet. Geological dating showed that the sediment in which the markings were made was some 355 million years old, which means that they may be the oldest footprints ever found on earth...
...plants' structure consists largely of carbon 12. What is more, the greater preponderance of that isotope becomes preserved in the earth's geological records when, for example, tiny green sea plants (plankton) die, sink to the ocean bottom, gradually decompose and become part of the sea-floor sediment. Still rich in carbon 12, this sediment is eventually compressed into rock and can be geologically dated with considerable accuracy. Thus, the researchers suggest, the 3.3-billion-year age of the South African rock layers in which the striking change in carbon ratios is recorded may well indicate the time...