G-6: DOMAINS OF THE EARTH

• The earth's surface is a complex zone in which three main components of the environment meet, overlap, and interact. These are the lithosphere (solid portion of the earth on which we live), Atmosphere (gaseous layers that surround the earth), and Hydrosphere (area of the Earth's surface having water on it). 

• The Biosphere is the narrow zone where we find land, water, and air together, which contains all forms of life.

A. Lithosphere (स्थलमंडल)

• The lithosphere comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements that sustain organisms. 
• There are two main divisions of the earth’s surface. The large landmasses are known as the continents and the huge water bodies are called the ocean basins. 
• All the oceans of the world are connected with one another. The level of seawater remains the same everywhere. Elevation of land is measured from the level of the sea, which is taken as zero.
• The highest mountain peak Mt. Everest is 8,848 metres above sea level. The greatest depth of 11,022 meters is recorded at Mariana Trench in the Pacific Ocean.

• The lithosphere is the solid crust or the hard top layer of the earth. It is made up of rocks and minerals and covered by a thin layer of soil. 
• It is an irregular surface with various landforms such as mountains, plateaus, plains, valleys, etc. Landforms are found over the continents and also on the ocean floors. 
• The lithosphere is the domain that provides us forests, grasslands for grazing, land for agriculture, and human settlements. It is also a source of mineral wealth.

Continents (महाद्वीप)

• There are seven major continents separated by large water bodies. These continents are – Asia, Europe, Africa, North America, South America, Australia and Antarctica.
• Asia is the largest continent. It covers about one-third of the total land area of the earth. 
• It lies in the Eastern Hemisphere. The Tropic of Cancer passes through this continent. 
• Asia is separated from Europe by the Ural Mountains on the west. The combined landmass of Europe and Asia is called the Eurasia (Europe + Asia).
• Europe is much smaller than Asia. The continent lies to the west of Asia. 
• The Arctic Circle passes through it. It is bound by water bodies on three sides which are: the Arctic Ocean, Atlantic Ocean, and Mediterranean Sea. 
• Africa is the second largest continent after Asia. The Equator runs almost through the middle of the continent. 
• A large part of Africa lies in the Northern Hemisphere. It is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass. 
• The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bound on all sides by oceans and seas. The world’s longest river the Nile, flows through Africa.
• North America is the third largest continent of the world. It is linked to South America by a very narrow strip of land called the Isthmus of Panama. 
  
• The continent lies completely in the Northern and Western Hemisphere. Three oceans surround this continent: the Arctic Ocean, the Pacific Ocean, and the Atlantic Ocean.
• South America lies mostly in the Southern Hemisphere. Two oceans surround it: the Atlantic Ocean on the east and, the Pacific Ocean on the west. 
• The Andes, the world’s longest mountain range, runs through its length from north to south. South America has the world’s largest river, the Amazon.
• Australia is the smallest continent that lies entirely in the Southern Hemisphere. It is surrounded on all sides by the oceans and seas. It is called an island continent. 
• Antarctica, completely in the Southern Hemisphere, is a huge continent. The South Pole lies almost at the center of this continent. 
• As it is located in the South Polar Region, it is permanently covered with thick ice sheets. There are no permanent human settlements. 
• Many countries have research stations in Antarctica. India also has research stations there which are named Maitri and Bharati.

B. Hydrosphere (जलमण्डल )

• The earth is called the blue planet. More than 71% of the earth is covered with water and 29% is with land. 
• The hydrosphere consists of water in all its forms as running water in oceans, rivers, and lakes, ice in glaciers, underground water, and water vapor in the atmosphere. 
• More than 97% of the Earth’s water is found in the oceans and is too salty for human use. A large proportion of the rest of the water is in the form of ice sheets and glaciers or under the ground and a very small percentage is available as fresh water for human use.

•  It comprises various sources of water and different types of water bodies like rivers, lakes, seas, oceans, etc. It is essential for all living organisms.

Oceans (महासागर)

• Oceans are a major part of the hydrosphere. They are all interconnected. 
• The ocean waters are always moving. The three chief movements of ocean waters are the waves, the tides, and the ocean currents. 
• The 5 major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean, in order of their size.
• The Pacific Ocean is the largest ocean. It is spread over one-third of the earth. 
• Mariana Trench, the deepest part of the earth, lies in the Pacific Ocean. The Pacific Ocean is almost circular in shape. Asia, Australia, North America, and South America surround it.
• The Atlantic Ocean is the second-largest Ocean in the world. It is ‘S’ shaped. 
• It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. The coastline of the Atlantic Ocean is highly indented. 
• This irregular and indented coastline provides the ideal location for natural harbors and ports. From the point of view of commerce, it is the busiest Ocean. 
• The Indian Ocean is the only ocean named after a country, that is, India. The shape of the ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa, and in the east by Australia. 
•  The Southern Ocean encircles the continent of Antarctica and extends northward to 60° south latitude. 
• The Arctic Ocean is located within the Arctic Circle and surrounds the North Pole. It is connected with the Pacific Ocean by a narrow stretch of shallow water known as the Berring Strait. It is bound by the northern coasts of North America and Eurasia.

C. Atmosphere (वायुमंडल)

• The earth is surrounded by a thin layer of gas called the atmosphere. This blanket of air is an integral and important aspect of the planet. 
• It provides us with the air we breathe and protects us from the harmful effects of the sun’s rays. The atmosphere extends up to a height of about 1,600 kilometers. 
• The gravitational force of the earth holds the atmosphere around it. It protects us from the harmful rays and scorching heat of the sun. 
• It consists of a number of gases, dust and water vapour. The changes in the atmosphere produce changes in the weather and climate.
• The atmosphere is divided into five layers based on composition, temperature, and other properties. 
• These layers starting from the earth’s surface are called the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere. 
  

• The atmosphere is composed mainly of nitrogen and oxygen, which make up about 99% of clean, dry air. Nitrogen 78%, oxygen 21%, and other gases like carbon dioxide, argon, and others comprise 1% by volume. 
• Oxygen is the breath of life while nitrogen helps in the growth of living organisms. Carbon dioxide, though present in minute amounts, is important as it absorbs heat radiated by the earth, thereby keeping the planet warm. It is also essential for the growth of plants. 
• The density of the atmosphere varies with height. It is maximum at the sea level and decreases rapidly as we go up. Due to this, the climbers experience problems in breathing because of a decrease in the density of air and have to carry with them oxygen cylinders to be able to breathe at high altitudes. The temperature also decreases as we go upwards. 
• The atmosphere exerts pressure on the earth. It varies from place to place. Some areas experience high pressure and some areas low pressure. Air moves from high pressure to low pressure. Moving air is known as wind.

D.  BIOSPHERE (जीवमंडल)

• The biosphere is the narrow zone of contact between the land, water, and air. It is in this zone that life, which is unique to this planet, exists.
• There are several species of organisms that vary in size from microbes and bacteria to huge mammals. All living organisms including humans are linked to each other and to the biosphere for survival. 
• The organisms in the biosphere are broadly divided into the plant kingdom and the animal kingdom. The three domains of the earth interact with each other and affect each other in some way or the other. 
• An increase in the amount of CO2 leads to an increase in global temperatures. It is termed as global warming. There is thus, a need to limit the use of resources of the earth to maintain the balance of nature between the domains of the lithosphere, the atmosphere, and the hydrosphere.

Facts

• In the Greek language, Lithos means Stone; Atmos means Vapour; Hudor means Water; and Bios means Life.
• Edmund Hillary (New Zealand) and Tenzing Norgay Sherpa (India) were the first men to climb the highest mountain peak Mt. Everest on the planet Earth on 29th May 1953. 
• Junko Tabei (Japan) was the first woman to reach the summit on 16th May 1975. 
• The first Indian woman to climb the highest peak on 23rd May 1984 was Bachendri Pal.