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Major Domains of the Earth







Our earth is a unique planet. It has life supporting features that make the existence of various forms of life possible on our planet. Life exists on the earth due to the presence of three domains-


1)   Occupied by land, 2) water and 3) air.


These domains represents the three major states in which matter exists- Solid, liquid and gas, respectively. The domains of land, water and air meet and interact on the surface of the earth. There is a fourth domain where these three meet and interact. It is this fourth domain where all life forms exist. The four domains of the earth have been geographically termed as-


Lithosphere or the domain of land that constitutes the solid portion of the earth.

Hydrosphere or the domain of water that comprises all water bodies on the earth.

Atmosphere or the domain of air that exists in the form of blanket of air around us.

Biosphere or the domain of the living world.



Lithosphere


The outermost solid layer of the earth, made up rocks and soil, is called the lithosphere. It is also known as the crust of the earth. About 71% of the total area of the lithosphere is covered by water. The remaining 29% is occupied by land. The large masses of land are called continents.  The vast water bodies are known as oceans. Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C) which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth. The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid, which seems to be in continual motion.


There are seven continents. In decreasing order of their size, these are- 



1.Asia, 
2.Africa, 
3.North America, 
4.South America, 
5.Antarctica, 
6.Europe and 
7.Australia.  






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World- Continents and Oceans



The continents are not evenly distributed over the surface of the earth. Two of these continents Europe and North America are completely in the Northern Hemisphere.

A brief description of all the continents is as follows-:



Asia


Asia is the largest continents in the world, both in terms of area and population. It extends from about 10S to 80 N latitudes and from about 25 E to 170 E longitudes. The north-south extent is about 8500 km and the east-west extent is about 9600 km. The total area of Asia, including Asian Russia (with the Caucasian isthmus) but excluding the island of New Guinea, amounts to some 17,226,200 square miles (44,614,000 square km), roughly one-third of the land surface of Earth. Major part of Asia is in the Northern Hemisphere.

Asia is surrounded by the Arctic Ocean in the north, the Indian Ocean in the south, and the Pacific Ocean in the east. It has the highest mountain peaks and the lowest points in the world. Some of the world’s largest rivers, such as the Yangtze, Euphrates, Indus and Ganga flow through this continent.

Asia is a land of high mountains, vast plateaus, extensive plains and fertile river valleys. The Himalayas are the highest mountain range and Tibet is the highest plateau in the world. The island groups of Japan, the Philippines and Indonesia lie towards the east and south-east of Asia. Some islands along the Pacific Ocean coast have dormant and active volcanoes.


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Map- Asia (Physical)








Africa


It is the second largest continents after Asia. The Equator runs almost through the middle of the continent. A large part of Africa lies in the Northern Hemisphere. It lies to south of Europe and is bordered by the Atlantic and Indian oceans. The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bounded on all sides by oceans and seas. The world’s longest river, the Nile, also flows through Africa. Africa almost touches Europe and Asia at the Strait of Gibraltar, the Isthmus of Suez and the Strait of Bab-el-Mandeb.

The continent has a huge plateau surface. There are no high mountains or extensive plains. Special physical features include vast deserts and the Great Rift valley. The peaks of volcanic origin are Mt Kenya and Mt Kilimanjaro. Nile is the most important river. Apart from the Sahara Desert, Kalahari and Namib are two other major deserts of Africa. The Congo basin is an important low-lying area.




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Map- Africa (Physical)





North America




With an area of about 24 million sq. Km, North America is the world’s third largest continent.

      It lies entirely in the Northern Hemisphere. It is linked to South America by the Isthmus of Panama. It is separated from Asia by the Bering Strait.

     North America has ancient plateaus, mountain ranges and extensive plains. The northern part of North America remains under snow cover almost throughout the year. Many glacial lakes are also found in this part. The five Great Lakes between Canada and USA, together with the St Lawrence river from the greatest inland waterway in the world.

      The Grand Canyon, carved out by the Colorado river, is the deepest canyon in the world. The coastal ranges are a part of the Ring of Fire which surrounds the Pacific Ocean.


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Map- North America (Physical)





South America



     South America is the fourth largest continent in the world. It lies mostly in the Southern Hemisphere. The Andes, the world’s largest mountain range, runs through its length from north to south. The Amazon, the world’s largest river in terms of total volume of water, flows through this continents. South America is surrounded by the Caribbean Sea in the north, the Atlantic Ocean in the east and the Pacific Ocean in the west. In the north, the Isthmus of Panama links it to North America. Towards the south, the continent is very close to Antarctica.

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Map- South America (Physical)





Antarctica





     Antarctica is the fifth largest continent in the world. It is centered roughly around the South Pole. Due to thick ice cover, it is known as the White Continent. Therefore, this large continent does not have any permanent human settlement. It lies completely in the Southern hemisphere.

    Many countries have research station here. Indian research stations are named Maitri and Dakshin Gangotri. The first Indian team touched the icy continent on 9th January 1982.



Europe



    Europe and Asia are a continuous landmass known as Eurasia. The two continents are however separated by the Ural Mountain.

     Europe is bounded by the Arctic Ocean in the north, the Atlantic Ocean in the west and the Mediterranean Sea in the south. It has a very irregular coastline, which extends to 38,000 km and is marked by bays and Fjords. Europe is also marked by thousands of lakes in Finland, Norway and Sweden. The Rhine, Rhone, Danube, Volga, Dnieper and Thames are some of the major rivers here.

      Europe is a continent of high mountains and vast plains. The Alpine system is a chain of high mountains extending from the Atlantic Ocean in the west to the Caspian Sea in the east. The region has many active volcanoes such as Vesuvius and Etna.


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Map- Europe (Physical)





Australia


     With an area of about 8.51 millions sq. Km, Australia is the smallest continent in the world. It lies entirely in the Southern Hemisphere.

      Australia is called the Island continent, as it is surrounded by oceans and seas on all sides. It extends from about 10⁰S to 44⁰S latitudes and from about 112⁰E to 154⁰E longitudes. Abel Tasman, a Dutch man explored parts of Australia in 1642. The major part of Australia is a plateau with a few low isolated mountain ranges. The main features include the Great Dividing Range towards the east, the central low land (Great Artesian Basin) and the western desert. The Great Barrier Reef along the north-eastern coast of Australia is a unique feature. It is made of corals and is a great attraction for tourists.

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Map- Australia ( Physical)




Hydrosphere



     Seen from the outer space, our planet earth looks blue in colour and hence it is called the Blue Planet. This is because approximately 71% of the surface of the earth is covered with water. All the water bodies such as the oceans, seas, rivers, lakes, etc. together make up the hydrosphere. It also includes the ice sheets in the polar and high mountain regions, underground water and water vapor in the air.



Oceans


      There are four major oceans in the world. In the decreasing order of their size, these are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic Ocean. The continent of Antarctica is surrounded by a water body which is actually an extension of the Pacific, the Atlantic and the Indian oceans. It is known as the Antarctic Ocean or the Southern Ocean.



The Pacific Ocean


      It is the world largest ocean. It is spread across one-third of the total area of the earth. Its area is even more than the combined areas of all the continents. It is also the deepest ocean. The Mariana Trench, the deepest place on the earth’s surface, lies in the Pacific Ocean. This ocean is almost circular in shape.

       In the north, it is connected to the Arctic Ocean through the narrow Bering Strait. In the south, it merges with the Atlantic and the Indian ocean.


Indian Ocean


      The Indian Ocean is the only ocean that has been named after a country. Its shape is roughly triangular. The continent of Asia lies to the north of Indian Ocean. India lies at the head of this ocean. Arabian Sea and Bay of Bengal are the two northward extensions of the Indian Ocean. To the east of this ocean lies Antarctica and to the west lies Africa. In the South, it merges with the Atlantic and the Pacific oceans. On the western side of the Indian Ocean is Africa and on the east lies Australia. The natural beauty of the volcanic island of Mauritius is simply breathtaking, surrounded by magnificent coral reefs and an abundance of colourful sea life.


The Atlantic Ocean


       It is the second largest ocean in the world. This ocean is flanked by North America and South Africa on the western side, and Europe and Africa on the eastern side. It is roughly half of size of the Pacific Ocean. The Atlantic Ocean is very irregular. It provides excellent locations for ports and harbours. In terms of passengers and cargo traffic, it is the busiest ocean. The Atlantic Ocean is home to a massive mountain range in its depths called the Mid Atlantic Range. The deepest known point in the Atlantic is an area called Milwaukee Depth. It descends 27,493 feet. That makes it about as deep as Mount Everest is tall. The point lies within an area called the Puerto Rico Trench, sitting less than 100 miles off the coast of Puerto Rico. The range marks the point where the Northern American and Eurasian continental plates meet. In some regions, it can be seen above the water in the form of islands such as in Iceland, Azores, and Ascension Island.


The Arctic Ocean


       Most of the Arctic Ocean is permanently covered with a vast floating raft of sea ice. Here, temperatures are very low, averaging -30C in winter and sometimes dropping to -70⁰C. The climatic conditions depend on the seasons; the sky is mostly cloudy over the Arctic ocean. Winter is long and lasts from September to May. The sea ice-packs are affected by wind and ocean currents. It 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 Bering Straits. It is bounded by northern coasts of North America and Eurasia. There are several ports in the Arctic Ocean. The biggest ports are Murmansk in Russia, Kirkenes in Norway and Nuuk in Greenland, Churchill in Canada and Barrow in Alaska/USA.



Importance of Ocean:


Oceans are the main source of moisture in the atmosphere. They exercise direct control over the atmosphere temperature.

All the oceans are the storehouse of various minerals and chemicals.

They are also the main source of fish and other marine life.

They provide a free and permanent highway for travel and trade.

The shortage of drinking water can be solved by treating ocean water.



Atmosphere


The atmosphere is the envelope surrounding the earth. It extends up to some 16,000 kilometres above the earth’s surface. It represents the gaseous realm of the earth. It is held to the earth by the force of gravity and rotates with earth. The air generally becomes thinner and cooler as we go up into the atmosphere.


Composition of Atmosphere


The atmosphere is composed of the following three constituents:-

Gases:- The Atmosphere consists of a mixture of gases. Nitrogen is the biggest component, constituting 78% of atmosphere. Oxygen is the second major component of the atmosphere accounting for about 21% of it. Other gases together form only 1%. These include Argon (0.93%), Carbon dioxide (0.03%), Hydrogen (0.01%) and other gases (0.05%). The composition of the atmosphere remains almost constant in its lower layers. Oxygen is the most important of all gases as it supports all forms of life. Nitrogen keeps the soil fertile and helps in the growth of living organisms. Carbon dioxide in the atmosphere is absorbed by plants for their growth and also absorbs heat, keeping the earth warm.



Water Vapour and Dust:


       Water vapour and dust particles are also confined to the lower layer of the atmosphere.

      The amount of water vapour and dust particles in the atmosphere vary not only from place to place but also from time to time.



Structure of the Atmosphere


The Atmosphere can be divided into five layers. There is a thin buffer zone between each two layers.


Troposphere is the lowest layer, with the clouds and all the weather occurrences, such as storms. Hence, the temperature decreases with height. The troposphere is heated from below. Sunlight warms the ground or ocean, which in turn radiates the heat into the air right above it. This warm air tends to rise. That keeps the air in the troposphere "stirred up".


Stratosphere is the region with the Ozone layer that absorbs the harmful ultraviolet rays emitted the Sun and prevents them from reaching us. Temperatures increase with height in this layer.


Mesosphere, it is the part of the earth’s atmosphere which is between 50 and 80 km from the ground, between stratosphere and thermosphere. Meteors or rock fragments burn up in the mesosphere.


Thermosphere is that part of atmosphere where the space shuttle orbits. The air particles inside this layer are very separate. This layer has this name only due to the high temperatures caused by already ionized gases. It is the layer that is located between the mesosphere and the exosphere. It has an extension that begins between 80 and 120 kilometers from the Earth. In this layer, the ultraviolet radiation, and especially the gamma rays and X rays originated by the Sun.



Exosphere is the outermost limit of our atmosphere. Here, the atmosphere merges into space. The exosphere is the fifth and outermost layer of the atmosphere, beginning at the upper boundary of the thermosphere and lower exosphere, referred to as exobase, exopause, and the 'critical altitude'. The exosphere begins at a distance of 311 to 621 miles from the earth's surface, and ends at approximately 6200 miles from the earth's surface. Although the exosphere is the most distance layer of earth's atmosphere it is the layer that is the planet's first line of defense against the sun's rays. It is also the first layer to come into contact and protect the earth from meteors, asteroids, and cosmic rays.




Importance of the Atmosphere


1. The atmosphere prevents the Sun’s radiations from reaching the surface of the earth.

2. Atmosphere contains the life supporting gases such as oxygen for human beings and animals; and nitrogen and carbon dioxide for plants.

3. The Ozone layer protects us from the harmful ultraviolet rays of the sun.

4. It regulates and optimizes temperatures during day and night, preventing them from reaching the extremes.

5. The Sun’s rays heat the atmosphere causing a range of natural weather related phenomena, such as winds, clouds, rain, etc. to occur.

6. The atmosphere moderates solar radiation during day time.

7. The atmosphere serves as the medium of air transport facilitating the flights of aeroplane.

8. Changes in weather also occur due to the presence of the atmosphere.

9. Sound waves are transmitted due to the presence of air.




Biosphere


      Biosphere is the narrow sphere, where the three realms of land, water and air meet. It is the home of living things. Our earth is the only planet in our solar system where life exists. That is why the biosphere is regarded as unique in the whole universe.


     The living organism of the biosphere fall broadly into two kingdoms- the plant kingdom and the animal kingdom. There are more than 15,00,000 varieties of animals and plants on the earth. Some of these are microscopic, which means we can perceive them only with the help of a microscope. Some others are quite big and huge like elephants and whales. Some animals are live under deep water. Others roam about on the earth or in the air. All living beings including man are dependent on each other and on the biosphere for survival.

     Any change in the environmental condition affects all forms of life. Plants make suitable adaptations like shedding their leaves in the dry season. Animals migrate from place to place to adjust to the environmental changes.


     Various industries and vehicles are polluting land, water and air, causing Global Warming. Nature normally regenerates and purifies itself, but within a certain limit. When it is disturbed too much, many of its resources may be destroyed and lost permanently. 

      Thus, there is an urgent need to protect nature and maintain its balance. To fulfil this need, which has now become unavoidable, we must use our natural resources efficiently and try to preserve our environment for the future generations.   











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