Question

why is the earth called a 'living planet' ?

Answer 1

because only earth contains water,atmosphere,favourable climate and living beings

Answer 2

earth called as a 'living planet' 
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earth called a 'living planet' because
1)it is the only planet which sustains life
2)only earth has an suitable atmosphere for the survival 
3)earth's distance from sun is not too far nor too near hence we get moderate amount of sunlight for our survival