The earth is said to be constituted of the same materials as the meteorites. The scientists have come to know about the materials that constitue the interior of earth from the molten material thrown up by the volcanoes. Let us learn about the structure of earth. It is easy to study what is on the surface of the earth but what do we know about the inside part of the earth?
On the basis of the study of physical property of the Earth�s surface, behavior patterns of seismic waves of earthquakes and the lava erupted from volcanoes, it is believed that the Earth is composed of three parts �
� Crust
� Mantle
� Core
Structure Of The Earth: Core
It lies at the centre part of the earth which is the most inaccessible. It is the densest part of the earth. It is also divided into outer and inner core. Do you know the other name for �core�? It is also called barosphere. As it occupies the centre of the earth this layer is also called centrospheres. The entire core is about 7000 km in diameter. It is further divided into
(i) Outer core
(ii) Inner core
The temperature ranges from about 4400oC to about 6000oC. It is generally believed, that the core is composed of iron (Fe) and nickel (Ni) which is responsible for earth�s magnetism. The magnetic field is oriented towards North and South Poles.
The solid state of the inner core is due to high density and pressure which have compressed the molten rock material. The S-waves disappear in the outer core which suggests it is in a molten state. Now let�s learn about the middle layer of the earth, Mantle.
Structure Of The Earth: Mantle
This layer lies above the core. It is the softest layer. It is approximately 2900 km thick and make up 84 per cent of the earth�s total volume. It is further divided into upper mantle and lower mantle. The lower mantle is hotter and denser than the upper mantle.
At the depth of around 100-410 km, the mantle is partially molten and is known as asthenosphere, whereas lower mantle is solid due to high pressure. Do you know how hot is this layer? The temperature in this layer varies between above 1000oC to around 3700oC.
Structure Of The Earth Questions:
1. Core is also called__________
a. Stratosphere
b. Lithosphere
c. Biosphere
d. Centrosphere
2. Which of the following is NOT one of the inside layers of the earth?
a. Core
b. Mantle
c. Crust
d. Biosphere
3. Which of the following did NOT help in understanding earth�s composition?
a. Physical property of earth�s surface
b. Behaviour pattern of seismic waves
c. Lava erupted from volcanoes
d. The size of the earth
4. The diameter of entire core is _________.
a. 2900 km
b. 1400 km
c. 3500 km
d. 7000 km
5. It is believed that the core is composed of _________.
a. Nickel and Silver
b. Silica and Aluminium
c. Silica and Iron
d. Iron and Nickel
Discontinuity
What are the two important discontinuities?
Gutenberg and Mohorovicic Discontinuity
There are two discontinuities which play an important role in the strcture of the earth. Do you know what are these?
These are
� Gutenberg Discontinuity
� Mohorovicic Discontinuity
What is Gutenberg Discontinuity?
The boundary between the mantle and the core or the mantle core interfare is known as the
Gutenberg Discontinuity.
� It begins at the depth of 2800 km.
� Here an abrupt change is observed in seismic waves. Primary seismic waves (P waves) decreases in velocity while secondary seismic waves (S waves) disapper completely.
What do you understand by these seismic waves?
The waves generated by earthquake or explosion are called seismic waves.
� It is dense probably due to a greater percentage of iron.
Structure Of The Earth: Crust
This layer is also called Lithosphere, but do you know why? Crust is also called Lithosphere because it is a sphere of solid rocks. The word �lithos� is a greek word which means �stone or rocks�. It is the top layer of the earth and contains all known life in the universe.
� This layer has a thickness of 60 km below high mountains and just 5-10 km below the oceans.
� The temperature of the upper part of the oceanic crust is estimated to be 0oC but it gradually increases towards the interior.
As we have learnt about Gutenberg discontinuity, let�s learn about mohorovic discontinuoity.
Mohorovicic Discontinuity
Do you know, who discovered Mohorovicic discontinuity? It was a Yugoslavian scientist Andreaja Mohorovicic, who discovered this discontinuity between the crust and the mantle in 1909. It is also known as �Moho Discontinuity�.
� It forms the boundary between the crust and the mantle.
� Like the crust, it does not exist at a uniform depth. It is found at about 8 km beneath the oceans and about 32 km beneath the continents.
� It has the characterisitics of both the upper layer (the crust) and its bottom layer (the mantle)
Structure Of The Earth Question
1. Gutenberg discontinuity begins at the depth of _______
a. 2000 km
b. 1500 km
c. 2000 km
d. 2800 km
2. The other name of crust is ____________.
a. Centrosphere
b. Barosphere
c. Stratosphere
d. Lithosphere
3. Mohorovicic discontinuity was discovered in ____________.
a. 1990
b. 1999
c. 1919
d. 1909
4. The temperature of the upper part of the oceanic crust is estimated to be ___________
a. -10oC
b. 20oC
c. 10oC
d. 0oC
5. The word �lithos� means __________.
a. Air
b. Lava
c. Iron
d. Rock
Fill in the blanks:
- The densest part of the earth inside part is called core.
- The thickness of the mantle is approximately 2900 km.
- The boundary between the mantle and the core is known as the Gutenberg Discontinuity.
- Crust is 5-10 km below the oceans.
- Mohorovicic Discontinuity is also called Moho Discontinuity.
True or False
- Andreja, discovered the Gutenberg Discontinuity. False
- In core, the temperature ranges from about 4400oC-6000oC.�True
- The mantle make up 50 per cent of the earth�s total volume.�False
- The denseness of Gutenberg Discontinuity is because of the greater percentage of iron. True
- Mantle is the top layer of the earth. False
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