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Unit 8 The Earth (8.4 Sedimentary rocks - solid rock formed when…

- - - - as it slowly decays and dissolves , minerals seep in and gradually replace the tissues - happens over a millions of years
        
        the minerals become rocks in the shape of the organism
        
        mud around the shape also turns into rock. a fossil has been formed
- - - - Mineral ==> made up of one chemical substance
    - - 3 minerals with large crystals
        
        quartz
        
        glassy crystals
        
        mica
        
        small black crystals
        
        feldspar
        
        pink and white crystls
  - - - bacteria and fungi break down dead plant and animal materials
    - - small particles
        
        clay
        
        clay soils have lots of tiny clay particles
        
        therefore only TINY AIR SPACES between particles
      - large particles
        
        sand
        
        sandy soils have lots of large sand particles
        
        therefore lots of BIG AIR SPACES between particles
    - - some plants prefer a particular kind of soil
- - - - therefore forming diff kinds of rocks when become solid
  - - - magma cooling deep underground ==> cools very slowly, because it is also surrounded by hot rock
        
        slow cooling allows time for large crystals to form
        
        example - granite
      - magma cooling closer to surface , through cracks in rocks ==> it cools at medium speed ==with exposure to the air
        
        fast cooling does not allow lots of time to form crystals ==> small crystal formation
        
        example - basalt
      - if magma escapes through hole in earth's surface as a liquid ==> cools very quickly
        
        no time for crystals to form at all
        
        example - obsidian
        
        Magma reaching surface of Earth = lava, which erupts from volcanoes
- - - - soil with lots of small sticky clay particles, packed closely together, which hold water and it cannot move
    - - sandy soils with lots of sand particles, bigger spaces between particles and water can drain quickly
- - - - water gets into the cracks and empty spaces in rocks, ==> when water freezers, it expands and causes the cracks to get larger, then when it melts ( temperature rises) , the larger cracks are left. the repeated cycle of freezing and expanding causes rocks to break up.
      - heat of Sun expanding rocks, and cool nigh temperatures making the rocks contract. the repeating cycle also causes rocks to crack
      - strong winds and running water also wear away rocks, and the rocks become smooth from the water running over them or the rocks may be marked by the direction of the wind
    - - the breaking up of rocks causes by living organisms
        
        example a plant growing in a crack in a rock causes damage to the rock
    - - example - acid rain phenomenon
        
        rainwater which is slightly acideic ( from pollution) attacks limestone causing a chemical reaction
        
        calcium carbonate from limestone reacts with acid ==> release CO2 , H2O and a salt. CO2 goes into air and other products washed by rain
        
        since rain is only weak acid, reaction is slight and slow. takes many years to notice changes
- - - - smaller rock fragments carried long way
      - larger rock fragments do not travel such a long distance
      - speed of river determined by how steep slope is and how much water in river
        
        fast flowing river can carry large rocks
        
        slow moving river carry small rock fragments
        
        when slope is less steep, river speed more slow
        
        some rocks which are too heavy settle on bed of river
        
        deposition
        
        build up and form sediments
        
        mud becomes shale +> sand becomes sandstone
        
        builds layers of sediment ==> sedimentary rock
        
        fragments are smoothed by running water
      - small rock fragments carried away while large ones are left behind , pebbles are deposited => deposits sand => fine sand and mud