Geography Class-7 Inside Our Earth Structure of Earth On the basis of varying density and other physical and chemical properties of rocks, the earth can be divided into three concentric layers. These are as follows- Crust Mantle Core
Types of rocks There are three major types of rocks: igneous rocks sedimentary rocks metamorphic rocks
When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. There are two types of igneous rocks: intrusive rocks and extrusive rocks Sedimentary rocks- The rock rolls down and hit each other and is broken down into small fragments. These smaller particles are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks. For example, sandstone. Metamorphic Rock Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble. Rock Cycle The process of transformation of the rock from one to another is known as the rock cycle. When the molten magma cools; it solidifies to become igneous rock. These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks. When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. The metamorphic rocks which are still under great heat and pressure melt down to form molten magma. This molten magma again can cool down and solidify into igneous rocks.
Question and Answers Ques.1 Name the main type of rock with one example of each. Ans.1 The main type of rocks are- 1. Igneous rocks- shale, basalt 2. Sedimentary rocks- Coal, pumic 3. Metamorphic rocks- marble, slate Ques.2 How are metamorphic rocks formed? Ans.2 The metamorphic rocks are actually igneous or sedimentary rocks which have been changed due to excessive heat and pressure inside the earth. Ques.3 What do you know about the structure of earth? Ans.3 On the basis of varying density and other physical and chemical properties of rocks, the earth can be divided into three concentric layers - Crust, Mantle and Core. Ques.4 How are rocks and minerals useful to us? Ans.4 1.In ancient times, rocks were used to make tools and weapons.
2. It is used in the construction of roads, houses and buildings. 3. Minerals like coal and petroleum provide the sources of power. 4. To make fertilizers also. 5. Soil is formed from rocks. Ques.5- Why is it said that the rock cycle has neither a beginning nor end? Ans.5 - It is said that rock cycle has neither a beginning nor an end because 1. It is in cyclic manner. 2. In this process the matter of the earth crust is not lost. Tick the correct answer. (i) The rock which is made up of molten magma is - (a) Igneous (b) Sedimentary (c) Metamorphic (ii) The innermost layer of the earth is - (a) Crust (b) Core (c) Mantle (iii) Gold, petroleum and coal are examples of - (a) Rocks (b) Minerals (c) Fossils (iv)rocks which contain fossils are - (a) Sedimentary rocks (b) Metamorphic rocks (c) Igneous rocks (v) The thinnest layer of the earth is (a) Crust (b) Mantle (c) Core CLASS VII CHAPTER THREE (GEOGRAPHY) THE CHANGING EARTH WEGENERS' THEORY OF CONTINENTAL DRIFT: Millions of years ago, all landmasses were joint together into a super continent, called the pangaea. Wegener suggested that the pangaea
broke and there was a horizontal displacement of the continents. VOLCANOES: Types of volcanoes: Active volcano: Active volcanoes erupt frequently and throw out lava, gases, ashes and rocks. Stromboli and etna in italy are active volcanoes. Dormant volcanoes: dormant volcanoes are volcanoes that have become quiet after erupting. Vesuvius in italy is a dormant volcano. Extinct volcanoes: Extinct volcanoes have not erupted for hundreds of years. Mt. Killimanjaro in africa and Rainier in U.S.A are extinct volcanoes. EARTHQUAKES: The shaking of the earths' surface is called earthquake. The place of an earthquake is called focus. The point on the earths' surface which is vertically above the focus is called epicentre. BHUJ EARTHQUAKE OF 2001: The reason for bhuj earthquake were: Sea-floor spreading of the Indian ocean at the rate of five cm per year. Gradual northward movement of the Indian plate. The reactivatedfaults below the surface in the Kachchh region.