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| Weathering is the beginning of _______ formation. |
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| Most ______ nutrients needed for plant growth are in the topsoil. |
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| Below the layer of topsoil is the ______ layer, which extends down to solid rock. |
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| Soil transported by water is known as sediment, or ______. |
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| Nitrogen-fixing bacteria on legume roots change nitrogen in the air into ______ that green plants can use as fertilizer. |
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| ____________ that is allowed to decay for several months becomes compost. |
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| ___________ is the thin, dark layer on tip of a soil profile consisting of decaying plants and animals. |
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| The _______ of its particles determines how well a topsoil can absorb air and water. |
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| __________ soils, which are a mixture of clay and sandy soils, are the most valuable soils to farmers. |
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| The greatest contribution of ______ to soil fertility is the decomposition of dead organisms. |
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| _______ soil is formed locally,while transported soil is carried by rivers to valleys and coastal regions. |
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| Physical and ___________ weathering causes mountains to disintegrate. |
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| Mosses and ___________ are the pioneers in weathering rocks. |
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| Rocks are chemically weathered by ________, hydration, and acid action. |
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| Iron particles in Dakota red sandstone have united chemically with oxygen and water to form iron _______. |
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| Water that seeps into cracks splits large rocks when it ________. |
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| Tree ______ exerts a force too powerful to resist when they grow into cracks in rocks. |
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| Wind blown __________ helps weather rocks, as shown by the hills and mountains around Durango, Colorado. |
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| Carbonic acid chemically unites with _______ and other calcite formations and causes the stone to crumble. |
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| Exfoliation is the weathering process that makes hills and boulders into ______. |
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| Rain water washes organic _______ acid down to solid rock where it attacks the rock structure and causes it to crumble. |
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| _________ dissolved in water may be redeposited in caves, where it forms stalactites and stalagmites. |
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| Because __________ keeps topsoil in place, it reduces the amount of silt in streams and rivers. |
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| Landslides, mudslides, and creep are examples of _________ erosion. |
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| A method of soil conservation that prevents water erosion of soil is ______ plowing. |
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| To prevent erosion on steep hills, farmers use _________. |
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| the presence of ______________ in the soil and expense are two factors to be considered in planning irrigation projects. |
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| Farmers can prevent wind erosion by ______ cropping. |
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| Crop ________ replaces lost minerals to the soil. |
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| Scratch lines called ________ were caused by glaciers scraping against valley walls. |
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| Frost action on glacier bottoms and sides helped form the _________ valleys characteristic of glacial action. |
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| A _________ stream carries moraine away from the terminus of a glacier and deposits it, layer upon layer, in an out-wash plain. |
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| Hills shaped like upside-down canoes and formed by advancing glaciers are ______. |
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| Glacial formations with rounded boulders were called ______ by the French. |
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| _________ formed when chunks of ice became covered with glacial debris; later the ice melted and formed a basin. |
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| Glaciers are full of gathered matter, or ground __________. |
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| If a ___________ stays in one place for several years, a ridge of deposits called a terminal moraine builds up across its end. |
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| A glacier's ___________ is the point where it melts as fast as it advances. |
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| __________, or glacial cracks, are a constant threat to explorers and scientists who travel the icy wastes of Antarctica or the North Pole. |
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