1. Answer the following questions.
(i) What are the three layers of the earth?
Ans. Crust, mantle, core
(ii) What is a rock?
Ans. Any natural mass of mineral matter that makes up the earth’s crust is called rock.
(iii) Name three types of rocks.
Ans. There are three types of rocks :-
- Igneous rock.
- Sedimentary rock.
- Metamorphic rock.
(iv) How are extrusive and intrusive rocks formed?
Ans. Extrusive rocks are formed due to rapid cooling and solidification of molten magma on the earth’s surface. Intrusive rocks are formed when molten magma cools down deep inside the earth’s crust.
(v) What do you mean by a rock cycle?
Ans. The change of one type of rock into another type under certain conditions in a cyclic manner is called a rock cycle.
(vi) What are the uses of rocks?
Ans. Following are some uses of rocks:
- They are used as fuels.
- They are used in industries.
- They are used in medicines.
- They are used in fertilizers.
(vii) What are metamorphic rocks?
Ans. The types of rocks formed when igneous and sedimentary rocks undergo heat and pressure are called metamorphic rocks.
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.
Has definite chemical composition.
Used for roads and buildings.
Change into slate.
Made of silicon and alumina.
4. Give reasons.
(i) We cannot go to the center of the earth.
Ans. The radius of the earth is more than 6000 km. to reach the center of the earth, we have to dig a hole to this depth,which is impossible. Plus it is very hot inside the earth because of the existence of magma.
(ii) Sedimentary rocks are formed from sediments.
Ans. Rocks breakdown into small fragments under various conditions. These fragments are called sediments, they are transported by wind ice and water. Layers of sediments are formed when loose sediments are compressed and hardened. These layers of sediments thus form sedimentary rocks.
(iii) Limestone is changed into marble.
Ans. Igneous and sedimentary rocks change their form under great pressure and temperature conditions to form metaphoric rocks. the same thing happens with limestone,which under the effect of heat and pressure change into marble, which is an example of metamorphic rocks.