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CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL UNIT II INTERIOR OF THE EARTH CONTENT The Earth’s Interior Its structure - Its layers and characteristics Rocks Classification Types of rocks based on mode of formation – Igneous Sedimentary Metamorphic Their formation and characteristics Rock Cycle Definition, Process and Significance Uses of Rocks Economic Significance for Man 1 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL UNIT -II INTERIOR OF THE EARTH INTRODUCTION Rocks, metals, minerals, water etc., have something common in relation to earth, the third planet from the Sun in our Solar System. These are the components that largely form the earth and make it one of the known, densest rocky planet that was formed 4.5 billion years ago. Man has always wondered about the occurrence of phenomena like earthquakes, tsunamis, volcanoes etc. The answer to this lies in the study of the interior of the earth. The interior of this rocky planet differs completely in nature which becomes evident from the information obtained from the study of different sources. It is the planet we evolved on. Our planet's rocks, soils, and the various processes that create and transform them, produce resources and materials that sustain our life. The Interior of the Earth – An Overview The earth comprises of three main realms – the lithosphere (the solid inorganic section), hydrosphere (the liquid section) and the atmosphere (the gaseous realm). The solid earth actually has a concentric layer structure comprising of the crust, the mantle and the core. The temperature within the earth increases with the depth at the rate of 1 oC for every 32 metres depth. This makes the average temperature at the centre of the earth touch 5000oC. The Layers of the Earth 2 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL 1. The Crust: The outermost layer also known as lithosphere. It is the thinnest layer of the earth that is 5 – 40 km thick. It is the most significant part of the earth’s surface with its name lithosphere being derived from Latin word ‘lithos’ meaning ‘rocks’ or ‘stones’. The crust is subdivided into two distinct parts according to its composition known as Sial and Sima. Sial: The topmost layer consists of granite rocks which on an average forms first 25 km of the crust and is lighter. It consists of silicates and aluminium along with other lighter metals. This layer is thick over the continents but is thin or absent on the ocean floors. Sima: It lies below the sial layer. A dense layer with an average thickness of 35 km, it consists pre-dominantly of silicates of magnesium, iron and other denser metals. It is a zone of basaltic rocks forming the ocean floors. Though these two layers are in a solid state, the lighter sial is considered as floating on denser sima layer. Do You Know? Scientists have discovered a large area thousands of square kilometres in extent in the middle of the Atlantic where the Earth’s crust appears to be missing. Instead, the mantle - the deep interior of the Earth, normally covered by crust many kilometres thick - is exposed on the seafloor, 3000m The Crust below the surface. Fact File Earth is the only known planet in the Solar System with crustal plates. The outer crust of the Earth is broken up into regions known as tectonic plates. These are floating on top of the magma interior of the Earth and can move against one another. 3 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL 2. The Mantle: Below the crust lies the mantle that extends up to a depth of about 2900 km. It is composed of mineral matter in a solid state, the chief constituents being silicates of iron and magnesium. Both the temperature and the density of the mantle increases with the increasing depth towards the centre of the earth. The zone of separation between the crust and the mantle is called Moho Discontinuity. (Moho, a simplification of the name of the Croatian seismologist Mohorovicic who discovered it). Moho marks the lower limit of the earth’s crust. It occurs at an average depth of 8km beneath the oceans and 32km beneath the continents. The mantle has two parts: (a)Upper Mantle: The thickness of the upper mantle is about 670 km. The top layer of the upper mantle is solid. Below this layer lies a soft mobile layer. This soft layer of the upper mantle is called asthenosphere (from the Greek word asthenes meaning weak). The lithosphere that consists of the crust and the hard uppermost part of the mantle floats over this asthenosphere. (b)Lower Mantle: This is about 2200 km thick. This part of the mantle is a solid region starting at about 700 km. It is composed of rocks of uniform thickness. The Mantle Do You Know? Heat in the earth's interior causes the magma in the mantle to expand and rise. As the magma spreads out beneath the plates, the plates are dragged along and move away from each other. As the magma cools and sinks, plates are dragged towards each other. The repeated heating 4 and rising of the magma sets up continuous convection currents in the mantle causing the plates to move. CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL 3. The Core: Scientists believe that as we go deep within the earth, there’s a huge ball of liquid and solid iron, which is the earth’s core. The thickness of the core is about 3500 km. It is the densest layer. When the earth was first formed, 4.6 billion years ago, it was a hot ball of molten rock and metal. And since it was mostly liquid, heavier elements like iron and nickel were able to sink down into the planet and accumulate at the core. The core is believed to have two parts: a solid inner core, with a radius of 1,220 km, and a liquid outer core that extends to a radius of 3,400 km. The two most abundant elements found in the core are iron and nickel. This is why it is called as NIFE. The inner core is solid, but the outer core is a hot liquid. At the core of the earth, temperatures may be as high as 5000oC. The Liquid Outer Core The Solid Inner Core Fact File The Gutenberg Discontinuity is the name given to the core – mantle boundary about 1800 miles below the surface. The Layers of the Earth Material required: An apple, a knife Procedure: The teacher will cut the apple with a knife and ask the students to observe........ Conclusion: The seed area of the 5 apple is the core, the flesh of the apple is the mantle and the peel is the crust. An apple used to show the layers of the Earth CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Do You Know? According to some scientists, at the centre of the earth, there is a nucleus of high density atoms that descended from the atoms that were the beginning of our solar system. The deepest hole ever drilled is in the north – west centre of Russia for scientific research. It reached to a depth of about 7.6 miles. The temperature at this depth was 180oC at which point the rock became more like plastic than a solid, stopping further drilling. Earth’s greatest source of heat, besides the sun, is its interior, which conducts a hundred billion calories of energy to the surface each year. So much energy radiates from inside the earth that it could satisfy all human energy needs three times over. Rocks: The earth’s crust is majorly composed of rocks. Rocks are combinations of one or more minerals that we find in nature. They have been an integral part of mankind since time immemorial. Rocks were initially used as tools for hunting and later as building materials to construct shelters and monuments. The different kinds of minerals and metals that we find in rocks have contributed significantly to human prosperity. Classification of Rocks on the basis of Mode of Formation Rocks Classification (On the basis of Mode of Formation) Igneous Rocks (Primary rocks) Sedimentary Rocks (Secondary Rocks I) Metamorphic Rocks (Secondary Rocks II) Igneous Rocks: All the rocks on the earth were initially igneous in nature. The term “igneous” comes from the Latin word ignis that means fire. Igneous rocks are formed as a result of cooling and solidification of the hot magma that originates from far below the 6 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL earth’s surface. On the basis of their occurrence, igneous rocks can be classified into two categories (i) Extrusive rocks (ii) Intrusive Rocks Extrusive Igneous Rocks are formed by cooling of lava on the surface of the earth. The cooling process takes place quite rapidly leading to the formation of small crystals and have fine grain particles. Such types of rocks are called extrusive rocks. These rocks are also called volcanic rocks. Basalt is the most common example of an extrusive igneous rock is basalt. Basalt Rhyolite Andesite Obsidian Intrusive Igneous Rock are formed when magma solidifies below the surface of the earth. The rate of cooling below the earth’ surface is very slow which leads to the formation of large crystals and have coarse grains. Such types of rocks are called as plutonic or intrusive rocks. The most common example of an intrusive igneous rock is granite. Other examples include gabbro, dolerite etc. Granite Dolerite Gabbro Do You Know? Granite is the signature rock of the continents. More than that, granite is the signature rock of the planet Earth itself. The other rocky planets—Mercury, Venus and Mars—are covered with basalt, as is the ocean floor on Earth. But only Earth has this beautiful and interesting rock type in abundance. 7 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Sedimentary Rocks: The various agents of erosion like running water, wind and moving ice carry small particles of rock. These particles of rocks are deposited on land or on the beds of oceans and rivers forming sediments. The sediments are deposited in layers. Over the years these sediments get harden due to the weight of the layers above. In the ocean or the river beds, the weight of the water also helps in hardening the layers. Such rocks that are formed by the deposition and the hardening of the layers of the sediments are called as sedimentary rocks. The most common example of sedimentary rock is coal. Other examples include sandstone, limestone, shale, gravel, clay etc. Limestone Conglomerate Sandstone Shale Case Study – The Neighbourhood Rock Coal is an organic sedimentary rock that is Formed mainly from plant debris. The plant Debris usually accumulates in a swamp environment. Sometimes we find coal in the soil near our home, along railroad tracks, or along beaches. Coal is combustible and is mainly used as a fuel. Coal Can you name a few areas where coal is used as a fuel? Find out the largest producer of coal in the world. Locate the major coal producing regions on a world map. Metamorphic Rocks: The word ‘metamorphosis’ means change of form. The igneous and sedimentary rocks are transformed by the action of intense heat and pressure deep inside the earth’s surface. The changed rock that is formed is called as metamorphic rock. In course of 8 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL time shale may change into slate and schist, limestone to marble, sandstone to quartzite and granite to gneiss. Marble Quartzite Gneiss Do You Know? Some rocks such as chalk, red sandstone and limestone have pores, cracks and joints in them which let water drained easily. They are known as permeable rocks. The size of the particles in the rocks and the way they are arranged affects how permeable they are. Rocks that do not let water pass through them are impermeable rocks. Mica, granite, slate are some examples of impermeable rocks. Case study – A Visit To Agra Felix was very excited as he was visiting his grandmother in India for the first time. He had read about India in his seventh grade history book and wanted to see the famous Taj Mahal. As he was going to miss his school for few days, his geography teacher gave him a special 9 Taj Mahal project based on types of rocks that were used to build monuments Agra Fort in India. A Visit to Agra – A City known for its Mughal architecture was the subject of study for Felix. Accompanied by his parents, Felix reached Agra and saw the Famous Taj Mahal and CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL The Rock Cycle: All the three types of rocks are formed in different ways. The rock cycle is the process that makes and recycles rocks. We know that most of the rocks on earth began as igneous rocks. Igneous rocks are formed from cooling and solidification of the magma. When igneous rocks are exposed on the surface due to erosion and weathering the rock breaks down into smaller and smaller pieces. Wind and water carry these smaller pieces of igneous rocks as sediments and deposit them in the ocean or the river beds. Over time the sediment beds get buried and the pieces of rock become cemented together to form a new type of rock called a sedimentary rock. It is the igneous rock that has changed into a sedimentary rock. If the sedimentary rock is exposed at the surface, it can be eroded away and eventually changed into new sedimentary rock. However, if the sedimentary rock gets buried deep in the Earth, due to excessive heat and pressure, metamorphosis takes place and the rock changes into a metamorphic rock. Metamorphosis can happen to igneous rocks as well. The metamorphic rocks due to weathering and erosion change into sedimentary rocks. If the metamorphic rock is forced deeper into the Earth, the rock melts and becomes magma and form the igneous rock. Igneous rocks and sedimentary rocks can also be forced down into the earth and melt into magma and form the igneous rocks. . 10 Cycle The Rock CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL In short, the rock cycle includes the processes that forms and recycles the different types of rocks found in or on the surface of the earth. Rocks begin the cycle as igneous rocks, erode into sedimentary rocks then change into metamorphic rocks; finally the rocks melt back to magma and start the process again Uses of Rocks: Rocks and minerals have played an important role in the development of human civilization. Rocks and stones have been used in making tools and implements and for construction of buildings and monuments. For the better understanding of the importance of rocks, the following are the uses of rocks: 1. Soils: Soils are derived from rocks. Soils are essential for all plant growth. Soils provide suitability for agricultural products. 2. Mineral Service: Rocks are a store house of mineral. Igneous and metamorphic rocks are rich in metallic minerals like iron, lead, copper, gold, silver, diamond etc. Sedimentary rocks contain valuable deposits of coal, oil and natural gas. These are needed for all industrial and economic activities. 3. Source of Building Material: Rocks are the source of different types of building materials. Rocks provide us building stones like marble, sandstone or granite. Limestone and gypsum are used for the manufacture of cement. 11 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL 4. Source of Raw Materials: Rocks provide raw material for large number of mineral based manufacturing industries like iron & steel, aluminium and other metals along with petroleum that forms the basis for petrochemical industries. 5. Precious Stones: Precious stones and metal are obtained from different metamorphic or igneous rocks. Diamond, gens, rubies etc are used in jewellery. Various Uses of Rocks Following are the examples of uses of different types of rocks: Coal from China's Xuan Wei County, widely used for Cooking and Heating 12 Clay a sedimentary rock is used in making pottery. (Pottery) CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Red Sandstone Limestone * Coal a sedimentary rock is used as a domestic fuel and in power plants to make electricity. * Limestone a sedimentary rock, is used in the production of lime, manufacture of paper, petrochemicals, insecticides, fibreglass, glass, carpet backing and as the coating on many types of chewing gum. * Sandstone a sedimentary rock is used chiefly for construction. Gabbro Granite Gneiss Basalt Gabbro an igneous rock is widely used as crushed stone for concrete aggregate, road metal, railroad ballast, etc. 13 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Basalt an igneous rock is used in construction, making cobblestones and in making statues. Gneiss a metamorphic rock is used as building stones and other structural purposes. Green Marble Marble a metamorphic rock is quarried for use as dimension stone for statuary, architectural and ornamental purposes. In spite of the rock cycle a single layer of sedimentary rock may take centuries to build. This brings us to the important concern of sustainable use of this resource keeping the need and requirement of future generation in mind. GLOSSARY: Asthenosphere: A thin semi-fluid layer of the earth below the lithosphere, forming part of the mantle and thought to be able to flow vertically and horizontally, enabling sections of the lithosphere to move. Atmosphere: The envelope of the air surrounding the earth. Biosphere: The life-bearing layer of the earth. Crust - The rigid, rocky outer surface of the Earth composed mostly of basalt and granite. The crust is thinner under the oceans. Hydrosphere: The water-bearing layer of the earth. Igneous Rock: The rocks that are formed due to cooling and solidification of hot lava on the earth’s surface and magma in the earth’s surface. Inner core - The solid iron-nickel center of the Earth that is very hot and under great pressure. Lava: When the hot magma flows on the earth’s surface. Lithosphere: The rock-bearing layer of the earth. Magma: The molten rock material under the earth’s crust from which igneous rock is formed by cooling. 14 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Mantle - A rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. Convection (heat) currents carry heat from the hot inner mantle to the cooler outer mantle. Metamorphic Rock: Rocks that change their form due to intense heat and pressure. Moho discontinuity: It is the boundary between the crust and the mantle. Also called ‘Moho’. Outer core - the molten iron-nickel layer that surrounds the inner core. Rocks: Rocks are naturally occurring solid aggregates of minerals. Sedimentary Rock: Rock formed from consolidated clay sediments. Seismology: The science that studies the earthquake waves. WORKSHEETS WORKSHEET-I Name of the Student: Class: Section: Label the given diagram showing the layers of the earth’s interior. Write two interesting facts about each layer. 15 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL A_____________________________________________________________________ ______________________________________________________________________ B_____________________________________________________________________ ______________________________________________________________________ C_____________________________________________________________________ ______________________________________________________________________ D_____________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ WORKSHEET-II Name of the Student: Class: Section: Collect rock samples from your neighbourhood and prepare a report under the following headings: i. Name of the rock ii. Identify the rock as igneous or sedimentary or metamorphic iii. Observe and record the characteristics of your rock sample iv. State the use of your rock sample. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 16 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ WORKSHEET-III Name of the Student: Class: Section: Create a fact file about major types of rocks. Paste your picture of Igneous Rock State two facts related to Igneous Rocks 17 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Paste your picture of Sedimentary Rock State two facts related to Sedimentary Rocks ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Paste your picture of Metamorphic Rock State two facts related to Metamorphic Rocks 18 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ __________________________________________________________________________ WORKSHEET-IV Name of the Student: Class: Section: Match the following terms with their explanation: 1. Lava (a) An example of a sedimentary rock 2. Basalt (b) Tiny pieces of rocks 3. Sediments (c) Melted rock above the earth’s surface 4. Magma (d) An example of an igneous rock 5. Limestone (e) Melted rock beneath the earth’s surface 6. Identify the following rocks: WORKSHEET-V 19 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Name of the Student: Class: Section: 1. Complete the given diagram of the rock cycle by colouring the arrows according to the given colour code: Weathering and Erosion: Blue Heat and Pressure: Red Melting: Purple Cooling: Yellow Compaction and cementation: Green 20 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL 2. Complete the given extract regarding the rock cycle by using the words given in the box against the appropriate blank: Recycle means to take something old and change into something new. So some of these old rocks that have been around for more than four billion years are being changed into different rocks. Of course, that doesn't happen overnight. It takes millions of years. To better understand how this happens, let's take a journey through the ______________. Journey of the rocks begins in the mantle. Here there is some red hot _________ that is being pushed up towards the _________. Some of this magma creeps into the cracks of the volcano; while, the rest is forced out of the top of the volcano. Once the magma is out of the volcano, it is called lava. The lava ______ and forms ______________rocks. Then some of the igneous rocks roll down the mountains formed by the volcanoes and eventually end up in the ocean. As they roll, bits and pieces of the igneous rocks are broken and form ___________. Layer after layer of sediments are pressed and cemented together forming ______________________________. Some of the sedimentary rocks lying deep under the overlying layers get hot because of the ____________ and change to _________________ rocks. When the metamorphic rock is buried deeper, it gets hotter and melts. Once again, it becomes magma and may eventually be pushed up and out of a volcano. The rock cycle _______________ all over again! 21 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL Magma Rock cycle Cools Crust Pressure Sediments Igneous Metamorphic Sedimentary Begins WORKSHEET-VI Name of the Student: Class: Section: 1. Identify the activity in relation to the uses of rocks being depicted in the given picture (a) (b) (c) (d) _(a)___________________________________________ _(b)___________________________________________ _(c)___________________________________________ _(d)___________________________________________ _(e)___________________________________________ (e) 2. Give an account of how are rocks useful to man? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 22 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ Resources: A textbook of Geography – Class 9 –Rita Rajen Our World – Then and Now – Part II – S.Mukherjee, K.K.Maltiar, S.R.Maltiar and V.Shukla http://www.jgms.ccs.k12.nc.us/WindJammers/Jones/_overlay/plates/1bookpgs/FTT01AAD.pdf http://www.geography4kids.com/files/earth_intro.html http://www.gisthai.org/resource/article/systematic_geo_eng.html http://www.ehow.com/info_8746061_earths-layers-science-project-ideas.html http://geology.com/nsta/earth-internal-structure.shtml http://www.kidsgeo.com/geology-for-kids http://www.universetoday.com http://ratw.asu.edu/aboutrocks_igneous.html http://tlc.howstuffworks.com/home/pottery2.htm http://www.lung-cancer-blog.com/blogs/permalinks/1-2010/lung-cancermystery.html sandstone.stoneworthindia.com indiamart.com flexiblelearning.auckland.ac.nz ed101.bu.edu geology.about.com kishangarhmarble.com http://www.mrsciguy.com/rocks.html (http://www.rocksforkids.com/RFK/uses.html) http://www.coaleducation.org/lessons/wim/20.htm (http://www.sciencedaily.com/releases/2007/03/070301103112.htm) http://library.thinkquest.org/20035/newpage4.htm http://facts.randomhistory.com/2009/09/17_earth.html http://geology.com/rocks/sedimentary-rocks.shtml http://geology.about.com/od/more_igrocks/a/granite.htm www.thefreedictionary.com http://www.computerclipart.com/ tnsindia.net india-server.com westernreservepublicmedia.org education.com www.cotf.edu wn.com oceanworld.tamu.edu 23 CBSE-i CLASS VII GEOGRAPHY STUDENTS’ MANUAL indiatalkies.com www.visitjohnstownpa.com/.../ Google Images mii.org soil-net.com csmres.jmu.edu pitt.edu eurasian.in galleries.com www.swisseduc.ch/.../glossary/basalt-en.html rocks-rock.com vijayacement.com www1.newark.ohio-state.edu flexiblelearning.auckland.ac.nz 24