Earth's Structure
Solutions for Geography, Class 9, ICSE
Choose The Correct Option
19 questionsAnswer:
the earth is made of same materials.
Answer:
Both A and R are true and R is the correct explanation of A.
Explanation — The name Sial is taken from Silica (Si) and Aluminium (Al). Sima is named after Silica (Si) and Magnesium (Mg). Sial appears to float above Sima because it has lower density than Sima.
Assertion (A): The thickness of the lithosphere is very fragile compared to the nature and composition of the earth.
Reason (R): There are continuous changes in the earth's crust due to forces of nature.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R does not explain 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 — Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A) because the lithosphere, though solid, is thin and constantly affected by natural forces like earthquakes and volcanic activity, leading to its fragile state.
Distinguish Between The Following
3 questionsAnswer:
| Crust | Core |
|---|---|
| The crust is the outermost layer of the earth. | The core is the innermost layer of the earth. |
| Crust is about 60 km thick below high mountains and just 5-10 km below the oceans. | Core is about 7000 km in diameter. |
| Crust has relatively low temperatures. | Core has very high temperature ranging from 4400°C to about 6000°C. |
| Crust is inhabited by living organisms. | Core is uninhabitable. |
Answer:
| Sial | Sima |
|---|---|
| Sial floats on top of Sima. | Sima lies under Sial. |
| Sial has less density. | Sima has more density. |
| Sial is composed of Silica and Aluminium. | Sima is composed of Silica and Magnesium. |
| Sial forms the continents. | Sima makes up the ocean floor. |
Answer:
| Moho Discontinuity | Gutenberg Discontinuity |
|---|---|
| Moho Discontinuity is the boundary between crust and mantle. | Gutenberg Discontinuity is the boundary between mantle and core. |
| It is found at about 8 km beneath the oceans and about 32 km beneath the continents. | It begins at a depth of 2800 km. |
Short Answer Questions
10 questionsAnswer:
The temperature in the core ranges from 4400°C to about 6000°C. Pressure and density increases towards the interior of the earth. The inner core is in solid state due to high pressure and density which compresses the molten rock material. Outer core is in liquid state as there is not enough pressure to keep it in a solid state.
Answer:
The crust of the earth is a sphere of solid rocks. It is only 1% of earth's mass. It is made up of rocks with large content of silicates, feldspar, mica etc.
The crust is divided into two broad divisions- SIAL and SIMA. SIAL is composed of Silica and Aluminium while SIMA is composed of Silica and Magnesium.
Answer:
The three layers of the earth's interior are Core, Mantle and Crust.
The boundaries between the three layers of the earth's interior are:
- Gutenberg Discontinuity — It lies between the mantle and the core.
- Mohorovicic Discontinuity — It lies between the crust and the mantle.
Answer:
Mantle lies below the crust. It makes up 84% of the earth's total volume. Mantle is divided into two parts — the upper mantle and the lower mantle.
Two chief characteristics of mantle are-
- Its average thickness is 2900 km.
- The temperature varies between about 1000°C to around 3700°C.
Answer:
At the Gutenberg Discontinuity, there is an abrupt change in the seismic waves (generated by earthquakes or explosions) that travel through the earth. Primary seismic waves (P waves) decrease in velocity while secondary seismic waves (S waves) disappear completely.
Structured Questions
8 questionsAnswer:
The layers of the interior of the earth are as follows:
1. Crust — It is the topmost layer of the earth. It is made up of rock with large content of silicates, feldspar, mica etc. It also contains silica and aluminium.
2. Mantle — It lies between the crust and core. It can be divided into upper and lower mantle. The upper mantle is solid while the lower mantle is partially molten. It is mainly composed of oxygen, silicon and magnesium.
3. Core — Core is the innermost inaccessible part of the earth. It is mainly composed of Nickel and Iron.
Answer:
The transitional zone between crust and mantle is Moho Discontinuity which is the dividing zone between solid and semi-solid state of rocks due to the increasing temperature as the depth increases. It is found at about 8 km beneath the oceans and about 32 km beneath the continents.
The boundary between mantle and core is known as Gutenberg Discontinuity. it begins at the depth of 2800 km. Below this zone, both density and temperature goes on increasing.
Answer:
(i) Due to enhancing density and pressure the temperature goes on increasing gradually towards inside of the interior of the earth.
(ii) The asthenosphere is in a semi-molten state because of high temperature, pressure and density.
(iii) The inner core of the earth is in a solid state due to high density and pressure.
Answer:
(i) The parts are:
(1) Atmosphere
(2) Crust
(3) Mantle
(4) Core
(5) Ocean
(ii) The states are:
(1) Atmosphere - Gaseous state
(2) Crust - Solid state
(3) Mantle - Semi-molten and solid state
(4) Core - Solid state
(5) Ocean - Liquid state
(iii) Crust is suitable for human habitation due to favourable conditions for survival, i.e. atmosphere for air, lithosphere for settlement due to ideal temperature, hydrosphere for hydrological cycle for providing rainfall and fresh water bodies on the earth and oceans for navigation and trade routes etc.
Answer:
Two chief characteristics of the earth's crust are-
- It is a sphere of solid rocks with a thickness of 60 km below high mountains and just 5-10 km below the oceans.
- It is made up of rocks with large content of silicates, feldspar, mica etc.
Answer:
(i) Nife is so called as Ni stands for Nickel and Fe stands for Iron.
(ii) The core of the earth is the most inaccessible part of the earth because it lies thousands of kilometers deep inside the earth.
(iii) The earth's crust undergoes many changes due to the forces of nature.
Thinking Skills
2 questionsAnswer:
Despite being only one percent of the Earth's mass, the Earth's crust contains a wealth of resources that are essential to human civilization, including:
- Mineral resources such as iron, copper, gold, and silver which are used in a variety of applications ranging from electronics to construction.
- Fossil fuels like coal, oil, and natural gas which are used to generate electricity, heat homes, and fuel transportation.
- Freshwater resources that are essential for human survival.
- Geothermal energy which is used to generate electricity and heat buildings.
Answer:
If the Earth's core were to cool down and the magma inside the Earth were to cool and harden, it would have serious consequences.
- The Earth's magnetic field, generated by the molten iron in the outer core, would weaken or disappear, leaving the surface exposed to harmful cosmic radiation.
- Tectonic activity would halt, which could cause earthquakes and volcanic eruptions to cease. This will impact nutrient recycling. Over time, this could also lead to the formation of a supercontinent, as there would be no mechanism to break apart the continents.
- Geothermal energy availability would be affected.
- The Earth's rotation would slow down, leading to longer days and shorter nights. This would have significant effects on the climate and the seasons.