NOTES ON INTERIOR STRUCTURE OF THE EARTH

 INTERIOR STRUCTURE OF THE EARTH

Sources of Information about the interior of the earth

Question1.
Why is the study of the interior structure of the earth necessary in geography?
Answer:
The earth’s interior structure has a direct impact on the earth’s surface. The study of internal structure of the earth is necessary in geography because the various topographies found on Earth’s surface are the result of geological processes. Occurring inside the earth.

Exogenous processes occurring in the exterior parts of the Earth and endogenous processes occurring in the interior parts bring changes on the Earth’s surface. The terrestrial form is the result of these transformational forces. Human activity and order of life are linked to these forces and landscapes. That is why, studying the interior structure of the Earth is essential.

Question 2.
Describe the sources that provide information about the interior structure of the Earth.
Answer:
Information that we get about the internal structure of the Earth, has two main types of sources:

1. Direct Sources:
Sources from which direct information about the interior structure of the Earth is obtained are called the direct sources. Such as: earth’s rock formation, substances obtained from volcanic eruptions, substances obtained from mining, etc.

2. Indirect Sources:
Sources in which information about the interior structure of the Earth is obtained indirectly are called the indirect sources. Such as: temperature, pressure, density, meteorite, gravity, seismic waves and magnetic fields, etc.

Question3.
Explain the variations of temperature in the context of Earth’s interior.
Answer:
The rate of temperature rise from the surface of the earth to the center is 1° Celsius per 32 meters. Due to the increase in temperature, all the substances under the earth?s interior should be in the molten state, but in fact, this does not happen. Due to increasing pressure with depth, the melting point of the rocks, and the rate of rise in the temperature decreases towards the center of the earth from a certain point beneath the surface. According to this calculation, the temperature in the center of the Earth is more than 2000°C.

Question 4 All the statistics of the Earth’s internal structure are based on indirect sources. How?

Answer:
Humans have no direct means to know the interior structure of the Earth. Human knowledge about the structure of this part is limited to very little depth. Direct knowledge of the structure of the earth can be found only by oil wells, mines to the depth of only 3 to 4 km in most places. It is very minuscule compared to the depth of the center of the Earth (about 6371 km).

By mining activity, we learn that as the depth of the Earth’s surface increases, the temperature and pressure also increase. According to an estimate, the temperature of the inner part of the Earth is approximately 2000°C. Due to such high temperature, it is completely impossible to obtain direct knowledge of the earth’s internal structure.

Therefore, direct study of the interior structure of the Earth is beyond the human capability. With this reason, for obtaining information about the interior part of the earth, man is dependent on indirect sources, like earthquakes, seismic waves, temperature, pressure, meteorites and gravity.

COMPOSITION AND DENSITY OF THE EARTH

The upper layer of the Earth’s crust is called lithosphere. It has 2 parts – upper part is granitic rocks and forms the continents. Its main constituent is Silica and Aluminum and is also called SiAl. It has a density of 2.7. The lower part is denser and is called SiMa [Silica, iron, magnesium]. As the SiAl is lighter than SiMa the continents are said to be floating on denser SiMa. The thickness of the crust is about 30 miles.

         Below the crust is the Mantle which is 1800 miles thick. It is made up of dense layer very rich in olivine. The interior of mantle is the core which has radius of 2100 miles. It is called NiFe layer as it is made up of Nickel and Ferrous/iron. The inner part of the core is solid.

 

The Earth has three layers:

a.       Outer layer: Continents [SiAl – Silica + Aluminum] are granite and oceans are basaltic

b.      Mantle and oceanic crust: SiMa; mantle is Olivine. Highly fluidic

c.       Inner layer: Core [NiFe – nickel + ferrous]. Outer core is liquid and inner core is solid.

 

Iron has highest composition in earth and oxygen has highest composition in Earth's crust. Continental crust is light and oceanic is heavy.

·         Due to increase in pressure and presence of heavier materials like Nickel and Iron towards the centre, the density of earth’s layers also gets on increasing towards the centre.

·         The average density of the layers gets on increasing from crust to core and it is nearly 14.5g/cm3 at the very centre

 

Explain the model of Suess in relation to the internal structure of the Earth.

Answer:
According to the classification of the inner structure of the earth by suess, the upper part of the crust is made up of Earth’s sedimanentary rocks. Under this part, Suess has divided the crust internal state of the earth mainly on the basis of the chemical composition.

1.Sial:
According to Suess, it is the uppermost layer of the Earth in which the substances called silica and aluminum are obtained. Therefore this layer is called Sial (Si + al = Sial). The average density of this layer is 2.9 grams per cubic cm. The average depth of this layer is 50 – 300 km. In this layer, the acid content is prominent. It contains rocky stones, basaltic rocks, granite rocks, etc.

2.Sima:
According to Suess, it is the intermediate layer of the Earth, which has the dominance of silica and magnesium. Therefore this layer is called the sima (Si + ma = Sima). The density of this layer is 2.9 – 4.7 grams per cubic cm. The depth of this layer is found to be 1000 – 2000 km. Its composition is from Basalt and Gebro rocks. It has a dominance of alkaline nature in it. Lava comes out of this layer during volcanic eruption.

3.Nife:
According to Suess, it is the innermost layer of the Earth. Nickel and ferrum are present in its formation, so this layer is called (Ni + fe = Nife). The density of this layer is 11 grams per cubic cm. This layer extends from the deepest end of the sima to the earth’s centre. This is the densest layer. The properties of magnetic power exist in it. This classification of Earth presented by Suess is depicted in Fig. 4.2.

 

Interior structure of the Earth/

 

Introduction: Core, mantle, and crust are divisions based on composition. The crust makes up less than 1 percent of Earth by mass, consisting of oceanic crust and continental crust is often more felsic rock. The mantle is hot and represents about 68 percent of Earth’s mass. Finally, the core is mostly iron metal. The core makes up about 31% of the Earth. Lithosphere and asthenosphere are divisions based on mechanical properties. The lithosphere is composed of both the crust and the portion of the upper mantle that behaves as a brittle, rigid solid. The asthenosphere is partially molten upper mantle material that behaves plastically and can flow.

 

Explain the interior structure of the earth based on the evidence of seismology.

Answer:

Seismology is the science in which earthquake waves are studied by marking the seismograph. The nature of these waves, their paths and directions are different. The variations in transmission and speed of these waves can be considered as the basis for knowing the internal structure of the Earth. On this basis, the internal structure of the earth is divided into the following parts:

1. The crust:

It is the topmost layer of the earth. Its average thickness is 30 km. This layer is made of heavy rocks and its density is 3 grams per cubic cm. The thickness of this crust is approximately 30 km on the continents. Under the mountainous parts, it has more depth. It is divided into two parts – 1. Internal crust 2. External crust. In this layer of earth, the prominence of a rock called granite is found. P and S waves are transmitted in this layer, which proves that this layer is made of rocks.

 

2. The mantle or substratum:

This layer extends to a depth of 2,900 km below the crust. The upper part of the mantle is known as the Astheno Sphere. This part is the main source of lava that reaches the surface of the volcano during its eruption. S waves vanish after the depth of 2,900 km, that is, it is made from unrecognized concrete tiles. In this layer, the waves called P and S have been observed by Gonrad Sir. This layer gives the primacy of basalt rocks. The part between crust and mantle is called Moho – discontinuity,

 

3. The Core:

The deepest part of the earth from 2900 km to 6371 km. is the most innermost part of the Earth whose average density is 11 grams per cubic cm. In this part, S waves cannot reach. In this layer, there are two parts –

 1. External Core

2. Internal Core.

The first part is in the liquid state, which extends from 2900 km to the depth of 5150 km. The boundary between the inelastic mantle and the core is called the Gutenberg discontinuity zone.

 

The inner core is a dense part which extends from 5150 km to 6371 km. The highest density in this part of the earth is 11 grams per cubic cm. It is made of highly rigid metallic content. These layers classified on the basis of earthquake science are depicted through the following diagrams.

RBSE Solutions for Class 11 Physical Geography Chapter 4 Interior of the Earth img-4

 

Describe the speed, nature and transmission of seismic waves in knowing Internal structure of the Earth.
Answer:
Transmission of seismic waves:
Seismic waves are the route taken by the tremor of the earthquake during the its occurrence. These waves are of three types. Primary, secondary and surface waves. Based oh the seams and motion of seismic waves, the information about the inner parts of the Earth is found. These waves move straight in the same density part.

But by marking these waves on the earthquake centers, it came to be known that these waves do not move in a straight direction but reflect the shape of the curved path. It proves that the density of the inner parts gets varied. As a result, their path also turns curved. Since the density towards the internal part increases, these waves (P and S) in the core become concave towards tjie surface.

S waves do not pass through liquid and they become extinct at more than 2900 km depth. It proves that the depth more than 2900 km is in a liquid state, which is broad around the center. With varying density of rocks, there is more difference in the speed of the waves at three places.

This motion of seismic waves and the variations found in them are depicted through the following picture:

Question 1.
Explain the opinion of Vander Gracht about the Interior of the Earth.
Answer:
Among the people who have made representations about the interior structure of the Earth, the prominent place is of Vander Gracht. Vander Gracht has described four layers in the interior structure of the earth. The details of these layers are as follows:

1.   Outer silica crust

2.   Inner silicate layer and mantle

3.   Zone of mixed metals and Silicate

4.   Metallic Nucleus

1. Outer silica crust:
The thickness of this layer varies at different locations. The thickness of this layer is 60 kilometers below the continents, 20 kilometers below the Atlantic Ocean and 10 kilometers below the Pacific Ocean. The density of this layer ranges from 2.75 to 3.1. This layer is made of silica, aluminum, potassium and sodium.

2. Inner silicate layer and mantle:
The thickness of this layer is 60 to 1200 kms. The density of this layer ranges from 3.1 to 4.75. This layer is made of silica, magnesium and calcium.

3. Zone of mixed metals and Silicate:
The thickness of this layer ranges from 1200 to 2900 kms. The density of this layer ranges from 4.75 to 7.8. This layer is made from the mixture of nickel, iron, silica, magnesium, etc.

MCQ

Question 1.

The constituent elements of the Sial layer are:

(a) Silica – magnesium

(b) Sodium – aluminum

(c) Silica – aluminum

(d) Silica – iron

Answer:

(c) Silica – aluminum

Question 2.

According to Vander Gracht, the maximum depth of the layer above is:

(a) 1,200 km

(b) 60 km

(c) 2,900 km

(d) 200 km

Answer:

(b) 60 km

Question 3.

The statement that is wrong in the perspective of the classification of Suess is:

(a) The density of the upper layer is 2.7

(b) The density of the boundary is lesser than 4.7

(c) Negative properties are found in Nife

(d) Sial is floating on Nife

Answer:

(d) Sial is floating on Nife

Question 4.

Interior of the Earth was divided into the form of Sial, Sima and Nife.

(a) By Van der Gracht

(b) By Dely

(c) By Homes

(d) By Suess

Answer:

(d) By Suess

 

Question 5.

Which of the following is the direct source of knowledge of interior of the Earth?

(a) Seismic waves

(b) Gravitational force

(c) Volcano

(d) Magnetism of the Earth

Answer:

(c) Volcano