SST Chapter 3 Abhraneel

7/24/2019 SST Chapter 3 Abhraneel

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THE SURFACE AND INTERIOR OF EARTH

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Abhraneel


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earths surface

The surface of the earth constitutes a greatassemblage of physical features.

These are mountains, valleys, plains and plateaus.

The height and depth is measured from a base

line called mean sea level.


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Interior of the earth

The interior of the earth has remained a mystery for allthese years. The intensive heat neither lets us to digdeep nor there is any possibilities of life deep insidethe earth. Our knowledge about Earth is, therefore

based on indirect observations likeThe behaviour of seismic waves or earthquakes.

The occurrence of volcanoes.


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picture


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ayers of the earth

The earths interior is made up of four layers

!rust

"antle

!ore


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The crust


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The crustThe thin solid layer covering the outside of the

earth is called crust. The thickness of crust di#ersfrom place to place. $eneath the sedimentary

rocks of of solid earth, the rocks are rich in sial%silica&aluminium' .(ial is made of lighter rockmaterial and is on an average )* km beneath thecontinents. $eneath the sial lies sima, rocks rich in

silica and magnesium. (ima is made of heavierrock material and is on an average +- km thickbeneath the ocean.


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The mantle


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The mantle$eneath the crust is a very thick layer of rocks

called the mantle. The mantle etends upto /011km in depth. The entire mantle is not

homogenous. The mantle is subdivided into twoparts namely, the upper mantle and the lowermantle. The upper mantle is upto 211 km indepth. $eyond this lies the lower mantle.


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The core


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The coreThe innermost part of the earth is known as core.

The core has a thickness of )+-1 km. It is furtherdivided into inner core and outer core. The core is

rich in iron and nickel.The temperature inside the earth converts the solid

rock into molten state. (ometimes the hotmaterial called lava comes out through cracks or

3oints. 4hen the molten material comes out frombeneath a sea 5oor. On the other hand, the landsurface makes mountains.


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6ock cycle


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The earth 7a treasure of rock

materials8 rock is a naturally occurring solid substance made

up of minerals. 8ll rocks hard. They maybe hardas granite and soft as clay or chalk. 9eologists

have classi:ed the rocks into three large groupson the basis of their formation. These are Igneous,(edimentary and "etamorphic rocks.


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Igneous rocksThe word igneous means;coming out of :re;. Thus,

the igneous rocks are formed due to intensiveheat and pressure where molten material calledmagma comes out and solidi:es over the earths

surface as lava e.g. basalt granite etc.


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(edimentary rocksIgneous rocks are sub3ected to weathering anddenudation over the agents of denudation. Thecontinuous action of these agents on rocks breaks

them into small rocks pieces that are carried byrivers. They are then deposited on the river bedsof sea beds. These deposits are called sedimentswhich form layers, one above the other.


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"etamorphic rocks6ocks which are actually are igneous orsedimentary rocks in nature, get changed incharacter and appearance due to heat and

pressure and are known as metamorphic rocks.=or instance, granite is a igneous rock but due toheat and pressure, it changes into gneiss. Thelimestone is a sedimentary rock but changes into

metamorphic as marble. (imilarly shale may beturned into slate.


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"inerals8 rock has single or a ;combination of severalminerals in addition to mass of the earthmaterial. These minerals are present in small or

large quantities at any given site of the earth. Themost common minerals occurring inside the earthare iron, silver, gold, mica, bauite and lead. Thecommon salt that we use in our food is also a

mineral. Of all the minerals known to us, diamondis the hardest while graphite is the softest."inerals are classi:ed on the basis of their colour,hardness and lustre.

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SST Chapter 3 Abhraneel