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VIII SS T1 ROCKS AND SOILS
UNIT 1
ROCKS AND SOILS…..
EVALUATION:
I. Choose the correct answer
1. Which of the following is known as sphere of rocks
a) Atmosphere b) Biosphere
c) Lithosphere d) Hydrosphere
Ans: c) Lithosphere
2. World soil day is observed on __________.
a) 15th August
b) 12th January
c) 15th October
d) 5th December
Ans: d) 5th December
3. Fossils are found in ___________.
a) Sedimentary rocks
b) Igneous rocks
c) Metamorphic rocks
d) Plutonic rocks
Ans: a) Sedimentary rocks
4. The top layer of soil is called as ___________.
a) organic layer or humas
b) topsoil
c) subsoil
d) bedrock
Ans: a) organic layer or humas
5. Ideal soil for growing cotton is _____________.
a) Red soil b) Black soil
c) Alluvial soil d) Mountain soil
Ans: b) Black soil
6. The major components of soil is ___________.
a) Rocks b) Minerals
c) Water d) All the above
Ans: b) Minerals
7. Which one of the following is the most widespread most and productive category of soil
a) Alluvial soil b)Black soil
c) Red soil d) Mountain soil
Ans: a) Alluvial soil
II Fill in the blanks
1. Scientific study of rocks is called _____________.
Ans: Petrology
2. _____________soil is highly suitable for millets cultivation.
Ans: Red soils
3. The “skin of earth” is _____________.
Ans: Soil
4. _____________is the kind of metamorphic rock using which Taj Mahal was built.
Ans: White marble
5. _____________is known as the primary rocks.
Ans: Igneous
III State whether the following statements are true or false
1. Igneous rocks are called primary rocks.
Ans: True
2. Slate is formed from shale.
Ans: True
3. Red soil is formed by the process of leaching.
Ans: False
4. M-sand is used as an alternative for natural sand in construction.
Ans: True
5. Volcanic mountains are covered with sedimentary rocks.
Ans: False
IV Match the following
1)
A. Granite 1. Bed rock
B. Soil layer 2. Plutonic rock
C. Barren island 3. Strip farming
D. Soil conservation 4. Active Volcano
A B C D
a) 2 1 4 3
b) 2 1 3 4
c) 4 3 2 1
d) 3 4 2 1
Ans: a) 2 1 4 3
2)
A. Basalt 1. Anthracite
B. Limestone 2. Extrusive igneous
C. Coal 3. Metamorphic rock
D. Gneiss 4. Sedimentary rock
A B C D
a) 2 4 3 1
b) 2 4 1 3
c) 3 1 2 4
d) 3 1 4 2
Ans: b) 2 4 1 3
V Choose the incorrect statement from the following
1. a) Igneous rocks are called the primary rocks.
b) Soil is the product of weathering of rocks.
c) Sedimentary rocks are the hardest ones.
d) Deccan plateau is the region of Igneous rocks.
Ans: c) Sedimentary rocks are the hardest ones.
2. a) Soil erosion decreases its fertility.
b) Dynamic metamorphism is caused by high temperature.
c) Soil is a renewable source.
d) Humus is a part of the top layer of soil.
Ans: b) Dynamic metamorphism is caused by high temperature.
VI Consider the following statements and choose the right option from the given ones
1) Statement (1): Sedimentary rocks consist of many layers.
Statement (2): Sedimentary rocks are formed by the sediments deposited at different points of time.
a) 1 and 2 are correct and 2 explains 1
b) 1 and 2 are correct but, 2 does not explain 1
c) 1 is correct but, 2 is incorrect
d) 2 is correct but, 1 is incorrect.
Ans: b) 1 and 2 are correct but, 2 does not explain 1
VII Give reasons
1. Chemical sedimentary rocks are found in the beds of reservoirs.
Ans: Chemical sedimentary rocks are formed by precipitating of minerals from water. It is formed usually through evaporation of chemical rich solutions.
2. Igneous rocks are found in the regions of volcanoes.
Ans: The igneous rocks are formed by the solidification of molten magma.
VIII Distinguish between
1. Metamorphic rock and sedimentary rock.
2. Soil conservation and Soil erosion.
IX Answer briefly
1. How are igneous rocks formed?
The igneous rocks are formed by the solidification of molten magma. These rocks are also called as the ‘Primary Rocks’ or ‘Parent Rocks’ as all other rocks are formed from these rocks.
2. Describe about the composition of soil.
The basic components of soil are mineral, organic matter, water and air. It consists of about 45% mineral, 5% organic matter, 25% of water and 25% air.
3. Define ‘rock’.
The rocks are the solid mineral materials forming a part of the surface of the earth and other similar planets. A rock is an aggregate of one or more minerals. Rock is an important natural resource and is found in solid state. It may be hard or soft in nature.
4. State the types of soils.
Alluvial soil, Black soil, Red soil, Laterite soil, Mountain soil, Desert soil
5. What is soil conservation?
Soil conservation is the process of protecting the soil from erosion to maintain its fertility.
X Answer in a Paragraph
1. Explain the process of soil formation.
Soil is a mixture of organic matter, minerals, gases, liquids and organisms that together support life.
Soil minerals form the basis of soil. It forms on the surface of the earth. It is known as the ‘skin of the earth’.
Soils are produced from rocks (parent material) through the processes of weathering and natural erosion.
Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material. It leads to the formation of loose material.
In course of time, they further break down into fine particles. This process releases the minerals locked in the rock fragments.
Later on, the vegetative cover which develop in that region forms humus content in the soil. This way the soil gets matured gradually.
2. Classify and explain the rocks.
Classification of Rocks
According to the mode of formation the rocks are classified into three types as follows.
1. Igneous Rocks
2. Sedimentary Rocks and
3. Metamorphic Rocks
Igneous Rocks
The igneous rocks are formed by the solidification of molten magma. These rocks are also called as the ‘Primary Rocks’ or ‘Parent Rocks’ as all other rocks are formed from these rocks.
Characteristics of Igneous Rocks
These rocks are hard in nature
These are impermeable
They do not contain fossils
Types of Igneous Rocks:
• Extrusive Igneous Rocks.
• Intrusive Igneous Rocks
1. Extrusive Igneous Rocks:
Molten magma which comes out from the interior of the earth’s surface, gets solidified and forms such rocks. Fine grained and glassy in nature. Ex. Basalt found in north western peninsular India.
2. Intrusive Igneous rocks:
Molten magma cools down deep inside the earth’s crust, becomes solid and forms such rocks. Form large grains. Deep seated rocks are plutonic rock and ones at shallow depths – Hypabysal rocks. Example Granite, Diorite,and Gabbro.
Sedimentary Rocks:
The sedimentary rocks are formed by the sediments derived and deposited by various agents. Due to high temperature and pressure, the undisturbed sediments of long period cemented to form sedimentary rocks. It is also known as ‘Stratified rocks’.
Characteristics of Sedimentary rocks
1. They have many layers. 2. They are non-crystalline rocks. 3. They contain fossils
Types of Sedimentary Rocks
1. Organic Sedimentary Rocks
These rocks are formed as a result of the decomposition of dead plants and animals. It contains fossils. Chalk, Talc, Dolomite and Limestone rocks are of this category.
2. Mechanical Sedimentary Rocks
These rocks are formed due to the disintegration of igneous and metamorphic rocks. The natural agents erode and transport these rocks and deposit them at some places. After a long period of time, they cemented to form rocks. Sandstone, Shale and Clay are the examples of rocks of this type.
3. Chemical Sedimentary rocks
These are formed by precipitating of minerals from water. It is formed usually through evaporation of chemical rich solutions. These rocks are also called as evaporates. Gypsum is an example of this kind.
Metamorphic Rocks:
”, Meta means change and Morpha means shape. When Igneous and sedimentary rocks subject to high temperature and pressure, the original rocks get altered to form a new kind of rock called metamorphic rocks. Metamorphism is of two types. They are
1. Thermal Metamorphism
2. Dynamic Metamorphism
Thermal Metamorphism:
If the change in the rocks is mainly caused by high temperature, the process is called 'Thermal Metamorphism'.
Dynamic Metamorphism
If the change in the rock is mainly caused by high pressure, the process is called as 'Dynamic Metamorphism'.
Characteristics of Metamorphic Rocks 1. Metamorphic rocks are mostly crystalline in nature. 2. They consist of alternate bands of light and dark minerals.
3. Give an account on: different layers of soil.
4. Classify and explain the soil.
Classification of soils
Soils are classified on the basis of their formation, colour, physical and chemical properties. Based on these, soil is classified into six major types. They are: Alluvial soil, Black soil, Red soil, Laterite soil, Mountain soil, Desert soil.
Alluvial soils
These soils are found in the regions of river valleys, flood plains and coastal regions. These are formed by the deposition of silt by the running water. It is the most productive of all soils. It is suitable for the cultivation of sugarcane, jute, rice, wheat and other food crops.
Black soils
These soils are formed by weathering of igneous rocks. Black soil is clayey in nature. It is retensive of moisture. It is ideal for growing cotton.
Red Soils
These soils are formed by weathering of metamorphic rocks and crystalline rocks. The presence of iron oxide makes this soil brown to red in colour. It is usually found in semi-arid regions. It is not a fertile soil. It is suitable for millet cultivation.
Laterite soils
These are the typical soils of tropical regions. These soils are found in the regions which experienced alternate wet and dry condition. As these soils are formed by the process of leaching, it is in fertile. It is suitable for plantation crops like tea and coffee. Mountain soils
These soils are found over the slopes of mountains. Soils in these regions are thin and acidic. However, soil differs from region to region based on the altitude.
Desert soils
These are sandy soil found in the hot desert regions. These soils are porous and saline. Since it is infertile agriculture in these soils are not so successful.
