Exercise - Question:
Que: Answer the following questions briefly.
- What are the three layers of the earth?
- What is a rock?
- Name three types of rocks.
- How are extrusive and intrusive rocks formed?
- What do you mean by a rock - cycle?
- What are the uses of rocks?
- What are metamorphic rocks?
Ans:
1. Three Layers of the Earth
- Crust
- Mantle
- Core
2. Rock
- A mess of mineral matter that makes up the crust of the earth is called rock.
- Aggregates of minerals are termed as rocks. Examples: See part
3. Three Types of Rocks
- Igneous Rocks
- Sedimentary Rocks
- Metamorphic Rocks
4. Formation of Extrusive and Intrusive Rocks
- Due to extreme heat in the interior of the earth, rocks are found in the form of molten material called magma.
- When magma comes out on the surface of the earth, it cools down and turns into soild rocks, Such rocks are termed as extrusive rocks.
Examples: Basalt, Deccan Trap is built of basalt.
- When the molten magma cools down within the interior of the earth, it becomes soild to form intrusive rocks.
Examples: Granite, Gabro.
5. Rock Cycle
Igneous rocks change into sedimentary rocks, igneous and sedimentary rocks under heat pressure change into metamorphic rocks, metamorphic rocks into igneous rocks or sedimentary rocks due to melting or wearing down. This process id called the rock cycle.
6. Uses of Rocks
- Hard rocks are used in making buildings and barrages.
- Houses and buildings are built of rocks (stones, slates, granite, marble).
- Stone are used in numerous games:
- Seven stone (phitthoo).
- Hopscotch ( stapu, kit).
- Five stones (gitti).
- Rocks (stones and slates) are used in building bridges, embankments.
7. Metamorphic Rocks
- When under heat and pressure igneous rocks and sedimentary rocks change their form and more precious rocks are formed to be known as metamorphic rocks.
Examples:
1. Granite into granite gneiss
2. Coal into slate
3. Slate into schist
4. Limestone into marble
Que: 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 example of
(a) Rocks
(b) Minerals
(c) Fossils
(iv) Rocks which contain fossils are
(a) sedimentary rocks
(b) Metamorphic rocks
(c) Igneons rocks
(v) The thinnest layer of the earth is
(a) Crust
(b) Mantle
(c) Core
Ans:
(i) - (a)
(ii) - (b)
(iii) - (b)
(iv) - (a)
(v) - (a)
Que: Match the skill:
(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
Ans:
(i) - (e)
(ii) - (d)
(iii) - (b)
(iv) - (f)
(v) - (c)
Que: Give reasons:
1. We cannot go to the centre of the earth.
2. Sedimentary rocks are formed from sediments.
3. Limestone is changed into marble.
Ans:
1. We cannot go to the centre of the earth because of the following reasons:
- The thickness (from crust to the core) is 6371 Km. (Radius of the earth).
- Themperature increases with depth @ 1o C per 32 metre.
- There is extreme heat and pressure of overlying rocks, everthing is in a molten state.
- There is no oxygen to survive.
2. Sedimentary rocks are formed from sediments because of the following reasons:
- Igneous rocks and metamorphic rocks, decompose, disintegrate and wear down due to weathering.
- This material is carried away by running water (rivers), wind, glacier.
- The material is then deposited in low lying areas and is called sediments.
- When sediments are solidified into layers due to pressure from overlying sediments they are called sedimentary rocks.
3. Limestone is changed into marble due to the following reasons:
- The overlying layers of rocks put pressure on the underlying rocks.
- From the surface to the interior of the earth, temperature and heat go on increasing.
- Due to pressure and heat, the original limestone changes into marble.
