In this article we have solved all the questions of second chapter of class 7 social science, inside our earth. Please read the article and get high score in your exam.
1. Answer the following questions.
(i) What are the three layers of the earth?
Answer: The three layers of the earth are Crust, Mantle and Core.
Crust: The uppermost layer over the earth’s surface is called the crust. It is the thinnest of all the layers. It is about 35 km. on the continental masses and only 5 km. on the ocean floors.
Mantle: Just beneath the crust is the mantle which extends up to a depth of 2900 km. below the crust.
Core: The innermost layer is the core with a radius of about 3500 km. It is mainly made up of nickel and iron and is called nife. The central core has very high temperature and pressure.
(ii) What is a rock?
Answer: The earth’s crust is made up of various types of rocks. Any natural mass of mineral matter that makes up the earth’s crust is called a rock. Rocks can be of different colour, size and texture. There are three major types of rocks: igneous rocks, sedimentary rocks and metamorphic rocks.
(iii) Name three types of rocks.
Answer: There are three major types of rocks: igneous rocks, sedimentary rocks and metamorphic rocks.
(iv) How are extrusive and intrusive rocks formed?
Answer: Lava is actually fiery red molten magma coming out from the interior of the earth on its surface. When this molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks. On the other hand, sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks.
(v) What do you mean by a rock cycle?
Answer: 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.
(vi) What are the uses of rocks?
Answer: Rocks are very useful to us. The hard rocks are used for making roads, houses and buildings. We use stones in many games. For example, seven stones (pitthoo), hop scotch (stapu/kit kit), five stones (gitti).
(vii) What are metamorphic rocks?
Answer: Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure (Fig. 2.3). For example, clay changes into slate and limestone into marble.
2. 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
3. Match the following:
(i) Core (a) Earth’s surface
(ii) Minerals (b) Used for roads and buildings
(iii) Rocks (c) Made of silicon and alumina
(iv) Clay (d) Has definite chemical composition
(v) Sial (e) Innermost layer
(f) Changes into slate
(g) Process of transformation of the rock
Answer: (i) – (e), (ii) – (d), (iii) – (b), (iv) – (f), (v) – (c)
(i) Core (e) Innermost layer
(ii) Minerals (d) Has definite chemical composition
(iii) Rocks (b) Used for roads and buildings
(iv) Clay (f) Changes into slate
(v) Sial (c) Made of silicon and alumina
4. Give reasons:
(i) We cannot go to the centre of the earth.
Answer: We can’t go to the centre of the earth because there have no oxygen to survive. Due to High pressure and heat, everything is in the molten state inside the earth.
(ii) Sedimentary rocks are formed from sediments.
Answer: Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks.
(iii) Limestone is changed into marble.
Limestone is a sedimentary rock. When it comes under the extreme heat and pressure limestone gets converted in marble rock which is an example of metamorphic rock.