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Term 2 — Chapter 2

Weathering and Soil Formation

Class 7 - Around the World Geography Solutions


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Question 1

Rearrange the letters to get the names of the rocks from which these landforms are formed. Then match the landforms with their names.

Rearrange the letters to get the names of the rocks from which these landforms are formed. Then match the landforms with their names. Weathering and Soil Formation, Around the World Geography Solutions ICSE Class 7.
Rearrange the letters to get the names of the rocks from which these landforms are formed. Then match the landforms with their names. Weathering and Soil Formation, Around the World Geography Solutions ICSE Class 7.
Rearrange the letters to get the names of the rocks from which these landforms are formed. Then match the landforms with their names. Weathering and Soil Formation, Around the World Geography Solutions ICSE Class 7.

(a) Pamukkale

(b) Giant's Causeway

(c) The Wave Rock

Answer

  1. SANDSTONE — (c) The Wave Rock
  2. LIMESTONE — (a) Pamukkale
  3. BASALT — (b) Giant's Causeway

Quick Quiz 1

Question 1

Soil is found in the (atmosphere/lithosphere).

Answer

Lithosphere

Question 2

Name two types of igneous rocks

Answer

Two types of igneous rocks are:

  1. Intrusive igneous rocks
  2. Extrusive igneous rocks

Question 3

Sandstone is an example of ............... rocks.

Answer

Sandstone is an example of sedimentary rocks.

Question 4

Excessive heat and pressure change granite into gneiss. True or False?

Answer

True

Question 5

Mention two uses of rocks.

Answer

Two uses of rocks are:

  1. In ancient times, rocks were used to make tools and weapons.
  2. Rocks are widely used in the construction of roads, houses and buildings.

Quick Quiz 2

Question 1

The decay of rocks as a result of chemical action is called (decomposition/disintegration).

Answer

The decay of rocks as a result of chemical action is called decomposition.

Question 2

Name two factors that affect weathering.

Answer

Two factors affecting weathering are:

  1. Types of Rocks
  2. Climatic conditions

Question 3

Granular disintegration is caused due to change in temperature. True or False?

Answer

True

Question 4

Name the different types of chemical weathering.

Answer

The different types of chemical weathering are:

  1. Solution
  2. Oxidation
  3. Hydration
  4. Carbonation

Question 5

..............., ............... and ............... are responsible for biological weathering.

Answer

Plants, animals and human activities are responsible for biological weathering.

Tick the correct answers

Question 1

The rocks which are formed from magma are called ............... rocks.

  1. sedimentary
  2. igneous
  3. metamorphic
  4. metallic

Answer

igneous

Question 2

Quartzite is ............... rock.

  1. an igneous
  2. a sedimentary
  3. a volcanic
  4. a metamorphic

Answer

a metamorphic

Question 3

Which of these is not a type of weathering?

  1. geological
  2. chemical
  3. biological
  4. mechanical

Answer

geological

Question 4

Carbonic acid disintegrates limestone as a result of

  1. frost action
  2. oxidation
  3. hydration
  4. carbonation

Answer

carbonation

Question 5

Which of these factors is not responsible for soil formation?

  1. climate
  2. human activities
  3. deforestation
  4. parent rock material

Answer

deforestation

Question 6

Which of these factors is responsible for soil erosion?

  1. crop rotation
  2. overgrazing
  3. afforestation
  4. terrace farming

Answer

overgrazing

Match the columns

Question 1

Sl.
No.
Column AColumn B
1.basaltsoil erosion
2.fossilsbiological weathering
3.frost actionsedimentary rock
4.quarryingsoil conservation
5.deforestationmechanical weathering
6.crop rotationigneous rock

Answer

Sl.
No.
Column AColumn B
1.basaltigneous rock
2.fossilssedimentary rock
3.frost actionmechanical weathering
4.quarryingbiological weathering
5.deforestationsoil erosion
6.crop rotationsoil conservation

Fill in the blanks

Question 1

The ............... igneous rocks cool below the earth's surface.

Answer

The intrusive igneous rocks cool below the earth's surface.

Question 2

............... metamorphoses into marble.

Answer

Limestone metamorphoses into marble.

Question 3

............... is also known as onion peeling.

Answer

Exfoliation is also known as onion peeling.

Question 4

When water chemically reacts with a mineral, it is called ............... .

Answer

When water chemically reacts with a mineral, it is called hydration.

Question 5

Soil formation is a very ............... process.

Answer

Soil formation is a very slow process.

Question 6

............... is the vertical section of soil from the surface to the parent rock.

Answer

Soil profile is the vertical section of soil from the surface to the parent rock.

Give reasons for the following

Question 1

Igneous rocks are called primary rocks.

Answer

Igneous rocks are called primary rocks because these rocks were the first to be formed.

Question 2

Rocks develop cracks due to change in temperature.

Answer

The rocks are heated during the day and cooled during the night. Different minerals present in the rocks expand and contract at different rates according to the changes in temperature. As a result of this unequal expansion and contraction of minerals in the rocks, a series of cracks develop on the outer surface of the rocks.

Answer these questions

Question 1

What are rocks? Name the main types of rocks with two examples of each.

Answer

Rocks are aggregates of one or more minerals, without having a definite chemical composition. The rocks may be composed of hard materials like granite and marble or soft like chalk, clay and sand.

The main types of rocks are:

  1. Igneous rocks or Primary rocks:
    1. Intrusive igneous rocks — For example, granite and dolerite
    2. Extrusive igneous rocks — For example, basalt, pumice
  2. Sedimentary rocks — For example, sandstone and limestone
  3. Metamorphic rocks — For example, marble and quartzite

Question 2

How are metamorphic rocks formed? Write two characteristics of metamorphic rocks.

Answer

When igneous or sedimentary rocks are subjected to excessive heat and pressure inside the earth, changes occur in their colour, hardness, texture and mineral composition. Such changed rocks are called metamorphic rocks.

Two characteristics of metamorphic rocks are:

  1. These rocks are very hard and have a high specific gravity.
  2. These rocks do not have empty spaces in them.

Question 3

What is mechanical weathering? How does freezing action of water affect weathering of rocks?

Answer

Mechanical weathering involves disintegration of rocks without the change in their chemical composition. It is mainly brought about by:

  1. Changes in temperature
  2. Freezing action of water

Freezing action of water — In mountainous regions or in areas with cold climate, the breaking of rocks is caused by the freezing action of water. The cracks and joints in the rocks fill up with water. At night, when the temperature falls, the water in the cracks or joints freezes. The conversion of water into ice increases its volume, thereby requiring more space. This causes widening of cracks and joints and finally leads to their disintegration. This is also called frost action.

Question 4

Distinguish between oxidation and hydration.

Answer

Sl.
No.
OxidationHydration
1.The decomposition of rock in which the minerals present in the rocks react with the atmospheric oxygen present in the rain water is called oxidation.The disintegration of rocks due to chemical union of water with the minerals present in the rocks is called hydration.
2.The colour of the rocks change in this process.The volume of rock increases causing stress which leads to disintegration of the rock.

Question 5

Discuss the role of plants and animals in biological weathering.

Answer

Role of plants — The penetration of roots in the rock cracks widens the cracks and disintegrates the rocks. The uprooting of trees by winds also breaks the rocks.

Role of animals — Animals such as worms, rabbits and moles dig burrows in the ground. In the process, they loosen the ground and disintegrate the rocks.

Question 6

What are soil horizons? Name the soil horizons.

Answer

The process of soil formation gives rise to four well-marked horizontal layers in the soil profile. These horizontal layers are called soil horizons. The soil horizons are:

  1. Horizon A (topsoil)
  2. Horizon B (subsoil)
  3. Horizon C (Rock Fragments)
  4. Horizon D (Parent Rock)
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