Word: sediment
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Dates: during 1970-1979
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...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...
...special problem. Houses that once perched storklike on stilts above the land now sit in the waters of the Gulf of Mexico; the earth beneath them has washed away. Ecologists blame the erosion on dikes built along the Mississippi River which have diverted the flow of sediment that used to replenish beaches eaten away by the Gulf. If the erosion is not stopped, water from the Gulf may soon slice through State Highway 1, leaving 2,500 Grand Isle residents stranded...
...site themselves, Tidwell and his colleagues found two more fossilized palm logs. Near by, in the same geological formation, an oil company discovered ancient palm pollen. Other scientists, highly skeptical of the purported age of these finds, contended that they could easily have been washed down into the older sediment from higher and younger geological formations...