Smart Notes on world geography (Physical) part - 2

Today we have discussed about earth’s interior and the sources which provide knowledge about the interior

Its most important topic to clear your basic knowledge.

From tomorrow get ready for highly conceptual topics of geomorphology

Earth’s Interior

Introduction -

1.       The earth is the only known planet where life is possible

2.       Earth is spherical in shape, hot water and molten lava eject out from earth’s interior

3.       World’s deepest mining is limited only to the depth of less than 5 km as the temperature below earth is very high.

4.       The interior of the earth –

5.       Because of huge size and changing nature of its internal composition, its not possible to make direct observation.

6.       We have limited information of earth’s interior, through mining and drilling operation , its so hot that it can even melt any tool for drilling.

Structure –

1.       The innermost layer surrounding the earth surface is called core.

2.       Core is the densest layer of the earth with its density more than 11.0.

3.       It is composed mainly of iron and nickel thus known as Nife.

4.       Core consist of two sub layers, the inner one is solid (C₂) and the outer one is semi liquid (C₁)

5.       The layer surrounding the core is mantle, is composed of basic silicates.

6.       Major constituent of mantle are magnesium and silicon, hence it’s also known as Sima (Silica+Magnesium).

7.       Its density varies from 3.1 to 5.1 and surrounded by the outermost layer of the earth, known as lithosphere and its density varies from 2.75 to 2.90.

8.       Major constituent elements of lithosphere are silica (Si) and aluminium (Al), it is also known as Sial.

9.       The outermost part of lithosphere is known as crust.

The sources which provide knowledge about the interior of the earth may be classified into

1.       Artificial sources

2.       Natural sources

3.       Evidence from the theories of the origin of earth

Artificial sources to understand Interior of the earth

We can know about the interior of the earth with the help of following sources

·         Temperature

·         Pressure

·         Density

Temperature

1.       It increases with the depth, as observed in the mines and deep wells

2.       The molten lava erupted from the earth’s interior also support this fact.

3.       It’s not uniform from the surface towards the earth’s centre, in beginning its increases at an average rate of 1 degree Celsius for every 32 meters increase in depth.

4.       With such a speed it will be 300 degree celcius at a depth of 10 km, and 1200 degree celcius at 40 km.

5.       But its interior is not in molten state, because rocks buried under the pressure of several km thicknesses of overlying rocks melt at higher temperature

6.       Than similar rock on the surface, a basaltic lava rock which will melt at 1250 degree celcius at surface, will take 1400 degree celcius at 32 km of depth.

So from where we get extra heat –

It is being produced by radioactivity, as the result of breakdown of atomic nuclei of minerals emitting radiant energy from in the form of heat from the rocks.

Pressure

1.       It also increases from the surface towards the centre of the earth due to huge weight of overlying rocks.

2.       In deeper portion pressure is tremendously high, its 3 to 4 million times near centre as compared with the pressure of atmosphere at sea level.

3.       Due to high pressure the molten material beneath earth acquires the property of a solid and is probably in plastic state.

Density

1.       It increases due to increase in pressure and presence of heavier materials towards the earth’s centre

2.       The outermost layer is composed of sedimentary rock; thickness varies from (0.8km to 1.6 km)

3.       The second layer is of crystalline rocks, the density of which ranges from 3.0 to 3.5 at different places.

4.       The average density of earth is about 5.5, so without doubt we can say that it will be more than 5.5 at the core.

Natural sources to understand Interior of the earth

We can know about the interior of the earth with the help of following sources

·         Vulcanicity

·         Seismology (EQ waves)

Vulcanicity

1.       On the basis of upwelling of and spread of hot and liquid lava on the earth surface during volcanic eruption, we can say that there is such a layer which is in liquid state.

2.       Such molten chamber has been termed as magma chamber which supplies magma and lava during volcanic eruptions.

Seismology (Earth quake waves)

1.       The place of the occurrence of earth quake is called focus, and place which experiences the seismic evens first called epicentre.

2.       It is located on the earth’s surface and is always perpendicular to the focus.

3.       The focus is always inside the earth, the deepest focus has been measured at the depth of 700km from the earth’s surface.

4.       There are three broad categories of seismic waves

Primary waves –

1.       Longitudinal or compressional waves or P waves, are analogous to sound waves, particles move both to and fro from the line of the propagation of the ray.

2.       It travels with fastest speed through solid materials.

Secondary waves –

1.       Also called transverse waves or distortional wave or simply S waves.

2.       These are analogous to water ripples or light waves, wherein the particles move at right angles to the rays.

3.       It cannot pass through liquid materials

Surface waves –

1.       Also called long period waves or simply L waves. These waves generally affects surface of earth and die out at smaller depth.

2.       This wave covers longest distances of all the seismic waves.

3.       Their speed is slower than P and S waves but these are most violent and destructive.

How seismic waves are helpful in determining the earth’s interior

1.       So we can say that the nature and properties of the composition of the interior of the earth may be successfully obtained on the basis of the study of these waves.

2.       The main aspects such as velocity and travel paths of these waves passing through a homogeneous solid body.

3.       But these waves reflect or refract while passing through a body having heterogeneous composition

4.       In reality the recorded seismic waves denote the fact that these waves seldom follow the straight line paths.

5.       Thus it become clear that earth is not made of homogenous materials rather there is variation of density inside the earth

Evidence from the theories of the origin of earth

Several attempts to explain the origin and evolution of the continent and ocean basin have been registered, the scientifically recognized are

1.       Planetesimal hypothesis

2.       Tidal hypothesis

3.       Nebular hypothesis

Planetesimal hypothesis

1.       The earth was originated due to accretion and aggregation of solid dust particles.

2.       Based on this corollary the core of the earth should in a solid state

Tidal hypothesis       

1.       The core of the earth should be in liquid state.

2.       According to this the earth have been formed from the tidal material ejected from the primitive sun

Nebular hypothesis

1.       It was coined by Laplace, and according to this theory the core of the earth should be in the gaseous state.

But from the above discussion we have already proved that these hypothesis have no place in current scenario, and now we have solid evidence to prove earth’s origin.
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