LYCOS RETRIEVER 
Water: Surface Water
built 270 days ago
Water is a chemical compound and polar molecule, which is liquid under STP conditions. It has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. Water is found almost everywhere on earth and is required by all known life. About 70% of Earth's surface is covered by water.
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Water has many purposes throughout the world, aside from human consumption and purposes related to that. With 70 percent of the earth's surface covered with water, it makes water the most common substance on earth. There are 326 million cubic miles of water on earth. Without water, there could be no life. Every living thing needs water to live, and every living thing is made of at least some water. For example, a chicken is about three-fourths water, and a pineapple is about four-fifths water.
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Water covers 71% of the Earth's surface; the oceans contain 97.2% of the Earth's water. The Antarctic ice sheet, which contains 90% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as clouds, contributing to the Earth's albedo.
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The water begins as rain or snow, is both filtered by and picks up minerals from the geological formations that it passes through. Rain or melted snow simply filters through permeable soil or rock until it is stopped underground by impervious rock, such as clay or granite. Shallow springs emerge at the junction of permeable and impermeable rocks, close to the surface. Mineral waters usually come from much deeper aquifers from which the water rises through fissures under the pressure created by superimposed layers. The very fact that the aquifer is ... sealed off above from ground water maintains purity and unchanging mineral content. This process can take years; in essence, the water matures, like a fine wine.
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Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers and lakes 0.6%. Water moves continually through a cycle of evaporation or transpiration (evapotranspiration), precipitation, and runoff, usually reaching the sea. Winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the precipitation of 107 Tt per year over land. Some water is trapped for varying periods in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land. Clean, fresh water is essential to human and other life.
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The strong hydrogen bonds give water a high cohesiveness and, consequently, surface tension. This is evident when small quantities of water are put onto a nonsoluble surface and the water stays together as drops. This feature is important when water is carried through xylem up stems in plants; the strong intermolecular attractions hold the water column together, and prevent tension caused by transpiration pull. Other liquids with lower surface tension would have a higher tendency to "rip", forming vacuum or air pockets and rendering the xylem vessel inoperative.
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Surface Water