NCERT-GEOGRAPHY-CLASS-07-CHAPTER-02

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Concentric layers

 

Layers we found around our earth centre.

   

 

Crust

    

·          This solid is the uppermost portion of the earth.

·          Or we can say the solid uppermost concentric layer of the earth.-

·          The crust has two division

01-  continental and

02-  oceanic.

·          The thickness of the crust is about 35 kilometres on the continental portion and about 5 kilometres on the ocean.

·          The crust is about 1% total mass of the earth.

 

SiAl

·          The continental crust portion is made up of

-          silica, 

-          Aluminium is called siAl.

·          The thickness of the sial is about 35 kilometres.

     

     

 

SiMa

 

·          On the other hand, the oceanic crust is made up of

-          silica

-          magnesium is known as SiMa.

·          The thickness of Sima is about 5 kilometres.

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Mantle

 

·          The structure of the earth, starting from the centre up to the crust, is divided into 3 major portions.

·          The innermost portion is the core while the outermost portion is the crust.

·          The portion in the middle of the core and the crust which is about 2900 km known as mantal.

·          It is the most active portion in the structure of the earth having around 84% total mass of the earth.

·          Mental is made up of pyroclastic material, which has silica and magnesium.

    

Core

 

·          The innermost portion of the earth has around 15% mass of the earth.

    

 

NiFe

 

·          In the structure of the core, the prominent constituent

-          Nickle about 80%, and

-          ferrous about 20%.

·          Cumulatively meaning called NiFe.

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Mineral

 

·          Those naturally occurring inorganic substances have certain physical and definite chemical properties known as minerals.

   

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Rock

      

·          Rock is a kind of mineral.

·          Any natural mass of mineral matter that makes earth's crust known as rock.

 

Magma

      

·          Molten or semi-molten material, which, in its mixture, having

-          molten rocks,

-          gases and

-          water vapour is known as magma.

·          It is formed in the mind the motion of the earth, as, is a product of heat and pressure.

·          The route through which Magma comes on the earth, the surface is known as a vent.

Lava

 

·          When the magma cools down on the crust portion to solidify known as Lava.

     

 

Igneous rocks

 

·          Rocks formed out of cooling down magma in the crust portion of the earth known as igneous rocks.

 

Primary rock

 

·          When we studied the Rock cycle we came to know that igneous rocks are the first to form and without the igneous rocks the Rock cycle couldn't be completed that's why igneous rocks are also known as primary rocks.

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Extrusive igneous rock

 

·          Igneous rocks are formed above the crust surface known as extrusive igneous rocks.

 

Intrusive igneous rock

 

·          Igneous rocks are formed beneath the crust surface then known as intrusive igneous rocks.

 

Sediments

 

·          Igneous rocks, metamorphic rocks, and, even sedimentary rocks under the process of weathering, roll down, crack and hit each other, so, break down into small particles known as sediments.

 

Sedimentary rocks

 

·          When sediments are transported and deposited by the vectors such as

-          running water,

-           wind

-           groundwater

-           river, and

-          glacier, in the presence of moisture, is deposited compressed and hardened form concentric layers of rocks known as sedimentary rocks.

·          Sedimentary rocks are also known as layered rocks.

 

Fossil

 

·          The organic remains of the plant Kingdom and the animal kingdom, which are trapped in the layers of rocks known as fossils.

 

Metamorphic rocks

 

· These sedimentary rocks and igneous rocks under great heat and pressure, through the transformation of chemical structure, transformed into a new type of Rock known as a metamorphic rock.

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Rock cycle

 

·          The rock cycle is a cyclic process in which rock formation and denudation take place simultaneously.

·          In the first stage of the cycle, igneous rocks are formed through magma.

·          Now under the impression of weathering new kind of rock that is sedimentary rocks could be formed or under tremendous heat and pressure igneous rocks could be transformed into metamorphic rocks.

· metamorphic rocks can also be formed through the sedimentary rocks or re-metamorphism of metamorphic rocks.

· sedimentary rocks can be formed out of igneous rocks and metamorphic rocks.

     

 

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