Chapter 2: Inside Our Earth
Overview of the Chapter
Understanding the Chapter
This chapter explores the structure and composition of the Earth’s interior. It explains the different layers of the Earth, the types of rocks, and the rock cycle, highlighting how these elements contribute to the formation and transformation of the Earth’s surface.
Structure of the Earth
Layers of the Earth
Crust: The outermost layer of the Earth. It is thin compared to other layers and forms the Earth’s surface.
Continental Crust: Thicker and less dense, mainly composed of granite.
Oceanic Crust: Thinner and denser, primarily composed of basalt.
Mantle: Located beneath the crust, it extends up to 2900 km below the Earth’s surface. It is composed of semisolid rock that moves slowly.
Core: The innermost layer of the Earth, consisting of two parts:
Outer Core: Liquid layer composed mainly of iron and nickel.
Inner Core: Solid, dense center primarily made of iron and nickel.
Types of Rocks
Igneous Rocks
Formation: Formed from the cooling and solidification of magma or lava.
Types:
Intrusive Igneous Rocks: Formed from magma that cools slowly beneath the Earth’s surface (e.g., granite).
Extrusive Igneous Rocks: Formed from lava that cools quickly on the Earth’s surface (e.g., basalt).
Sedimentary Rocks
Formation: Formed from the compaction and cementation of sediments. These sediments are often deposited in layers.
Types:
Clastic Sedimentary Rocks: Formed from mechanical weathering debris (e.g., sandstone).
Chemical Sedimentary Rocks: Formed from dissolved minerals precipitated from water (e.g., limestone).
Organic Sedimentary Rocks: Formed from the accumulation of plant or animal debris (e.g., coal).
Metamorphic Rocks
Formation: Formed from existing rocks that are changed by heat, pressure, or chemical processes.
Types:
Foliated Metamorphic Rocks: Have a layered or banded appearance (e.g., gneiss).
Nonfoliated Metamorphic Rocks: Do not have a layered or banded appearance (e.g., marble).
The Rock Cycle
Understanding the Rock Cycle
Process: The rock cycle describes how rocks are transformed from one type to another through various geological processes.
Stages:
Formation of Igneous Rocks: Magma cools and solidifies.
Formation of Sedimentary Rocks: Rocks are weathered, eroded, deposited, compacted, and cemented.
Formation of Metamorphic Rocks: Rocks are subjected to heat and pressure, causing them to change.
Significance of Rocks
Uses of Rocks
Construction Materials: Rocks like granite and marble are used in building construction.
Industrial Use: Rocks like limestone are used in cement manufacturing.
Gemstones and Minerals: Precious stones like diamonds and minerals are extracted from rocks.
Conclusion
Summary of the Chapter
The Earth is composed of different layers: the crust, mantle, and core.
There are three main types of rocks: igneous, sedimentary, and metamorphic.
The rock cycle explains how rocks are formed, transformed, and recycled over time.
Additional Information
Key Terms and Concepts
Crust: The outermost layer of the Earth.
Mantle: The layer beneath the crust, composed of semisolid rock.
Core: The innermost layer of the Earth, consisting of the outer and inner core.
Igneous Rocks: Rocks formed from the cooling of magma or lava.
Sedimentary Rocks: Rocks formed from the compaction and cementation of sediments.
Metamorphic Rocks: Rocks formed from the transformation of existing rocks by heat, pressure, or chemical processes.
Rock Cycle: The continuous process of rock formation and transformation.
Important Examples and Places
Granite: An example of intrusive igneous rock found in continental crust.
Basalt: An example of extrusive igneous rock found in oceanic crust.
Sandstone: A clastic sedimentary rock commonly found in deserts and riverbeds.
Limestone: A chemical sedimentary rock used in construction.
Marble: A nonfoliated metamorphic rock used in sculptures and buildings.
Notable Geological Processes
Weathering: The breaking down of rocks into smaller pieces by natural forces.
Erosion: The movement of sediments by wind, water, or ice.
Compaction and Cementation: Processes that form sedimentary rocks from sediments.
Heat and Pressure: Forces that transform rocks into metamorphic rocks.
Frequently Asked Questions (FAQs)
The crust, the mantle, and the core.
The crust is the outermost layer of the Earth, composed of solid rock.
Continental crust and oceanic crust.
The mantle is the layer beneath the crust, composed of semisolid rock that moves slowly.
The outer core and the inner core.
The outer core is made of liquid iron and nickel.
The inner core is solid and composed mainly of iron and nickel.
Igneous rocks are formed from the cooling and solidification of magma or lava.
Intrusive igneous rocks are formed from magma that cools slowly beneath the Earth’s surface, like granite.
Extrusive igneous rocks are formed from lava that cools quickly on the Earth’s surface, like basalt.
Sedimentary rocks are formed from the compaction and cementation of sediments.
Clastic sedimentary rocks are formed from mechanical weathering debris, like sandstone.
Chemical sedimentary rocks are formed from dissolved minerals precipitated from water, like limestone.
Organic sedimentary rocks are formed from the accumulation of plant or animal debris, like coal.
Metamorphic rocks are formed from existing rocks that are changed by heat, pressure, or chemical processes.
Foliated metamorphic rocks have a layered or banded appearance, like gneiss.
Non-foliated metamorphic rocks do not have a layered or banded appearance, like marble.
The rock cycle is the continuous process of rock formation and transformation.
Igneous rocks are formed from the cooling and solidification of magma or lava.
Sedimentary rocks are formed from the compaction and cementation of sediments.
Metamorphic rocks are formed from existing rocks that are subjected to heat and pressure.
The rock cycle explains how rocks are formed, transformed, and recycled over time.
Rocks are used as construction materials, in industrial processes, and as sources of gemstones and minerals.
Weathering is the breaking down of rocks into smaller pieces by natural forces.
Erosion is the movement of sediments by wind, water, or ice.
Chapter 2: Inside our Earth MCQs
1. What is the outermost layer of the Earth called?
2. Which type of crust is thicker and less dense?
3. What is the mantle primarily composed of?
4. What is the core mainly made of?
5. What are igneous rocks formed from?
6. What type of igneous rock is formed from magma that cools slowly beneath the Earth’s surface?
7. Which type of rock is formed from the compaction and cementation of sediments?
8. What type of sedimentary rock is formed from mechanical weathering debris?
9. What are metamorphic rocks formed from?
10. What type of metamorphic rock has a layered or banded appearance?
11. What process describes the continuous formation and transformation of rocks?
12. What is the breaking down of rocks into smaller pieces by natural forces called?
Access comprehensive short notes for all chapters of the Class 7 History NCERT book ‘Our Pasts-II,’ tailored for CBSE students. Click here to view the complete collection of notes.
