Inside our Earth Class 7 Notes CBSE Geography Chapter 2 [Free PDF Download]

1. Earth is the third planet of the solar system and unearths fascinating facts about its core. For now, Earth is the only celestial body that has life on which 29% of the earth surface is land and 71% is water. Scientists believe that the earth was formed around 4.5 billion years ago.

2. Layers of Earth

To understand the layers under the earth. Take an example of a cabbage, when cut vertically, we see layers of leaves and then an extreme core section. Earth’s structure is similar to it. 

Earth is made of three layers namely:

a. Crust:

i. Outermost layer of the Earth’s surface. 

ii. It is made of mainly Silicate. Its thickness can vary up to 5 km in the case of the oceanic crust or 35km in the case of continental crust.

iii. This Crust is made up of Sedimentary material and under this lies crystalline, igneous and metamorphic rocks, that are acidic in nature.

iv. Continents cover the crust area and are composed of lighter Silicate which is a mixture of Silica and Aluminum.

v. On the other hand, the ocean crust area is made up of heavier Silicate i.e. Silica + Magnesium (Sima).

vi. Around 1% of the Earth's volume falls under the crust.

b. Mantle:

i. Found beneath the Crust layer lies that runs for about 2900 km thick.

ii. It occupies 84% of the earth’s volume and holds about 66% of the earth’s mass.

iii. Made up of silicate rich in Iron and Magnesium.

iv. The temperature varies from 2000 degrees Celsius to 40000 degrees Celsius increasing as it moves towards the centre of it.

v. The high temperature allows the Silicate material to loosen up without changing its characteristics.

vi. The heat generated in the Mantle region causes the transfer of material in different directions that leads to landscape formation of the Earth. It also causes movement in tectonic plates which in turn causes volcanic eruptions, earthquakes, seabed movements and mountain formation.

c. Core:

i. Earth’s core is more like a furnace from where tremendous heat flows out and pressure which is known as geothermal gradient.

ii. The core is made up of Iron & Nickel.

iii. The core consists of two parts - The outer Core has a liquid portion which is quite malleable. The churning of this liquid portion creates and sustains the earth’s magnetic field. On the other hand, the Inner core is very hot and is a dense ball of Iron. The density and pressure inside this region prevent the iron from melting.

3. Rocks and Minerals

A rock is a mixture of several different minerals which are tightly held in a solid form. They occur naturally. 

On the basis of their formation, they can be categorised into:

a. Igneous Rock: Formed by the solidification of lava or magma. Magma is obtained from the melted forms of rocks found in the mantle or crust. It is mainly of two types:

i. Intrusive or Plutonic Rock: Those rocks formed when the magma cools and crystallizes inside Earth’s Crust itself. Granite is an example of plutonic rocks. 

ii. Extrusive or Volcanic Rock: In these, the magma comes out on the surface of the earth as a thick semi-solid form like lava and cools down. For example pumice or basalt rock.

b. Sedimentary Rock: These rocks are formed in water due to the accumulation and cementation of very small pieces of broken rocks, minerals, and organisms. Sandstones, limestone and shale are some of its examples. Several times sedimentary rocks contain fossils.

c. Metamorphic Rock: When either the sedimentary rocks or igneous rocks are subjected to high pressure and temperature conditions, their physical properties and chemical composition change. This phenomenon is known as metamorphism. Quartzite, marble etc. are examples of this.

4. Minerals: 

Minerals are naturally occurring elements or compounds that have certain physical properties and definite chemical composition. Minerals are quite useful to us. They can be used in many ways like fuels (e.g, coal), natural gas and petroleum; in the industries in the form of iron, aluminium, gold, uranium to form other objects. They can also be used as fertilizers and as raw materials for minerals.

Class 7 Social Science Geography Chapter 2 Inside Our Earth Notes

Overview of The Earth 

Earth can be a very dynamic planet. There are so many changes that are constantly going on, both outside the earth and inside it. There are three different layers that constitute the interior of the Earth. These layers are known as the Crust, Mantle, and Core. Most rocks are situated in the Crust of the earth. Rocks can be classified into three major groups known as Igneous, Sedimentary, and Metamorphic. Most minerals tend to occur naturally and have some physical properties as well as definitely the composition of chemicals. Students need to have Inside our Earth Class 7 notes to completely understand these topics and score good marks. 

A Look into The Earth’s Interior

There are various concentric layers that make up the Earth. These concentric layers are inside one another. The Crust is basically the layer that is uppermost and it is the thinnest one of all. The crust consists of 35km of landmasses and just 5 km of the floors of oceans. The constituents which make up most of the continental landmasses on the crust are alumina and silica. Hence, it is known as SiAl. Also, the minerals which make up the ocean masses are Magnesium and Silica. Hence, it is known as SiMa. You can find more details in the notes of Our Earth for class 2. 

The layer which is situated beneath the Earth’s crust is known as Mantle. The depth of the entire layer of Mantle is about 2900 km right below the earth. The layer which is beneath the Mantle is known as the core and it is the innermost one. The total radius of the core is about 3500 km. Hence, it is definitely the largest one of the layers. The main materials found in the core are iron and nickel and it is known as NiFe. One of the most important things to know about the core is that it has a very high temperature and very high pressure. Students can find the details in the Class 7 Geography Chapter 2 notes. 

Different Rocks and Minerals 

A rock can be defined as any particular and natural mass consisting of mineral matter. Rocks are meant to cover up the earth’s crust. There are different sizes, colours, and textures of rocks. 

The crust of the earth has a lot of different types of rocks that constitute the entire layer. We are going to classify these rocks into major groups. 

1. Igneous Rocks 

In the Inside our Earth Class 7 notes, there are details about Igneous rocks. These rocks are formed after the cooling down of magma. The magma turns solid and forms these types of rocks. Igneous rocks are Primary rocks. Igneous rocks can be classified into 2 types: Intrusive and Extrusive Igneous Rocks. 

• Intrusive Igneous Rocks: These are the rocks that are formed inside the layer of the earth’s crust due to the magma cooling-off deep inside. One great example of an intrusive igneous rock is Granite. This rock is used to create grinding stones. 

• Extrusive Igneous Rocks: These rocks are formed on the surface of the earth due to the cooling off of magma instantly after coming out. One such example of an extrusive igneous rock would be basalt. One of the facts states that the entire Deccan plateau consists of basalt rocks. 

2. Sedimentary Rocks

These are the rocks that are formed after they fall down, hit one another, and crack to form smaller fragments. These fragments are known as sediments and these are transported properly and deposited at a certain location by water and wind. One of the examples of sedimentary rocks is Sandstone. 

3. Metamorphic Rocks

The Sedimentary and Igneous rocks, when subjected to great pressure and heat, often turn to metamorphic rock. Limestone changing to marble and clay changing to slate are a few examples. 

The entire process through which the rocks go on changing from one form to another form can be known as the rock cycle. We hope that these Inside our Earth Class 7 notes are able to help you out properly in the examination.