Q 1. Answer the following questions:
(i) What are the three layers of the earth?
ANS- The three layers of the earth are-
- The Crust
- The Mantle
- The Core.
(ii) What is a rock?
ANS- A rock refers to any natural mass of mineral matter that makes up the earth’s crust.
(iii) Name three types of rocks.
(iv) How are extrusive and intrusive rocks formed?
ANS- Both extrusive and intrusive rocks are examples of igneous rocks.
- Extrusive rocks are formed when the molten magma present inside the earth’s interior comes out onto the earth’s surface, cools down and becomes solid. Example, basalt.
- Intrusive rocks are formed when molten magma cools down and solidifies deep inside the earth’s crust. Example-Granite.
(v) What do you mean by a rock cycle?
ANS- The transformation of one type of rock into another, under certain conditions and in a cyclic manner is referred to as the rock cycle.
(vi) What are the uses of rocks?
ANS- Some of the uses of rocks are as follows:
- For building roads, houses and constructing buildings.
- For making jewellery.
- The fossilised remains of plants and animals present in rocks help in scientific research.
(vii) What are metamorphic rocks?
- Metamorphic rocks are the rocks that get formed under great heat and pressure.
- Igneous and sedimentary rocks, when subjected to heat and pressure, get transformed into metamorphic rocks. For example, clay changes to slate and limestone into marble.
Q2. Tick the correct answer.
(i) The rock which is made up of molten magma is
(a) Igneous (b) Sedimentary (c) Metamorphic
ANS- (a) Igneous
(ii) The innermost layer of the earth is
(a) Crust (b) Core (c) Mantle
ANS- (b) Core
(iii) Gold, petroleum and coal are examples of
(a) Rocks (b) Minerals (c) Fossils
ANS- (b) Minerals
(iv) Rocks which contain fossils are-
(a) Sedimentary rocks (b) Metamorphic rocks (c) Igneous rocks
ANS- (a) Sedimentary rocks
(v) The thinnest layer of the earth is
(a) Crust (b) Mantle (c) Core
ANS- (a) Crust
Q 3. Match the following.
(i) Core (e) Innermost layer
(ii) Minerals (d) Has definite chemical composition
(iii) Rocks (b) Used for roads and buildings
(iv) Clay (a) Changes into slate
(v) Sial (c) Made of silicon and alumina
Q4. Give reasons.
(i) We cannot go to the centre of the earth.
- The center of the earth lying about 6000 kms from the ocean floor.
- There is extremely high temperature and pressure.
- There is only molten magma at earth’s center.
- Oxygen is absent there.
- Such conditions do not permit the survival of any living organism. Thus, we cannot go to the centre of the earth.
(ii) Sedimentary rocks are formed from sediments.
- When big rocks break down into small fragments (or sediments).
- The fragments are transported and deposited by factors like water and wind.
- The loose sediments compress and harden over the years to form layers of rocks. These rocks are known as sedimentary rocks.
(iii) Limestone is changed into marble.
- Limestone is an example of a sedimentary rock.
- When it is subjected to conditions of extreme heat and pressure.
- It gets converted into marble, which is a metamorphic rock.