Question 1

Question 1What are rocks? Name the main types of rocks with two examples of each.

Accepted 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:Igneous rocks or Primary rocks:Intrusive igneous rocks — For example, granite and doleriteExtrusive igneous rocks — For example, basalt, pumiceSedimentary rocks — For example, sandstone and limestoneMetamorphic rocks — For example, marble and quartzite

Question 2

Question 2How are metamorphic rocks formed? Write two characteristics of metamorphic rocks.

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

Question 3

Question 5Discuss the role of plants and animals in biological weathering.

Accepted 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 4

Question 6What are soil horizons? Name the soil horizons.

Accepted 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:Horizon A (topsoil)Horizon B (subsoil)Horizon C (Rock Fragments)Horizon D (Parent Rock)

Question 5

Question 4Explain the following terms:(a) Exfoliation(b) Hydration(c) Weathering(d) Rocks(e) Minerals(f) Denudation(g) Mechanical weathering

Accepted Answer

(a) Exfoliation — The changes in temperature during summer and winter and in case of arid region, during day and night, cause expansion and contraction in the rock surfaces. This causes the rocks to break-up or peel off. Rectangular rock blocks are thus, gradually rounded by splitting away of sharp corners. This process is called exfoliation.(b) Hydration — Hydration is the chemical reaction of water with minerals present in rocks. It changes the proportion and composition of rocks and minerals. It weakens the rocks and ultimately the rock breaks-up.(c) Weathering — Weathering is described as the breaking down or dissolving of rocks and minerals on the surface of the earth. Water, ice, acids, salts, plants, animals and changes in temperature are all agents of weathering. It is a static process and leads to the formation of soil.(d) Rocks — Rocks are aggregates of minerals and have no definite chemical composition. Rocks makeup most of the solid materials of the lithosphere. On the basis of their formation rocks are classified into three types:Igneous rocksSedimentary rocksMetamorphic rocks.(e) Minerals — A mineral is a naturally occurring, homogenous solid that has definite chemical composition with its own chemical and physical properties, e.g., silicates and quartz.(f) Denudation — Denudation is a dynamic process that includes the disintegration and decomposition of rocks, transportation of the eroded material and deposition of it at some other place. Therefore, process of denudation is two-fold process that is both destructive and constructive.(g) Mechanical weathering — Mechanical weathering is responsible for the disintegration of rocks by the elements of weather such as heat, frost and wind. Mechanical weathering does not change the composition of rocks. It depends on the following factors:Extremes of temperatureNature of rocksStructure of rocksFrostWindSlope of lands

Question 6

Question 5Differentiate between:(a) Chemical and mechanical weathering(b) Weathering and denudation

Accepted Answer

(a) Difference between chemical and mechanical weathering:S.No.Chemical weatheringMechanical weathering1.It involves the breaking down of rocks by altering or dissolving the rock minerals due to chemical action or changesIt is responsible for the disintegration of rocks by the elements of weather such as heat, frost and wind.2.The processes involved in chemical weathering are Oxidation, Carbonation, Hydration and Solution.The processes involved in mechanical weathering are Exfoliation, Granular disintegration and Block disintegration.3.Chemical weathering is slow as compared to mechanical weathering.Mechanical weathering is comparatively faster.(b)	Difference between weathering and denudation:S.No.WeatheringDenudation1.Weathering involves disintegration and decomposition of rocks where they exist.Denudation involves both disintegration of rocks and transportation and deposition of the weathered material at some other place.2.Weathering is a destructive process.Denudation is a destructive and constructive process.3.Weathering is a static process.Denudation is a dynamic process.4.Weathering is a short term process.Denudation is a long term process.

Question 7

Question 6(c)What is meant by denudation?

Accepted Answer

Denudation is a dynamic process that includes disintegration and decomposition of rocks as well as the wearing away of the rocks. It is a two-fold process, both destructive and constructive. It is destructive as it breaks down the rocks. It is constructive as it transports the eroded material and deposits it at some other place.

Question 8

Question 6(d)What is meant by biological weathering?

Accepted Answer

Biological weathering refers to the breakdown of rocks by living organisms. This can occur through various means, such as root growth, burrowing activities, acid secretion by certain organisms, and the physical actions of organisms like mosses and lichens.

Question 9

Question 6(e)How does biological weathering take place?

Accepted Answer

Biological weathering is caused by following agents:Plants — The roots of plants grow into the cracks and crevices in search of water or nourishment. They exert pressure on rocks and break them. Sometimes, the roots release carbonic acid which changes the chemical composition of minerals and help in weathering.Animals — Burrowing animals cause loosening or weakening of the rocks and expose them to other agents of weathering.Human activities — Construction of roads, mining, farming and deforestation lead to weathering of rocks.

Question 10

Question 6(f)Name the factors responsible for weathering.

Accepted Answer

The various factors responsible for weathering are:Extremes of temperatureFrostWindSlope of landWaterOxygenAcidsPlantsAnimalsHuman activities

Question 11

Question 6(g)What is meant by exfoliation?

Accepted Answer

The changes in temperature during summer and winter and also during day and night (in case of arid region), cause expansion and contraction in the rock surfaces. This causes the rocks to break-up or peel off. Rectangular rock blocks are thus, gradually rounded by splitting away of sharp corners. This process is called exfoliation.

Question 12

Question 6(h)How does climate affect weathering? Explain giving examples.

Accepted Answer

Climatic factors like rainfall, wind, frost and extremes of temperature affect weathering.Wind has sand particles that erode the softer rocks.Water or frost when present in crevices of rocks exert pressure on rocks and breaks it.Extreme high temperature leads to expansion in rocks and extreme low temperature causes contraction. The repetitive expansion and contraction lead to weathering of rocks.Rain, snow and other forms of precipitation contribute to weathering by providing water that can dissolve and transport minerals and rocks. For example, water that contains dissolved carbon dioxide can create a weak acid that can dissolve limestone and erode them leading to the formation of caves and other features.

Question 13

Question 6(i)What is meant by soil? State the method adopted to prevent soil erosion.

Accepted Answer

The thin topmost layer of the earth's crust, made up of fine rock particles and organic matter is termed as soil. It is a layer of unconsolidated materials at the earth's surface.Some methods to prevent soil erosion are:AfforestationTo check overgrazingConstructing dams and barragesImprove techniques of agriculture

Question 14

Question 6(j)State any two importance of rocks.

Accepted Answer

Two importance of rocks are:Rocks are used as building material.Rocks supply precious metals like gold and silver.

Question 15

Question 6(k)Name the three different types of rocks.

Accepted Answer

On the basis of their formation rocks are classified into following three types:Igneous rocksSedimentary rocksMetamorphic rocks

Question 16

Question 6(l)What are the two types of igneous rocks? Give examples.

Accepted Answer

Two types of igneous rocks are:Intrusive rocks — E.g., granite.Extrusive rocks — E.g., Basalt.

Question 17

Question 6(m)How are igneous rocks formed?

Accepted Answer

Igneous rocks were formed as the molten magma solidified either inside the earth or on the surface of the earth

Question 18

Question 6(n)How are sedimentary rocks formed?

Accepted Answer

Sedimentary rocks are formed from sediments, accumulated over long periods in seas, lakes, rivers and glaciers. They are deposited in distinct layers or strata. Therefore, they are also called stratified rocks.

Question 19

Question 6(o)What are the different types of sedimentary rocks?

Accepted Answer

Sedimentary rocks are divided into three classes according to their formation:Mechanically formed sedimentary rocksOrganically formed sedimentary rocksChemically formed sedimentary rocks

Question 20

Question 6(p)Give examples of each type of sedimentary rocks

Accepted Answer

Examples of each type of sedimentary rocks are:Mechanically formed sedimentary rocks — E.g., Sandstone, Shale, Clay.Organically formed sedimentary rocks — E.g., Coal, Limestone, Coral.Chemically formed sedimentary rocks — E.g., Rock Salt, Gypsum, Dolomite .

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