Earth's Structure
Solutions for Geography, Class 9, ICSE
Analytical Questions
2 questionsAnswer:
A is false but R is true.
Explanation — Sial floats on Sima, as Sial is less dense than Sima.
Assertion (A): The Gutenburg discontinuity is situated between Mantle and core.
Reason (R): There is a sudden change in the velocity of earthquake waves between mantle and core.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer:
Both A and R are true and R is the correct explanation of A.
Explanation — The Gutenburg discontinuity is situated between the Mantle and the core. This is the area where some earthquake waves are absorbed or change speed, hence there is sudden change in the velocity of these waves.
Answer The Following Questions
14 questionsAnswer:
It is the layer of silicate rock between the crust and the outer core. The depth of Mantle varies between 35 to 2900 km. It consists of dense and rigid rocks containing magnesium and iron. The Mantle is divided into two parts:
- the Upper Mantle or Asthenosphere
- the Lower Mantle or the Mesosphere
Answer:
The properties of the core of the Earth are:
- It consists of Nickel and Iron with a temperature estimated to be 2700°C.
- The inner core also consists of nickel and iron and is forced into a solid state by increased pressure.
Answer:
The earth's crust consists of two layers - SIAL and SIMA.
The material of the upper or continental part of the earth's crust, characterized by relatively low density is called the SIAL layer.The SIAL layer has predominance of Silica and Aluminium. It is also known as granite layer which floats on SIMA.
The lowest layer of the earth's outer crust that underlies the SIAL is SIMA layer. It consists of Silica and Magnesium and it is also known as basaltic layer.
Answer:
High pressure in the interior of the earth exercises a powerful influence on the temperature and physical state of the earth. The temperature of the earth's interior goes on increasing at the rate of 1°c for every 32 metres. Thus, the temperature increase as we go down(underground).
Answer:
S. No. | Sial | Sima |
---|---|---|
1. | This is the uppermost layer of the earth's crust. | This is below the Sial layer. |
2. | Its thickness is nearly 20 km. | Its average thickness is about 25 to 30 km. |
3. | It is composed of Silica(Si) and Aluminium(Al). | It is composed of Silica(Si) and Magnesium(Mg). |
4. | It is not a continuous layer. It is not found on ocean basin. | It is a continuous layer. |
5. | It is less dense. | It is more dense. |
6. | It is Granite layer. | It is Basaltic layer. |
Choose The Correct Option
12 questionsWhat is the rate of change of temperature inside the earth?
- Temperature decreases at the rate of 1°C for every 32 metres of descent.
- Temperature increases at the rate of 1°C for every 32 metres of descent.
- Temperature remains constant
- Temperature decreases at the rate of 32°C for every 1 metre of descent.
Answer:
Temperature increases at the rate of 1°C for every 32 metres of descent.
Define The Following Terms
4 questionsDiagram
1 questionDistinguish Between The Following Pairs
2 questionsAnswer:
S. No. | Crust | Core |
---|---|---|
1. | The crust is the outermost layer of the earth. | The core is the innermost layer of the earth. |
2. | Crust is about 60 km thick below high mountains and just 5-10 km below the oceans. | Core is about 7000 km in diameter. |
3. | Crust has relatively low temperatures. | Core has very high temperature ranging from 4400°C to about 6000°C. |
4. | Crust is inhabited by living organisms. | Core is uninhabitable. |
Answer:
S. No. | Sial | Sima |
---|---|---|
1. | This is the uppermost layer of the earth's crust. | This is below the Sial layer. |
2. | Its thickness is nearly 20 km. | Its average thickness is about 25 to 30 km. |
3. | It is composed of Silica(Si) and Aluminium(Al). | It is composed of Silica(Si) and Magnesium(mg). |
4. | It is not a continuous layer. It is not found on ocean basin. | It is a continuous layer. |
5. | It is less dense. | It is more dense. |
6. | It is Granite layer. | It is Basaltic layer. |
Give Reasons For The Following
3 questionsAnswer:
The Earth’s core, especially the outer core, is made up of molten iron and nickel. Due to the rotation of the Earth, these liquid metals move and generate electric currents. This movement of electrically charged fluid produces a magnetic field around the Earth.
This phenomenon is called the dynamo effect, and it is the reason why the Earth behaves like a giant magnet, with a North and South Magnetic Pole.
Question On Critical Thinking
2 questionsAnswer:
The temperature inside the Earth increases with depth, about 1°C for every 32 meters. In the mantle region, temperatures can reach around 2200°C. At such high temperatures, rocks melt and exist in a hot, molten state called magma. During volcanic eruptions, this extremely hot magma rises and escapes to the surface, which is why the material that comes out is always hot.
Answer:
The Earth's magnetic field is generated by its core, which is composed mainly of iron and nickel. The movement of molten iron in the outer core creates electric currents, which in turn produce the magnetic field. This magnetic field acts as a shield, protecting our atmosphere from harmful solar winds