(CLASS - 7th) CHAPTER - 3 The Surface and Interior of the Earth (Questions and the Answers)
1.What is the special feature of sedimentary rocks ?
This type of rocks are layered and therefore, are also called stratified rocks.
2. How are metamorphic rocks formed ?
Rocks which originally are igneous or sedimentary in nature, get changed in character and appearance due to the heat and pressure.
3. What is lava ?
The temperature inside the earth converts the solid rock into molten state. Sometime the hot material called the lava comes out through cracks or joints.
4. Why are igneous rocks called the primary rocks ?
The igneous rocks are also called primary rocks as they were formed first over the earths surface from molten material that come out from earth surface from the lava.
5. What are sediments ?
The igneous rocks are subjected to weathering and denudation over the years by the agents of gradation. The continuous action of the agents on rocks breaks them into small rock pieces that are carried by rivers. They are then deposited on the river beds or sea beds.These deposits are called Sediments.
E
1. Differentiate between the P-wave and the S-Wave.
P-Wave - They can travel through both solid and liquid mediums.
They are faster in speed.
S-Wave - They can pass through only a solid medium.
They are slower in speed.
2. Write two characteristics of each of the following.
a) Crust - The thin solid layer covering the outside of the earth is called the trust. The thickness of the crust differs from place to place. It is thicker under the continents than on the ocean floor.
b) Mantle - Beneath the crust is very thick layer of rocks called the Mantle. The mantle extends upto 2900 km in depth . The entire mantle is not homogenous. The mantle is sub-divided into two parts namely, the upper mantle and the lower mantle.
c) Core - The innermost part of the earth is known Core. The core has a thickness of 3470 km. It is further divided into inner core and outer core. The core of the earth is rich in iron and nickel (NIFE).
3. What are fossils fuels ? Name any two fossil fuels and specify their importance.
The remains of animals and plants gets buried and trapped under the layers and over a period of time get converted into coal, oil and natural gas. That is why , they are called fossil fuels.
The fossil fuels have a great economic importance all over the world as they are a major source of energy.
4. Why is the knowledge of the earth's interior based on indirect observation ?
We know little about it because deep down, the temperature is very high . We have been dig as deep as 3.5 km below the earth's surface. Therefore our knowledge is based on indirect observations like
The behaviour of seismic waves or earthquakes.
The occurrence of Volcanoes.
5. What are minerals ? On what basis can the minerals be identified ? Give examples.
Minerals are solid inorganic substance of natural occurrence. Minerals are identified on the basis of their colour , hardness and lustre
Example: Limestone - white in colour:
Diamond - hardest
Marble - Lustress
This type of rocks are layered and therefore, are also called stratified rocks.
2. How are metamorphic rocks formed ?
Rocks which originally are igneous or sedimentary in nature, get changed in character and appearance due to the heat and pressure.
3. What is lava ?
The temperature inside the earth converts the solid rock into molten state. Sometime the hot material called the lava comes out through cracks or joints.
4. Why are igneous rocks called the primary rocks ?
The igneous rocks are also called primary rocks as they were formed first over the earths surface from molten material that come out from earth surface from the lava.
5. What are sediments ?
The igneous rocks are subjected to weathering and denudation over the years by the agents of gradation. The continuous action of the agents on rocks breaks them into small rock pieces that are carried by rivers. They are then deposited on the river beds or sea beds.These deposits are called Sediments.
E
1. Differentiate between the P-wave and the S-Wave.
P-Wave - They can travel through both solid and liquid mediums.
They are faster in speed.
S-Wave - They can pass through only a solid medium.
They are slower in speed.
2. Write two characteristics of each of the following.
a) Crust - The thin solid layer covering the outside of the earth is called the trust. The thickness of the crust differs from place to place. It is thicker under the continents than on the ocean floor.
b) Mantle - Beneath the crust is very thick layer of rocks called the Mantle. The mantle extends upto 2900 km in depth . The entire mantle is not homogenous. The mantle is sub-divided into two parts namely, the upper mantle and the lower mantle.
c) Core - The innermost part of the earth is known Core. The core has a thickness of 3470 km. It is further divided into inner core and outer core. The core of the earth is rich in iron and nickel (NIFE).
3. What are fossils fuels ? Name any two fossil fuels and specify their importance.
The remains of animals and plants gets buried and trapped under the layers and over a period of time get converted into coal, oil and natural gas. That is why , they are called fossil fuels.
The fossil fuels have a great economic importance all over the world as they are a major source of energy.
4. Why is the knowledge of the earth's interior based on indirect observation ?
We know little about it because deep down, the temperature is very high . We have been dig as deep as 3.5 km below the earth's surface. Therefore our knowledge is based on indirect observations like
The behaviour of seismic waves or earthquakes.
The occurrence of Volcanoes.
5. What are minerals ? On what basis can the minerals be identified ? Give examples.
Minerals are solid inorganic substance of natural occurrence. Minerals are identified on the basis of their colour , hardness and lustre
Example: Limestone - white in colour:
Diamond - hardest
Marble - Lustress
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