Rocks And Soils Online Test 8th Social Science Lesson 5 Questions in English

The four realms of the earth, namely lithosphere, hydrosphere, atmosphere and biosphere.

Lithosphere is the upper most and significant layer of the earth.

Lithosphere is composed of solid rocks and unconsolidated materials. The literal meaning of lithosphere is “The sphere of rock”.

The rocks are the solid mineral materials forming a part of the surface of the earth and other similar planets. The earth’s crust (Lithosphere) is composed of rocks.

An estimation reveals that there are 2,000 different types of minerals found on the earth surface out of Which only 12 are the basic minerals commonly found all over the earth.

Rock is an important natural resource and is found in solid state. It may be hard or soft in nature. Minerals are chemical substances Which exist in nature. They may occur either in the form of elements or compounds.

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.

The igneous rocks are formed by the solidification of molten magma.

characteristics of Igneous rock are 1.These rocks are hard in nature 2. These are impermeable 3. They do not contain fossils 4. They are associated with the volcanic activities 5. These rocks are useful for construction works.

The igneous rocks are also called as the ‘Primary Rocks’ or ‘Parent Rocks’ as all other rocks are formed from these rocks.

Igneous Rocks are of two types. They are: 1. Extrusive Igneous Rocks 2. Intrusive Igneous Rocks.

Lava is actually a fiery red molten magma comes out from the interior of the earth on its surface.

After reaching the earth surface the molten materials get solidified and form rocks. Rocks formed in such a way on the crust are called Extrusive igneous rocks.

The molten magma sometimes cools down deep inside the earth’s crust and becomes solid. The rocks formed this way is called ‘Intrusive Igneous Rocks’

Extrusive igneous rocks are fine grained and glassy in nature due to rapid solidification. Basalt found in the north western part of peninsular India is the example for this type of rock.

Intrusive Igneous rocks are of two types. The deep seated rocks are called ‘Plutonic rocks’ and the ones formed at shallow depths are called ‘Hypabysal rocks’.

Granite, Diorite and Gabbro are the examples of plutonic rocks and Dolerite is an example of hypabysal 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.

Sedimentary rocks consist of many layers Which were formed by the sediments deposited at different periods. As it consists of many strata, it is also known as ‘Stratified rocks’.

Since the intrusive Igneous rocks consist of large crystals, they are also called as ‘Crystalline rocks’.

Characteristics of Sedimentary rocks 1. They have many layers. 2. They are non-crystalline rocks. 3. They contain fossils. 4. They are soft and get eroded easily.

Organic Sedimentary Rocks are formed as a result of the decomposition of dead plants and animals. It contains fossils.

Mechanical Sedimentary Rocks are formed from the disintegration of igneous and metamorphic rocks.

Chemical sedimentary rocks are formed by precipitating of minerals from water. It is formed usually through evaporation of chemical rich solutions.

Chalk, Talc, Dolomite and Limestone rocks are organic sedimentary rock.

The natural agents erode and transport mechanical sedimentary rocks and deposit them at some places. After a long period of time, they cemented to form rocks.

If the change in the rocks is mainly caused by high temperature, the process is called as thermal metamorphism.

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.

Rock Salt is an example of chemical sedimentary rock. Sandstone, Shale and Clay are the examples of Mechanical Sedimentary rocks.

Chemical Sedimentary rocks 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

If the change in the rock is mainly caused by high pressure, the process is called as Dynamic Metamorphism

Granite into gneiss caused by dynamic metamorphism. Sandstone into quartz caused by thermal metamorphism.

Igneous rocks are the primary rocks formed first on the earth.

the rocks of the earth crust keeps on changing from one form to another form under various natural forces and agents. The endless process is referred as Rock Cycle.

Characteristics of Metamorphic Rocks 1. Metamorphic rocks are mostly crystalline in nature. 2. They consist of alternate bands of light and dark minerals.

Basalt into slate caused by thermal metamorphism. Shale into slate caused by thermal metamorphism.

The metamorphic rocks are also get disintegrated and deposited to form sedimentary rocks.

Rocks are highly valuable and important to almost all aspects of our economy. The minerals and metals in rocks have been found essential to human civilization.

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.

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.

Alluvial 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.

Black soils are formed by weathering of igneous rocks. Black soil is clayey in nature. It is retentive of moisture.

Red soils are formed by weathering of metamorphic rocks and crystalline rocks. The presence of iron oxide makes this soil brown to red in colour.

Laterites soils These are the typical soils of tropical regions. These soils are found in the regions Which experienced alternate wet and dry condition.

Red soils are usually found in semi-arid regions. It is not a fertile soil.

Laterites soils are formed by the process of leaching, it is in fertile. It is suitable for plantation crops of tea and coffee.

Mountain soils are found over the slopes of mountain. Soils in these regions are thin and acidic.

Alluvial soil is suitable for the cultivation of sugarcane, jute, rice, wheat and other food crops.

Dessert soils are porous and saline. Since it is infertile agriculture in these soils are not so successful.

Black soil is clayey in nature. It is retentive of moisture. It is ideal for growing cotton.

Sheet erosion, Rill erosion and Gully erosion are the major types of soil erosion.

Soil erosion is the removal or destruction of the top layer of soil by natural forces and human activities. Soil erosion reduces the fertility of soil Which in turn reduces the agricultural productivity.

Running water and wind are the major agents of soil erosion.

Soil conservation is the process of protecting the soil from erosion to maintain its fertility.

The methods that are widely practiced for conserving soil are afforestation, controlled grazing, construction of dams, Crop rotation, Strip farming, contour ploughing, terrace farming, checking shifting cultivation, wind break etc.,

The time needed to form a soil depends on the Climate.

The environments Which is characterized by mild climate, takes 200400 years to form one cm of soil and in wet tropical area, soil formation is faster and takes up to 200 years.

The minerals present in the soil enhance and nourishes the crops and plants.

Soil is used in making of ceramics or pottery.

Soil acts as natural filter of water and purifies it. Soil supports ecosystem and play an important role in land management.

The word ‘Sedimentary’ has been derived from Latin word ‘Sedimentum’ means settling down.

Some major Active Volcanoes: Mount Vesuvius, Mt. Stromboli and Mt. Etna in Italy and Mauna Loa and Mauna Kea in Hawaii Islands.

Red soil is not a fertile soil. It is suitable for millet cultivation.

Layers of soil are O-Horizon or Humus, A- Horizon or Top Soil, E- Horizon or Elevated layer, B- Horizon or Sub-soil, C- Horizon or Parent Rock, R- Horizon Parent Rock.

O-Horizon or Humus layer is dominated by organic material (leaves, needles, twigs, moss and lichens).

B- Horizon or Sub soil layer reflects the chemical or physical alteration of parent material. Thus iron, clay, aluminium and organic compounds are found accumulated in this horizon.

E- Horizon or Elevated layer is significantly leached of clay, iron, and aluminium oxides, Which leaves a concentration of ore.

Horizon or Top Soil, composed of organic matter mixed with mineral matter.

The environments Which is characterized by mild climate, soil takes 200 to 400 years to form one cm of soil and in wet tropical area, soil formation is faster and takes up to 200 years. To become a well matured soil, it takes about 3000 years.

Sedimentary rocks are the important source of natural resources like coal, oil and natural gas.

Oldest sedimentary rocks of the world has been identified in Greenland and estimated as 3.9 billion years old.