Very Short Answer Type Question
1. What is called the uppermost layer of the earth? [Imp.]
Answer: It is called the crust.
2. What is the special feature of this layer? {Imp.]
Answer. It is the thinnest of all the layers
3. Name the main mineral constituent of the continental mass.
Answer: Silica and alumina
4. Name the constituents of the oceanic crust. [V. Imp.]
Answer: Silica and magnesium.
5. What is the radius of the core?
Answer: The radius of the core is about 3500 km.
6. What are the main constituents of the core?
Answer: The main constituents of the core are nickel and iron. It is usually known as nife (ni – nickel and fe – ferrous i.e. iron).
7. What is the earth’s crust made of? [V.Imp.]
Answer: It is made up of different types of rocks.
8. What are called igneous rocks?
Answer: When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks.
9. What are fossils?
Answer: The remains of the dead plant and animals trapped in the layers of rocks are called fossils.
10. What happens when igneous and sedimentary rocks go under great heat and pressure?
Answer: They change into metamorphic rocks.
11: Define rock cycle?
Answer: The process of transformation of the rock from one to another is known as rock cycle.
Short Answer Type Questions
1: What are the uses of rocks?
Answer: Rocks are very useful to man, used for making roads, houses and buildings. Rocks are the source of precious metals like gold, silver, and platinum. We use stone in many games. For example, seven stone, top scotch, five stones
2: Define fossil.
Answer: The remains of dead plants and animal beneath the layer of rocks are called fossils.
3: What is mantle?
Answer: It is an intermediate layer lies between the crust and the core of the earth .Its avg thickness is about 29,00 km. It is believed to consist of solid ultra basic rocks, rich in iron and magnesium.
4: What do you know about the core?
Answer: The innermost part of the earth is known as the core. The thickness of whole layer comprising the outer and the inner core is 4671 km. The outer core starts at the depth of 2900 km, rich in iron and nickel.
5: What is the importance of outer crust to us?
Answer: The solidified outer crust of the earth is of great importance to us .This thin crust just like the skin of an apple, forms the stage on which human life and civilization have developed. It has the valuable soil and gives us most of our minerals.
6: What is mineral?
Answer: A mineral is a naturally occurring substance having a definite chemical composition and physical properties.
7: Give example of all the three major forms of rocks?
Answer: Igneous-granite, basalt
Metamorphic rocks- marble, slate, graphite
Sedimentary- limestone, sandstone.
8: What do you know about extrusive and intrusive rocks formed?
Answer: When the molten lava comes on earth’s surface; it rapidly cools down and become solid. Rocks formed in such a way on the crust are called Extrusive igneous rock. Sometimes molten magma cools down deep inside the earth crust, solid rocks so formed are called Intrusive igneous rocks.
9: Define the following?
(i) Igneous rocks
(ii) Sedimentary rocks
(iii) Metamorphic rocks
Answer: (i) Igneous rocks: Igneous rocks are formed by the solidification of hot and molten magma, also termed as primary rocks or the parent rocks.
(ii) Sedimentary rocks: Sedimentary rocks are formed the sediments, particles, grains or fragments derived from existing primary rocks. These sediments are soft but in course of time they become hard and compact.
(iii) Metamorphic rocks: Because of tremendous pressure and high temperature both igneous and sedimentary rocks may be altered so greatly in appearance and composition that they entirely lose their original character. They are termed as metamorphic rocks
10: What is the source of knowing of the layered structure of the earth?
Answer: The layered structure of the earth has been known on the basis of variation in temperature, pressure and the density of the material in the interior. The behaviour in the earth quake shock waves travelling from the centre of their origin in all directions has been much helpful to this end.
Long Answer Type Questions
1. What are minerals? How are they useful for mankind? [V. Imp.]
Answer: Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.
Minerals are very useful for mankind. Some minerals like coal, natural gas and petroleum are used as fuels. They are also used in industries. Iron, aluminium, gold, uranium etc. are used in medicine, in Fertilizers etc.
2. Mention various types of rocks. [Imp.]
Answer: Rocks are of the three types:
(i) Igneous rocks
(ii) Sedimentary rocks
(iii) Metamorphic rocks
Igneous rocks: When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks. They are also called primary rocks. They are of two types—intrusive rocks and extrusive rocks.
(a) Extrusive rocks: When molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in this way on the crust Eire called extrusive igneous rocks. For example, basalt.
(b) Intrusive rocks: Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they form large grains. For example, granite.
Sedimentary rocks: Small fragments of rocks are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form sedimentary rocks. For example, sandstone is made from grains of sand.
Metamorphic rocks: When igneous and sedimentary rocks Eire subjected to great heat and pressure they change into metamorphic rocks. For example, clay changes into slate and limestone into marble.
3. What do you know about the interior of the earth? [V. Imp.]
Answer: Our earth is made up of several concentric layers with one inside another. These layers are three in number – crust, mantle and core.
Crust. It is the uppermost layer over the earth’s surface. It is the thinnest of all the layers. It is about 35 km on the continential masses and only 5 km on the ocean floors.
The continental masses are made up of silica and alumina. It is thus called sial (si-silica and al-alumina). The oceanic crust mainly consists of silica and magnesium. It is thus called sima (si-silica and ma-magnesium).
Mantle: It is just beneath the crust. It extends up to a depth of 2900 km below the crust
Core: It is the innermost layer. Its radius is about 3500 km. It is mainly made up of nickel and iron and is known as nife (ni-nickel and fe-ferrous, Le., iron). The central core has very high temperature and pressure.
