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how do sedimentary rocks form?if you could please explain in simple terms...

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enimsaj1996 | Student, Grade 9 | (Level 3) eNoter

Posted October 27, 2011 at 12:27 PM via web

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how do sedimentary rocks form?

if you could please explain in simple terms how these rocks are formed.

Also, how do features such as rock type and amount of joints affect the way sedimentary landforms change? what are joints and how do they affect the way it changes? (ie. erosion)

 

Thank you! :)

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hellohello14 | Student, Undergraduate | (Level 1) eNoter

Posted October 27, 2011 at 3:18 PM (Answer #1)

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For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

Sedimentary rocks are formed in places where there has been water at one time.  Dead animals, plants, and pieces of rocks or minerals are carried to these places by wind, water, ice, or even gravity.  They are usually dropped off in bodies of water where they sink to the bottom.  Little by little they make layers that build on top of each other.  This puts pressure on the lower layers. So, the weight of all of the layers of rocks, minerals, dead animal skeletons, and plants pushes down the lower layers until they harden into rock.  This takes millions of years to happen. During that time, the ocean, lake, or other body of water dries up.  This makes the sedimentary layer, that used to be under water, become a surface layer.
Each layer of the rock might be different if erosion and weathering drop different things to the bottom of the water for each layer.  This is why you see streaks of different colors or textures in sedimentary rock. 
Scientists can tell how old the rock is by fossils that were trapped there and by studying how the layers formed.  This is how they figure out what it was like in the time of the dinosaurs.  Since sedimentary rock is found where there used to be oceans and seas or other bodies of water, finding it in the desert tells the scientist that there was water there at one time.




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joseph10 | College Teacher | (Level 1) eNoter

Posted October 31, 2011 at 10:36 PM (Answer #2)

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Sedimentary rocks are formed through  different processes over a period of time (millions of years); rocks when exposed to earth surface begins to weather out, that is, breaking down into small pieces due to temperature change or due to the act of erosion through wind or rain.

The small  particles formed are called sediments and are carried away by wind, rainfall or even as a result of gravity and they settles down through a process called deposition according to their sizes. the bigger heavier sediments settles down first while the small particles settles last.

The settled sediments undergoes lithification which is a process of compacting the sediments together and also cementing the sediments by use of dissolved minerals which  fills the gaps between rocks and also acts as the cement thus forming sedimentary rocks.

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