2.2 Text Questions :
Answer the following question :
(1) What are the three layers of the earth.
Ans: The three layers of the earth are crust, mantle and core.
(2) What is a rock.
Ans: A rock is a natural mass of mineral matter that makes up the earth’s crust.
(3) Name the three types of rocks.
Ans: The three types of rocks are Igneous rocks , sedimentary rocks and metamorphic rocks.
(4) How are extrusive and intrusive rocks formed.
Ans: When the molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. These rocks are called extrusive igneous rocks.
Sometimes the molten lava cools down deep inside the earth’s crust. Solid rocks are formed called intrusive igneous rocks.
(5) What do you mean by a rock cycle.
Ans: One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle.
(6) What are the uses of rocks.
Ans: Hard rocks are used to make roads, houses and buildings. Coal is a type of rock that has numerous uses.
(7) What are metamorphic rocks.
Ans: When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. Eg: clay changes into slate and limestone to marble.
Tick the correct answer:
(i) The rock which is made up of molten magma is _______ .
(a) Igneous √ (b) Sedimentary (c) Metamorphic
(ii) The innermost layer of the earth is ______ .
(a) Crust (b) Core √ (c) Mantle
(iii) Gold, petroleum and coal are examples of ______ .
(a) Rocks (b) Minerals √ (c) Fossils.
(iv) Rocks which contain fossils are __________ .
(a) Sedimentary rocks √ (b) Metamorphic rocks (c) Igneous rocks.
(v) The thinnest layer of the earth is ______ .
(a) Crust √ (b) Mantle (c) Core.
Match the following:
i) Core (a) changes into liquid .
ii) Minerals (b) used for roads and buildings.
iii) Rocks (c) Made of silicon and alumina .
iv) Clay (d) Has a definite chemical composition.
v) Sial (e) Innermost layer.
Answers :
1. Core — (e) Innermost layer.
2. Minerals — (d) has definite chemical composition .
3. Rocks — (b) used for rocks and buildings.
4. Clay — (f) changes into liquid .
5. Sial — (c ) made of silicon and alumina.
Give reasons :
i) We cannot go to the centre of the earth.
ii) Sedimentary rocks are formed from sediments.
iii) Limestone is changed into marble.
Answers:
i) To reach the centre of the earth we will have to dig a hole 6000 km deep on the ocean floor. This is quite impossible so we cannot go to the centre of the earth.
ii) Rocks break down into small fragments known as sediments. These sediments are transported and deposited by wind, water.
These loose sediments are compressed and hardened to form layers of rocks known as sedimentary rocks.
iii) Limestone is changed into marble because igneous and sedimentary rocks change into metamorphic rocks under a great heat and pressure.
Fill in the blanks:
1. The —- is the thinnest of all the layers.
2. —— and ——– are the constituent of the ocean crust.
3. The radius of the core is about ——- km.
4. The earth’s crust is made up of ——.
5. When molten magma cools it becomes —— rocks.
6. —— are remains of dead plants and animals trapped in layers of rocks.
Answers:
1. The crust is the thinnest of all the layers.
2. Silicon and magnesium are the constituents of the ocean crust.
3. The radius of the core is about 3500 .
4. The earth’s crust is made up of Rocks .
5. When molten magma cools it becomes Igneous rocks .
6. Fossils are remains of dead plants and animals trapped in layers of rocks.