Word: sediments
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Dates: during 1980-1989
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Every summer the ancient Egyptians threw a beautiful virgin into the Nile to propitiate the river god. The Nile was Egypt's lifeblood: its waters renewed the parched land, and its sediment enriched the soil. But at times there was too much water, engulfing fields and villages, or too little, bringing famine and death...
...excavated at the site of what once was a fast-moving stream that flowed into a great salt marsh along the Gulf of Mexico. Bodies of dead animals collected in the water, and the remains sank to the bottom of the stream. As layer after layer of sediment piled up, the stream eventually vanished, but the bones of the fauna were fossilized and preserved...
They are great underground mountains of salt, some of them six miles deep and three miles across. They were formed tens of millions of years ago-some even before the age of the dinosaurs-by the evaporation of ancient saline seas. Layer upon layer of sediment piled atop the dried-up ocean beds. Gradually, columns of the lighter salt were forced upward by the pressure, like putty squeezed through the fingers of a slowly clenching fist. In the U.S. alone, there are more than 500 such salt domes, all of them in or around the Gulf of Mexico...
...effects spread beyond the lakes. In some areas, humans may also be affected. In the Lac la Croix lake system of Ontario, where the Ojibway Indians fish for their livelihood, catches are showing high levels of mercury. Reason: the toxic metal, ordinarily concentrated in sediment, changes into an organic form, methyl mercury, in acid water and is then easily absorbed by the fish. While the threat to plants is not as well understood, acid rain can eat away at leaves, leach nutrients from the soil, interfere with photosynthesis, and affect the nitrogen-fixing capabilities of such plants as peas...