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Which are the four realms of earth ?
The four realms of the Earth are :

     (i) Lithosphere :
         Lithosphere is the outer-most layer or the crust of the earth. It occupies about 29% of the total surface area of the earth. Lithosphere of the earth consists of several landforms, such as continents, mountains, plateaus and plains.

    (ii) Hydrosphere

         Hydrosphere includes all the water found on the surface of the earth. About 71%  of the earth’s surface is covered by water. The earth’s water is mainly found in oceans, rivers, lakes and ponds. However hydrosphere also includes underground water, glaciers and snow and atmospheric water vapour.

   (iii) Atmosphere

       Atmosphere is the blanket of colourless, odorless and tasteless gases that covers the earth. It is about 700 km thick and is held together by the gravitational force of the earth. Atmosphere consists of different layers, The atmosphere helps in protecting living beings. On the earth by absorbing ultraviolet sun rays. It also helps in reducing temperature differences between day and night.
        
   (iv) Biosphere

        Biosphere is a limited and defined geographical area where land, Water and air meet and where all living beings dwell. For life to exist, it is essential for all the three realms, lithosphere, hydrosphere and atmosphere, to come together. Biosphere is a combination of the three spheres where life forms exist and interact with each other and with their environment.


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