1
7th – April - Geography-
Points to remember:
1) The earth is constantly undergoing changes,both inside and outside.
2) The Earth is made up of several layers – one inside the other out side.
3) The top most layer of the earth’s surface i.e. the crust is the thinnest of all
layers, consisting of mineral constituents called Sial and Sima.
4) Just beneath the crust is the mantle.
5) The innermost layer – the core,is mainly made up of nickel and iron having very
high temperature and pressure.
6) The crust is made up of various types of rocks of different colour,size and
texture.
7) Rocks can be classified into three heads –
i)
Igneous rocks
ii)
Sedimentary rocks.
iii)
Metamorphic rocks.
8) Igneous rocks or primary rocks, formed by the cooling of motlen magama, are
two types :i)
Intrusive
ii)
Extrusive rocks.
9) Sedimentary rocks are a result of continous erosion,deposition and weathering
of compressed and hardened sediments.
10)
Under great and pressure the Igneous and sedimentary rocks can change
into metamorphic rocks.
11)
Rocks are very seful to us.
12)
Rock cycle is the process of transformation from one form to another.
13)
Rocks are made up of minerals which have physical properties and
definite chemical composition.
1
2
Inside our earth.
ANSWER THE FOLLOWING:-
{1 Mark }
Q1) What is the approximate life of the earth?
Ans:- The approximate life of the earth is 4600 million years ago.
Q2) Into how many layers is broadly divided?
Ans:- Earth is broadly divided into 3 layers they are:1.lithosphere
2.mantle
3.core
Q3)Define lithosphere?
Ans:- The surface the earth consists of rocks of various types. these rocks form
a relatively thin layer known as crust or lithosphere
Q4)What is the average thickness of lithosphere?
Ans:- The average thickness of lithosphere is 60 kms.
Q5) what is density of core and what is the estimated temperature?
Ans: The density of core varies from 11to15 .The core has estimated temperature
of 5000c
2
3
Q6) What are plutonic rocks?
Ans:- The deep seated igneous rocks are known as plutonic rocks.
7) What is magma?
Ans:- Ingenious rocks formed by the process of solidification of molten material
called magma.
_________________________________________________________________
2marks:Q1) Describe the mantle of the earth?
Ans:- The mantle layer lies beneath the sial layer .It extends up to a depth of 2900
kms .The layer consists of inner silicates or sima.It is rich in silica and magnesium
This layer is made up of silicates and magnesium.
Q2) How are intrusive rocks formed?
Ans:- Intrusive rocks are formed by solidification of magma below the surface of
the earth in cracks or joints .Inside the earth magma cools very slowly and thus
form crystals.
Q3) What are extrusive rocks formed?
Ans:- During the volcanic eruption when magma errupts and on reaching the
earth's surface ,it gets cool and solidifies .Due to the solidification . Rocks are
formed on the earth's surface known as extrusive igneous rocks or volcanic rocks.
_____________________________________________________________
{ 3marks} :Q1)why are igneous rocks called primary rocks?
Ans:-All the rock material originating from beneath the earth form igneous rocks.
These are parent rocks .Igneous rocks are also known as primary rocks.
Q2) why are sedimentary rocks formed in layers?
Ans:- 1.sedimentary rocks are the rocks which are layered and formed with
agencies of running water, wind or glacier.
3
4
2.These agents brake and erode the igneous and other rocks and transport them to a
certain place where they are deposited and formed as layers.
Q3)Define the term rock?
Ans:- 1.A rock is a natural deposit that forms the sold part of the earth's crust .
2. This really means that a rock may be as hard as a granite or may be as soft as
clay and sand.
3. The rock is not a chemical compound but a conglomeration of minerals.
Q4) Define minerals and give two examples of metals and non metals ?
Ans:- minerals are the natural inorganic substances which have definite chemical
composition and physical properties. There are some metallic minerals like copper,
iron,gold etc. Non metallic minerals like gypsium, mica etc.
Q5)Name the different types of rocks with examples?
Ans:{A} Chemically formed sedimentary rocks
eg:-gypsum, potash, nirates etc...
{b}.originally formed sedimentary rocks
eg:-coal, limestone ,chalk etc.....
{c}.extrusive igneous rocks
eg:-basalt
{d}.intrusive igneous rocks
eg:-granite,dolerite,plutonic rocks
{e}.mechanically formed sedimentary rocks
eg:-sandstone,shale,gravel etc.....
Q6)What is rock cycle ?name some primary rocks which changes into secoundary
rocks?
Ans:- 1.The chaining of one type of rock to the other is called rock cycle.
2. Lime stone changes into marble, shale changes into slate, coal changes into
graphite and sand stone changes into quartzite.
3. The change of one type of rock to the other is called rock cycle.
4
5
Q7) Describe the structure of the earth?
Ans:-Our earth is a unique planet in the solar system. It is the only planet which
contains life.Altough the exact origin of the earth is still not known ,yet it is
believed that earth came into being at 4600 million years ago .The earth reached its
present form though many phases. It was molten stage in the beginning but
gradually started cooling and thus crust was formed.
Q8) Write about chemically formed sedimentary rocks with examples?
Ans:- a)chemically formed sedimentary rocks:-these rocks are formed by the
process of evaporation of water containing mineral salts in solution. In deserts or
shallow lakes water gets evaporated living behind a layer of salts .These salts get
consolidated into sedimentary rocks .common salt, gypsum, potash and nitrates are
the examples of chemically formed sedimentary rocks.
Q(ii). What is rock?
Answer. Any natural mass of mineral matter that makes up the earth’s crust is called
rock.
Q(iii). Name three types of rocks?
Answer.There are three types of rocks:
1.Igneous rock.
2.Sedimentary rock.
3.Metamorphic rock.
Q(iv). How are extrusive and intrusive rock formed?
Answer. 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.
Q(v). What do you mean by a rock cycle?
Answer.The change of one type of rock into another type under certain conditions in a
cyclic manner.is called a rock cycle.
Q(vi) What are the uses of rock?
Answer. Following are some uses of rocks:
1.They are used as fuels.
2.They are used in industries.
3.They are used in medicines.
4.They are used in fertilizers.
Q(vii) What are the metamorphic rocks?
Answer.The types of rocks formed when igneous and sedimentary rocks undergo heat
and pressure are called metamorphic rocks.
5
6
Question2. Tick the correct answer.
Q(i)The rock which is made up of molten magma is.
(a)Igneous. (b) Sedimentary. (c) Metamorphic.
Answer.(a)Igneous.
Q(ii) The innermost layer of the earth is.
(a)Crust. (b) Core. (c) Mantle.
Answer.(b)Core.
Q(iii) Gold, petroleum and coal are example of.
(a)Rocks.(b) Minerals. (c) Fossils
Answer.(b)Minerals.
Q(iv)Rock which contain of.
(a) Sedimentary rocks. (b) Metamorphic rocks. (c) Igneous rocks.
Answer.(a)Sedimentary rocks.
Q(v) The thinnest layer of the earth is.
(a)Crust. (b) Mantle. (c) Core.
Answer.(a)Crust.
Question 3.Match the following.
1 Core
(a) Change into slate.
2 Minerals. (b) Used for roads and buildings.
3 Rocks.
(c) Made ofsilicaand alumina.
4 Clay.
(d) Has definite chemical compositon
5 sial.
(e) Innermost layer.
Answer.
1 Core
(a) Innermost layer.
2 Minerals. (b) Has definite chemical compositon.
3 Rocks.
(c) Used for roads and buildings.
4 Clay.
(d) Change into slate.
5 sial.
(e) Made of silicon and alumina.
Question4.Give Resons:
Q(i)We cannot go to the centre of the earth.
Answer: The radius of the earth is more than 6000 km. to reach the centre of ther
earth, we have to dig a hole to this depth,which is impossible.
6
7
Q(ii). Sedimentary rocks are formed from sediment.
Answer: Rocks breakdown into small fragments under various conditions.These
fragments,called sediments, are transported by wind and water. Layers of sediments
are formed when loose sediments are compressed and hardened. These layers of
sediments thus form sedimentary rocks.
Q(iii). Limestone is changed into marbles.
Answer. Ingenous and sedimentary rocks change their form under great pressure and
temperature conditions to form metaphoric rocks. the same thing happens with
limesone,which under the effect of heat and pressure chjange into marble, which is an
example o fmetmorphic rocks.
Question 5. For fun.
Q(i)What are the minerals most commonly used in the following objects?
Answer:
1 Karhai.
------ iron.
2 Ornaments. ------ gold, silver.
3 Pan/Tawa. ------ iron.
4 Bell.
------ Copper, zinic, iron.
5 Hammer.
------ iron.
6 Lamp.
------ Copper, zinic.
(ii) Identify some more objects made up of different minerals.
Answer. Some more objects:
Object
Mineral
1 Ring.
---- silver,gold.
2 Bucket.
---- iron,aluminium.
3 Electric wire. ---- copper,aluminium.
7