Download 6 - Bal Bharati Public School

BAL BHARATI PUBLIC SCHOOL, PITAMPURA, DELHI – 110034
HALF YEARLY
CLASS 7
Inside Our Earth
Q1. What are the three layers of the interior of the earth?
Ans. Crust – It's the outermost layer of the earth’s crust.
Mantle – It is the second layer of the earth.
Core – It is the innermost layer of the earth.
Q2. Name three types of rocks. Give examples of each type of rock.
Igneous rocks- Granite, basalt
Sedimentary – Sandstone
Metamorphic – Slate, marble
Q3. Define, ‘rock’.
It is a natural mass of mineral matter that makes up the earth’s crust.
Q4. Why is it not possible to reach the centre of the earth?
The central core has very high temperature and pressure and hence it is not possible to
reach the centre of the earth.
Q5. What are the main mineral constituents of continental and oceanic mass?
Continental mass – Silica and alumina.
Oceanic mass – Silica and magnesia.
Q6. What are Lithospheric plates?
Our lithosphere is broken into a number of plates called Lithospheric plates. The
plates move because of molten magma inside the earth.
Q7. What are minerals? How are they useful?
Minerals are naturally occurring substances which have certain physical properties
and definite chemical composition.
Some are them used as fuels. For example, coal, natural gas and petroleum. They are
also used in industries – iron, aluminium, gold, uranium, etc, in medicine, in fertilisers,
etc.
Q8. Distinguish between extrusive and intrusive igneous rocks.
Extrusive – when the molten lava comes on the earth’s surface, it rapidly cools down
and becomes, solid. Rocks formed in such a way, are called extrusive igneous rocks.
They have a very fine, grained structure.
Intrusive – Sometimes, the molten lava cools deep inside the earth’s crust. Solid rocks
so formed are called intrusive igneous rocks. Since they cool down slowly, they form
large grains.
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Q9. Describe the process of formation of sedimentary rocks.
Rocks roll down, crack, & hit each other and are broken down into smaller fragments.
These smaller particles are called ‘sediments’. These sediments are transported and
deposited by wind, water, etc.
These loose sediments are compressed and hardened to form layers of rocks. These
types of rocks are called sedimentary rocks.
Q10. How are metamorphic rocks formed?
Igneous and sedimentary rocks are transformed to metamorphic rocks under great
heat and pressure.
Q11. How are rocks useful to us?
Rocks are useful to us in the following ways –
Hard rocks are used to make roads, houses and buildings.
Stones are used for playing several games.
Sculptures are also made out of rocks.
Q12. Describe the rock cycle.
One type of rock changes to another under specific conditions in a cyclical manner.
This process of transformation of rocks from one to another is known as the rock
cycle. We know that, when molten magma cools, it solidifies to become igneous rocks.
This igneous rock is broken down into smaller particles that are transported and
deposited to form sedimentary rocks.
When igneous and sedimentary rocks are subjected to heat and pressure, they change
into metamorphic rocks. The metamorphic rocks those are still under heat and
pressure melt down to form molten magma. This molten magma cools down to form
igneous rocks, and so the cycle repeats.
Q13. Explain the 3 layers of rock.
Crust- It is the uppermost layer of the earth’s surface. It is the thinnest of all the
layers. It's about 35 km on the continental masses and only 5 km on the ocean floor.
Mantle- Just beneath the crust is the mantle which extends to a depth of 2900 km into
the earth.
Core- It is the innermost layer of the earth. It is mainly made up of nickel and iron
called ‘nife’. The core has very high temperature and pressure.
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