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The Earths Crust.

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Sedimentary Rock Sedimentary rocks are layers of dirt, sand or little pieces of rock that are compressed very tight to form a single rock. Sedimentary rocks are formed somewhere where there is loose bits of sand, dirt or little pieces of rock. It needs an area of pressure where the rock can be compressed, like a very deep ocean which will force the rock down. The dirt falls on the bottom of the sea bed and slowly accumulates layer after layer, while the pressure from the ocean compresses it. Only sedimentary rocks contain fossils. Metamorphic rocks and igneous rocks have been through too much heat to have any fossils left in them. Fossils are very useful to identify the age of the rock, because they can be compared to known ages. Sandstone is an example of sedimentary rock. This is formed from sand and it looks like sand. The rock looks like sand squashed very tightly together. There are two different types red sandstone and yellow sandstone. Limestone is formed from sea shells. Mostly formed with calcium carbonate, which is grey or white coloured. ...read more.


Then again the metamorphic rock can either rise to the surface or descend further where it will become magma. When magma reaches the surface it cools and becomes igneous rock, extrusive rock comes straight out of the volcano, but intrusive rock sets below as a big bump below the surface. When all of the rock reaches the surface, the weathering will begin to gradually wear down the rock and it will be carried of to the sea. The process then starts again at the beginning. Weathering/Water cycle Weathering is the process in which rocks are broken up and worn down. There are three types: Physical weathering which is caused by the ice in the cracks of rocks. This is where rain water floods into the cracks in the rocks, and when the temperature drops below zero the water turns into ice, as the water freezes the expansion pushes the rock apart. This happens repeatidly until the rock is pushed apart enough for a piece to break off. Chemical weathering is caused by acid rain onto limestone. All rain is a very weak acid, so very slowly it will dissolve the limestone. Biological weathering which is caused by plant roots in the cracks of rocks. ...read more.


These magnetic stripes were only discovered in the 1960's. Plate Boundaries. Plate boundaries are between tectonic plates, they're usually trouble like volcanoes and earthquakes there are three different ways that plates interact: Colliding, separating and sliding past each other. Oceanic and continental plates sliding past each other. The oceanic plate is always forced underneath the continental plate. This is called a subduction zone. As the oceanic crust is pushed down it melts and pressure builds up due to all the melting rock. This molten rock finds its way to the surface and volcanoes form. There are also earthquakes as the two plates slowly grind past each other. A deep trench forms on top of the ocean floor where the oceanic plate is being forced down. The continental crust crumples and folds forming mountains at the coast. When two continental plates collide and meet head on. Any sediment layers lying between the two continent masses get squeezed between them. These sediment layers inevitably start crumbling and folding and soon form into big mountains. The Himalayan Mountains are an example of this. Sea floor spreading. When tectonic plates move apart, magma rises up to fill the gap and produces new crust made of basalt. The mid-atalnatic ridge runs the whole length of the atlantic and actually cuts thorugh the middle The Earths Crust Page 1 ...read more.

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