PSEB Punjab Board Class 7 Social Science Textbook Solution Chapter 2 The Internal and External face of the Earth Exercise Questions and Answers
Chapter 2
The Internal and External face of the Earth
(I) Give answer to the following questions approximately in 1-15 words.
(i) How many shells of the earth are there? Name them.
Ans: There are three shells of the earth. They are – SIAL, SIMA and NiFe or Lithosphere, Mantle core.
(ii) How many types of rocks are found on the earth?
Ans: There are various types of rocks found on the earth based on their nations. They are classified as follows:
(a) On the basis of Porosity – Porous Rock, Non-porous rock
(b) On the basis of Penetrability – Permeable Rocks, Impermeable rock.
(c) On the basis of chemical formation – Alkaline rocks, Acidic rocks.
(d) On the basis of formation – Igneous rocks, sedimentary rocks, metamorphic rocks.
(iii) Write down about the mantle part of the earth.
Ans: Mantle is the second layer of the earth, and is 2900km deep into the earth. This layer is subdivided into two parts – Upper mantle and lower mantle. Mantle is known as SIMA and is made up of Silicon and Magnesium.
(iv) By which name the inner most part of the earth called? What are the components of this part?
Ans: The inner most part of the earth is called core.
Core consists of two parts – outer core & inner core. Core is mainly made up of two elements i.e. nickle & ferrous.
(v) How can we avoid soil erosion?
Ans: Various ways of avoiding soil erosion are – Planting of more trees, prevention of overgrazing, adopting better agricultural practices etc.
(II) Give answer to the following questions approximately in 50-60 words.
(i) What are igneous rocks? How many types are there in these rocks? Write about the intrusive rocks.
Ans: Igneous rocks are formed out of the cooling of the hot and liquid material from the interior of the earth, which is known as “Magma”.
Igneous rocks are of two types – Intrusive igneous rock, Extrusive igneous rock.
Intrusive igneous are formed by the cooling of magma in the interior of the earth. Intrusive rocks are of two types – Plutonic igneous rock and hypabyssal igneous rocks.
(ii) What are the sedimentary rocks? How many types are there of these rocks?
Ans: Sedimentary rocks are formed by the hardening of the layers of the matter brought by agents of denudation (water, air, river etc) and are deposited in law lands in the form of sediments that turns into rocks.
(iii) Write about the metamorphic rocks, Give specific example of these rocks.
Ans: Metamorphic rocks are the
(iv) What kind of mineral is Mica, for what purpose is it used?
Ans: Mica is non-metallic mineral. It is use for making electric goods paints, Rubber, paper etc.
(v) Which mineral is called as ‘Liquid Gold’. Give brief introduction.
Ans: Petroleum is known as “Liquid Gold”.
The word “Petroleum” is a combination of two words “Petra” meaning rock and “Oleum” meaning oil. So the oil extracted from rock is called petroleum. The largest oil reserve of world is in south west Asia like in Iran, Iraq, Kuwait Saudi Arabia etc.
(vi) Write down the importance of the soil on the Earth.
Ans: Soil is a very important land resource whose signification lies in its fertility. Human beings have always been keen to live in fertile plains since their origin. Ancient civilizations have also developed in fertile river valleys.
(III) Write the answer to the following questions approximately in 125-130 words.
(i) Write in detail about the rocks available on the earth.
Ans: There are different types of rocks found on earth. The rocks can b classified on the bails of several criterion as follows:
(a) Porous Rock – These rocks have excess of sand particles.
(b) Non-porous rocks – These rocks have excess of clayey particles.
(c) Permeable rocks – These rocks have an easy passage of water through it.
(d) Impermeable rocks – These rocks have no passage of water through it.
(e) Alkaline rocks – The chemical content of alkalies is persistent.
(f) Acidic rocks – The acidic content is more than 60% in these rocks.
(g) Igneous rocks – These rocks are formed by cooling of hot liquid called magma.
(h) Sedimentary rocks – These rocks are made by hardening of the layer of the matter brought down by river water, air etc.
(i) Metamorphic rocks – These rocks have been transformed as a consequences of effect of temperature, pressure etc.
(ii) What are minerals? Which minerals are available on the earth? Classify them and write about the metallic minerals.
Ans: The materials that forms rocks are called minerals.
The minerals available on the earth are iron, copper, gold silver, sulphur, Mica, Gypsum, Potash, Phosphate etc.
Minerals can be classified under three types – Metallic minerals.
Non-metallic minerals, energy-minerals
Metallic minerals: The minerals that contain metals in them are known as metallic minerals like – iron, copper, Tin, Gold, silver, aluminum etc.
(iii) What are mineral fuels? Give details of any mineral fuel.
Ans: Mineral fuels are mineral oil, coal, natural gas.
Coal – It is a major mineral fuel and is used for producing thermal electricity. Coal is produced as a result of submergence of forest in deep layers of the crust in the long post, and as a result of heat and pressure of the upper layer.
(iv) Write in detail about the soil available in India.
Ans: Various types of soil available in India are as follows:
(a) Alluvial Soil – alluvial is formed due to the deposition of soil, carried out by rivers. This is one of the most fertile soil found on earth. It is mainly found in the delta region of rivers of northern plain.
(b) Black soil: This type of soil is formed from volcanic rocks or the black soil consisting of fine particles. Due to its dominance of cotton cultivation, it is also called cotton soil.
(c) Red soil: This soil is formed from igneous rock and is found in hot areas of eastern and southern parts of peninsula.
(d) Laterite soil: This soil is found in hot and moist region with a heavy seasonal rainfall. Due to found presence of iron oxide, it is red in colour and not suitable for cultivation.
(e) Dry sandy soil: Found in desert areas of Rajasthan and Gujarat and is known as desert soil.
Also See – PSEB Class 7 Social Science Chapter 1 Environment Question Answer