Download Bal Bharati Public School Class – 7 Subject

Bal Bharati Public School
Class – 7
Subject – Social Science ( Geography )
CHAPTER – Inside Our Earth
1. What are the three layers of the interior of the earth?
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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.
2. Name three types of rocks. Give examples of each type of rock.
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Igneous rocks- Granite, basalt
Sedimentary – Sandstone
Metamorphic – Slate, marble
3. Define, ‘rock’.
It is a natural mass of mineral matter that makes up the earth’s crust.
4. What are the main mineral constituents of continental and oceanic mass?
Continental mass – Silica and alumina.
Oceanic mass – Silica and magnesia.
5. 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.
6. 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.
7. How are metamorphic rocks formed?
Igneous and sedimentary rocks are transformed to metamorphic rocks under great heat and
pressure.
8. How are rocks useful to us?
Rocks are useful to us in the following ways –
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Hard rocks are used to make roads, houses and buildings.
Stones are used for playing several games.
Sculptures are also made out of rocks.
9. 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 I.R. are 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 M.R. which 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.
10. Explain the 3 layers of rock.
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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.
11. 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.
Bal Bharati Public School
Class – 7
Subject – Social Science ( Geography )
CHAPTER – Our Changing Earth
1. What is the difference between weathering and erosion ?
Weathering is the breaking up of the rocks on the earth’s surface.
Erosion is the wearing away of the landscape by different agents like water, wind, and ice.
2. What are endogenic and enogenic forces?
The forces which act in the interior of the earth, are called endogenic forces.
The forces which act on the surface of the earth are called enogenic forces.
3. What is a volcano ?
A volcano is a vent in the earth’s crust through which the molten material erupts.
4. Explain the work of a river in the lower course.
As the river approaches the sea, the speed of the flowing water decreases, and the river begins to
break up into a number of streams called distributaries. The river becomes so slow that it begins to
deposit its load. Each distributary forms its own mouth. The collection of sediments from all the
mouths forms a delta.
5. Name the features made by sea waves.
Sea waves, sea arches, stacks, sea cliffs and beaches.
6. What are the major features formed due to river action ?
Waterfalls, meanders, ox-bow lakes, floodplains, levees, distributaries and deltas.
7. What are glacial moraines ?
The material carried by glaciers such as big and small rocks, sand and silt are called glacial moraines.
8. How are sea caves, arches and stacks formed ?
Sea waves continuously strike at the rocks. Cracks develop. Over time they become larger and wider.
Thus hollow- like caves are formed. These are called sea caves. As these cavities become bigger, and
bigger, only the roof of the caves remain, forming arches. Further erosion breaks the roof, and only
the walls remain. These walls are called stacks.
The steep rocky coast rising almost vertically above sea level is called sea cliff. Sea waves deposit
sediments along the shores, forming beaches.
9. How are different landforms created in earth ?
Weathering is the breaking up of the rocks on the earth’s surface. Erosion is the wearing away of the
landscape by different agents like water, wind and ice. The eroded material is carried away or
transported by water, wind, etc. and eventually deposited. This process of erosion and deposition
create different land forms on the surface of the earth.
10. How are flood plains formed ?
At times the river overflows it banks. This leads to the flooding of the neighbouring areas. As it
floods, it deposits layers of fine soil and other material called sediments along its banks. This in turn
leads to the formation of a flat fertile floodplain.
11. Describe how meanders, and ox-bow lakes are formed.
As the river enters the plains, it twists and turns forming large bends called meanders. Due to the
continuous erosion and deposition along the sides of the meander, the ends of the meander loop
come closer and closer. In due course of time the meander loop cuts off from the river and forms a
cut-off lake also called an ox-bow lake.
12. What is an earthquake? How is it caused? Mention some common earthquake prediction
methods.
When the lithospheric plates move, the surface of the earth vibrates. The vibrations travel all around
the earth. These vibrations are called earthquakes. The place in the crust where the movement
starts is called the focus. The place on the surface above the focus is called the epicentre.
The greatest damage is usually the closest to the epicentre and the srtengh of the earthquake
decreases as we move away from the epicentre. The common methods adopted by the people
include studying animal behaviour; fish in ponds get agitated, snakes come up to the surface.
13. Explain wind as an agent of erosion and deposition.
Work of wind
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Wind is an active agent of erosion and deposition in the deserts.
Important landforms caused by wind are—mushroom rocks, sand dunes and loess.
Mushroom rocks- winds erode the lower section more than the upper part. After a period of
time, such rocks have narrower base, and wider top representing a mushroom
Sand dune- when the wind blows it transports sand from one place to another. When it
stops blowing, or strikes a barrier, the sand falls and gets deposited into low, hill-like
structures called sand dunes.
Loess- the wind can carry fine and light sands over very long distances when such sand is
deposited in a large area, it is called a loess.