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    Isl-islam mahmoud
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    مُساهمة من طرف Isl-islam mahmoud في 2007-10-26, 7:31 pm

    Step 1: Weathering (Destroying Rock!)













    Rocks are broken apart by two types of weathering.
    By chemical weathering, the minerals in rocks are dissolved into rainwater or changed from one type of mineral into another. Climate is an important factor determining the rate of chemical weathering. Warm, moist environments have more chemical weathering because water is needed for the chemical changes and warmth facilitates the reactions. Not all minerals are susceptible to chemical weathering. Rocks made of the mineral calcite, like limestone and marble, are very likely to dissolve when in contact with weakly acidic rain water. Feldspar and quartz, the most common minerals in the igneous rock granite, have very different levels of resistance to chemical weathering. Quartz doesn’t chemically weather very easily, but feldspar does. It chemically changes into clay minerals over hundreds and thousands of years.
    By physical weathering, rocks are mechanically broken apart into smaller pieces. A variety of agents can be responsible for breaking up rocks including water and wind. Tree and plant roots often push rocks apart, especially when they grow in areas with little topsoil. If water freezes into cracks in a rock it will expand as it freezes, opening the crack even more. Large amounts of ice were responsible for physical weathering of rocks during the last Ice Age. They scraped the surface of vast areas of the land, removing bits of the rocks they moved across. Smaller glaciers continue this process in some areas of the Earth today.
    Silicate minerals that form at high temperatures in Bowen’s series are less stable when they are at the cool Earth’s surface. They will weather away before silicate minerals that formed at lower temperatures.
    Weathered rock fragments are either transported by water or wind, or they become a part of the soil. Soil is formed as rocks are weathered at the surface and combined with organic material like plant and animal remains. There are many different types of soil depending on rock weathering and the amount of organic material available


    Step 2: Erosion and Transport (Sediments on the Move!)















    Sneeze into a pile of dust and the particles fly everywhere. Sneeze into a pile of rocks and they stay put. That’s because they have more mass. You need more force than a sneeze to move those rocks. Wind and water can have enough force to move rocks. Just compare what’s on the bottom of a fast moving river with what’s at the bottom of a calm lake. The fast moving river will carry away the smaller sediments leaving large gravel and even boulders. The calm lake allows even very small sediments carried in the water to settle to the bottom.
    Moving water in rivers and moving air in wind sort particles by size. Larger particles can be carried in a stronger current, like fast moving water. Very small particles like silt and clay settle very slowly and so they only form layers at the bottom of quiet water areas like lakes, swamps, or lagoons.
    The size of the sediments in a clastic sedimentary rock usually relates directly to the energy of the wind or water that they were deposited in. Particles that can sink to the bottom in a fast moving river must be very large and heavy. Smaller particles are carried away. However, in a calm lake, even very small pieces of sediment are able to settle to the bottom.
    Step 3: Deposition (Sediments Settling Down!)













    When water or wind looses energy and slows down, sediment can no longer be carried in it. The particles of sediment fall through the water or air and form a blanket of sediment on the bottom of a river, a lake, ocean, or on the surface of the land. This process is called deposition.
    Settling out of the wind or water depends on the size of the clast. Larger clasts with high mass will settle more quickly than smaller clasts with less mass. Conversely, it takes more energy to move larger clasts through the water or air (a process called entrainment).
    How does deposition happen?
    Try this and find out!




    1. Add a handful or two of sediment to a jar that includes particles of different sizes such as pebbles, sand and mud.
    2. Fill the jar with water and seal the lid on top.
    3. Shake the jar and watch the pebbles and dirt become entrained in the water.
    4. Let the jar sit still for a few minutes. What has been deposited on the bottom of the jar? Are any of the small particles still in the water? (The heaviest items fall out of the water more quickly than the small ones once you stop shaking the jar.)

      Step 4: Lithification (From Pile of Sand to Solid Rock)











      Sediment that has formed, been transported, and deposited, is not a sedimentary rock unless it is all bound together. The process of sediment becoming a rock is called lithification. It can take tens to hundreds of thousands of years.
      The material that holds sedimentary particles together into a rock is called cement. Like the cement that holds bricks together in a wall, the cement in a sedimentary rock holds the bits of sediment together. However, the cement that holds a sedimentary rock together is a bit different because it is made of mineral crystals that form in-between the clasts and holds them together. Mineral crystals form from seawater or groundwater that travels through the empty spaces in-between clasts. The mineral precipitates out of water that contains the necessary chemical ingredients. Minerals like calcite, quartz, and sometimes hematite form the cement in sedimentary rocks.
      Compaction also helps a pile of sediment to become a sedimentary rock. Compaction occurs when a layer of sediment is buried under other, younger layers of sediment, the clasts become squished closely together, filling in some of the porosity
    Done by:ISL
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    abdovolcano
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    مُساهمة من طرف abdovolcano في 2007-11-03, 3:44 pm

    موضوع مهم وجامد جدا
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    mohamed elzhar
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    مُساهمة من طرف mohamed elzhar في 2007-11-19, 2:45 am

    ?ok what's more
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    uno
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    مُساهمة من طرف uno في 2007-11-25, 1:13 am

    well, after lithification, the cycle is repeated and repeatet... etc.
    lol!


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    prof_icy
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    مُساهمة من طرف prof_icy في 2007-11-27, 9:51 pm

    جزاك الله خيرا
    الموضوع فعلا مهم جدا
    يعتبر اساس علم الطبقات
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    Yassin Mohamed
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    مُساهمة من طرف Yassin Mohamed في 2007-11-27, 9:54 pm

    موضوع مهم جدا وياريت تتابع على نفس الموضوع دة بس بتوسع شوية

      الوقت/التاريخ الآن هو 2018-09-21, 8:35 pm