EarthSci_LecturePPT_Ch05_final.pptx

EarthSci_LecturePPT_Ch05_final.pptx - EARTH SCIENCE Stephen...

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5 A Surface Veneer: Sediments and Sedimentary Rocks EARTH SCIENCE EARTH SCIENCE Stephen Marshak Robert Rauber Stephen Marshak Robert Rauber © 2017 by W. W. Norton & Company, Inc.
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Introduction The Mediterranean seafloor Salt and gypsum Clay and shells © 2017 by W. W. Norton & Company, Inc.
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Sediments and Sedimentary Rocks Sediment: loose fragments of rocks or minerals Sedimentary rock: consolidated sediment that has been cemented together © 2017 by W. W. Norton & Company, Inc.
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Weathering: the combination of processes that gradually break up or chemically change and weaken rock exposed to air and water Weathering A statue that shows the effects of weathering. This outcrop shows the contrast between weathered and fresh granite. Note the hammer for scale. The white dashed line is the boundary between weathered and fresh. © 2017 by W. W. Norton & Company, Inc.
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Physical Weathering Cracking and breaking up of rock Joints: natural cracks in rock Wedging Vertical joints break beds of sedimentary rock into blocks that fall to the base of this 100-m-high cliff. Exfoliation joints on this granite hillslope break the rock into onion-like sheets. © 2017 by W. W. Norton & Company, Inc.
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Frost Wedging Occurs when water trapped in joints alternates between freezing and thawing © 2017 by W. W. Norton & Company, Inc.
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Root Wedging Occurs when plant roots grow into a joint and pushes it open Root wedging pushes open a joint, slowly separating a block from the cliff. © 2017 by W. W. Norton & Company, Inc.
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Salt Wedging Salt wedging: growth of salt crystals and pushing apart the surrounding grains Salt wedging led to the disintegration of these gravestones in Whitby, England. © 2017 by W. W. Norton & Company, Inc.
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Chemical Weathering Dissolution: minerals in water break down into ions Dissolution occurs when water molecules pluck ions from grain surfaces. Dissolution along joints intersecting the surface of limestone bedrock in Ireland produced these troughs. © 2017 by W. W. Norton & Company, Inc.
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Chemical Weathering Hydrolysis: Reactions with water break down minerals and form new minerals. Oxidation: reactions of iron-bearing minerals with oxygen (rust) Hydration: when water molecules form bonds within a mineral crystal © 2017 by W. W. Norton & Company, Inc.
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Physical and Chemical Weathering Working Together Chemical weathering weakens rock, so it breaks apart. As this happens, the surface area increases, so chemical weathering happens still faster. Eventually, the rock completely disaggregates to form sediment. Weathering of granite produces quartz sand and clay. © 2017 by W. W. Norton & Company, Inc.
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Differential Weathering Differential weathering: Rocks weather at different rates based on variations in composition or number of joints. Inscriptions on a granite headstone (left) last for centuries, but those on a marble headstone (right) may weather away in decades. These gravestones are in the same cemetery and are about the same age.
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  • Fall '15
  • JudyMcIlrath
  • W. W. Norton

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