Four Realms Of The Earth BOSEM Class 6 Social Science

Chapter Name: Four Realms Of The Earth
Subject: Social Science
Lesson: 5
Class: 6
Board: Board Of Secondary Education Manipur (BOSEM/BSEM)
Contents: Chapter, Questions and Answers, Important points to Remember.

Chapter 5: Four Realms Of The Earth

The Earth is a unique planet. Unlike other planets of the solar system, life is known to exist on the earth. It is found on land, in water, and in the air. The realm of land is called lithosphere while the realm of water is known as hydrosphere. The realm of air is called the atmosphere. These are the three major realms of the earth. Thus, all life forms are found in a narrow zone where land, water, and air meet.

This narrow zone, where life exists, is called the biosphere. It is the fourth realm of the earth. What is the reason for the existence of life on the earth? One of the reasons is that the earth has plenty of water on its surface. Did you know that the first life on the earth originated in water? All living beings are made of a considerable amount of water.

Lithosphere

The outer solid layer of the earth is called the crust or lithosphere. The word lithosphere comes from the Greek word Lithos which means rock. So, the crust or lithosphere is made up of rocks. About one-third of the earth’s surface is occupied by land and the rest is covered with water.

Continents

Vast land masses rising above the sea level are called continents. There are seven continents in the world. They are Asia, Africa, Europe, Australia, North America, South America and Antarctica.

The figure shows that most of the landmasses are located in the northern hemisphere. The continents are separated by huge bodies of water called oceans. The height of the land or the depth of the ocean is measured from the sea level.

The highest point on the earth’s surface is Mount Everest in the Himalayas. It is 8,848 meters high above the sea level.

Asia is the largest continent in the world. Our country India lies in the southern part of this continent.

Europe extends westwards from the continent of Asia. In fact, these two continents form a single landmass. They are separated by the Ural Mountains and the black sea. These two continents are collectively known as Eurasia.

Africa is the second largest continent next to Asia. It is the only continent through which the Tropic of Cancer, the Equator, and the Tropic of Capricorn pass.

North America and South America are connected by the narrow strip of land called the Isthmus of Panama. North America lies in the northern hemisphere. The Andes mountain which is the longest in the world lies in South America.

Australia is the smallest continent. It lies in the southern hemisphere. Since it is small and surrounded by oceans on all sides it is called a Continent.

Antarctica is situated in the southernmost part of the earth. The South Pole lies at the center of this continent. As the continent is in the south polar region, it is covered by thick ice all year round. Because of ice-covering, this continent is seen as snow-white. Therefore, it is also known as the white continent. The climate of this continent is not suitable for human habitation.

Major Landforms

The surface of the continents is not the same everywhere. It is very high in some places and low and levelled in others. Highland regions having pointed peaks are called mountains. Some of the highland regions have flat summits. They are known as plateaus. There are also lowland regions of flat and level surfaces called plains. Mountains, plateaus, and plains are called major landforms of the earth.

Mountains are highlands with pointed peaks. They rise several thousand meters above the sea level. When such highlands form a long chain, they are known as mountain ranges. In some places, they may occur in a series of parallel ranges.

The Himalayas and the Rockies are young mountains while the Aravalli and the Urals are old mountains. Young mountains are very high but old mountains are low and rounded. Old mountains become low and rounded because they have been eroded over the years. Mountains are unsuitable for human settlement because of rugged topography, poor transportation, and harsh climate.

Plateaus are also highlands with flat summits. Because flat summits, look like a table. Therefore, they are known as tablelands. The Deccan plateau of India is a good example of tableland. A plateau has one or more sides with steep slopes. Sometimes they extend over thousands of square kilometres.

Look at the map of Asia in your atlas and find the plateau of Tibet. This plateau is the highest in the world. So it is often called the roof of the world. In contrast with mountains, plateaus have well-developed transportation systems. Thus, plateaus are moderately populated.

Plains are lowland regions of flat surface. They are found along the sea coasts or in the river valleys. Generally, they are not more than 200 meters above sea level. Rivers originating from mountains carry large amounts of silt. They deposit the materials either in the sea or along their banks. These deposits are responsible for the formation of plains.

You will see that the largest plains are formed along the river valleys all over the world. The Ganga Plain and the Mississippi Plain are the examples. Silt deposits made by the river are known as the alluvium. Alluvial deposits form the most fertile lands. Thus, plains are suitable for agricultural activities. The Ganga Plain is noted for the production of different crops.

Plains are the most fertile regions. Transport systems are also well-developed. Thus, plains are thickly populated.

Hydrosphere

The earth is called a watery planet because more than two-thirds of its surface is covered with water. Water is collected in large depressions of the earth. Thus, oceans, seas, lakes, and rivers are formed. These water bodies are collectively known as hydrosphere.

Oceans

Oceans are vast water bodies. All the oceans of the earth are interconnected. The level of the oceans is all the same. This level of water is called the sea level. There are four oceans on the earth’s surface. They are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic Ocean. The Pacific, the Atlantic, and the Indian Oceans meet in the southern part of the earth to form the Southern Ocean.

The Pacific Ocean is the largest in the world. It is also the deepest. The Mariana Trench, off the Guam Islands in the Pacific, is 11,022 meters deep. This ocean lies between Asia and Australia on one side and North and South America on the other.

The Atlantic Ocean is about half the size of the Pacific. It resembles the letter S in shape. It is bounded by North and South America on the west and Europe and Africa on the east.

The Indian Ocean does not open out on the north because it is bounded by the continent of Asia. Therefore, it is called half an ocean. It is the only ocean named after a country.

The Arctic Ocean is located around the North Pole. It is surrounded by the northern parts of the continents of Asia, Europe, and North America. Being situated in the North Frigid Zone. It remains frozen for most part of the year. Therefore, this ocean is not important for trade or navigation.

Do you know that exports and imports of a country are done through ports and harbours?

These are located along the sea coast. Indented coastlines provide excellent sites for ports and harbours. Look at your atlas and compare the coastlines of the United Kingdom with those of India. Which coastline will be suitable for the location of ports and harbours?

Atmosphere

The earth is surrounded by a layer of air. This blanket of air surrounding the Earth is called the atmosphere. The atmosphere extends up to 1600 kilometres from the earth’s surface. It is made up of gases like nitrogen, oxygen, carbon dioxide, argon, etc. Some of these gases are essential for living beings.

The air we inhale is Oxygen. Carbon dioxide helps plants to manufacture their food. Nitrogen is the most dominant gas. It constitutes about 78% of the atmosphere. It helps the living organisms to grow. Oxygen, the life of human beings, constitutes about 21%. Thus, nitrogen and oxygen constitute about 99% of the atmosphere.

The remaining 1% is made up of other gases like argon, carbon dioxide, hydrogen, etc.

The air is very dense near the surface of the earth. It becomes thinner and less dense when we go high up in the sky. On the top of high mountains, a lesser amount of oxygen in the air makes us discomfort in breathing. That is why mountaineers who climb Mount Everest carry oxygen. The atmosphere keeps us warm and protects us from the harmful effects of the rays of the sun.

The air we exhale is carbon dioxide which the plants take in. The plants, on the other hand, release oxygen which we inhale. So there is a cycle in the atmosphere which helps in maintaining the natural balance on the earth.

Biosphere

The narrow zone on the earth’s surface, where life exists, is called the biosphere. This is the most important realm of the earth. The word bio means life. So it is the realm of life. All the life forms are found in a narrow zone where land, water, and air meet. This zone extends a few kilometres above and below sea level. Human beings, plants, animals, birds, fishes, and other microbes are found in this realm.

Life forms are classified into two groups or kingdoms. They are animal kingdoms and plant kingdoms. Human beings are included in the animal kingdom. They are called men. They can make decisions based on reason. Thus, we often say man is a rational animal. Human beings are the most important members of the animal kingdom. We know that there is interdependence between the animal kingdom and the plant kingdom. Therefore, we should work to maintain a balanced nature for the survival of the two.

All the realms of the earth are very much interrelated. When something happens to one realm, that will affect other realms too. Do you know that the roots of the plants fasten the soil? If we cut many trees on the land, the soil will be loosened. The loose soils are easily carried away by rainwater and deposited in the river beds. It leads to the silting of river beds. At the time of heavy rain, the river will not be able to hold the water in its shallow bed.

The river overflows its banks and floods occur. Floods destroy the lives and properties of people. Moreover, the felling of trees will reduce the amount of oxygen in the atmosphere. It may threaten the existence of human beings on the earth. Therefore, we must try not to disturb the realms of the earth as much as we can.

Things to Remember

Bosem Solutions For Class 6 Social Science Chapter 5

Q1. Which is the smallest continent in the world?

Ans: Australia

Q2. Why is the Indian Ocean called half an ocean?

Ans: The Indian Ocean does not open on the north because it is bounded by the continent of Asia. Therefore, it is called half an Ocean.

Q3. What is Atmosphere?

Ans: The blanket of air surrounding the earth is called the atmosphere.

Q4. Explain the four realms of the earth.

Ans: The four realms of the earth are:

Lithosphere: The realm of the land, i.e. the outer solid layer of the earth is called the lithosphere.

Hydrosphere: The realm of water i.e., water bodies on the earth’s surface like oceans, lakes, rivers, and seas are known as Hydrosphere.

Atmosphere: The realm of air i.e., the blanket of air surrounding the earth is called atmosphere.

Biosphere: The realm of the earth where life exists, I,e. the narrow zone where land, water, and air meet is called Biosphere.

Q5. Name the continents of the world.

Ans: The continents of the world are Asia, Africa, North America, South America, Australia, and Antarctica.

Q6. What are the three major landforms of the earth?

Ans: The three major landforms of the earth are Mountains, Plateaus, and plains.

Q7. What are the two most dominant gases in the atmosphere?

Ans: The two most dominant gases of the atmosphere are Nitrogen and Oxygen. They constitute 99% of the atmosphere.