Download - Rocks and Weathering
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Rocks and Weathering
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Which mountain range is older?
The Sierras are rocky and steep, higher than the Appalachians.
The Appalachians are more rounded and gently sloping, and are covered with soil and plants.
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Which mountain range is older?
The Sierras formed within the last 10 to 20 million years ago.
The Appalachians formed more than 250 million years ago.
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Q: How can you tell that the Sierra Nevadas formed much more recently than the Appalachians?
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How is Earth's surface shaped?
1. Weathering- the process that breaks down rock and other substances at Earth's surface.
2. Erosion- the transportation of sediment by wind, water, ice, or gravity.
weathering vs. erosion video
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Q: What is the difference between weathering and erosion?
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The principle of uniformitarianism
-an assumption that the same processes that operate today operated in the past.
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Two Types of Weathering
Mechanical-When rock is
physically broken into smaller pieces.
Keep the same chemical composition.
Chemical-The process that
breaks down rock through chemical changes.
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Is this the cause of mechanical or chemical weathering?
Plant growth
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Is this the cause of mechanical or chemical weathering?
oxidation
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Is this the cause of mechanical or chemical weathering?
weak acid from plant roots or lichens
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Is this the cause of mechanical or chemical weathering?
freezing and thawing
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Ice wedging1st - water seeps into cracks of rocks2nd- water freezes 3rd - water expands when it freezes and
breaks rock
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Is this the cause of mechanical or chemical weathering?
pressure release
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The causes of mechanical weathering
• freezing and thawing• release of pressure• plant growth• actions of animals• abrasion
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The causes of chemical weathering
• water dissolves minerals• oxygen combines with iron in the presence
of water forms rust (oxidation)• carbon dioxide dissolves in water to form
carbonic acid• living organisms- root tips and lichens can
form weak acid• acid rain is formed when pollutants combine
with water vapor
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What determines how fast weathering occurs?
• surface area• type of rock• climate
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Increasing the surface area of rock increases the rate of a chemical reaction
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Q. Which type of stone weathers faster?
granite
marble - dissolves in acid, and is more permeable
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Climate
Weathering is faster in hot and wet climate.