CBSE Class 7 - Geography - CH2 - Inside Our Earth

Inside Our Earth

(Q & A)

Q1: What are the three layers of the earth?

Answer: The three layers of the earth are: crust, mantle and core.

Q2(MCQ): The innermost layer of the earth is

(a) Crust
(b) Core
(c) Mantle

Answer: (b) Core


Q3: How deep one has to dig to reach the centre of the earth?

Answer: 6000 km (appox.)


Q4: What is crust?

Answer: The uppermost layer over the earth’s surface is called the crust.


Q5: What is the depth of the crust?

Answer: Crust is about 35km deep on the continental masses and only 5km on the ocean floors.

Q6: What are the main mineral constituents of the continental mass?

Answer: The main mineral constituents of the continental mass are silica and alumina. It is collectively called sial (si-silica and al-alumina).

Q7: What are the main mineral constituents of ocean crust?

Answer: The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)

Q8(MCQ): The thinnest layer of the earth is

(a) Crust

(b) Mantle

(c) Core

Answer: (a) Crust

Q9: How deep is the mantle?

Answer: About 2900 km

Q10: What are the mineral constituents of rock?

Answer: Silicate

Q11: What is the radius of the core?

Answer: 3500 km

Q12: What are the main mineral constituents of the core?

Answer: The core is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron).

Q13: What is a rock?

Answer: Natural aggregate of minerals that makes up the earth is called ‘rock’.


Q14: Name three types of rock.

Answer: The three types of rocks are:

1. Igneous rock, 
2. Sedimentary rock, 
3. Metamorphic rock.

Q15: How are extrusive and intrusive rocks formed?

Answer: Due to extreme heat in the interior of the earth, rocks are found in the form of molten material known as ‘magma’. Because of any volcanic activity or some other reasons when magma comes on the surface of the earth, it cools down and turns into solid rocks. Such rocks are termed as ‘extrusive rocks’ e.g. Basalt.
When the magma cools down within the interior of the earth, it becomes solid known as ‘intrusive rocks’ e.g. Granite.


Q16: What do you mean by a rock cycle?

Answer:

1. One rock type changes into another rock type under certain natural conditions in a cyclic manner. This process of transformation of the rock from one to another type is called ‘Rock Cycle’. 
2. When the molten magma cools down, it solidifies to become igneous rocks. These igneous rocks are broken down into small particles. 
3. By the actions of various natural agencies like - water, wind, glacier, human activities etc. they are transported and deposited to form sedimentary rocks. 
4. When these igneous and sedimentary rocks are subjected to heat and pressure beneath the earth, they change into metamorphic rocks. 
5. The metamorphic rocks, which are still under great heat and pressure, melt down to form molten magma.

Q17: What are metamorphic rocks?

Answer: When the igneous and sedimentary rocks are subjected to heat and pressure beneath the earth, they change into metamorphic rocks for example,

1. Granite changes into Gneiss.
2. Coal into Slate.
3. Slate into Schist.
4. Limestone into Marble.                    

Q18: What are the uses of rocks?

Answer: Rocks have numerous uses.

1. Hard rocks are used for various construction purposes such as buildings, roads, dams, embankments etc. 
2. From rocks, we get different types of minerals after their benefaction. Some rocks are used as gemstones.

Q19(MCQ):  The rock which is made up of molten magma is

(a)  Igneous
(b)  Sedimentary
(c)  Metamorphic

Answer: (a)  Igneous


Q20(MCQ): Natural Gas, petroleum and coal are examples of

(a)   Rocks
(b)   Minerals
(c)   Fossils

Answer: (c)   Fossils


Q21: Rocks which contain fossils are

(a) Sedimentary rocks
(b) Metamorphic rocks
(c) Igneous rocks
 
Answer: (a) Sedimentary rocks


Q21: What does “plate tectonics” refer to?

Answer: The theory that the earth’s lithosphere is broken into plates which float on top of the mantle. These plates shift, causing earthquakes.